3β-OH-tibolone acutely dilates rat muscle arterioles similar to 3α-OH-tibolone

Abstract

In an earlier study, we focused on the vasoactive effect of 3alpha-OH-tibolone on spontaneously constricted isolatedfemale rat gracilis muscle arterioles. Vasodilator effects (from 10 to 10 M) of 3alpha-OH-tibolone were similar to those of 17beta-estradiol. It was reported that 3beta-OH-tibolone like estradiol altered GABAB activation in neurons through a membrane estrogen receptor, whereas the 3alpha-OH metabolite did not. We therefore hypothesized that the 3beta-OH metabolite may also have a vasodilating effect in our isolated arteriole model. The results indicate that 3beta-OH-tibolone induces a vasodilator effect in small arterioles that is comparable with that of 3alpha-OH-tibolone at the same concentration. This is intriguing because the binding affinity of 3alpha-OH-tibolone to the estrogen receptor is almost twice that of 3beta-OH-tibolone. Other mechanisms may play a role.