Investigation of the Role of Prolactin in the
Development and Function of the Lacrimal and
Harderian Glands Using Genetically Modified Mice
Kathleen A. McClellan,1,2 Fiona G. Robertson,3 Jon Kindblom,4 Håkan Wennbo,4
Jan Törnell,4 Brigitte Bouchard,5 Paul A. Kelly,5 and Christopher J. Ormandy 3
PURPOSE. To determine whether prolactin receptor is essential
for normal development and function of the lacrimal gland and
whether hyperprolactinemia can alter lacrimal development.
METHODS. Lacrimal gland morphology and function were examined in two genetic mouse models of prolactin action: a
prolactin receptor knockout model that is devoid of prolactin
action and a transgenic model of hyperprolactinemia.
RESULTS. Image analysis of lacrimal and Harderian gland sections was used to quantify glandular morphology. In females,
lacrimal acinar area decreased by 30% and acinar cell density
increased by 25% over control subjects in prolactin transgenic
animals, but prolactin receptor knockout mice showed no
changes. In males, transgenic animals showed no changes, but
prolactin receptor knockout mice showed a 5% reduction in
acinar area and an 11% increase in acinar cell density, which
was lost after castration. The morphology of the Harderian
glands underwent parallel changes but to a lesser degree. A
complete loss of porphyrin accretions was seen in the Harderian glands of male and female knockout animals. No differences in tear protein levels were seen in knockout animals by
two-dimensional gels. Enzyme-linked immunosorbent assay
(ELISA) and Western blot analysis showed that the level of
secretory component and IgA in knockout mouse tears remained unchanged. There was no change in the predisposition
of the 129 mouse strain to conjunctivitis in the knockout
animals.
CONCLUSIONS. Prolactin plays a small role in establishing the
sexual dimorphism of male lacrimal glands. In females, hyperprolactinemia causes a hyperfemale morphology, suggesting a
role in dry eye syndromes. Prolactin is required for porphyrin
secretion by the Harderian gland but plays no essential role in
the secretory immune function of the lacrimal gland. (Invest
Ophthalmol Vis Sci. 2001;42:23–30)
From the 1Department of Ophthalmology, University of Sydney,
Sydney Eye Hospital, Australia; the 3Cancer Research Program, Garvan
Institute of Medical Research, Sydney, Australia; the 4Department of
Physiology, Research Centre for Endocrinology and Metabolism, Göteborg University, Sweden; and 5Institut National de la Santé et de la
Recherche Médicale (INSERM), Faculté de Médecine Necker-Enfants
Malades, Paris, France.
2
Present affiliation: Department of Ophthalmology, University of
Texas Southwestern Medical Center at Dallas, Texas.
Supported by the Ophthalmic Research Institute of Australia
(KAM, CJO), the National Health and Medical Research Council of
Australia and the New South Wales Cancer Council (CJO), INSERM
France (BB, PAK), and the Swedish Cancer Foundation (HW, JT).
Submitted for publication July 5, 2000; revised September 11,
2000; accepted October 6, 2000.
Commercial relationships policy: N.
Corresponding author: Christopher J. Ormandy, Cancer Research
Program, Garvan Institute of Medical Research, 384 Victoria Street,
Darlinghurst, Sydney 2010, Australia. c.ormandy@garvan.unsw.edu.au
Investigative Ophthalmology & Visual Science, January 2001, Vol. 42, No. 1
Copyright © Association for Research in Vision and Ophthalmology
I
n women, dry eye syndromes occur mostly during alteration
in the endocrine environment caused by pregnancy, lactation, oral contraceptive use, or menopause, with consequences ranging from discomfort and contact lens intolerance
to persistent pain and corneal damage leading to blindness.1,2
The cause of the disease lies in the disruption of the stability of
the tear film, causing poor lubrication between eyelid and
globe, resulting in mechanical and inflammatory damage to the
corneal epithelium. Disruption of the tear film can be caused
by changes in tear composition, supply, drainage, or evaporation and results from deficiencies in the external adnexa including low or excessive tear or tear protein production by the
lacrimal gland, poor production of oils by the meibomian
gland, low mucus production by the conjunctival goblet cells,
and/or abnormal drainage through the tear duct. Adverse environmental conditions such as low humidity, high temperature or high dust levels can exacerbate these deficiencies.3
Current routine treatment relies on artificial tear supplementation or surgical intervention to reduce tear drainage through
the canaliculi.
