Stimulation of gastric proteases in the neonatal pig by a rise in adrenocortical secretion at parturition

Abstract

In many species adrenocortical activity and glucocorticoid secretion increase in late gestation and reach a peak at birth. In this study, we investigated the hypothesis that glucocorticoids stimulate the synthesis of gastric protease zymogens in the perinatal period of pigs. Pigs were delivered by Caesarean section 3-4 days prior to term (to circumvent the natural cortisol surge) and treated daily with either saline (n = 11), metyrapone (an inhibitor of cortisol synthesis, n = 12), adrenocorticotropic hormone (ACTH, n = 14) or cortisol-acetate (n = 6). The pigs were killed at 3 or 6-7 days of age and concentrations of protease zymogens in gastric mucosal extracts determined by electroimmunoassay. Zymogen contents were also determined in control (untreated) pigs from one week before birth to four weeks after birth. In control pigs, concentration of prochymosin increased rapidly before term, peaked at birth, and decreased in the postnatal period; concentrations of pepsinogen A, pepsinogen B and progastricsin were low in newborn pigs and increased in the weeks after birth. Caesarean-delivered pigs injected with saline had lower concentrations of prochymosin and pepsinogen A at 6-7 days than vaginally delivered pigs of the same postnatal age. The concentrations of these zymogens were further reduced after metyrapone treatment (depressed cortisol secretion) but were increased after treatment with ACTH (stimulated cortisol secretion) or cortisol-acetate (exogenous glucocorticoid). No consistent effects were observed for the two minor gastric protease zymogens in the pig, pepsinogen B and progastricsin. The results suggest that the normal pre-partum surge in circulating cortisol stimulates the development of the major gastric protease zymogens in the pig, prochymosin and pepsinogen A.