PEGylated cholecystokinin prolongs satiation in rats:: dose dependency and receptor involvement

Background and purpose: Acute intraperitoneal (i.p.) administration of cholecystokinin (CCK) is known to induce a significant, but short-lasting, reduction in food intake, followed by recovery within hours. Therefore, we had covalently coupled CCK to a 10 kDa polyethylene glycol and showed that this conjugate, PEG-CCK9, produced a significantly longer anorectic effect than unmodified CCK9. The present study assessed the dose-dependency of this response and the effect of two selective CCK1 receptor antagonists, with different abilities to cross the blood-brain barrier (BBB), on PEG-CCK9-induced anorexia. Experimental approach: Food intake was measured, for up to 23 h, after i.p. administration of different doses ( 2, 4, 8, 16 and 32 mu g kg(-1)) of CCK9 or PEG-CCK9 in male Wistar rats. Devazepide (100 mu g kg(-1)), which penetrates the BBB or 2-NAP (3 mg kg(-1)), which does not cross the BBB, were coadministered i.p. with PEG-CCK9 (6 mu g kg(-1)) and food intake was monitored. Key results: In PEG-CCK9-treated rats, a clear dose-dependency was seen for both the duration and initial intensity of the anorexia whereas, for CCK9, only the initial intensity was dose-dependent. Intraperitoneal administration of devazepide or 2-NAP, injected immediately prior to PEG-CCK9, completely abolished the anorectic effect of PEG-CCK9. Conclusions and implications: The duration of the anorexia for PEG-CCK9 was dose-dependent, suggesting that PEGylation of CCK9 increases its circulation time. Both devazepide and 2-NAP completely abolished the anorectic effect of i.p. PEG-CCK9 indicating that its anorectic effect was solely due to stimulation of peripheral CCK1 receptors.