Evidence for Participation of a Catecholaminergic Mechanism in the Post-Castration Rise in Plasma Gonadotropins

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Abstract
Orchidectomy produced a rise in plasma gonadotropin levels after 16 h, which was completely prevented by an intraperitoneal injection of DL-α-methyltyrosine (α-MT). When α-MT was injected 18 h after castration, a sharp fall in plasma LH, but not of FSH, followed. L-dihydroxyphenylalanine (l-DOPA) and dihydroxyphenylserine (DOPS) were given to restore catecholamine (CA) or norepinephrine (NE) synthesis, respectively. When given intraperitoneally 16 h after α-MT, the precursors did not alter LH levels; however, plasma FSH was significantly increased by either l-DOPA or DOPS. When α-MT was given 8 h after castration and precursors were injected 30 min later, l-DOPA increased both LH and FSH levels significantly 10 h after injections. When α-MT was injected 18 h after castration and precursors were injected 30 min later, DOPS prevented the fall in plasma LH, but l-DOPA was ineffective. The selective blockade of NE synthesis with diethyl dithiocarbamate (DDC) injected intraperitoneally 18 h after castration at two doses, 500 or 250 mg/kg, markedly decreased LH levels but did not alter plasma FSH. l-DOPA or DOPS, injected 30 min later, did not reverse the effect of the higher dose of DDC; however, when DOPS was injected 15 min after the lower dose of DDC, it partially prevented the decrease in plasma LH. Even at a dose of 200 mg/kg l-DOPA was ineffective. The selective blockade of DA receptors with Pimozide did not alter the rise in LH that follows orchidectomy, but partially blocked the rise of plasma

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