Prenatal and Postnatal Ovine Adrenal Cell responses to Prostaglandin E2

Abstract

Objective: To examine the secretory effect of prostaglandin E₂ (PGE₂) and ACTH on the adrenal glands of prenatal and postnatal sheep.

Methods: Immunocytochemistry was used to examine the adrenal cortex and medulla for 17α-hydroxylase and tyrosine hydroxylase immunoreactivity. Microphysiometric technique was used to measure [H⁺] after exposure of whole dispersed prenatal and postnatal adrenal glands to PGE₂, ACTH, or both.

Results: Immunocytochemistry showed many cortical-type cells in all adrenal medullae and many medullary-type cells in fetal adrenal cortices. Maximum H⁺ responsiveness to PGE₂ deceased with increasing age. The developmental age-related pattern of maximum percentage change in [H⁺] during ACTH exposure was similar to previous findings with cortisol production as the endpoint. ACTH stimulated H⁺ production at 80 days' gestation and at all ages greater than 125 days' gestation (P <.05). The molar concentration of ligand required to elicit a response that was 50% of maximum response (EC₅₀) for the ACTH response was lower in fetuses than in newborn lambs (< 1 day and 3 days old), but there was no change in EC₅₀ for PGE₂ across the ages studied. Adrenal cell response to ACTH after prior ACTH and PGE₂ exposure was higher (P <.05) compared with ACTH after ACTH or ACTH alone at 110 days' gestation only and was lower in 3-day-old lambs.

Conclusions: Based on the ACTH results, microphysiometry was a valid method for investigating dispresed adrenal cell physiology. Prostaglandin E₂ stimulated dispersed adrenal cells during the mid-gestation ACTH refractory period, but this effect decreased with increasing age. Prostaglandin E₂ sensitized adrenal cells to ACTH at 110 days' gestation but inhibited ACTH effects at postnatal day 3.