Comparison between the central effects of CRH and AVP in steers.

In cattle, the in vivo effects of centrally administered corticotropin-releasing hormone (CRH) or arginine vasopressin (AVP) from the perspective of stress regulation have not been fully elucidated. We compared behavioral, adrenocorticotropic, and autonomic nervous responses to intracerebroventricularly infused bCRH or AVP in steers. Intracerebroventricular infusions of both bCRH and AVP (0.2, 2, 10 and 20 nmol/500 mul/30 min) evoked a dose-related increase in plasma concentrations of ACTH and cortisol. At 10 nmol, the AUC response of cortisol concentration to bCRH tended to be higher than that in response to AVP (p=0.075). There were significant differences among treatments in the total number of head shaking (Friedman's test, chi2=22.79, p=0.004), upright posture (chi2=16.80, p=0.032), head rubbing (chi2=23.93, p=0.002), tongue playing (chi2=27.18, p=6.58E(-4)), and bleating (chi2=26.84, p=7.54E(-4)). AVP 10 and 20 nmol treatments induced more head shaking and tongue playing than vehicle treatment (Nemenyi multiple comparisons: p<0.1). Ten nmol (32.8+/-40.2 times) and 20 nmol (34.8+/-19.9 times) of bCRH induced bleating, but no dosage of AVP induced bleating. These findings indicate that both bCRH and AVP could activate HPA axis in steers when infused intracerebroventricularly and that bCRH was more potent to stimulate HPA axis than AVP. As for the effects on behavioral function, high dosages of both peptides induced stereotyped behaviors and the types of stereotyped behaviors induced were different between bCRH and AVP.