Estrogen is likely involved in the gender specific differences in coping with stress. Activation of catecholamine (CA) biosynthetic enzyme gene expression in central and peripheral CA systems plays a key role in response to stress and in regulation of the cardiovascular system. Here we examined whether estradiol can modulate response of hypothalamic-pituitary-adrenal axis (HPA), gene expression of enzymes related to CA biosynthesis in several noradrenergic locations, tetrahydrobiopterin (BH4) concentration and blood pressure (BP) in response to immobilization stress (IMO) of ovariectomized female rats. Rats were injected with 25 mu g/kg estradiol benzoate (EB) or sesame oil once daily for 16 days and subsequently exposed to two hours of IMO. The IMO triggered elevation in plasma ACTH was lessened in EB-pretreated animals. However, estradiol did not alter the IMO-elicited rise of tyrosine hydroxylase mRNA levels in adrenal medulla (AM) and in the nucleus of solitary track (NTS) compared with controls. The response of GTP cyclohydrolase I (GTPCH) mRNA in AM to IMO was also similar in both groups. Several responses to IMO in EB-treated rats were reversed. Instead of IMO-elicited elevation in dopamine beta-hydroxylase mRNA levels in the locus coeruleus, GTPCH mRNA and BH4 levels in the NTS, they were reduced by IMO. In a parallel experiment, BP was monitored during restraint stress. The elevation of BP in response to single or repeated restraint stress was sustained during 2 h in controls and reduced after 70 min stress in EB treated rats. One month after withdrawal of EB treatment, the BP response to restraint was similar to that of rats which never received EB. The results demonstrate that estrogen can modulate responses to stress affecting HPA axis, CA biosynthesis, in central and peripheral noradrenergic systems, and BP. (c) 2005 Published by Elsevier Ltd on behalf of IBRO.