Tear deficiency due to declining lacrimal gland function is
the major cause of tear film instability and dry eye.4 It carries
the additional problem of reduced secretory immunity, because the lacrimal gland is the major source of IgA in tears.5
Two major causes have been identified: primary tear deficiency, the most prevalent cause of dry eye, which results from
lacrimal gland destruction by a round cell infiltrate,4 and
Sjögren’s syndrome, an autoimmune disease resulting in lymphocytic invasion and destruction of the epithelium of the
lacrimal gland.6 The cause of primary tear deficiency remains
unknown, but age-related endocrine changes have been hypothesized as a factor involved in the onset of dry eye.7
Endocrine regulation of the lacrimal gland8 is apparent from
its sexually dimorphic morphology and function: women experience dry eye problems, and especially Sjögren’s dry eye,
more frequently than men. In male rodents, the glands are
larger, contain larger acini, and show lower acinar cell density.9 Functionally, male glands secrete higher levels of IgA and
secretory component.5,10,11 Castration of males results in the
loss of sexual dimorphism. Glands assume a more female morphology, and the levels of IgA and secretory component are
reduced. Treatment of castrated animals with androgens reestablishes male morphology and increases IgA and secretory
component output.1,12–15 Of note, in mouse models of autoimmune disease, androgen treatment can suppress the immunopathologic lesions of the lacrimal glands.16 –18 Topical androgen application has been suggested for treatment of both
Sjögren’s and non-Sjögren’s dry eye syndrome.19
Androgens do not act alone on the lacrimal gland. Mice
without androgen receptors do not have a deficit in lacrimation.19 Hypophysectomy or pituitary transplant can prevent
androgen-induced restoration of tear volume, IgA, and secretory component levels after castration.1,12–15 The identity of
this pituitary factor is unknown, but because transplanted
pituitaries secrete high levels of prolactin, and prolactin treat23
24
McClellan et al.
ment of dwarf mice has trophic effects on the lacrimal gland,8
it has been hypothesized to be a second hormone influencing
lacrimal morphology and function. Short-term treatment with
prolactin can restore the lacrimal expression of a number of
genes that are altered after hypophysectomy, and can prevent
dihydrotestosterone restoration of the levels of other genes,
suggesting that prolactin modulates the lacrimal gland, both
alone and in combination with androgens.1 These findings
suggest that physiological levels of prolactin are required for
the trophic actions of androgens on the lacrimal gland and that
both hyper- and hypoprolactinemia may prevent this action.
This hypothesis is consistent with the hormonal states in
which dry eye is most common, but there is no convincing
evidence in its favor. Because androgen receptors20 and prolactin and its receptor21 are expressed by the acinar cells of the
lacrimal gland, this interaction may occur directly within the
lacrimal gland.
We have used two genetic mouse models of prolactin action; a transgenic mouse (PRLtg), hyperprolactinemic because
of overexpression of rat prolactin,22 and a prolactin receptor
knockout mouse (PRLR⫺/⫺) that has no prolactin receptors,23
to examine the hypothesis that prolactin is the pituitary factor
involved in the function and maintenance of the lacrimal gland.
These models allow two fundamental questions to be investigated using animals exposed to altered prolactin function from
the early embryonic stage: Is prolactin essential for normal
lacrimal development and function? Can increased levels of
prolactin modulate lacrimal development?
MATERIALS
AND
METHODS
Mice
The prolactin receptor knockout mouse (PRLR⫺/⫺) was generated by
replacement of exon 5 of the PRLR gene, which encodes cysteine
residues essential for ligand binding and receptor activation, with the
NEO cassette.23 PRLR⫺/⫺ mice used in these experiments were derived from chimeric animals made using E14 embryonic stem cells
(129/OlaHsd) bred to 129/Sv Pas mice. Genetically similar wild-type
control mice (PRLR⫹/⫹ ) were obtained from heterozygous matings.
