Meal intake similarly reduces circulating concentrations of octanoyl and total ghrelin in humans.
ABSTRACT Several data show that meal intake and nutritional status regulate circulating ghrelin concentrations in humans. Ghrelin mainly circulates in two different forms: octanoyl and des-octanoyl ghrelin. Most circulating ghrelin is des-octanoyl ghrelin which is considered inactive because it lacks endocrine activity. However, recent evidence suggests that des-octanoyl ghrelin exerts biological activity such as stimulation of adipogenesis, cardiovascular effects and control of cell growth. In healthy humans, although the total ghrelin concentration is known to peak before meals and to be reduced by food intake, no data are available about the octanoyl ghrelin response in the absorptive state. Therefore, after an overnight fast, we compared the effects of a mixed meal ingestion (meal study) or of additional 240 min fasting (control study) on plasma concentrations of octanoyl and total ghrelin in 6 healthy subjects (body mass index: 23 +/- 0.7). At baseline, octanoyl-ghrelin accounted for 3.15 +/- 0.2% of total circulating ghrelin without differences between the two sessions. A similar ratio was maintained in the absorptive state with no differences between the studies and basal values. Compared with control, meal intake significantly suppressed (nadir at 90 min) octanoyl and total ghrelin by 38 +/- 3 and 40 +/- 3% of basal values, respectively. In the meal study, multivariate analysis of variance showed that serum insulin best predicted plasma octanoyl-ghrelin concentrations accounting for 97% of its variation (r2 = -0.97,p = 0.0016). In conclusion: in healthy humans, octanoyl-ghrelin represents about 3-4% of total circula-ting ghrelin and this ratio is closely maintained in post-absorptive and absorptive states.
Article: Endogenous circulating ghrelin does not mediate growth hormone rhythmicity or response to fasting.[show abstract] [hide abstract]
ABSTRACT: GH secretory profiles in humans are pulsatile and exhibit nocturnal elevation during the early hours of sleep. Fasting augments GH output and rhythmicity. Ghrelin was suggested to exhibit nocturnal increases and to rise in response to nutritional deprivation. We examined whether ghrelin may be an underlying mechanism of GH rhythmicity and response to fasting. We studied nine young healthy subjects during normal feeding and after 2 d of complete fasting. Plasma GH was measured every 10 min, and plasma total and active ghrelins were measured every 20 min. Fasting augmented mean daily plasma GH (1.47 +/- 0.25 vs. 3.30 +/- 0.6 microg/liter; P = 0.012). Neither mean daily total ghrelin (4.19 +/- 0.64 vs. 4.35 +/- 0.74 microg/liter; P = 0.75) nor mean daily active ghrelin (0.13 +/- 0.02 vs. 0.13 +/- 0.02 microg/liter; P = 0.34) changed as a result of fasting. All subjects exhibited nocturnal augmentation of GH secretion; there were no corresponding nocturnal increases in either total or active ghrelin concentrations. Similarly, cross-correlation analysis failed to find any relation between GH and ghrelin pulses. We conclude that ghrelin is unlikely to be of importance in the generation of rhythmic or nutritionally mediated GH secretion.Journal of Clinical Endocrinology & Metabolism 06/2005; 90(5):2982-7. · 6.50 Impact Factor