Abstract
Summary
The ability of growth hormone in vitro to stimulate amino acid and sugar uptake by diaphragm muscle from normal rats declines from age 15 days to age 30 days. In 15-day-old intact rats, as in older, hypophysectomized rats, GH has a biphasic effect on amino acid transport: a transient stimulatory phase, followed by a period of refractoriness to stimulation by additional GH. It appears that after age 15 days the refractoriness phase becomes progressively dominant. GH actions are not affected by prolactin or by adrenalectomy. However, during midlactation, exogenous glucocorti-coid may reduce refractoriness, thus enhancing the response to additional GH.
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