Acute orexin effects on insulin secretion in the rat: In vivo and in vitrostudies

Orexin-A and orexin-B are members of a family of newly described orexigenic hypothalamic neuropeptides. Scanty data are available suggesting the invol vement of orexins in regulation of the secretion of pituitary hormones and in control of energy homeostasis. Present studies aimed to explain whether orexins affect blood insulin concentration and insulin secretion in the rat . To check this possibility, adult female rats were subcutaneously injected with different doses (1 or 2 nmol) of orexin-A or orexin-B. A bolus admini stration of orexin-A resulted in an increase in blood insulin (up to min 12 0) and glucose (60 min after injection) concentration. The higher dose of o rexin-B, on the other hand, exerted effect on insulin secretion only at min 60 of experiment and neither doses changed blood glucose level. Only orexi n-A stimulated insulin secretion in an in vitro perfusion system of the rat pancreas preparation, while orexin-B was less effective. The results demon strate that orexins belong to a group of neuropeptides influencing insulin secretion and acting directly on the pancreas. Direct, at least partial, ef fect of orexin on insulin secretion may be connected with the regulation of metabolism by this peptide.