Adrenocortical activity in the newborn spontaneously hypertensive rat

Blood pressure is reportedly elevated in the spontaneously hypertensive rat (SHR) neonate, the etiology of which remains unclear. Aberrations in the h ypothalamic-pituitary-adrenal axis have been implicated, as it is well acce pted that excess corticosteroids are associated with hypertension. We exami ned aspects of adrenocortical activity in the neonatal SHR 1 to 21 days old and its normotensive genetic control, the Wistar-Kyoto rat (WKY). We found a fourfold greater abundance of P450scc mRNA in adrenals of SHR versus WKY day 1 neonates, and increasing but comparable abundance of adrenal P450c11 B mRNA on neonatal days 1 to 21. The pattern of P450c11AS mRNA expression w as distinctly different in the adrenals of SHR and WKY neonates; the relati ve abundance of this mRNA in SHR increased 15-fold over the 21-day period e xamined, whereas that in WKY remained fairly stable. RT-PCR for the presenc e/abundance of adrenal P450c11B3 mRNA showed absence in day 1 SHR and WKY, comparable abundances on neonatal days 7 and 14, and a distinctly greater a bundance in the day 21 SHR adrenals. Peripheral corticosterone levels were threefold greater in the day 1 SHR neonate; aldosterone levels were elevate d in both the SHR and WKY day 1 neonate. Thereafter, corticosterone and ald osterone levels were comparable on Rays 7, 14, and 21, although the anticip ated depression in circulating corticosterone levels typical of the stress hyporesponsive period was noted in both SHR and WKY neonates. Although patt erns of adrenocortical activity differ in the newborn SHR and WKY rat, our findings do not support an etiologic role for corticosteroids in the report ed hypertension of the SHR. However, observed differences in corticosteroid profiles may augment or have a permissive effect upon the etiologic factor (s). (C) 1999 American Journal of Hypertension, Ltd.