title: Serum insulin but not leptin is associated with spontaneous and growth hormone (GH)-releasing hormone-stimulated GH secretion in normal volunteers with and without weight loss.
abstract: Weight loss in humans is associated with elevated hypothalamic-pituitary growth hormone (GH) secretion. This study evaluates the effects of weight loss on the hypothalamic-pituitary (GH-releasing hormone [GHRH]-GH) axis in 14 normal-weight (body mass index [BMI], 25+/-1 Kg/m2) subjects, of whom half had undergone a diet-induced weight loss of 14%+/-2% (mean+/-SEM). Insulin-like growth factor-1 (IGF-1), insulin, oral glucose tolerance, leptin, and GH pulse patterns were determined in both groups after weight maintenance for 1 week. Of note, we tested the effects of recent weight loss (3 months) and not a recent dietary intake, since both groups ingested a normal calorie diet for 2 days in the Clinical Research Center (CRC) prestudy. Serum insulin (3.8+/-0.7 v 9.0+/-0.9 microU/mL, P < .01) and C-peptide (0.44+/-0.06 v 0.59+/-0.04 ng/mL, P < .05) were significantly lower in the weight loss group. Serum leptin was not different. Endogenous GH pulse height (11.9+/-4.8 v 1.3+/-0.1 microg/L, P < .05), area per GH pulse ([AUC] 57+/-28 v 6+/-1 microg/L, P < .05), and mean GH (3.91+/-0.76 v 0.85+/-0.16 microg/L, P < .01) were increased in the weight loss group. The serum insulin level was inversely associated with the mean GH concentration (r=-.678, P < .01) and GH pulse height (r=-.733, P < .01). In addition to spontaneous GH secretion, the GHRH-stimulated GH pulse height (41.8+/-18.1 v7.1+/-1.6 microg/L, P < .05) and AUC (161+/-35 v46+/-13 microg/L/min, P < .05) were also increased in the weight loss group. The insulin concentration was also inversely correlated with the GHRH-stimulated GH pulse height (r=-.718, P < .01). The leptin concentration was correlated with the BMI (r=.554, P < .05) and body fat (r=.744, P < .01), but not with GH secretion. In summary, even though these patients were on a normal calorie diet, a history of recent weight loss in young men and women of normal weight and health can be associated with a significant increase in spontaneous GH pulse height and GHRH-stimulated pulse height. Weight loss was also associated with a reduced serum insulin level. The observed increase in GH secretion may be secondary to the reduction in insulin or alterations of other factors acting at the site of the pituitary.
authors.affiliation: Department of Medicine, Harbor-UCLA Medical Center, Torrance, CA, USA.
authors.forename: S
authors.initials: S
authors.lastname: Manglik
authors.forename: B
authors.initials: B
authors.lastname: Cobanov
authors.forename: G
authors.initials: G
authors.lastname: Flores
authors.forename: R
authors.initials: R
authors.lastname: Nadjafi
authors.forename: J A
authors.initials: JA
authors.lastname: Tayek
mesh_terms: D001823:Body Composition; D005260:Female; D005951:Glucose Tolerance Test; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology*; D019382:Human Growth Hormone / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000097:blood*; D007334:Insulin-Like Growth Factor I / Q000032:analysis; D020738:Leptin; D008297:Male; D011506:Proteins / Q000032:analysis*; D015431:Weight Loss
chemical_list: D007328:Insulin; D020738:Leptin; D011506:Proteins; D019382:Human Growth Hormone; D007334:Insulin-Like Growth Factor I; D013007:Growth Hormone-Releasing Hormone