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Title:   Author  item
                                            Carroll, Jeffery

                                                         - *Jeff Carroll*item
                                            MCARTHUR, N - TEXAS A&M UNIVERSITYitem
                                            WELSH, JR., T - TEXAS A&M UNIVERSITY
  Submitted to: Journal of Veterinary Medicine
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 10/12/2006
                                    Publication  Date: 1/15/2007
                                    Citation: Carroll, J.A., McArthur, N.H., Welsh, Jr., T.H. 2007. In vitro and in vivo temporal aspects of ACTH secretion: Stimulatory actions of corticotropin-releasing hormone and vasopressin in cattle. Journal of Veterinary Medicine. 54:7-14.Interpretive Summary: Exposure to a stressor activates neurotransmitters which mediate the secretion of corticotropin-releasing hormone (CRH) and vasopressin (VP) by neurons in the hypothalamus. The coexpression of CRH and VP by some neurons suggests a biological interaction between these two peptides. CRH and VP can independently stimulate corticotrophs in the adenohypophysis to release adrenocorticotropic hormone (ACTH) which in turn stimulates adrenocorticosteroidogenesis (i.e., adrenal gland synthesis and secretion of progesterone and cortisol). Although CRH and VP are both capable of stimulating the release of ACTH, the relative potency of these neurohormones has been reported to be species specific. Therefore, the objective of the present study was to evaluate the temporal aspects associated with CRH and VP stimulated bovine ACTH secretion in vitro and in vivo. For the in vitro studies, bovine anterior pituitary glands were used to establish primary cell cultures. On day 5 of culture, cells were challenged for 3 h with medium alone (Control) or various combinations and concentrations of bovine CRH and VP. Both CRH and VP each increased ACTH secretion. Maximal increases in ACTH secretion occurred in response to 0.1 micromolar CRH (5.5-fold) and 1 micromolar VP (3.7-fold). The in vivo portion of the study examined possible temporal differences in the activation of the pituitary-adrenal axis by CRH and VP in docile, non-lactating Jersey cows. Plasma samples were collected at 15-min intervals for 4 h pre- and for 6 h post-treatment; samples were also taken at 1, 5, and 10 min post-treatment. Plasma concentration of ACTH did not differ among treatment groups for the 4-h pre-treatment period.  At 1 min post-treatment, bCRH + VP, VP, and bCRH increased ACTH secretion by 22.4-, 9.6-, and 2.2-fold respectively, relative to Control (32.7 + 7.2 pg/ml). Maximal plasma concentration of ACTH occurred at 5, 10, and 15 min post-treatment for the VP (1017.7 + 219.9 pg/ml), bCRH + VP (1399.8 + 260.1 pg/ml) and bCRH (324.8 + 126.2 pg/ml) treatment groups, respectively. Both our in vitro and in vivo data demonstrate that the CRH activity, as compared to VP, is slower in onset in terms of ACTH stimulation, however, it elicits a pituitary response of longer duration. The differential stimulatory activity of CRH and VP may reflect a biological need for dual neurohormonal regulation of ACTH secretion. The biological response needed to maintain homeostasis during a physical versus a psychologically stressful event may require differential activation of the HPA axis. In a previous study, we demonstrated that CRH directly stimulates adrenocortical cortisol secretion in a time- and dose-related manner whereas the direct stimulatory action of VP on cortisol secretion was time-related but not dose-related. Collectively, these data further support the concept that CRH and VP possess differential roles in the maintenance of homeostasis by selective regulation of various levels of the hypothalamic-pituitary-adrenal axis in domestic livestock.
                                Technical Abstract: The objective of the present study was to evaluate the temporal aspects associated with corticotropin-releasing hormone (CRH) and vasopressin (VP) stimulated bovine adrenocorticotropin (ACTH) secretion in vitro and in vivo. For the in vitro studies, bovine anterior pituitary glands were enzymatically dispersed to establish primary cultures. On Day 5 of culture, cells were challenged for 3 h with medium alone (Control) or various combinations and concentrations of bovine CRH and VP. Both CRH and VP each increased (P < 0.05) ACTH secretion. Maximal increases in ACTH secretion occurred in response to 0.1 uM CRH (5.5-fold) and 1 uM VP (3.7-fold), relative to Control cells. The in vivo portion of the study examined possible temporal differences in the activation of the pituitary-adrenal axis by CRH and VP. Jersey cows were randomly assigned to one of four groups (n = 8 cows/group): 1) Control (saline); 2) bovine CRH (bCRH; 0.3 ug/kg BW); 3) VP (1 ug/kg BW); and 4) bCRH (0.3 ug/kg BW) + VP (1 ug/kg BW). Jugular blood samples were collected at 15-min intervals for 4 h pre- and for 6 h post-treatment; samples were also taken at 1, 5, and 10 min post-treatment. Plasma concentration of ACTH did not differ among treatment groups for the 4-h pre-treatment period. At 1 min post-treatment, bCRH + VP, VP and bCRH increased ACTH secretion by 22.4-, 9.6-, and 2.2-fold respectively, relative to Control (32.7 + 7.2 pg/ml). Maximal plasma concentration of ACTH occurred at 5, 10, and 15 min post-treatment for the VP (1017.7 + 219.9 pg/ml), bCRH + VP (1399.8 + 260.1 pg/ml) and bCRH (324.8 + 126.2 pg/ml) treatment groups, respectively. Both the in vitro and in vivo data demonstrated that while VP acutely activates the bovine pituitary-adrenal axis, CRH induced ACTH secretion is slower in onset, but of longer duration. The present study also provides insight into the dynamics of ACTH and cortisol (CS) responsiveness to CRH and VP in cattle.


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