Pharmaco-ontogenic modulation of feeding by oxytocin, bombesin, and their antagonists

Oxytocin (OX) and bombesin (BN) can both suppress food intake in adult rats. In light of important transient fluctuations in peptide and/or receptor expression early after birth, this study characterized the feeding-suppressant effects of OX and BN during early development and explored their physiological relevance, using BN or OX antagonists, [D-Phe⁶,des-Met^6-14]BN(6-14), ethyl amide (des-Met), and [des-Glycinamide⁹,d(CH₂)₅¹,O-Me-Tyr²,Thr⁴,Orn⁸]vasotocin (vasotocin), respectively. On postnatal days (PD) 1, 5, 10, and 15, groups of food-deprived Sprague-Dawley rat pups (n = 8-11) were injected SC with saline (control) or BN (0.6, 0.06, or 0.006 mg/kg), des-Met (10 mg/kg), OX (1.2, 0.6, 0.3, or 0.15 mg/kg), or vasotocin (1.0 mg/kg), and their intake of milk (from a piece of absorbent paper saturated with warm milk) was monitored. Results revealed that BN and OX suppressed milk intake from PD 1 to PD 15. Although the milk intake varied with the peptide dose, this effect was age dependent. The doses of BN (but not OX) required to suppress feeding were higher than those needed in adults. When administered alone, OX or BN antagonists did not affect food intake, except at PD 15 for des-Met and PD 1 and PD 10 for vasotocin, where they enhanced feeding. These results suggest that pharmacological effects to OX and BN are apparent from hours after birth and that these peptides may play a role in the regulation of ingestive behavior from early on in ontogeny.