Effect of Obesity on Ambient Plasma Glucose, Free Fatty Acid, Insulin, Growth Hormone, and Glucagon Concentrations*

Abstract

Fasting and postprandial plasma concentrations of glucose, FFA, insulin, glucagon, and GH concentrations were determined in 10 nonobese and 10 obese subjects with normal glucose tolerance. Measurements were made at 0800 h (after a 14-h fast) and at hourly intervals from then until 1600 h. During this time period all individuals ate breakfast at 0800 h (20% of total daily calories) and lunch (40% of total daily calories). Although plasma glucose concentrations were similar throughout the 8-h period in the 2 groups, plasma insulin concentrations were significantly (P less than 0.001) higher in the obese individuals. However, despite the presence of hyperinsulinemia, the obese group also had higher (P less than 0.001) plasma FFA concentration throughout the day. On the other hand, both the absolute and the relative declines in plasma FFA concentration after meals were similar in the 2 groups. Since plasma glucagon and GH concentrations were similar in the 2 groups, altered production of these lipolytic hormones was not responsible for the elevated plasma FFA levels in the obese individuals. These data document the presence in obese individuals of a disassociation in their ability to maintain normal plasma glucose as opposed to plasma FFA homeostasis, and indicate that the increase in plasma FFA concentrations in obesity occurs in the presence of hyperinsulinemia and is not related to abnormalities of either glucagon or GH secretion.

Growth hormone in obesity

“…147,148 In obesity, therefore, the blunted GH secretion might limit the enlargement of the pool of adipocyte precursor cells available for lipid deposition. Likewise, it may prevent a further increase of the already elevated plasma concentrations of NEFA, 103,104,149 which are known to worsen glucose metabolism. 150 In spite of the above, treatment with rhGH has consistently been shown to improve the body composition of obese patients, especially when they have been submitted to severe hypocaloric regimens.…”

“…102 In fact, in normal subjects, the increase in NEFA serum concentrations blunts the somatotropin responses to both GHRH and suprapituitary stimuli. Based on the notion that serum levels of NEFA are commonly elevated in obese patients, 103,104 several studies have been performed in these subjects using acipimox, a nicotinic acid analogue, able to block lipolysis and thus to lower serum NEFA concentrations. The acute administration of this drug to obese subjects has been shown to improve spontaneous and stimulated (GHRH, pyridostigmine, GHRH plus pyridostigmine, GHRH plus GHRP-6) GH secretion.…”

Aspectos neuroendócrinos da síndrome metabólica

“…A quantidade de tecido adiposo está diretamente relacionada aos níveis plasmáticos dos AGL (53). Notese que os AGL estão mais aumentados em pacientes com obesidade central-visceral, e já foi demonstrado que elevações agudas ou crônicas nos AGL são capazes de inibir a liberação de GH pela hipófise (54).…”

Influence of body fat distribution on free fatty acid metabolism in obesity.

“…Free fatty acid metabolism in obesity has, therefore, been the subject of many studies over the last thirty years. Unfortunately, conflicting conclusions regarding several aspects of FFA metabolism have appeared, including the antilipolytic effectiveness ofinsulin in obesity (1,2), the relationship of FFA release to the amount of body fat (3)(4)(5), and the lipolytic responsiveness of obese individuals to catecholamines (6)(7)(8). These potential differences in FFA metabolism between lean and obese humans may be of considerable importance in that they reflect either abnormalities of adipose tissue or of the body's ability to hormonally regulate adipose tissue lipolysis.…”