Prolongation of intermeal interval by gastrin-releasing peptide depends upon time of delivery

We have previously shown that brief, vena caval infusion of gastrin-releasing peptide1-27 (GRP), delivered shortly (5 min) after the end of the first spontaneous nocturnal meal, significantly prolongs the postprandial intermeal interval (IMI) without affecting the size of the subsequent meal in freely-feeding rats. In the present study, we tested whether varying the time at which GRP was delivered during the IMI affected its ability to prolong the interval. Specifically, rats (n = 9), fed milk ad lib and with indwelling inferior vena caval catheters, were infused for 1 min with saline or 10 nmol/kg of GRP either 5, 15, or 30 min after the end of the first spontaneous nocturnal meal. Each received a single infusion on any given test day. Infusions and recording of individual licks were fully automated and computer-controlled. When delivered 5 or 15 min after termination of the first nocturnal meal, GRP significantly increased the IMI from a control level of 82 +/- 12 min to 111 +/- 13 min and 106 +/- 18 min, respectively. Infusion of GRP 30 min after meal termination did not significantly alter the IMI. No effect on the size of the subsequent meal was observed under any condition. These results are consistent with the hypothesis that endogenous GRP acts in conjunction with events occurring shortly after meal termination to extend the duration of the IMI.