Birth by caesarian section alters postnatal function of the hypothalamic-pituitary-adrenal axis in young pigs

Eight crossbred sows were selected for the present study (n = 4 vaginal del ivery and n = 4 Caesarian section [C-section]). Gestation length did not di ffer between vaginal delivery and C-section pigs (113.6 +/- .1 and 113.2 +/ - .3 d, respectively; P > .16). Blood and tissue samples from 38 pigs were collected at birth. All remaining pigs were sustained with vaginal-delivery sows until 2 wk of age (n = 39). At 2 wk of age, remaining pigs were cathe terized for blood sample collection to assess pituitary-adrenal responsiven ess to an injection of corticotropin-releasing hormone (CRH; 10 mu g/kg). B lood samples were collected at -30, -15, 0, 5, 10, 20, 40, 60, and 90 min; pigs received CRH or saline at time 0. Pigs were killed and tissue samples were collected immediately following the last blood sample. Serum concentra tions of ACTH and cortisol (CS) were measured. Total RNA was isolated from the pituitary and adrenal glands to evaluate gene expression for mRNA speci fic for proopiomelanocortin (POMC) and for the ACTH receptor. Centrifuged c lot:blood ratio was reduced in the C-section pigs at birth (P < .001) and a t 2 wk of age (P < .043), compared with the vaginally delivered pigs. Basal serum concentration of ACTH was greater in C-section than in vaginally del ivered pigs at birth (P = .01) but did not differ at 2 wk of age (P = .42). Basal serum concentration of CS was not different at birth (P = .86) but w as greater in C-section pigs than in vaginally delivered pigs at 2 wk of ag e (P < .04). Serum concentration of ACTH was not different (P > .99) betwee n the two groups of pigs following the CRH: challenge. However, serum conce ntration of CS was; greater (P < .05) in C-section pigs following the CRH c hallenge. Expression of ACTH receptor mRNA tended to be greater in C-sectio n pigs at birth (P < .063) and at 2 wk of age (P < .016). There was no diff erence in POMC mRNA between treatments (P > .73); however, there was a deve lopmental increase (P < .001) from birth to 2 wk of age. These data indicat e that the birth process plays an important role in postnatal function of t he hypothalamic-pituitary-adrenal axis in young pigs.