EVIDENCE FOR STIMULATION OF INSULIN SECRETION BY GROWTH HORMONE IN THE RAT1

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Abstract
Based on the observation that only insulin will increase the concentration of glycogen in rat adipose tissue both in the presence and the absence of the pancreas, evidence for insulin secretion in response to growth hormone treatment was sought by measuring adipose tissue glycogen levels in fed intact and eviscerated rats. It had previously been shown that growth hormone had no influence on adipose tissue glycogen in 48-hour fasted rats, but the pancreas of these animals may be presumed to have been depleted of insulin. In fed rats given 2 mL of 50 per cent glucose by stomach tube both insulin and growth hormone brought about significant increases in the glycogen content of the dorsal interscapular brown fat pad. Acutely eviscerated rats, which lack the pancreas, showed no accumulation of adipose tissue glycogen in response to a subcutaneous glucose load compared to intact controls unless given insulin. In the latter instance adipose tissue glycogen levels were comparable to those in intact rats given the same dose of glucose and insulin. Growth hormone had no influence on adipose tissue glycogen values in eviscerated rats even when given together with insulin. These data suggest that the pancreas is necessary for the adipose tissue glycogen response to growth hormone and that the effect is not mediated by growth hormone potentiating the action of circulating or tissue bound insulin. It is concluded that growth hormone stimulates the secretion or release of insulin from the pancreas, but data are reviewed which indicate that this is only one of several mechanisms involved in the action of growth hormone on carbohydrate metabolism.