Acute intravenous acyl ghrelin infusion induces thirst but does not affect sodium excretion: two randomized, double-blind, placebo-controlled crossover studies in hypopituitary patients.

Abstract

Acyl ghrelin, which is the endogenous ligand for the growth hormone secretagogue receptor, potently stimulates pituitary growth hormone release, and to some degree adrenocorticotropic hormone and prolactin. Ghrelin is also orexigenic and has recently been shown to stimulate renal sodium absorption in rodent models. Increased thirst sensation has been observed as a side effect of acyl ghrelin administration in some human studies. The objective of this clinical trial was to investigate the direct effects of acyl ghrelin on thirst sensation and sodium excretion in hypopituitary patients. Hypopituitary patients on stable replacement with hydrocortisone and growth hormone were investigated in two double-blind and placebo-controlled crossover studies. The patients received a 5-h intravenous infusion of acyl ghrelin (5 pmol/kg/min in the first study and 1 pmol/kg/min in the second study). Thirst sensation was measured on a Visual Analog Scale (VAS). In the second study plasma osmolality, vasopressin, copeptin, water intake, diuresis and urinary excretion of sodium and creatinine were measured. In the initial study, acyl ghrelin (5 pmol/kg/min) increased thirst sensation (time × treatment analysis of variance for the effect of acyl ghrelin infusion P = 0.003). In the second study acyl ghrelin (1 pmol/kg/min) also increased thirst (P = 0.04) but did not affect urinary excretion of either sodium or water. We demonstrate that acyl ghrelin infusion increases thirst sensation, without affecting sodium excretion or diuresis in human subjects.