Metabolic Clearance Rates of Synthetic Human Growth Hormone in Lean and Obese Male Rhesus Monkeys*

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Abstract
The MCR of synthetic human GH was studied in eight adult male rhesus monkeys (Macaca mulatta). Four monkeys were lean (< 20% body fat), and four were obese (> 35% body fat). The monkeys were given a single bolus injection of GH (2.5 .mu.g/kg BW), followed by a constant infusion of GH (250 .mu.g/h) for 2.5 h. venous blood samples were collected before the infusion and every 10 min during the infusion. In both groups a plateau of the plasma GH concentrations, indicating a steady state, was reached 70 min after the start of the infusion. The MCR of GH was calculated from the ratio of the constant GH infusion rate and the plateau plasma GH concentration in each monkey. The MCR of synthetic GH was 12.7 .+-. 1.7 (.+-. SD) L/24 h in the lean group and 19.5 .+-. 2.9 L/24 h in the obese group (P < 0.007). However, the MCR/kg ratio in the lean monkeys was the same as that in the obese animals. We conclude that 1) MCR of GH is directly proportional to body weight; and 2) the lower plasma GH levels in obesity may be due to an increase in its MCR not compensated for by an appropriate increase in the rate of GH secretion.