Pancreatic endocrine responses to substance P and calcitonin gene-related peptide in conscious calves

Both substance P (SP) and calcitonin gene-related peptide (CGRP; 0.13 micrograms.min-1.kg-1 for 10 min) produced a significant rise in arterial plasma pancreatic polypeptide (PP) concentration, and additive responses were obtained when both peptides were infused simultaneously and/or with acetylcholine (0.7 micrograms.min-1.kg-1 ia). The PP response to SP was abolished by intravenous infusions of glucose, whereas those to CGRP and acetylcholine were not significantly affected. Neither SP nor CGRP had any effect on plasma insulin concentration, either in the presence or absence of exogenous glucose, whether infused singly or together, or in the presence of acetylcholine. SP, but not CGRP, produced a small but statistically significant rise in mean plasma glucagon concentration when infused together with acetylcholine. These results suggest that SP and CGRP may modulate the secretion of PP and glucagon in the normal conscious calf but not that of insulin. It is also possible that SP modulates secretion of pancreatic glucagon in these animals.