EFFECTS OF THE NOVEL CHOLECYSTOKININ ANALOG SUC-TRP-N(ME)-NLE-ASP-PHE-NH2 ON FEEDING AND CORTISOL RELEASE IN PIGS

Suc-Try-N-(Me)-Nle-Asp-Phe-NH2 is a succinylated tetrapeptide derived from the C-terminal sequence of cholecystokinin octapeptide (CCK-8), w hich has been shown to have high agonist affinity for CCKB receptors. To test the validity of the hypothesis that implicates central CCKB re ceptors in the aetiology of stress-related disorders, such as anxiety and panic, we argued that activation of these receptors by a CCKB rece ptor agonist should (i) suppress feeding motivation in hungry animals and (ii) increase plasma concentrations of the stress hormone cortisol . The effects of systemic and central administration of Suc-Try-N-(Me) -Nle-Asp-Phe-NH2 were, therefore, investigated on operant food intake and cortisol secretion in pigs. Intravenous administration of Suc-Try- N-(Me)-Nle-Asp-Phe-NH2 (0.5-5 mu g/kg) did not affect operant feeding in food-deprived pigs, although the highest dose (5 mu g/kg) produced a small but significant (p < 0.05) increase in plasma cortisol levels 5-30 min after injection. Intracerebroventricular injection of Suc-Try -N-(Me)-Nle-Asp-Phe-NH2 (1-5 mu g) had no effect on operant feeding an d cortisol secretion in this species. The results obtained in this stu dy indicate that central CCKB receptors are unlikely to be involved in stress-related behaviours in pigs.