PRLR⫺/⫺ animals show defects in fertility,23,24 bone development,25
mammary gland development,23,24,26,27 and maternal behavior,28 but a
normal immune system29 and prostate development (Ormandy et al.,
manuscript in preparation). The prolactin transgenic (PRLtg) animal22
was generated by microinjection of a plasmid construct driving expression of the rat prolactin gene by the metallothionein promoter into
C57Bl/6xCBA-f2 embryos, resulting in constitutive and generalized
tissue expression. Genetically similar wild-type control animals
(PRLwt), were generated from heterozygous matings. This animal
shows altered mammary development and tumors30 and prostate enlargement and hyperplasia.22 All mice were housed in a 12-hour day/
night cycle at 22°C and 80% relative humidity with access to food and
water ad libitum and were treated according to the ARVO Statement
for the Use of Animals in Ophthalmic and Vision Research.
Histology and Morphometric Analysis
Individual lacrimal and Harderian glands were excised, laid flat onto
filter paper (4 M; Whatman, Clifton, NJ) to maintain morphology
during fixation, and fixed overnight in 10% neutral buffered formalin.
Specimens were paraffin embedded, sectioned at 5 m, and stained
with hematoxylin-eosin. Specimens were photographed using a microscope (DMRB; Leica, Heidelberg, Germany) fitted with a CCD video
camera (model 3; Sony, Tokyo, Japan) coupled to an image analysis
program (Q500MC; Leica) running on a desktop computer. Acinar
areas were measured using images captured at ⫻10 magnification.
Epithelial cells were counted in images captured at ⫻20 magnification
using the image analysis software.
IOVS, January 2001, Vol. 42, No. 1
2-D Gel Analysis of Tear Proteins
Mouse tears were collected from the eye with a 3-mm2 piece of filter
paper by insertion between the orbit and lower eyelid of anesthetized
mice. The portion of tear-soaked paper was added to 125 l of a
solution containing 5 M urea, 2 M thiourea, 100 mM dithiothreitol, 2%
3-([3-cholamidopropyl]dimethylammonio)-2-hydroxy-1-propanesulfonate (CHAPS), 2% sulfobetaine 3-10, 0.5% 3/10 Pharmalytes (Amersham
Pharmacia Biotech, Amersham, UK), 40 mM Tris, and 0.001% bromophenol blue for 1 hour, after which the solution was vortexed. Sevencentimeter pH 3-10 immobilised pH gradient strips (IPGs; Amersham
Pharmacia Biotech) were rehydrated with solution for 6 hours. Isoelectric focusing was conducted using a 2-dimensional gel electrophoresis
apparatus (Multiphor II; Amersham Pharmacia Biotech) at 20°C and
was maintained for 14,000 Vh. Two-dimensional (2-D) separation was
conducted using 12.5% polyacrylamide gels in which the immobilized
pH gradient strips were embedded with 1% (wt/vol) agarose and then
run at 10 mA/gel. The gels were fixed and silver stained, and protein
maps were constructed.
Enzyme-Linked Immunosorbent Assay
To determine IgA levels in tears, an isotype-specific sandwich enzymelinked immunosorbent assay (ELISA) was performed, using a direct
plate binding assay. Plates were coated with a goat anti-mouse IgA
capture antibody (PharMingen, San Diego, CA), and bound immunoglobulin was revealed by a second biotinylated goat anti-mouse IgA
(Southern Biotechnology, Birmingham, AL) followed by streptavidinalkaline phosphatase and specific substrate (p-nitrophenylphosphate
[pNPP]). Plates were read using an ELISA plate reader at 405 nm.
Quantification was performed by comparison with a standard curve
established using purified mouse IgA (PharMingen).
Western Blot Analysis
The sample was separated by sodium dodecyl sulfate–polyacrylamide
gel electrophoresis (SDS-PAGE; 8% acrylamide), transferred to membranes (Immobilon P; Amersham) using a semidry transfer apparatus
(Bio-Rad; Herts, UK) and probed with either a polyclonal rabbit antiserum against rat secretory component, cross-reacting with the murine
secretory component (courtesy of Jean Paul Vaerman), or a biotinconjugated rabbit polyclonal anti-murine IgA (Zymed Laboratories,
South San Francisco, CA). For the IgA blots, membranes were incubated directly with streptavidin-horse radish peroxidase (Amersham),
and revealed using enhanced chemiluminescence (ECL; Amersham).
For the secretory component blots, membranes were incubated with a
biotin-conjugated anti-rabbit antibody (Vector, Peterborough, UK), before streptavidin-horse radish peroxidase and ECL assays. All incubations and washes were in phosphate-buffered saline (PBS) with 0.05%
Tween.
