Developmental regulation of preproenkephalin (PENK) gene expression in the adrenal gland of the ovine fetus and newborn lamb: effects of hypoxemia and exogenous cortisol infusion

Abstract

Development of the fetal adrenal gland is crucial not only for maturation of several fetal organ systems and the initiation of parturition, but also for the development of the fetal response to stress. The enkephalin-related peptides are present in the chromaffin cells of the fetal adrenal medulla and are secreted in response to stress and with sympathetic stimulation. However, changes in expression of preproenkephalin (PENK) with gestation and in response to stress have not been studied in detail. Therefore we examined the developmental pattern of PENK gene expression in the adrenal gland of fetal and newborn lambs, and of adult sheep. We also determined whether levels of PENK mRNA in the fetal adrenal gland changed in response to exogenous glucocorticoids in late gestation, or in response to hypoxemia. Adrenal glands were removed from fetal sheep, lambs and adult sheep at different stages of development for measurement of PENK mRNA. Cortisol was infused (5 micrograms/min) for 12, 24 or 96 h beginning on day 124-129 of gestation. Moderate hypoxemia was induced for 48 h beginning on day 126-130, or at day 134-136 of gestation, by lowering the maternal fractional inspired oxygen. At the end of the treatment periods, the ewes and fetuses were euthanized. Adrenal PENK mRNA were measured by Northern blot analysis. PENK mRNA levels in fetal adrenals were significantly higher (P < 0.05) on days 140-141 of gestation than earlier in pregnancy, and then decreased significantly with the onset of parturition (days 142-146). After cortisol infusion to the fetus for 96 h there was a significant reduction in adrenal PENK mRNA levels. Hypoxemia resulted in a significant increase in PENK mRNA levels in fetuses at day 126-130 of gestation, but not at the later time in pregnancy when endogenous plasma cortisol concentrations were higher. We conclude that there is a decrease in levels of PENK mRNA in the fetal adrenal gland before parturition at the time of the endogenous prepartum rise in plasma cortisol. Hypoxemia led to an elevation of PENK mRNA levels in fetuses at less than 130 days, but after that time, when the basal and stimulated cortisol responses had risen, there was no significant effect of hypoxemia on PENK mRNA. Cortisol infusion to the fetus at this stage of pregnancy resulted in a decrease in adrenal PENK mRNA levels. We suggest that cortisol may play an important role in the regulation of fetal adrenal PENK mRNA levels and enkephalin synthesis by the adrenal gland of the fetal sheep.

Effect of Cerebral Hypothermia on Cortisol and Adrenocorticotropic Hormone Responses after Umbilical Cord Occlusion in Preterm Fetal Sheep

“…Fetal plasma ACTH and cortisol levels were measured using specific radioimmunoassays (RIA) established and validated for ovine plasma (25). Total immunoreactive cortisol concentrations were determined in triplicate after extraction with diethyl ether by an in-house RIA validated for use with maternal and fetal ovine plasma.…”

Effect of Cortisol on C-Type Natriuretic Peptide in Ovine Pregnancy: Differential Responses in Fetal and Placental Tissues

“…Cortisol was measured by RIA with inhouse produced anticortisol rabbit sera (F1M1), after extraction of plasma with diethyl ether (17). The antibody was validated for sheep plasma and exhibited low cross reactivity with derivatives of cortisol (3.3% for 11-deoxycortisol, 0.18% for cortisone, 0.5% for corticosterone, 0.015% for progesterone, 0.002% for 11␣-hydroxyprogesterone at 50% binding, no detectable cross reactivity for 17␣-hydroxypregnenolone, pregnanediol, 21-deoxycortisone, aldosterone, cholesterol, or dexamethasone) (18).…”

“…Peptide standards were made from synthetic human proCNP (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19), taking into account the purity data supplied (Chiron Technologies, Victoria, Australia).Within-and between-assay coefficients of variation were 4.9 and 6.4%, respectively, at 22 pmol/L.…”

Gene expression following fetal hypoxemia

“…ämischen Feten signifikant und stimmte mit anderen Befunden überein, die bei den älteren hypoxämischen Feten eine persistierenden Zunahme der Cortisolkonzentrationen zeigen [5]. Im Gegensatz zu der ansteigenden Cortisolkonzentration bei den hypoxämischen Feten blieb die Androstendionkonzentration im fetalen Plasma unverändert und zeigte bei den jüngeren hypoxämischen Feten tendenziell eine Abnahme.…”

“…In weiterführenden Untersuchungen wurde gezeigt, dass sich die Menge an mRNA für regulatorische Moleküle der fetalen Nebennierenrinde, wie das Preproenkephalin (PENK), durch die fetale Hypoxämie ändert [5].…”