92 Intra-nasal oxytocin treatment does not attenuate the hypothalamo-pituitary-adrenal axis in beef heifers subjected to isolation stress or restraint and isolation stress

Abstract

Abstract Changes in the physiological, psychological, and behavioral manifestations of stress are observed in association with increases in circulating oxytocin. Providing oxytocin intra-nasally attenuates stressor-induced hypothalamo-pituitary-adrenal (HPA) axis activation in humans and rodents. The present study was conducted to investigate effects of intra-nasal oxytocin supplementation on stressor-induced activation of the HPA axis in beef cattle. We hypothesized that oxytocin would attenuate activation of the HPA axis, ultimately decreasing plasma cortisol. Bos taurus heifers (n = 28) were blocked by bodyweight and randomly allocated to one of four treatment groups, in a 2 × 2 factorial arrangement: 1) Saline, isolated, standing, and unrestrained (S-IS, 0.015mL/kg BW 0.9% isotonic saline, n = 7); 2) Saline, isolated, and restrained (S-RIS; 0.015 ml/kg BW 0.9% isotonic saline; n = 7); 3) Oxytocin, IS (OXT-IS, 0.3 IU/kg BW oxytocin; n = 7); and 4) Oxytocin and isolated and restrained (OXT-RIS, 0.3 IU/kg BW oxytocin; n = 7). Oxytocin and saline were administered intra-nasally. Appropriate stressors were applied 30 minutes following intra-nasal treatment. Blood samples were collected directly following imposing the stressor, and every 10 minutes thereafter, for 2 h. Cortisol concentrations increased over time in animals exposed to restraint and isolation stress (P < 0.01) and decreased over time in animals exposed to isolation stress (P < 0.01). In the present study, oxytocin did not affect measured indicators of HPA axis activation. Greater plasma oxytocin concentrations were observed in restrained animals administered saline, compared with their standing counterparts administered oxytocin (P < 0.01), indicating some endogenous release of oxytocin in response to restraint stress. Overall, restraint stress increased cortisol and oxytocin in Bos taurus heifers compared with heifers subjected only to isolation. Finding a more intermediate stress model may allow for more precise detection of effects of oxytocin on the stress response.