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.