Statistical Analysis
Cell density, acinar area, and porphyrin secretions of lacrimal and
Harderian glands were compared using an unpaired, two-tailed Students t-test (Statview 4.0; Abacus, Berkeley, CA). Incidence of conjunctivitis was analyzed using Kaplan–Meier survival analysis (Statview 4.0)
and probabilities were calculated using the Mantle–Cox log rank
method.
RESULTS
Lacrimal Gland Development
The role of prolactin in the development of the sexually dimorphic morphology of the lacrimal glands was examined in
mature animals (12–16 weeks) by comparison of PRLR⫺/⫺
with PRLR⫹/⫹ and PRLtg with PRLwt. The lacrimal is a tubuloalveolar gland composed of ducts (acini) without a clearly
distinguished lumen. The ducts are surrounded by a fibrous
IOVS, January 2001, Vol. 42, No. 1
Prolactin and Lacrimal Development
25
FIGURE 1. Lacrimal histology from
mature animals (12–16 weeks of
age), stained with hematoxylin-eosin:
(A, B, and C) females; (D, E, and F)
males. (A, D) Histology in PRLR⫹/⫹
animals was very similar to PRLwt
animals (not shown). (B, E) PRLR⫺/⫺
animals and (C, F) PRLtg animals.
Original magnification, ⫻20.
basement membrane and contain two major cell types: the
secretory epithelial cells (acinar cells), identified by large
round nuclei located at the basement membrane surface of a
cytoplasm replete with secretory vesicles, and less frequent
myoepithelial cells closely associated with the basement membrane and displaying elongated nuclei. A mainly acellular
stroma fills the intraductal space. These glands showed typical
sexual dimorphism; female glands (Figs. 1A, 1B, 1C) showed
smaller acini and increased acinar cell density when compared
with male glands (Figs. 1D, 1E, 1F).
The degree of sexual dimorphism was quantified by measurement of lacrimal acinar area using image analysis software,
and acinar and acinar cell density by direct counting per field.
Results were expressed as a percentage of female control
levels, using elements per field, which correlated very well
with direct area measurements. This allows comparison between the different mouse strains used. The sexual dimorphism of the lacrimal gland was easily detected by this technique. Male control animals (PRLR⫹/⫹, PRLwt) had
approximately 75% of the female control number of acini per
field because of an increase in average acinar area. Acinar cell
density decreased to 75% of female levels (Fig. 2).
In PRLtg females, hyperprolactinemia caused the lacrimal
glands to assume a hyperfemale state with average acini per
field increasing to 130% (P ⫽ 0.0016) of control because of a
decline in average acinar area associated with a similar increase
(25%, P ⫽ 0.0087) in acinar cells per field. The morphology of
male PRLtg glands remained unchanged (P ⫽ 0.07). These
changes increased the degree of sexual dimorphism seen in
these animals.
In female PRLR⫺/⫺ animals, loss of the prolactin receptor
had no effect on the morphology of the lacrimal gland. In
PRLR⫺/⫺ males there was a small (5%) but significant (P ⬍
0.0001) increase in acini per field, caused by a decrease in
acinar area associated with an 11% (P ⫽ 0.0034) increase in
acinar cell density. Thus, in this model we also saw the acinar
area decline and cell density increase, but in males not females,
indicating a decrease in the degree of sexual dimorphism (Fig.
2). The small magnitude of this effect may not be physiologically relevant.
To determine whether we had missed a transient effect of
hypoprolactinemia in the PRLR⫺/⫺ animals during the onset of
sexual dimorphism at puberty, we examined the lacrimal
glands of animals at 4, 6, and 8 weeks of age (Fig. 3). The onset
of sexual dimorphism was seen in females as a slight decrease
in acinar area and slight increase in acinar cell number and in
males as an increase in acinar area and dramatic decrease in
acinar cell number, indicating that it is the male gland that
most alters its morphology during puberty, consistent with the
hypothesized trophic role of androgens. There was no difference in the rate of onset of sexual dimorphism between
PRLR⫹/⫹ and PRLR⫺/⫺ animals of either gender.
FIGURE 2. Lacrimal morphometric analysis from mature animals. The
number of acini and acinar cells were counted in 10 random microscope fields per animal, three to five animals per group, and statistically
analyzed. Results are expressed as a percentage of female PRLR⫹/⫹ for
the knockout model and as a percentage of female PRLwt values for
the transgenic model.
26
McClellan et al.
