The effect of oestradiol and neta on immunohistochemical staining of iNOS and eNOS in coronary arteries of ovariectomized rats.

AIM: The postmenopausal period is associated with increased risk for coronary atherosclerosis, and the effect of hormone replacement therapy in reducing this risk is controversial. Previous studies reported that nitric oxide synthetase (NOS) level might be important for the development of atherosclerosis, but no study has shown the interaction between hormone replacement therapy and endothelial NOS and inducible NOS intensity on coronary arteries yet. Our goal was to find out the immunostaining intensity of endothelial NOS and inducible NOS in ovariectomized rats which received oestradiol and norethisterone treatment.
METHODS: We performed bilateral ovariectomy in 15, female, 90-day-old Wistar rats with an average weight of 250 grams. After waiting for 4 weeks for the menopausal state, they were divided into 3 groups to receive either placebo, 0.1 mg/day 17-beta-oestradiol (group E2), or 0.1 mg/day 17-beta-oestradiol + 0.1 mg/day norethisterone acetate (group E2-NETA) for 5 weeks. Another group included 5, normal, adult, female intact rats and served as controls. At the end of the treatment, all rats were sacrificed and coronary arteries were stained with inducible NOS and endothelial NOS polyclonal antibodies using streptavidin-biotin technique.
RESULTS: The immunostaining of inducible NOS was prominent in perivascular connective tissue of the ovariectomized group but not in the control group. The inducible NOS immunostaining immunoreactivity was not detected in either treated groups. Immunostaining intensity of endothelial NOS did not differ in any 4 groups with similar staining.
CONCLUSION: The present findings indicate that hormone replacement therapy down-regulates iNOS expression in coronary arteries of ovariectomized rats, and reduced iNOS may likely be involved in estrogen's beneficial effects.