Renee L. Kaswan

Androgen support of lacrimal gland function

The effects of dihydrotestosterone (DHT) (1 mg/kg) on biochemical parameters related to lacrimal secretion, basal tear flow rate, and pilocarpine-stimulated lacrimal gland fluid secretion, in mature ovariectomized rabbits were studied. The effects of the synthetic estrogen, diethylstilbestrol (DES) (100 μg/kg), on lacrimal gland biochemical parameters in normal mature female rabbits was also studied. Ovariectomy decreased the total serum levels of testosterone (T) by 88.5% and androstenedione by 35.9%, without changing the levels of dehydroepiandrosterone (DHEA) or its sulfate. Ovariectomy caused a significant regression of the lacrimal glands, decreasing total DNA by 35%, and total protein by 22%. DHT treatment of ovariectomized animals prevented lacrimal gland regression, increasing total gland DNA (31%) and total protein (18%). DHT treatment also increases Na+,K+-ATPase activity (29%) and ß-adrenergic receptor binding sites (23%) compared to the ovariectomized group. DHT increased pilocarpine stimulated lacrimal gland fluid secretion (13.26±1.47 μL/min) compared to the ovariectomized group (7.72±0.41 μL/min), but DHT treatment paradoxically decreased basal tear flow rate (1.02±0.04 μL/min) as compared to the ovariectomized rabbits (1.96±0.12 μL/min). DES decreased the total serum T from 59.33±10.54 pg/mL to 21.5±6.06 pg/mL. DES decreased total Na+,K+-ATPase by 12% and increased ß-adrenergic receptor binding sites by 83.3%. These results suggest that androgens play a major role in supporting lacrimal gland secretory function. Additionally, they suggest that estrogens may influence certain aspects of lacrimal functions, although it is not clear to what extent those actions are elicited directly or indirectly.

A new perspective on canine keratoconjunctivitis sicca. Treatment with ophthalmic cyclosporine.

Keratoconjunctivitis sicca is the major cause of chronic or recurrent conjunctivitis in dogs. The diagnosis of KCS is often delayed or mistaken for allergic or bacterial conjunctivitis and inappropriate or insufficient treatment leads to progressive corneal scarring and blindness in many dogs. The cause of KCS in dogs has not been proven, but evidence supports an immune-mediated etiology for the majority of cases. In an attempt to specifically treat the cause of KCS, a new immunosuppressant drug, cyclosporine, has been used in a topical preparation. Treatment results using ophthalmic cyclosporine are dramatic compared with historical treatments. Resolution of corneal scarring and increased lacrimation are seen in most dogs. Investigations of the mechanism of action of ophthalmic cyclosporine suggest the efficacy may have been serendipitous. A local neuroendocrine effect of cyclosporine on the lacrimal gland may actually be responsible for the increased lacrimation. Early diagnosis of KCS and treatment with ophthalmic cyclosporine may avert a major cause of blindness in dogs.

Influence of vehicle and anterior chamber protein concentration on cyclosporine penetration through the isolated rabbit cornea.

The transcorneal penetration of cyclosporine A has been determined from each of three vehicles across isolated cornea into simulated aqueous humor containing either 50 mg % protein (0.5 mg/ml; as found in a normal eye) or 5000 mg % protein (50 mg/ml; as found in an inflamed eye). Cyclosporine entered the corneal epithelium and stroma/endothelium as well as passed through the cornea from an alpha cyclodextrin vehicle. Entry into the epithelium and stroma/endothelium occurred from an ointment vehicle with limited detectable anterior chamber penetration using 50 mg % protein solution in the anterior chamber. From corn oil vehicle, cyclosporine penetrated across the cornea with a permeability equal to that of alpha cyclodextrin vehicle. The concentration of cyclosporine in both corn oil and ointment vehicles is 8 times greater than that in alpha cyclodextrin vehicle resulting in a flux from corn oil vehicle about 7 or 8 times greater than that seen after alpha cyclodextrin vehicle. The amounts retained in the cornea, however, were relatively low after corn oil compared to cyclodextrin. The penetration of cyclosporine from either the cyclodextrin vehicle or ointment was at least doubled in the presence of 5000 mg % protein in the simulated aqueous humor relative to that seen in 50 mg % protein. This data indicates that the (presumed) absorption and binding of drug by the excess protein in the simulated aqueous humor may have removed free cyclosporine from the solution and sustained a high concentration gradient of free solute across the cornea.(ABSTRACT TRUNCATED AT 250 WORDS)

Characteristics of a Canine Model of KCS: Effective Treatment with Topical Cyclosporine

For the past 12 years, we’ve studied keratoconjunctivitis sicca (KCS) in dogs to develop a therapeutic intervention to benefit both veterinary and human KCS patients. The spectrum of ocular surface pathology in canine KCS can support a battery of assessment criteria for therapeutic evaluation. Although there are multiple causes of canine KCS, the vast majority appear to be immune mediated.

Survey of canine tear deficiency in veterinary practice.