IOVS, January 2001, Vol. 42, No. 1
fewer acinar cells than females. Quantification, as used for the
lacrimal glands, showed smaller but similar effects of hyper- or
hypoprolactinemia on acinar size or cell number in adults
(Fig. 6).
Female PRLtg glands showed an 8% decrease in acinar area
that failed to reach statistical significance (P ⫽ 0.15) and a 10%
(P ⫽ 0.05) increase in acinar cell density. Male PRLtg animals
showed no changes. Female PRLR⫺/⫺ morphology remained
unchanged, but male glands showed a 2% decrease in area that
failed to reach statistical significance (P ⫽ 0.09) and a 10% (P ⫽
0.007) increase in cell density. These changes exactly mirror
those seen in the lacrimal gland, but their small magnitude
places them close to the level of detection for the quantification technique that was used.
Female acini, and male acini to a lesser extent, contained
solid accretions of porphyrin in the 129 mouse strain used to
make the prolactin receptor knockout (Figs. 5A 5D). Hypo-
FIGURE 3. Lacrimal morphometric analysis during puberty. Lacrimal
histology was analyzed in 10 random microscope fields per animal,
three to five animals per group, during early puberty (4 weeks),
midpuberty (6 weeks), late puberty (8 weeks), and at maturity (12
weeks). Results are expressed as the number of acinar cells or acini in
PRLR⫹/⫹ or PRLR⫺/⫺.
We examined the role of prolactin in the maintenance of
sexual dimorphism by castrating PRLR⫹/⫹ and PRLR⫺/⫺ males
and examining lacrimal morphology 21 days later (Fig. 4). In
PRLR⫹/⫹ animals, castration resulted in a 10% decrease in
acinar area and a 12% decrease in acinar cell density. PRLR⫺/⫺
animals underwent much the same change in acinar area,
resulting in a 7% (P ⬍ 0.0001) difference. Acinar cell density
showed a greater proportional change, so that no significant
difference (P ⫽ 0.43) between genotypes was then seen in
acinar cell density. These results indicate that the small reduction in acinar area resulting from a loss of the prolactin receptor is independent of androgen action, but that acinar cell
number may be influenced by an interaction between prolactin
and androgen. Again, however, the small magnitude of this
effect calls into question its physiological relevance.
Harderian Gland Development
Histologic investigation (Fig. 5) showed that the Harderian
glands of the mouse strains used in this study had larger acini
with a defined lumen and more acinar cells than the lacrimal
glands. They also exhibited sexually dimorphic characteristics
similar to the lacrimal glands. Male glands had larger acini and
FIGURE 4. Effect of castration on male PRLR⫹/⫹ and PRLR⫺/⫺ lacrimal
glands. Mature males were castrated, and lacrimal morphology was
analyzed 21 days later in 10 random microscope fields per animal,
three to five animals per group.
IOVS, January 2001, Vol. 42, No. 1
Prolactin and Lacrimal Development
27
FIGURE 5. Harderian gland histology from mature animals (12–16
weeks of age) stained with hematoxylin-eosin: (A, B, and C) females; (D,
E, and F) males. Panel descriptions
are the same as in Figure 1. Porphyrin accretions are seen in the acini as
dark-staining oval-shaped figures.
Original magnification, ⫻20.
prolactinemia resulted in a complete loss of these solid porphyrin accretions in both males and females (Figs. 4B, 4E),
quantified by counting accretions per field (Fig. 7). In males a
97% loss was seen (P ⫽ 0.0026), and in females an 83% (P ⬍
0.0001) reduction occurred. The mouse strain used for construction of the transgenic model shows virtually no porphyrin
accretions, making this analysis difficult. In males a 33% (P ⫽
0.096) increase was seen and in females a 266% (P ⫽ 0.16)
increase was seen, but the overall small number of accretions
found prevented reliable statistical analysis of this effect.
FIGURE 6. Harderian gland morphometric analysis from mature animals. The number of acini and acinar cells were counted in 10 random
microscope fields per animal, three to five animals per group, and
statistically analyzed. Results are expressed as a percentage of female
PRLR⫹/⫹ counts for the knockout model and as a percentage of female
PRLwt counts for the transgenic model.
Lacrimal and Harderian Function
To determine whether hypoprolactinemia alters the function
of the lacrimal or Harderian glands, we took a number of
approaches. Tear proteins were analyzed by 2-D gels, IgA and
secretory component levels were analyzed by ELISA and Western blot, and alteration to the genetic susceptibility of the 129
mouse strain to conjunctivitis was searched for during an aging
study.
