DIFFERENTIAL CEREBROVASCULAR RESPONSIVENESS IN SPONTANEOUSLY HYPERTENSIVE RATS FOLLOWING ANTIHYPERTENSIVE TREATMENT WITH CLONIDINE AND VERAPAMIL

Numerous studies have been reported examining the effects of antihyper tensive treatment on peripheral vascular responsiveness in spontaneous ly hypertensive rats (SHR). This study was conducted to determine the effects of chronic treatment with 2 antihypertensive agents on cerebro vascular responsiveness in male SHR and Wistar-Kyoto (WKY) rats. SHR a nd WKY (3-4 weeks old) received either placebo, clonidine (CLON, 10 mg pellet) or verapamil (VER, 5 mg pellet). Vascular reactivity studies on the basilar artery, using standard smooth muscle bath techniques, w ere conducted following 6 weeks of treatment. Both CLON and VER signif icantly attenuated the rise in blood pressure in SHR. Basilar artery r esponsiveness to KCl, serotonin (5-HT), and calcium were significantly increased whereas responses to acetylcholine (ACH), isoproterenol (IS O) and sodium nitroprusside (SNP) were significantly reduced in SHR co mpared to WKY. CLON had no effect on basilar artery responsiveness to either the contractile or relaxation agents in SHR. However, although responses to KCl, 5-HT and calcium were not affected by VER in SHR, VE R significantly increased the responses to ACH, ISO and SNP. Neither C LON nor VER treatment affected basilar artery responsiveness to any of the agents in WKY. These data demonstrate that, even though CLON and VER have similar antihypertensive effects, differential effects of the 2 agents on cerebrovascular responsiveness in the SHR are apparent. T his would suggest that the vascular effects of VER and CLON are depend ent upon the mechanism of action of the agents and not simply due to p revention of the elevation in blood pressure.