Suppression of serum LH-RH and LH in rats by an inhibitor of norepinephrine synthesis

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Abstract
The inhibition of pituitary LH [luteinizing hormone] release by the norepinephrine depletor, U-14,624 [l-phenyl-3-(2-thiazolyl)-2-thiourea] was investigated in ovariectomized rats. Serum LH-RH [luteinizing hormone-releasing hormone] was signficantly reduced in treated rats in both experiments. These low circulating concentrations of LH-RH in rats treated with U-14,624 were accompanied by significantly depressed serum LH levels. Amounts of LH-RH in the MBH [medial basal hypothalamus] and the POA [preoptic area] were not significantly altered following U-14,624 injection. The present results are the only ones known to suggest that the disruption of norepinephrine systems in the hypothalamus leads to impaired release of LH-RH, although LH-RH content in the MBH and the POA did not appear to be affected. Secretory activity of the LH-RH-reducing elements in the preoptic-tuberal pathway is apparently markedly affected by the subnormal levels of brain norepinephrine induced by the catecholamine synthesis inhibitor.