Silver staining of 2-D gels of tears from PRLR⫹/⫹ and
PRLR⫺/⫺ animals and comparison to consensus gels of mouse
serum identified many spots specific to the tear film. Repeated
tear sampling and 2-D analysis (10 replicates) indicated that
FIGURE 7. Harderian gland porphyrin accretions. Accretions were
counted per ⫻10 field, 10 random fields per animal, three to five
animals per group. A very low frequency of porphyrin accretions in the
mouse strain used to produce the PRLwt and PRLtg animals prevented
an accurate analysis of the role of hyperprolactinemia.
28
McClellan et al.
IOVS, January 2001, Vol. 42, No. 1
none of these spots showed reproducibly altered patterns of
expression (data not shown), leading to the conclusion that
synthesis and secretion of the major tear proteins was unchanged. Individual spots could, however, show different relative levels in a single experiment, underlining the need for
multiple replicates for reliable results using this technique.
The secretory immune function of the eye is maintained
through the concentration of IgA in tears. IgA is synthesized by
the acinar cells of the lacrimal gland and is transferred to tears
in association with the polymeric IgA receptor, secretory component. IgAs protect the cornea and conjunctiva from inflammatory and infectious disease. To determine whether the levels
of IgA and secretory component in tears is dependent on
prolactin, we measured these species by Western blot and
ELISA (Fig. 8). In tears from PRLR⫺/⫺ animals, Western blot
analysis showed IgA and secretory component levels were
identical with levels found in tears from PRLR⫹/⫹ animals. This
was confirmed by ELISA for IgA. These experiments discount
any essential role for prolactin in the maintenance of the major
molecular species involved in the secretory immune system of
the eye.
We used a genetic characteristic of the 129 strain to test for
reduced ocular immune function. The 129 mouse strain is
susceptible to conjunctivitis, which begins as mild suppurative
palpebral conjunctivitis and progresses to the mucocutaneous
junction at the exit of the meibomian duct, where a suppurative process develops within and adjacent to the duct, associated with the formation of small ulcers over the conjunctiva. A
genetic deficiency in secretory immunity appears to be the
cause.31 As the disease advances, the eyelid becomes swollen
and the surrounding hair becomes matted, and in our facility,
mice at this stage are culled. To determine whether the secretory immune system of the eye was further compromised in
PRLR⫺/⫺ mice, we aged a group of PRLR⫹/⫹ and PRLR⫺/⫺
animals and compared their survival. Animals that died or were
culled for other causes were removed from the study. By 18
months of age the overall culling rate due to conjunctivitis was,
for females, PRLR⫹/⫹ 4 of 10 (40%) and PRLR⫺/⫺ 9 of 25
(36%), and for males, PRLR⫹/⫹ 8 of 18 (44%) and PRLR⫺/⫺ 3
of 14 (21%). These data were analyzed further by Kaplan–Meier
survival analysis (Fig. 9). Calculation of probabilities indicated
no significant difference between genotypes when analyzed
without reference to gender (P ⫽ 0.16 Mantle–Cox log rank)
or when analyzed separately by gender (males P ⫽ 0.82,
females P ⫽ 0.98, Mantle–Cox log rank). These experiments
detected no essential role for prolactin in the function of the
secretory immune system of the eyes of animals predisposed to
conjunctivitis.
DISCUSSION
The results demonstrate that in females, prolactin plays no
essential role in the development or maintenance of the morphology or function of the lacrimal glands, but that prolactin in
excess can alter lacrimal gland morphology. Application of
these findings to the previous investigation of the endocrine
control of the lacrimal gland revealed unseen difficulties in the
interpretation of results. In experiments using hypophysectomy in females or female pituitary dwarf mice, it is now clear
that loss of prolactin was not the cause of the alterations in
lacrimal gland morphology and function. Prolactin is not the
pituitary factor lost in these models that influences the lacrimal
gland, nor is it the pituitary factor that modulates androgen
action in these experimental paradigms. These experiments
also show that the effects in females of pituitary transplant or
prolactin injection were due to the hyperprolactinemic result
of these manipulations and did not reveal an effect of normal
FIGURE 8. Secretory component and IgA levels in the tears of
PRLR⫹/⫹ and PRLR⫺/⫺ mice. (A) Western blot of IgA or secretory
component in tears from PRLR⫺/⫺ (⫺/⫺) or PRLR⫹/⫹ (⫹/⫹) animals.
