POSTNATAL OXYTOCIN INJECTIONS CAUSE SUSTAINED WEIGHT-GAIN AND INCREASED NOCICEPTIVE THRESHOLDS IN MALE AND FEMALE RATS

The aim of the present study was to investigate possible long-term eff ects of postnatally administered oxytocin on weight gain, gastrointest inal hormone levels, and nociceptive thresholds in rats. For this purp ose, s.c. daily injections of oxytocin (1 mg/kg) or saline (NaCl, 0.9% ) were given to male and female rat pups on d 10-14 after birth. The a nimals were killed at the age of 60 or 94 d. Treatment with oxytocin r esulted in higher body weight in males, 60 d after birth, and in femal es from d 60 and throughout the rest of the experiment, compared with controls. The higher body weight was due to an increased weight gain i n oxytocin-treated rats, compared with controls, which was most pronou nced between 40 and 60 d after birth. Oxytocin-treated male rats had i ncreased circulating levels of cholecystokinin, a tendency to increase d plasma levels of insulin (p = 0.066), and relatively more adipose ti ssue in the thigh and interscapular region, compared with controls. At the age of 60 d, oxytocin-treated female and male rats had a prolonge d withdrawal latency when measured in the tail-hick test, compared wit h controls. This study shows that oxytocin can induce long-lasting cha nges in weight,gain, hormone levels, and nociceptive thresholds, when administered postnatally, in female and male rats.