Pregnancy and the Lacrimal Gland: Where Have All the Hormones Gone?

Abstract

Abstract: : Purpose: We are investigating changes in lacrimal gland function associated with pregnancy, and the content and distribution of lacrimal gland hormones and growth factors in the lacrimal gland and in lacrimal fluid. Here we report our data on the prolactin (PRL) studies. Methods: Lacrimal glands from non–pregnant and pregnant rabbits were analyzed by light– and electron microscopy, immunocytochemistry (ICC), Western blot and RT–PCR. Schirmer’s test, tear break up time (TBUT) and Rose Bengal were used to evaluate the ocular surface. Results: Non–pregnant rabbits: ICC demonstrated faint immunopositivity for PRL in ductal epithelial cells (apical cytoplasm), and minimal or no immunopositivity in acinar cells. Base lacrimal gland fluid production = 0.36±0.04 µl/min; 5.45±0.48 µl/min after pilocarpine stimulation, and lacrimal fluid protein = 22.23±1.2 µg/µl. Western blots demonstrated PRL at 23 KD in lacrimal gland lysates and lacrimal fluid. Schirmer, TBUT and Rose Bengal tests were unremarkable. Term pregnant rabbits: ICC demonstrated strong immunopositivity for PRL in ductal epithelial cells, apically and basally, and moderate immunopositivity in acinar cells. Base lacrimal fluid production = 0.07±0.02 µl/min, 0.85±0.12 µl/min after pilocarpine stimulation, and lacrimal fluid protein = 13.75±0.77 µg/µl. PRL was detected by Western blotting in lacrimal gland lysates, but not in lacrimal gland fluid. RT–PCR for PRL mRNA was slightly elevated at term compared to non–pregnant rabbits. Schirmer’s test was less than normal at term but varied widely throughout pregnancy. TBUT decreased during pregnancy; Rose Bengal staining was moderate to severe at term, although not consistently in all animals. Conclusions: Content of PRL in the lacrimal gland remains high in pregnancy, but PRL appears not to be released into the final lacrimal effluent. Rather, PRL produced by the acinar cells appears to be taken up by the ductal cells while the primary lacrimal fluid is being transported through the ductal system, and released basally from ductal epithelial cells. This PRL may function as a cytokine, along with other factors, influencing periductal immune cells and inducing immune responses that may eventually result in compromised acinar cell function. Diminished lacrimal fluid production and protein content, including absence of PRL in lacrimal fluid, indicate significant changes in lacrimal function associated with pregnancy.

Keywords: lacrimal gland • microscopy: light/fluorescence/immunohistochemistry • immunomodulation/immunoregulation