Expression of Nitric Oxide Synthase isoforms in the anterior pituitary during the estrous cycle.

M. CANDOLFI; G. JAITA; V. ZALDIVAR; D. PISERA; A. SEILICOVICH

Philadelphia, USA

Congreso; 85o Annual Meeting of the Endocrine Society; 2003

  A body of evidence indicates that nitric oxide (NO) participates in the regulation of anterior pituitary hormone secretion. NO is synthesized from L-arginine by three different isoforms of NO synthase (NOS). Neuronal NOS (nNOS) and endothelial NOS (eNOS) have been localized in gonadotropes, lactotropes and folliculo-stellate cells whereas inducible NOS (iNOS) was shown to be induced by cytokines in a subpopulation of folliculo-stellate cells and was detected in cultured lactotropes and somatotropes. In the present work, we investigated the expression of NOS isoforms (by RT-PCR) in  the anterior pituitary of  rats sacrificed in selected stages of the estrous cycle and in anterior pituitary cells of cycling or ovariectomized (OVX) rats cultured in the presence of Tumor Necrosis Factor-a. The expression of nNOS and eNOS in the anterior pituitary was two-fold higher in rats in proestrus than in estrus and slightly higher than in glands from diestrus rats. iNOS  expression was not detected in the anterior pituitary. In cultured anterior pituitary cells, no differences were detected in the expression of nNOS  between cells from rats killed in proestrus or diestrus or between cells from OVX rats cultured in the abscence or presence of 10-9M 17b-estradiol (E2). The expression of iNOS was four-fold higher in anterior pituitary cells from rats killed in proestrus than in diestrus, but did not differ between cells of OVX rats cultured with or without E2. The incubation of pituitary cells with TNF-a (50 ng/ml) for 6 h markedly increased the expression of iNOS but did not modify nNOS expression. Our results suggest that variations in NOS expression in the anterior pituitary during the estrous cycle may depend on the reguilatory influence from the hypothalamus. The expression of iNOS in cultured pituitary cells may respond to culturing conditions. However, iNOS expression was higher in cells from rats sacrificed in proestrus suggesting that at this stage anterior pituitary cells are more susceptible to iNOS induction.