FAILURE OF HISTAMINE TO INDUCE THE RELEASE OF LUTEINIZING HORMONE IN CASTRATED RATS PRIMED WITH SEX STEROIDS

Abstract

Instituto de Investigaciones Cerebrales, Facultad de Ciencias Médicas, Universidad Nacional de Cuyo, Mendoza, Argentina (Received 10 March 1978) Injection of histamine into the third ventricle causes the release of luteinizing hormone (LH) in ovariectomized, steroid-primed and pro-oestrous rats (Donoso, Banzan & Borzino, 1976; Donoso, 1978). In oestrous rabbits, intraventricular injection of large doses of histamine or injection of histamine into the mediobasal hypothalamus induces ovulation and secretion of progesterone by the ovaries (Sawyer, 1955; Endröczi & Hilliard, 1965). However, histamine has no effect on the concentration of LH in the plasma of male rats (Donoso & Banzan, 1976). Together, these results suggest that histamine is able to induce the release of LH both before ovulation and in the presence of an adequate hormonal background. The positive feedback effects of oestradiol and progesterone on the release of gonadotrophins are absent in male rats. Injection of oestradiol, progesterone or testosterone into steroid-primed