Effects of the novel cholecystokinin analogue 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-B), which has been shown to have high agonist affinity for CCKB receptors. To test the validity of the hypothesis that implicates central CCKB receptors in the aetiology of stress-related disorders, such as anxiety and panic, we argued that activation of these receptors by a CCKB receptor 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 micrograms/kg) did not affect operant feeding in food-deprived pigs, although the highest dose (5 micrograms/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 micrograms) had no effect on operant feeding and cortisol secretion in this species. The results obtained in this study indicate that central CCKB receptors are unlikely to be involved in stress-related behaviours in pigs.