Effect of Lesion Size in the Ventromedial Hypothalamus on Growth Hormone and Insulin Levels in Weanling Rats

Abstract

Electrolytic lesions of three different sizes were placed in and around the ventromedial hypothalamic nuclei (VMN) in weanling rats. After three weeks, during which food intake was measured, the rats were killed and the following parameters were measured: plasma growth hormone (GH), insulin and glucose, carcass fat, water and lean body mass, pituitary weight and GH content, and ponderal and linear growth. Progressive decreases in pituitary weight, pituitary and plasma GH, linear growth, and carcass water and lean body mass were produced by increasing lesion size. Concomitant increases occurred in plasma insulin and carcass fat. Ponderal growth and plasma glucose were unaffected by any of the lesions and none of the experimental groups exhibited hyperphagia. The data indicate that the VMN are a control site for GH and insulin secretion. The lack of correlation between parameters of growth and those of obesity suggests that the two hormonal control mechanisms are subserved by independent neuronal assemblies.

Effects of Obesity-Inducing Ventromedial Hypothalamic Lesions on Pulsatile Growth Hormone and Insulin Secretion: Evidence for the Existence of a Growth Hormone-Releasing Factor*

“…In the present study, both pituitary wet weight and pituitary GH concentration were significantly reduced 16 days after the lesion. These results are in agreement with the majority of previous reports (6,8,9,19). Only those studies in which the pituitary GH concentration was measured within 48 h after surgery (17,18) report no effect of the lesion, suggesting that the pituitary GH depletion is gradual.…”

“…Since the first experiments by Hetherington and Ranson (3), it has been well documented that animals with VMH lesions show reduced linear growth (4)(5)(6)(7). Subsequent studies have suggested an impairment in GH secretion, since both weanling (8,9) and adult (10) VMH-lesioned rats exhibit suppressed plasma GH levels. These studies, however, were carried out before delinea-tion of the ultradian rhythm for GH secretion in the rat (11) and were performed in animals that did not exhibit the classic VMH lesion-induced increase in body weight.…”

“…Plasma insulin and glucose were simultaneously moni-212 GH AND IRI IN OBESE VMH-LESIONED RATS 213 tored. In addition, a second study was designed to investigate changes in the pituitary GH concentration in view of previously reported inconsistencies regarding the effects of VMH lesions on the pituitary GH concentration (6,8,9,(17)(18)(19).…”

Effects of monosodium glutamate administration in the neonatal period on the diabetic syndrome in KK mice

“…As with hyperglycaemia the elevated plasma insulin levels in the MSG treated KK mice do not appear to be a direct consequence of the obesity, the degree of hyperinsulinaemia appears to be clearly related to oral substrate intake. Studies in ventromedial nucleus lesioned animals have shown that at least part of the hyperinsulinaemia which occurs is independent of hyperphagia and may be a direct consequence of the hypothalamic lesion [27,29]. No comparable studies have been undertaken in MSG treated animals.…”

“…The reason why only some treated mice developed hyperglycaemia or hyperinsulinaemia may be related to the extent of the lesion produced by MSG. Bernardis & Frohman [29] have shown that the extent of the electrolytic lesions produced in the region of the ventromedial nuclei of weanling rate affected the levels of growth hormone and insulin in plasma. No systematic study of lesion size was made in the present group of animals although in six representative mice it was confirmed that the lesions were located in the arcuate nuclei.…”