Abstract:
The observation that chronic oral potassium supplementation could cause a decrease in blood pressure in normotensive rats led to the design of the present study aimed at understanding the nature of vascular reactivity to some drugs. Responses of aortic ring preparations were obtained from two groups of Wistar rats: One given normal feeds and tap water (control) and the other given normal feeds and 0.75% KCl solution for 5 weeks (potassium-adapted). Isometric contractions were measured in rings exposed to noradrenaline (NA), 5-HT, KCl and CaCl2 while relaxations were measured in the presence of acetylcholine (ACh), sodium nitroprusside (SNP) and Levcromakalim. Results show significant decreases (p<0.05) in both pD2 and Emax values for NA and 5-HT in rings from K-adapted rats. In the case of KCl, although the pD2 values were significantly different, the Emax were the same. Maximum responses to CaCl2 were not significantly altered but threshold concentrations were significantly raised in rings from K+-adapted rats. Following NA pre-contraction, responses to ACh in endothelium-intact vessels did not change but relaxation was significantly enhanced in endothelium-denuded vessels from K+-adapted rats. Responses to SNP and levcromakalim were significantly enhanced and were only partially reversed by tetraethylammonium (TEA). The results suggest the non-involvement of endothelial nitric oxide but suggest the possible roles of potassium-channels in the altered vascular reactivity in aortic rings from normotensive K+-adapted rats.
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