[The central and peripheral components in the action of cardioselective beta-adrenoblockaders]

The effects of two cardioselective beta-blockers metoprolol and atenolol (2 mg/kg, intravenously) on the activity of the sympathetic renal nerve as well as the sensitivity of the chronotropic and sympathetic components of the baroreceptor reflex tested by using phenylephrine or sodium nitroprusside. In the experiments on conscious Wistar rats only the more lipophilic agent metoprolol significantly decreased the baseline level of the activity of the sympathetic nerve by 15%. The sensitivity of the chronotropic baroreceptor reflex elicited by a decrease of arterial blood pressure with sodium nitroprusside was reduced significantly both by metoprolol and atenolol. The tendency towards a decrease of the sensitivity of the chronotropic reflex elicited by phenylephrine-induced elevation of blood pressure was noted. The baroreflectory modification of the sympathetic activity did not change significantly under the influence of metoprolol and atenolol. The presence of the central component of action (of metoprolol) and the peripheral component (of the studied beta-blockers) is concluded.