Melatonin treatment and undernutrition affect expression of uterine estrogen and progesterone receptors in ewes during the reproductive and the anestrous seasons

VAZQUEZ, M.I.; SARTORE, I.; ABECIA, J A; FORCADA, F; SOSA, C; PALACÍN, I; CASAO, A; MEIKLE, A.

Budapest, Hungría

Congreso; 16º International Congress on Animal Reproduction; 2008

Melatonin treatment in ewes increases prolificacy and fertility. A reduction in PGF2a in vitro secretion by endometrial cells after melatonin addition has been reported, suggesting that melatonin could act directly on sheep endometrium. In previous studies we have shown that undernutrition affects endometrial sensitivity to estradiol and progesterone by decreasing their receptor concentration (ERα and PR, respectively) which could explain the lower pregnancy rates found in undernourished ewes. In this study we tested the hypothesis that melatonin treatment could counteract subnutrition effects, and thus ERα and PR content in different endometrial cell types were studied in undernourished ewes. Adult Rasa Aragonesa ewes were assigned to a 2 x 2 factorial design performed both in the reproductive (RS, n=25) and anestrous seasons (AS, n=24). They were treated (+MEL) or not (-MEL) with a subcutaneous implant of melatonin for 42 days (Melovine®, CEVA) and fed to provide 1.5 (Control, C) or 0.5 (Low, L) times daily maintenance requirements from synchronization day with intravaginal pessaries. Ewes were mated at oestrus (Day=0) and slaughtered on Day 5, when pieces of uterus were collected to determine PR and ERα by immunohistochemistry. There was an effect of season on the staining intensity of PR (P<0.0001), and a tendency for ERα (P=0.10); the expression was higher during the anestrous season, being more evident in the deep stroma. No effect of undernutrition or melatonin was observed during the AS in any cell type. However, differences were found during RS: C ewes had greater ERα staining than L ewes (luminal epithelium, P<0.05); PR staining was greater in C+MEL than in L+MEL (superficial stroma, P<0.05). Treatment with melatonin in undernourished ewes decreased PR expression in both superficial and deep glandular epithelia and in superficial stroma (P<0.05). This study shows that neither melatonin nor nutrition treatment had an effect on ERα and PR expression during anoestrous. Melatonin treatment could not counteract the detrimental effects of undernutrition on sex steroid receptors; moreover, it even provoked a higher decrease in PR content in undernourished ewes which was associated with lower embryo viability during reproductive season.