The role of leucine-enkephalin on insulin and glucagon secretion from pancreatic tissue fragments of normal and diabetic rats.
Leucine-enkephalin (Leu-Enk) has been shown to be present in endocrine cells of the rat pancreas and may play a role in the modulation of hormone secretion from the islets of Langerhans. Since little is known about the effect of Leu-Enk on insulin and glucagon secretion, it was the aim of this study to determine the role of Leu-Enk on insulin and glucagon secretion from the isolated pancreatic tissue fragments of normal and diabetic rats. Pancreatic tissue fragments of normal and streptozotocin-induced diabetic rats were incubated for 1 h with different concentrations of Leu-Enk (10(-12)-10(-6)M) alone or in combination with either atropine or yohimbine or naloxone. After the incubation period the supernatant was assayed for insulin and glucagon using radioimmunoassay techniques. Leu-Enk (10(-12 )-10(-6)M) evoked large and significant increases in insulin secretion from the pancreas of normal rats. This Leu-Enk-evoked insulin release was significantly (p < 0.05) blocked by atropine, naloxone and yohimbine (all at 10(-6)M). In the same way, Leu-Enk at concentrations of 10(-12)M and 10(-9)M induced significant (p < 0.05) increases in glucagon release from the pancreas of normal rats. Atropine, yohimbine but not naloxone significantly (p < 0.05) inhibited Leu-Enk-evoked glucagon release from normal rat pancreas. In contrast, Leu-Enk failed to significantly stimulate insulin and glucagon secretion from the pancreas of diabetic rats. In conclusion, Leu-Enk stimulates insulin and glucagon secretion from the pancreas of normal rat through the cholinergic, alpha-2 adrenergic and opioid receptor pathways.
Adeghate
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Department of Human Anatomy, Faculty of Medicine and Health Sciences, United Arab Emirates University, Al Ain, United Arab Emirates. eadeghate@uaeu.ac.ae
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D000818:Animals; D001285:Atropine / Q000494:pharmacology; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism*; D004743:Enkephalin, Leucine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D005934:Glucagon / Q000032:analysis / Q000378:metabolism*; D007328:Insulin / Q000032:analysis / Q000378:metabolism*; D000078790:Insulin Secretion; D009270:Naloxone / Q000494:pharmacology; D010179:Pancreas / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D015016:Yohimbine / Q000494:pharmacology
D007328:Insulin; D015016:Yohimbine; D009270:Naloxone; D004743:Enkephalin, Leucine; D001285:Atropine; D005934:Glucagon