Serum leptin levels and leptin expression in growth hormone (GH)-deficientand healthy adults: Influence of GH treatment, gender, and easting

Growth hormone (GH) treatment is associated with a reduction in fat mass in healthy and GH-deficient (GHD) subjects. This is mainly mediated via a dir ect GH action on adipose cells and stimulation of lipolysis. Leptin is secr eted from adipose tissue and may be involved in signaling information about adipose tissue stores to the brain. Hormonal regulation of leptin is still not fully elucidated, and in the present study, we investigated both the l ong-term (4-month) and short-term (28-hour) GH effects on serum leptin and leptin gene expression in subcutaneous adipose tissue. In GHD adults (n = 2 4), leptin correlated with most estimates of adiposity (r = .62 to .86), as previously found in healthy subjects. However, no correlation was observed with intraabdominal fat determined by computed tomographic (CT) scan (INTR A-CT). GH treatment for 4 months had no independent effect on either serum leptin or leptin gene expression. In a short-term study, we found that fast ing gradually reduced leptin levels in both healthy men and GHD adults, wit h a maximum reduction of 58% to 60% (P < .01) after 31 hours. No independen t effect of GH suppression or GH substitution on serum leptin was found dur ing fasting. Adipose tissue leptin mRNA correlated with serum leptin (r = . 51, P < .01) and the body mass index ([BMI] r = .55, P < .05). Serum leptin levels and gene expression were significantly higher in women compared wit h men (26.6 +/- 5.8 v 10.0 +/- 1.30 ng/mL, P < .05). However, in regression analysis accounting for the gender differences in subcutaneous femoral adi pose tissue (FEM-CT), the difference in serum leptin disappeared, indicatin g that subcutaneous femoral fat or factors closely related to femoral fat ( eg, sex hormones) may be causal factors for the gender difference in leptin . Copyright (C) 1998 by W.B. Saunders Company.