ALPHA-1-NORADRENERGIC INHIBITION OF GROWTH-HORMONE SECRETION IS MEDIATED THROUGH THE PARAVENTRICULAR HYPOTHALAMIC NUCLEUS IN MALE-RATS

In the present work we investigated a possible role of an alpha 1-nora drenergic (NA) pathway involving the hypothalamic paraventricular nucl eus (PVN) in the central regulation of growth hormone (GH) release. A week after bilateral electrolytic lesions of the PVN, pulsatile GH-sec retory patterns were monitored in unanesthetized, freely moving contro l or lesioned male rats. While the pulsatility of GH secretion was mai ntained, the amplitude of the pulses and the area under the curve duri ng an 8-hour sampling period were twice as high in PVN-lesioned than i n control rats. Trough levels of GH were similar in the two groups. In activation of PVN alpha(1)-receptors by local infusion of an alpha(1)- NA antagonist, prazosin (50 ng/rat), also induced an increase in GH re lease. In control animals, intravenous injection of the alpha(1)-NA ag onist methoxamine (0.02 mg/100 g body weight) elicited a decrease in G H release but was ineffective when administered to PVN-lesioned rats. These data show that alpha(1)-NA receptors, mediating GH inhibition, a re located in the PVN. In light of the analogous effects observed here in on PVN-lesioned animals and, previously, after locus coeruleus (LC) lesions it is suggested that GH inhibition by the LC is relayed by th e PVN via a local alpha(1)-receptor population.