Effects of a physiological GH pulse on interstitial glycerol in abdominal and femoral adipose tissue

Physiologically, growth hormone (GH) is secreted in pulses with episodic bu rsts shortly after the onset of sleep and postprandially. Such pulses incre ase circulating levels of free fatty acid and glycerol. We tested whether s mall GH pulses have detectable effects on intercellular glycerol concentrat ions in adipose tissue, and whether there would be regional differences bet ween femoral and abdominal subcutaneous fat, by employing microdialysis for 6 h after administration of GH (200 mu g) or saline intravenously. Subcuta neous adipose tissue blood flow (ATBF) was measured by the local Xenon wash out method. Baseline of interstitial glycerol was higher in adipose tissue than in blood [220 +/- 12 (abdominal) vs. 38 +/- 2 (blood) mu mol/l, P < 0. 0005; 149 +/- 9 (femoral) vs. 38 +/- 2 (blood) mu mol/l, P < 0.0005] and hi gher in abdominal adipose tissue compared with femoral adipose tissue (P < 0.0005). Administration of GH induced an increase in interstitial glycerol in both abdominal and femoral adipose tissue (ANOVA: abdominal, P = 0.04; f emoral, P = 0.03). There was no overall difference in the response to GH in the two regions during the study period as a whole (ANOVA: P = 0.5), but d uring peak, stimulation of lipolysis abdominal adipose tissue was, in absol ute but not in relative terms, stimulated more markedly than femoral adipos e tissue (ANOVA: P = 0.03 from 45 to 225 min). Peak interstitial glycerol v alues of 253 +/- 37 and 336 +/- 74 mu mol/l were seen after 135 and 165 min in femoral and abdominal adipose tissue, respectively. ATBF was not statis tically different in the two situations (ANOVA: P = 0.7). In conclusion, we have shown that a physiological pulse of GH increases interstitial glycero l concentrations in both femoral and abdominal adipose tissue, indicating a ctivated Lipolysis. The peak glycerol increments after GH were higher in ab dominal adipose tissue, perhaps due to a higher basal rate of lipolysis in this region.