The differential effects of stereoisomers of ropivacaine and bupivacaine on cerebral pial arterioles in dogs

We investigated whether the stereoisomers of ropivacaine and bupivacaine ex ert differential effects on the cerebral microcirculation. Pentobarbital-an esthetized dogs (n = 16) were prepared for measurement of cerebral pial ves sel diameters by using a closed cranial window preparation. We administered three different concentrations (10(-7), 10(-5), and 10(-3) M) of each of t hree drug solutions [R(+), racemic, and S(-) forms of ropivacaine (n = 8) o r bupivacaine (n = 8)] under the window in a randomized manner and measured cerebral pial arteriolar diameters. Various physiologic data were obtained before and after topical application of each test solution. All three form s of ropivacaine constricted cerebral pial arterioles, each in a concentrat ion-dependent manner. The rank order for degree of vasoconstriction was S(- ) ropivacaine > racemic ropivacaine > R(+) ropivacaine. In contrast, R(+) a nd racemic bupivacaine dilated, but S(-) bupivacaine constricted, cerebral pial arterioles, each in a concentration-dependent manner. We could find no difference in vascular reactivity to these drugs between large (greater th an or equal to 100 pm) and small (< 100 mum) arterioles. Topical applicatio n of these drugs induced no changes in mean blood pressure or heart rate. T he observed differences in the microvascular alterations induced by the ste reoisomers of ropivacaine and bupivacaine suggest that the vasoactive effec ts of these drugs on cerebral arterioles could, at least in part, depend on their chirality.