Modification by hypothalamic Lesions of the release of growth hormone (GH) following stimulation of the ventromedial hypothalamic nucleus in the rat

Abstract

This study was designed to clarify the localization(s) of hypothalamic area(s) concerned with the regulation of growth hormone (GH) release evoked by electrical stimulation of the hypothalamic ventromedial nucleus (VMH) of rats. Bipolar concentric stimulating electrodes were implanted in the bilateral VMH or dorsal premammillary nucleus and the jugular vein was cannulated for blood sampling one week prior to the experiments. At the same time lesions of the anterior periventricular nucleus or dorsal premammillary nucleus were performed with an anodal current. The rats were pretreated with α-methyl- p-tyrosine to prevent spontaneous GH bursts. As previously reported, stimulation of the VMH for 10 min appeared to suppress GH release during the period of stimulation but within 10 min after termination of stinulation plasma GH had risen from a resting level of 19.3 ± 2.3ng/ml plasma, to 275.3 ± 62.3ng/ml. The apparent suppression of GH release during the VMH stimulation was abolished in the anterior periventricular nucleus-lesioned rats. In these rats, GH release occurred during the VMH stimulation and plasma GH increased to 905.4 ng/ml by 10 min, at which time the stimulus was terminated. On the other hand, the VMH stimulation completely failed to raise plasma GH levels in rats with dorsal premammillary nucleus lesions either during or after VMH stimulation. Although lesions of the dorsal premammillary nucleus blocked the delayed VMH-induced rise, stimulation of the dorsal premammillary nucleus itself caused no change in the plasma GH level. These results indicate that the stimulation of VMH exerts an inhibitory effect on GH release through the anterior periventricular nucleus and that the dorsal premammillary nucleus is important in the delayed GH release induced by VMH stimulation.