Abstract
Laying hens were injected (i.m.) with either progesterone or arachis oil and 90 min later plasma LH levels and steady state concentrations of dopamine, noradrenaline, adrenaline, 5-hydroxytryptamine and certain of the monoamine metabolites in the anterior hypothalamus-preoptic regions (AH-POR) and in the posterior hypothalamus (PH) were determined. Progesterone promoted a significant increase in the concentration of LH in the plasma and significant increases in the concentrations of dopamine and noradrenaline in the AH-POR and of adrenaline in the PH. Progesterone did not affect either the concentration of 5-hydroxytryptamine, its principle metabolite 5-hydroxyindoleacetic acid, or of the two metabolites of dopamine, homovanillic acid and dihydroxyphenylacetic acid. The implications of these results to a possible catecholaminergic involvement in the positive feedback actions of progesterone on LH secretion in the hen are discussed.