Submitted to: Biology of the Neonate
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 11, 1995
Publication Date: N/A
Interpretive Summary: The neonatal period is a fragile time for pigs that requires many adjustments to the extrauterine environment. Steroid hormones of the adrenal cortex not only function to maintain homeostasis--a constant internal environment--but also have profound effects on growth, tissue differentiation, and immunity. In neonatal rats there is a 2-week period of greatly reduced adrenal function. If such a phenomenon exists in pigs it could contribute to poor neonatal growth and health. The current study was conducted to determine if there is a period of reduced adrenal function in neonatal pigs at three ages: 12, 19, and 26 days of age. Measurements were made of basal--normal--and stress-associated adrenal steroids and the pituitary-derived hormone ACTH which regulates these steroids. The data clearly show no greatly reduced pituitary-adrenal function at the ages studied. There were age-related changes in functioning of the pituitary-adrenal axis in neonatal pigs which suggest postnatal development of these glands. Thus, beneficial--as well as deleterious--effects of adrenal steroids should be present. Artificial regulation of adrenal function could prove extremely useful in optimizing growth and health of neonatal pigs.
A study was conducted with neonatal boars to measure in vivo and in vitro age-related changes in functioning of the pituitary-adrenocortical axis. Piglets were randomly assigned to control (n = 7 to 9/age) or treated (1- min restraint, n = 9 to 11/age) groups to be sampled at 12, 19, or 26 days of age. Blood samples were taken via catheter 10 min before and 3, 10, and 20 min after restraint or at similar time intervals in controls. One day later, piglets were killed and in vitro responses of adrenocortical cells to ACTH(1-24) measured. Basal plasma ACTH was greatest (P = .035) on day 12 when compared with later ages, but basal plasma cortisol was comparable at the three ages. When compared with controls, restraint elevated incremental and integrated plasma ACTH and cortisol responses at each age (P < .025). On day 12, plasma ACTH (P = .08) and cortisol (P < .017) responses to restraint were greater than at later ages. Similarly, the ratio of plasma cortisol/log ACTH was greatest on day 12 (P < .05). On the contrary, basal- and ACTH-stimulated maximal in vitro cortisol production by adrenocortical cells was greatest (P <.05) on day 20 compared with other ages. In vitro sensitivity to ACTH did not change with age. Binding to adrenal ACTH receptors was greatest (P < .05) at day 13, which may help explain the apparently increased in vivo response of the adrenal gland to ACTH at this time. These data suggest subtle age- related changes in functioning of the pituitary-adrenal axis in neonatal boars. Differences between in vivo and in vitro responses undoubtedly reflect the involvement not only of secretion but also of clearance in determining plasma hormonal concentrations and the need for the in vivo milieu for accurate expression of cellular responses.