Insulin and growth hormone in lean and obese pigs.

Plasma glucose, immunoreactive insulin (IRI), and growth hormone (GH) were determined in fasted lean and genetically obese pigs at 1, 3, and 6 mo of age. Rate of glucose clearance and plasma IRI and GH response in provocative stimulation were also measured. Fasting glucose was similar in lean and obese pigs, whereas glucose clearance rate was more rapid in lean pigs. Obese pigs were not hyperinsulinemic but had lower plasma GH than lean pigs. At 1 mo of age, both lean and obese pigs had higher plasma IRI and GH as compared to 3 and 6 mo. Glucose infusion produced increases in plasma IRI at 1, 3, and 6 mo, respectively, with the greatest increases at 6 mo. Plasma IRI peaked at the same level in both pig types at a given age; but due to a more prolonged response in obese pigs, the overall IRI response to glucose infusion was greater in obese pigs. Arginine infusion caused much smaller IRI responses than glucose, but the response of obese pigs was significantly greater than that of lean pigs. Both provocative stimuli caused increases in plasma GH. The GH response to glucose infusion in obese pigs was considerably less than in lean pigs. These observations suggest mild insulin insensitivity and a reduced GH secretory potential in the obese as compared to lean pigs.