Correlation between plasma beta-cell tropin concentrations and body weight in obese rhesus monkeys

The fasting plasma concentration of the pituitary peptide beta-cell tropin [beta-CT, adrenocorticotropic hormone-(22-39)] was measured in 17 rhesus monkeys from a colony known to develop spontaneous obesity. The weight of the animals was 9.4-23.9 kg (12-46% body fat). Plasma beta-CT concentrations were 0.03-0.84 nmol/l and were strongly correlated with body weight (P = 0.014, r = 0.584). Plasma beta-CT was also correlated with plasma insulin concentration as a power function (P = 0.011, r = 0.600) and with percent body fat up to 40% (P = 0.003, r = 0.0804). Plasma insulin is also correlated with body weight (P = 0.015, r = 0.578) but does not decline when body fat is in excess of 40%, supporting the hypothesis that beta-CT may be involved in a feed-back control mechanism, perhaps mediated by insulin. Because beta-CT has been shown in rodent studies to be a potent insulin secretagogue and lipogenic agent, it is possible that beta-CT is causally involved in the development of obesity and that there may be central determinants of obesity mediated through pituitary secretion of beta-CT.