Effects of estrogen and progestin on the CO2 sensitivity of hemispheric cerebral blood volume.

ABSTRACT

OBJECTIVE: High CO2 sensitivity is one of the major characteristics of the cerebrovascular bed. It has been shown to be influenced by many differrent factors (eg, sex hormones). DESIGN: The effect of ovariectomy and subsequent female sexual hormone treatment on the steady-state hemispheric cerebral blood volume and CO2 responsiveness of the hemispheric blood vessels was studied on anesthetized, ventilated, normotensive, normoxic rats. Cerebral blood volume was measured with Tomita's photoelectric method with Sandor's modification. RESULTS: Steady-state cerebral blood volume values in ovariectomized rats did not differ from those found in control animals. The CO2 responsiveness of hemispheric blood vessels was higher in ovariectomized and progestin-treated, but not estrogen-treated, animals compared with controls. CONCLUSIONS: Our results demonstrate that the CO2 sensitivity of the hemispheric vessels is sex hormone dependent. Estrogen and progestin treatment have opposite effects on this cerebral circulatory parameter.