The effect of ovariectomy and oestrogen replacement on small artery biomechanics in the rat

Objective To determine the effects of oestrogen deficiency and hormone repl acement therapy on the biomechanical properties of a small artery. Sample Thirty non-pregnant female Sprague-Dawley rats. Methods Twenty animals were pharmacologically ovariectomised by triptorelin and received either oestradiol propionate or its vehicle. Tell other anima ls received only the vehicle for the same period of time (control group). A fter 12 weeks of treatment, cylindrical segments of the saphenous artery we re isolated and cannulated at both ends. Pressure-diameter curves were reco rded from segments in normal Krebs-Ringer, using norepinephrine, and then w ith papaverine. The vessel segment close to the examined one was histologic ally evaluated. Serum levels of oestradiol and cortisol were determined. Main outcome measures Biomechanical parameters based on the pressure-diamet er curves. Results Pharmacological ovariectomy decreased the passive diameter of the a rteries and oestrogen replacement therapy prevented this. Decreased reactiv ity to norepinephrine was also restored by oestrogen treatment. Pressure in duced myogenic tone was decreased significantly by oophorectomy and increas ed after oestradiol treatment. No significant changes were found in wall th ickness, distensibility, elastic modulus or tangential stress. No significa nt histological alterations were seen in tl le vessel wall. Oestradiol leve ls were significantly decreased in the castrated animals compared with the other two groups. Conclusions These results suggest that oestrogen deficiency decreases and o estrogen replacement increases the passive diameter of small peripheral art eries, and that oestrogen enhances the reactivity of vascular smooth muscle . These responses may provide the background mechanisms For the increased i ncidence of arterial hypertension and hot flushes during the menopause and the ability of oestrogen substitution to prevent them.