PIP: The stimulatory effects of estrogen and progesterone on luteinizing hormone (LH) and follicle-stimulating hormone (FSH) release were studied in rats to investigate the possible participation of catecholamines (CA) in mediating steroid-feedback effects. Progesterone or estrogen administration caused a sharp increase in levels of LH and FSH in estradiol-primed spayed females. Phenoxybenzamine block of alpha-adrenergic receptors completely eliminated the gonadotropin peaks. Haloperidol had a similar effect. The administration of alpha-methyl-p-tyrosine (alpha-MPT), which produces a marked decline in noradrenaline (NA) and dopamine (DA), also blocked the progesterone-induced increase in FSH and LH. Diethyldithiocarbamate (DD C) and 1-phenyl-3-(2-thiazolyl)-2-thiourea (u-14, 624) were each effective in blocking the progesterone- or estrogen-induced increase in gonadotropin release. Treatment with dihydroxyphenylaline (DOPA) or dihydroxyphenylserine (DOPS) restored DA and/or NA levels. However, when conversion of DA to NA was blocked by DDC, the admininstration of DOPA was ineffective in restoring levels of LH and FSH in alpha-MPT-treated rats, although DOPS was effective. The results indicate that NA has a predominant role in transmitting the stimulatory effects of estrogen and progesterone on the release of LH and FSH.