ASSOCIATION OF ENDOGENOUS INSULIN-SECRETION AND MODE OF THERAPY WITH BODY-FAT AND SERUM LEPTIN LEVELS IN DIABETIC SUBJECTS

Insulin is one of the hormonal regulators of leptin synthesis and part icipates in adipose tissue maintenance. The present study was undertak en to clarify the association of endogenous insulin secretion and mode of therapy with body fat and serum leptin levels in diabetic subjects . We measured the fasting serum C-peptide level, as an estimate of end ogenous insulin secretion, and the serum leptin level in 176 Japanese diabetic subjects (79 men and 97 women; age, 55.9 +/- 14.3 years; body mass index [BMI], 23.8 +/- 4.1 kg/m(2) [mean +/- SD]). Thirty-one sub jects were treated with diet therapy alone, 66 with sulfonylurea (SU), and 79 with insulin (including 29 with type I diabetes mellitus). Bod y fat was analyzed by the impedance method, Serum leptin levels signif icantly correlated with the BMI and body fat and were higher in women, mainly because of their greater body fat, Serum C-peptide concentrati ons positively correlated with body fat and serum leptin in subjects t reated with diet and SU. In insulin-treated type II diabetic subjects, both serum C-peptide and the daily insulin dose were weakly associate d with body fat and serum leptin. In those subjects, despite a lower p ercent body fat and body fat mass, serum leptin concentrations (10.3 /- 8.4 ng/mL) were comparable to the levels in subjects treated with d iet (8.8 +/- 8.5 ng/mL). When compared within the same BMI and body fa t groups (BMI 20 to 25 and > 25 kg/m(2)) including the control subject s matched for age and sex, serum leptin levels were higher in insulin- treated type II diabetic subjects versus the control subjects and diab etic patients treated with diet or SU, Stepwise regression analysis fo r all of the diabetic subjects showed that both the serum C-peptide le vel and exogenous insulin administration, as well as the BMI, gender, and age, were determinants of the serum leptin level. In conclusion, e ndogenous insulin secretion is closely associated with body fat and se rum leptin in diabetic subjects treated with diet therapy and SU, In J apanese insulin-treated type II diabetic subjects, both endogenous and exogenous insulin are associated with body fat and serum leptin, whic h is maintained at levels comparable to or somewhat higher than the le vels in control subjects and diabetic patients treated without insulin . Copyright (C) 1998 by W.B. Saunders Company.