17b-estradiol and prolactin inhibit nitric oxide pathway in anterior pituitary cells in culture from adult, ovariectomized rats

CABILLA JP; RONCHETTI SA; NUDLER SI; MILER EA; QUINTEROS AF; DUVILANSKI BH

Rio de Janeiro

Congreso; 13th International Congress of Endocrinology; 2008

International Society of Endocrinology

It has been previously reported that E2 indirectly decreases nitric oxide synthase-1 (NOS-1) activity in anterior pituitary gland through inhibition of hypothalamic GnRH release. Results from our lab have shown that E2 treatment modifies the expression and down-regulates the activity of soluble guanylyl cyclase, main nitric oxide (NO) receptor (1). Besides, we have demonstrated that exposition to NO inhibits PRL release from anterior pituitary gland (2), and E2 modifies the sensitivity of the gland to this inhibitory effect (3). Based in our evidence, the objectives of this work were to study 1) if E2 is able of directly inhibit NOS-1 mRNA expression and NO production, 2) if PRL, which release is increased by E2, could mimic E2 action in anterior pituitary cells in vitro. Materials and methods: anterior pituitary cultures from ovariectomized (OVX) rats were used because NOS-1 expression and activity are increased. Cells were incubated with the treatments for 24 to 72 h. NOS-1 mRNA expression was studied by semi-quantitative PCR. NO production was determined indirectly by nitrites measurement (Griess method). Results: E2 treatment (1 nM) significantly decreased NOS-1 mRNA levels . Similarly, PRL treatment (0.5 mg/ml) reduced NOS-1 mRNA expression at the times tested. Conclusions: these findings show that E2 directly down-regulates NOS-1 expression and NO production in a time-dependent manner in anterior pituitary cells. The same effect is caused by PRL. Since E2 increases PRL release, it is likely that E2 exerts its effects through this hormone, thus providing new insights to E2 actions on anterior pituitary gland and supporting a negative feedback of PRL on NO pathway.