Leptin serum levels during an oral glucose tolerance test in growth hormone deficiency and acromegaly

Growth hormone (GH) is a lipolytic hormone. GH deficient patients (GHD) have elevated fat mass, whereas active acromegalic patients' (pat) fat mass is reduced compared to normal subjects. Leptin is secreted in adipose tissues and is positively correlated to fat mass, BMI and food intake. During an oral glucose tolerance test (OGTT), leptin generally does not change in normal weight subjects, but increases in some obese subjects. We performed a cross-sectional study in order to investigate the influence of GH on leptin taking GHD and acromegaly as paradigm. Leptin was measured during an 3h lasting OGTT in 52 GHD (21 f/31m, median age 52yrs (range 27–82)) and 43 acromegalic pat (23 f/20m, 50yrs (20–80)). 22 GHD were on GH substitution (GH-sub) for a median of 10yrs (2–42). 30 GHD pat were not substituted for at least 2yrs (non-sub). 18 acromegalic pat had an active disease (act) measured by IGF-I levels, 25 were inactive (inact). Leptin was measured using an immunfluorometric in-house assay. Concentrations of GH and IGF-I were determined using the same commercial immunoassay (Immulite 2000®). In GHD, body composition was measured by Dual-Energy-X-Ray-Absorptiometry. Age and BMI were not significantly different between GHD groups and acromegalic pat. Fat mass was significantly higher in non-sub compared to GH-sub (37% (20–52) vs. 31% (13–54), p<0.01), so were basal leptin (16µg/l (3.3–89) vs. 7.5µg/l (0.5–130), p<0.05) and the area-under-the-curve (AUC) of leptin (p<0.05). Basal leptin and AUC of leptin were significantly lower in act (7.9µg/l (1.6–23.6)) compared to non-sub (p<0.01), whereas act and GH-sub as well as act and inact (10.7µg/l (0.7–56)) did not differ significantly. Leptin decreased significantly after glucose with a minimum at 60min in all groups (p<0.001). The lack of lipolytic GH might lead to higher fat mass of non-sub and consequently lead to their higher leptin levels whereas act and GH-sub have higher GH levels, less fat mass and lower leptin levels. The reason for decreasing leptin levels during OGTT in all groups remains unclear.