Dopaminergic input to the ventromedial hypothalamus facilitates the oestrogen-induced luteinizing hormone surge in ewes

Abstract

In this study we examined the release of dopamine and noradrenaline in the ventromedial hypothalamus (VMH) of ovariectomized ewes during the oestrogen-induced luteinizing hormone (LH) surge by measuring their respective metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and methoxyhydroxyphenylglycol (MHPG) using microdialysis. Further we investigated whether inhibition of catecholamine synthesis in the VMH by bilateral reverse dialysis of α-methyl-p-tyrosine (α-MPT) would block the oestrogen-induced LH and/or prolactin surges. Oestradiol treatment (50 μg oestradiol benzoate) of ovariectomized ewes resulted in a biphasic LH response, significantly (p < 0.05) decreasing LH concentrations fro..