Tear samples (10 l) were separated by SDS-PAGE and transferred to
membranes. (B) ELISA. Tear concentration of IgA.
prolactin levels on the lacrimal glands. Thus, when prolactin
treatment or pituitary transplant are combined with hypophysectomy, the effects of hyperprolactinemia are overlaid on the
independent effects of hypophysectomy. Effects previously
attributed to a physiological role of prolactin are in fact due to
superphysiological levels of the hormone, which causes female
lacrimal glands to assume a hyperfemale morphology. Translating this result to humans suggests hyperprolactinemia may
Prolactin and Lacrimal Development
IOVS, January 2001, Vol. 42, No. 1
FIGURE 9. Kaplan–Meier survival analysis of conjunctivitis in
PRLR⫹/⫹ and PRLR⫺/⫺ mice. The 129 strain used to make the
PRLR⫹/⫹ and PRLR⫺/⫺ animals carries a genetic susceptibility to suppurative conjunctivitis. Survival analysis showed no difference in susceptibility between PRLR⫹/⫹ (closed symbols) and PRLR⫺/⫺ animals
(open symbols) when analyzed without reference to gender (top) or by
gender (bottom).
predispose to dry eye, and support for this conclusion has been
published.
A correlative study7 of serum hormone levels and parameters of lacrimal gland activity, such as tear osmolarity, volume
flow, and turnover, found that patients in menopause not using
hormone replacement therapy had a positive correlation between tear volume and testosterone, but in women using
hormone replacement therapy a strong negative correlation
was found between serum prolactin level and multiple parameters of lacrimal function.
In males, a small but significant requirement for prolactin in
the establishment of sexual dimorphism was found, with both
acinar area and cell number affected. This effect was very
small, however, and may not affect the physiology of the gland.
After castration, the difference between genotypes on acinar
cell number was lost, indicating an interaction between prolactin and androgen to control acinar cell density. A similar
situation occurs in the androgen-regulated ventral prostate and
seminal vesicle. Both glands are lighter in prolactin knockout
animals.32
The external adnexa of the eyes of mice (and all other
species with a third eyelid) also includes the Harderian gland,
located within the orbit behind the eye and almost encircling
the optic nerve. It is found in humans in vestigial form during
embryonic development and occasionally as a developmental
abnormality.33 This gland adds lipids to the tear film through a
duct that opens onto the surface of the nictitating membrane.
29
The gland also contains porphyrins, which are thought to be
involved in sensing day length.34 Neonatal rat pups with undeveloped eyes or blind moles with vestigial eyes continue to
respond to changed photoperiod when their eyes are removed, but not when their eyes and Harderian glands are
removed.33,35 A number of these photoperiod responses involve the pineal gland, and the Harderian gland synthesizes
melatonin and contains melatonin receptors, suggesting that it
may have endocrine activity.33 The Harderian gland is sexually
dimorphic and sensitive to steroid and pituitary hormones
including prolactin.36 Our results indicate that the Harderian
gland responds to prolactin in the same way as the lacrimal
gland but that it is less sensitive, resulting in effects at the level
of detection of our techniques. An essential role for prolactin
was found in the formation of porphyrin accretions by the
Harderian glands of male and female mice. Because testosterone levels in male PRLR⫺/⫺ animals are normal25 this observation establishes prolactin as a major and essential hormone
controlling porphyrin accumulation in mice, as hypothesized
from hypophysectomy and prolactin-bromocriptine treatment
studies in rodents.36 Why prolactin should control accumulation of porphyrins in the Harderian gland remains an open
question, but given prolactin’s diverse reproductive actions23,24 and the photo period sensing and signaling ability of
the Harderian gland, it is tempting to speculate that it may have
a role in the control of seasonal breeding.
It is important to distinguish between the endocrine state
produced by an absence of prolactin action and that produced
by hyperprolactinemia. These conditions can be considered to
be separate endocrine states and demonstrate that the failure
to show an essential role for a hormone in a process does not
indicate that an excess of that hormone will similarly be without effect. This is the case with prolactin in the female lacrimal
gland. Although not essential for normal development, hyperprolactinemia produces a hyperfemale morphology that may
predispose to dry eye.
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