Intracerebroventricular Injection of Proinsulin C-peptide does not Influence Food Consumption in Male Long-Evans Rats

Abstract

Insulin and C-peptide are released in equimolecular concentrations in the circulation after food ingestion as they result from the enzymatic cleavage of proinsulin. In the brain, insulin inhibits food intake through hypothalamic receptors. In the present study, we tested the ability of C-peptide to modulate food intake when injected in the brain lateral ventricle of Long-Evans rats. For this purpose, 10 adult male rats (BW 320 - 350 g) were deprived of food overnight. They were intra-cerebroventricularly injected with 10 microg C-pepitde or vehicle (artificial cerebrospinal fluid [CSF]) during the first hour of the light period and chow intake was measured 1, 3, 6 and 24 hours after injection. Chow availability immediately triggered food consumption. Food intake was not different between CSF- and C-peptide-injected rats either after one hour (5.7 +/- 0.6 g [CSF] vs. 6.7 g +/- 0.5 g; ns) or after 24 hrs (23.3 +/- 1.4 g [CSF] vs. 25.1 g +/- 1.4 g; ns). In addition, a higher dose (20 microg/rat) had no effect at all in satiated rats one hour after injection or later contrary to the 100 % increase measured after injection of 2 microg of neuropeptide Y. Thus, we conclude that contrary to insulin, C-peptide does not regulate feeding behaviour in normal rats whatever their insulin status.