Distribution of NPY and SP and their effects on glucagon secretion from the in vitro normal and diabetic pancreatic tissues

Neuropeptides modulate the function of classic neurotransmitters in the regulation of body function. The role of neuropeptides in the regulation of endocrine secretion from the pancreas of diabetic rat is poorly understood. This study examined the pattern of distribution of neuropeptide-Y (NPY) and substance P (SP) in normal and diabetic rat pancreases. In addition to this, the effect of NPY and SP on glucagon secretion was also examined in the pancreases of normal and diabetic rats. Four weeks after the induction of diabetes, the pancreaseses of normal and diabetic rats were removed and processed for immunohistochemistry and glucagon secretion. The pattern of distribution of glucagon in the pancreas of diabetic rat was conspicuously deranged after the onset of diabetes. The pattern of distribution of NPY and SP was, however, similar in the pancreases of both normal and diabetic rats. Stimulation of normal rat pancreatic tissue with NPY (10(-12) and 10(-9) M) evoked large and significant (P < 0.001) increases in glucagon secretion compared to basal. In contrast to this, NPY inhibited glucagon secretion from the pancreas of diabetic rat. Treatment of pancreatic tissue fragments of normal rat with 10(-9) M SP resulted in significant (P < 0.03) increases in glucagon secretion. SP inhibited glucagon secretion from diabetic rat pancreas. In conclusion, NPY and SP stimulated glucagon secretion from the pancreas of normal rat. In contrast, NPY and SP inhibited glucagon secretion from diabetic rat pancreas.