Comparison of several insulin-like effects of growth hormone

Three different insulin-like effects of growth hormone were studied in segments of adipose tissue obtained from hypophysectomized rats. The onset of each response was preceded by a characteristic lag period: antilipolysis was seen only after a 10--15 minute exposure to growth hormone; stimulation of glucose oxidation was significant 20 minutes after exposure to growth hormone and increased leucine oxidation was seen only after 30 minutes. Each of the responses was measurable without a detectable delay when the tissues were exposed to hormone during a prior incubation period. Accelerated leucine oxidation was detected when 0.01 microgram/ml growth hormone was present in the incubation medium; the other responses required a minimum of 0.1 microgram/ml. Inhibitors of protein synthesis of concentrations which decreased the incorporation of 14C leucine into protein by 99% had no effect on either the antilipolytic action of growth hormone or the stimulatory action on glucose oxidation, but abolished the acceleration of leucine oxidation. In contrast to findings in diaphragm muscle, theophylline was without effect on any of the insulin-like actions of growth hormone in adipose tissue, even though it decreased the basal rate of glucose and leucine oxidation.