Effect of Drugs Modifying Catecholamine Synthesis on LH Release Induced by Preoptic Stimulation in the Rat

Abstract

Electrochemical stimulation of the preoptic or median eminence-arcuate region of proestrous rats anesthetized with ether led to an elevation of plasma LH within an hour following stimulation. The elevation was greater following median eminence-arcuate stimulation than after preoptic stimulation and the response to preoptic stimulation was dependent on the current strength. The elevation in plasma LH induced by medial preoptic stimulation was partially blocked by pretreatment of the animals with alpha-methyl-ptyrosine to block catecholamine synthesis. The blockade could be reversed by the administration of either L-dopa or dihydroxyphenylserine shortly after treatment with alpha-methyl-p-tyrosine to reverse the blockade of catecholamine or norepinephrine synthesis, respectively. Pretreatment of the animals with diethyldithiocarbamate to lower norepinephrine levels selectively also blocked the response to preoptic stimulation and this blockade could be partially reversed by the administration of dihydroxyphenylserine, whereas L-dopa had little effect. The blocking drugs failed to alter the response to median eminence-arcuate stimulation. Sham stimulation and the administration of the various drugs together with sham stimulation failed to modify plasma LH. The results are interpreted to mean that a noradrenergic synapse may lie between the points of stimulation in the preoptic area and the LRF-releasing elements located more caudally. It is postulated that this synapse is in the pathway involved in stimulation of LH release in the preovulatory period and after administration of estrogen and progesterone. (Endocrinology93: 356, 1973)