Galanin: a novel pancreatic neuropeptide

Abstract

Immunofluorescent staining for galanin in canine pancreatic tissue was performed together with an evaluation of the effects of synthetic galanin on pancreatic output of glucagon, somatostatin, and insulin in pentobarbital-anesthetized dogs. A dense network of galaninlike immunoreactive nerve fibers was visualized in association with the islets of Langerhans and occasional galanin immunoreactive fibers were seen to course through the exocrine parenchyma of dog pancreas. During intravenous infusion of synthetic porcine galanin (25 pmol X kg-1 X min-1) pancreatic glucagon output rapidly doubled, and the output of both somatostatin and insulin decreased by 70%. Because arterial and pancreatic venous catecholamine levels remained unchanged, the effects on hormone secretion were not secondary to activation of the sympathetic nervous system. The direct pancreatic action of galanin was confirmed by infusing a peripherally ineffective dose of galanin (0.25 pmol X kg-1 X min-1) into the pancreatic artery, which also stimulated glucagon (+90%) and suppressed somatostatin (-50%) and insulin (-70%) release. The presence of galaninlike immunoreactive neurons in dog islets, together with the direct action of galanin on pancreatic hormone release, suggest that this recently discovered peptide could serve as an important neuromodulator of endocrine pancreatic function.

Autonomic regulation of islet hormone secretion - Implications for health and disease

“…Galanin and NPY are also localised to nerve cell bodies in the celiac ganglion, as shown in dogs [56]. Furthermore, galanin is released from the pancreas upon electrical activation of the sympathetic nerves [77] and galanin and NPY both inhibit insulin secretion, in vivo and in vitro [77±81]. The involvement of galanin in inhibition of insulin secretion induced by activation of sympathetic nerves is particularly important in dogs, where galanin is released into the venous effluent of the pancreas during pancreatic sympathetic stimulation in a quantity which is sufficient to inhibit insulin secretion [82].…”

“…These neuropeptides are both localised to the islet sympathetic nerve terminals. This is evident from several different species in which they are co-localised to the adrenergic marker, tyrosine hydroxylase or greatly depleted by 6-hydroxy-dopamine which selectively destroys the sympathetic nerve terminals [56, 77,78]. Galanin and NPY are also localised to nerve cell bodies in the celiac ganglion, as shown in dogs [56].…”

“…In mice and pigs, NPY seems to be a constituent not only of sympathetic nerve terminals but also of parasympathetic nerve terminals [55,84]. Although a potent inhibition by galanin of insulin secretion has been reported in vivo in dogs [77] no such effect is evident in humans [85]. Inhibition by NPY of glucose-stimulated insulin secretion has been found in studies on rodents [55, 79±81] but no clear effect in dogs [86].…”

Galanin-like Immunoreactive Neural Elements in Domestic Ruminant Pancreas.

“…Immunohistochemical studies have demonstrated galanin in the neural elements of the pancreas of several mammalian species such as pig [14,16], dog [5,14,23], cat [6], rat and mouse [13], baboon [23] and human [1,14,19]. Recently, we have reported striking findings on the presence of galanin-like immunoreactivity not only in the neural elements but also in the endocrine cells of the large islets of cattle, a large ruminant species [2,17].…”

“…One of the extensively studied biological effect of galanin is its ability to regulate insulin secretion in pig [16], dog [5,9,15], rat [8,12,18], mouse [11] and human [1,3]. This physiological action of galanin coupled with its effect on pancreatic exocrine secretion [18,23] and release of other pancreatic hormones such as pancreatic polypeptide [3,20], glucagon [3,5,9,11,12,16] and somatostatin [3,5,9,16] [1,14,19]. Recently, we have reported striking findings on the presence of galanin-like immunoreactivity not only in the neural elements but also in the endocrine cells of the large islets of cattle, a large ruminant species [2,17].…”