In vitro, nitric oxide (NO) stimulates LH secretion and partially preventsthe inhibitory effect of dopamine on PRL release

In recent years nitric oxide (NO) has emerged as an important intra- and in tercellular transmitter involved in the control of hypothalamic-pituitary a xis. In order to discriminate the potential actions of NO at hypothalamic o r pituitary level in the control of PRL and LH release, we have studied PRL and LH secretion by dispersed pituitary cells obtained from males, cycling and lactating females in the presence of 1) sodium nitroprusside (SNP), a NO donor; 2) cyclic guanosine monophosphate (cGMP), the second messenger fo r a wide range of NO actions; 3) N-w-nitro-L-arginine methyl ester (NAME), a competitive inhibitor of NO synthase (NOS) and 4) oxadialoquinoxalione (O QD) and LY 83,583, antagonists of guanylyl cyclases. We found that SNP (at doses of 100 and 500 mu mol) stimulated LH and FSH release and partially bl ocked the inhibitory action of dopamine (50 and 100 nmol) on prolactin secr etion. These effects were not mimicked by cGMP and remained in the presence of OQD and LY 83,583. NAME alone had no significant effect on hormone secr etion. These results suggest that NO plays a role in the control of gonadot ropins and prolactin secretion acting directly at the pituitary level and t hat these effects are mediated by mechanisms other than changes in cGMP lev els. (J. Endocrinol. Invest. 22: 772-780, 1999) (C)1999, Editrice Kurtis.