17 beta-estradiol inhibits ovariectomy-induced expression of inducible nitric oxide synthase in rat aorta in vivo

The objective of this study was to elucidate a role of ovarian steroid horm ones in the production of immunologic nitric oxide (NO) synthases in the fe male rat aorta in vivo. Aortic homogenates were analyzed by using western b lot with isoform-specific antibodies against endothelial NOS (eNOS) and ind ucible NOS (iNOS). Two weeks after ovariectomy (OVX), rats (10-week-old) we re treated with 17 beta-estradiol (E-2) and/or progesterone (P-4) for 5 day s, and aortae were obtained from these rats on the following day. OVX marke dly increased the levels of INOS protein in abdominal aorta, whereas treatm ent with E-2 or a combination of E-2 and P-4 inhibited the induction of iNO S in the aorta. The present findings indicate that endogeneous estrogen neg atively regulates the expression of iNOS in abdominal aorta, and suggest th at changes in the levels of circulating estrogen may affect vascular functi on, (C) 2000 Elsevier Science Inc.