Keratoconjunctivitis sicca (KCS, dry eye) is a common cause of ocular morbidity and blindness in dogs. Typical clinical signs are mucoid to mucopurulent discharge, rubbing and pawing eyes, and progressive corneal scarring. Canine KCS can result from a number of causes including trauma, canine distemper virus, and sulfonamide toxicity, but most cases are thought to have an autoimmune pathogenesis.1–4 Like human dry eye, canine dry eye may occur as an isolated disorder or in association with a number of autoimmune diseases, such as atopy, hyperadrenocorticism, diabetes mellitus, and hypothyroidism.4,5

ANDROGEN SUPPORT OF LACRIMAL GLAND FUNCTION IN THE FEMALE RABBIT

Dry eye is a major reason for visits to an ophthalmologist’s office. The most probable cause for dry eye is primary lacrimal deficiency (PLD).1 PLD is usually detected in women, most frequently after menopause, during pregnancy or lactation, or when taking estrogen-containing oral contraceptives. These various endocrine states exhibit a complete range of plasma estrogen levels from very low to very high. Thus, plasma estrogen concentrations do not appear to be a common variable in PLD. However, plasma free androgen levels are potentially decreased in all of these states. We have previously demonstrated that ovariectomy of female rabbits2 and hypophysectomy of female rats3 result in a decrease in biochemical correlates of lacrimal gland function. Treatment of these endocrinectomized animals with the potent androgen dihydrotestosterone (DHT) restores the decreases in the biochemical markers of secretion,2,3 specifically, lacrimal gland protein, DNA, Na,K-ATPase, and s-adrenergic receptors. Androgens have been shown to be responsible for the male-like morphological and functional characteristics of the gland, including larger acini,4 greater secretion of IgA,5 and greater production of polymeric IgA receptor, measured as secretory component (SC).6 When female rats are treated with androgens, the morphology of the lacrimal gland changes and resembles the male lacrimal gland.7 However, the major neurotransmitter receptor coupled to secretion in the lacrimal gland, the muscarinic cholinergic receptor, is regulated by circulating levels of prolactin, not androgens.3

Structural Analysis of Secreted Ocular Mucins in Canine Dry Eye

The tear film is vital for the normal function of the ocular surface, influencing transparency, optical quality, and defense against the external environment. A functional understanding of the tear film depends on a knowledge of its components and their interactions. Recent data indicate the thickness of the trilaminar tear film to be 35–40 μm, the majority (~30 μm) contributed by a mucous gel situated adjacent to the epithelial surface.1–3 This gel contains mainly secreted mucins, which interact with a variety of other components, including a number of highly glycosylated components of the ocular surface glycocalyx.4–7

Conjunctival Impression Cytology from Dogs with Keratoconjunctivitis Sicca

Keratoconjunctivitis sicca (KCS), or dry eye, is a major cause of ocular morbidity in humans and dogs.1,2 Although the cause of KCS in dogs often cannot be determined, as in non-Sjogren’s dry eyes, histopathologic and serologic studies suggest that canine KCS frequently results from immune-mediated lacrimal gland destruction or dysfunction. Tear film deficiencies cause changes in the conjunctival epithelium that may account for many of the clinical symptoms and the corneal morbidity in these cases. The normal conjunctival surface is composed of nonkeratinized, stratified, squamous epithelium with goblet cells. These cells and the products from them, including mucin, are critical for ocular surface integrity. Squamous metaplasia from cuboidal epithelium to increasing keratinization and goblet cell loss is associated with KCS in patients with Sjogren’s syndrome and with ocular problems in postmenopausal women.2–4 Methods for staging squamous metaplasia by impression cytology have been established for use in humans.2,5–7Although KCS in dogs and response to treatment with cyclosporine have been characterized histologically by biopsy of lacrimal glands, there are no reports on conjunctival cytology from dogs with KCS.1,8 Clinical trials in dogs and humans have supported the validity of treating KCS with cyclosporine. In this project we characterized conjunctival cytology from dogs with KCS before and after treatment with cyclosporine in order to determine the effect of topical cyclosporine treatment on the conjunctival epithelium.

Effects of Dihydrotestosterone and Prolactin on Lacrimal Gland Function

Because both Sjogren’s and non-Sjogren’s lacrimal insufficiencies affect women much more frequently than men, it is reasonable to predict that there is a hormonal basis for both conditions, and attention turns to the estrogens as plausible candidates. However, the hormonal states during which women are most likely to experience lacrimal insufficiency are characterized by widely differing estrogen levels. Both Sjogren’s and non-Sjogren’s lacrimal insufficiencies are commonly regarded as afflictions of the postmenopausal state, which is characterized by dramatic decreases in ovarian estrogen production. However, women also tend to experience lacrimal insufficiency particularly frequently during estrogen-based oral contraceptive use, which is characterized by high estrogen levels; pregnancy, which is characterized by high estrogen and increasing prolactin levels; and lactation, which is characterized by low estrogen and high prolactin levels.