Involvement of Catecholaminergic and Cholinergic Mechanisms in the Pulsatile Release of LH in the Long-Term Ovariectomized Rat

Abstract

In the long-term ovariectomized rat the secretion of LH has a pulsatile character. In such rats no difference was observed between morning and afternoon LH secretion. The administration of phenoxybenzamine, an α-adrenergic blocker, resulted in depressed plasma LH levels. α-Methyl-tyrosine (α-MT), an inhibitor of tyrosine hydroxylase, had no effect on plasma LH levels, whereas bis(4 methyl-1-homopiperazinil-thiocarbonil) disulphide (FLA 63), an inhibitor of dopamine-β-hydroxylase, induced decreased plasma LH levels and disappearance of the pulsations. The same effect was observed after the administration of apomorphine, a dopaminic receptor stimulating drug, whereas the administration of 1-hydroxy-3-amino-pyrrolidone-2 (HA-966), which blocks dopamine release, significantly raised plasma LH levels. Scopolamine, a cholinergic muscarinic receptor blocking drug, had no effect on plasma LH levels, whereas mecamylamine, a cholinergic nicotinic receptor blocking agent, decreased them. These results are consistent with the hypothesis that the pulsatile release of LH in the long-term ovariectomized rat is caused by the stimulating activity of adrenergic and cholinergic, probably nicotinic, systems and the inhibitory activity of a dopaminergic system.