[Effect of metoprolol on water drinking activity in Wistar Kyoto rats]

The study was undertaken to elucidate the effect of beta 1 adrenoceptor blocking agent, metoprolol, on water drinking activity in Wistar Kyoto rats (WKY). Both 7 day (10mg/kg/day) oral administration of metoprolol and propranolol did not produce any changes in the systolic blood pressure of WKY. However, metoprolol produced a significant decrease in heart rate in WKY. Neither the propranolol treated rats nor the control (non-drug group) rats showed any significant changes in heart rate. Heart rates were significantly changed in the metoprolol group as compared with the other two groups. This finding reconfirms that metoprolol has beta 1 selectivity. Drinking activity, an indicator of central nervous function, did not change after metoprolol administration. Power spectral analysis of water drinking activity did not reveal any changes in rhythm in respect to periodicity in the metoprolol group. Although water drinking activity is synchronized with urinary catecholamine and aldosterone excretion rates, urinary catecholamine and aldosterone excretion rates did not change after metoprolol administration. These findings suggest that it is the beta 1 adrenergic blocking action of a bradycardia-producing dose of metoprolol that prevented any change in water drinking behavior in WKY.