Stimulation of guanosine 3',5'-monophosphate accumulation in anterior pituitary glands in vivo by synthetic luteinizing hormone-releasing hormone.

The in vivo effect of an iv injection of synthetic LHRH on cAMP and cGMP concentrations in the anterior pituitary gland of pentobarbital (31.5 mg/kg BW)-injected proestrous rats and ovariectomized estradiol (10 micrograms)-primed rats was studied. At a specific time after an injection of LHRH or saline (as the control), the animals were sacrificed by microwave irradiation to the head. LHRH (100 ng/100 g BW) injection in the proestrous rat caused a significant increase in the cGMP level from 10-20 min associated with an increase in the serum LH level, whereas it exerted no effect on cAMP. No changes were observed in saline-injected animals. In the ovariectomized estradiol-primed rat, LHRH (50 ng/100 g BW) injection performed under ether anesthesia also induced a significant elevation of cGMP level, after 5-10 min, in parallel with an elevation of serum LH level. Saline injection caused no change in cGMP. cAMP concentrations were increased 5-10 min after either LHRH or saline injection. These results suggest the involvement of a guanylate cyclase-cGMP mechanism in the mediation of LHRH action in the pituitary.