PARTURITION UP-REGULATES NITRIC-OXIDE SYNTHASE ACTIVITY IN THE RAT ANTERIOR-PITUITARY GLAND

RECENT evidence suggests that endogenous nitric oxide (NO) contributes to the modulation of hormonal secretion from the anterior pituitary g land according to the physiological state of the animal. In this study , nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) his tochemistry and specific neurochemical assay were used to assess possi ble changes of NO synthase (NOS) activity in the anterior pituitary du ring pregnancy and parturition in rats. The anterior pituitary showed (weak) NADPH-d activity throughout pregnancy. Parturition increased th e number and intensity of NADPH-d-positive cells. The NADPH-d-positive cells co-localized with immunofluorescent LH-positive cells. No varia tion in NADPH-d activity was apparent during the various stages of the oestrous cycle. Furthermore, NOS activity during parturition increase d significantly when compared with non-pregnant and pregnant rats. Inc reases in both specific activity and NADPH-d activity gradually decrea sed within 24 h postpartum, suggesting that NO may modulate anterior p ituitary function during parturition.