RELATIONSHIP BETWEEN HYPOTHALAMIC CATECHOLAMINES AND GONADOTROPHIN SECRETION IN RATS

¹ Departments of Chemical Pharmacology and Metabolic Chemotherapy, Lederle Laboratories, American Cyanamid Co., Pearl River, New York

Reserpine, a catecholamine releaser, and -methyl-p-tyrosine, a catecholamine synthesis inhibitor, lowered hypothalamic catecholamines, induced pseudopregnancy and blocked ovulation in rats. These results suggested that when hypothalamic catecholamines were reduced, the secretion of luteotrophic hormone (LtH) was stimulated while that of luteinizing hormone (LH) was suppressed. Iproniazid pretreatment prevented all the observed effects of reserpine, whereas bretylium pretreatment was ineffective. Pargyline, given simultaneously with -methyl-p-tyrosine, failed to prevent pseudopregnancy and ovulation blockade; however, it also was ineffective in antagonizing the reduction of the hypothalamic catecholamines. Pargyline alone increased catecholamines without affecting LtH and LH release. Studies designed to illustrate the relationship between hypothalamic catecholamine levels and gonadotrophin secretion with respect to time of reserpine treatment indicated that the rate of synthesis, uptake and/or release of catecholamines appeared to be more critical than the absolute concentrations of the amines. These data provide direct support for the hypothesis that gonadotrophin secretion may be regulated by a sympathetic tone originating in the hypothalamus.

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