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Plasma concentration and pituitary content of growth hormone (GH) have been measured by radioimmunoassay in female and male mice under various experimental conditions known to elicit GH secretion in primates. Complete cross reactivity between mouse and rat GH was observed. Both plasma GH concentration and pituitary GH content were higher in male than female mice. None of the procedures employed (except 2-deoxyglucose administration in males but not in females) altered pituitary GH content. The stress of ether and/or bleeding on conscious mice resulted in a prompt fall in plasma GH. Thus the mouse, like the rat, responds to stress by an apparent inhibition of GH secretion in contrast to primates where stress stimulates GH secretion. Insulin-induced hypoglycemia resulted in a fall in plasma GH which was statistically significant in female mice but not in males. Neither arginine nor 2-deoxyglucose injections altered plasma GH levels. Plasma GH was unchanged in mice fasted 24 hr, or in fasted mice injected with glucose 20 min before blood sampling. The failure of fasting, insulin-induced hypoglycemia, or 2-deoxyglucose to evoke GH secretion, or of hyperglycemia to lower plasma levels of GH in mice suggests that glucose is not involved in feedback control of GH in this species. None of the stimuli used, which are known to cause GH secretion in primates, was effective in the mouse; thus, this work emphasizes the species differences in GH secretion and control. {Endocri-nology 9 1 : 483, 1972)

A modification of the Halász-Pupp neurosurgical knife was used in female rats to completely or partially isolate the medial basal hypothalamus from the adjacent central nervous. Changes in body weight and length, plasma GH levels, and GH metabolism were measured. Whereas complete or anterior knife cuts resulted in increased body length and weight, posterior cuts had no effect. At 7 months following surgery, non-stress plasma GH levels were not elevated in any group, including those exhibiting enhanced linear growth. Ether stress decreased mean plasma GH levels significantly in all groups except that with complete cuts; nevertheless, most animals with complete cuts responded to stress with decreases in plasma GH. GH turnover rates in heavy animals of normal length did not differ from those in intact controls. In contrast, animals that were both heavier and longer than controls exhibited a decreased turnover rate and increased t_1/2 of ¹²⁵I-labeled GH. Volumes of distribution of GH were comparable in intact and operated rats of normal length but markedly increased in those of exceptional length. Although no increase in non-stress plasma GH levels was observed at 7 months following surgery in animals

The effects of surgical isolation of the medial basal hypothalamus (MBH) on growth were studied in adult female rats. Isolation of MBH caused a gradual increase in naso-anal (N-A) length. N-A length was significantly increased 92 days after surgery and the augmented rate of growth continued until autopsy at 139 days. The increase in N-A length was accompanied by a marked gain in body weight and by conspicuous obesity. Non-stress and stress levels of plasma growth hormone (GH) were determined by radio-immunoassay at 7–11 weeks after surgery. Rats with MBH isolation had circulating non-stress levels of GH that were approximately 6 times higher than those of controls (p < 0.01) at both 7 and 11 weeks. Whereas intact controls demonstrated a marked decrease in GH levels following ether stress, those with MBH isolation showed variable responses: some demonstrated normal decreases; others showed no responses; while yet another group showed marked increases. These results confirm and extend prior findings and suggest that the MBH receives neural connections that normally inhibit growth and plasma GH levels.

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