Age-dependence of the effects of pinacidil on rat aorta

The effect of the K+ channel opening drug, pinacidil, has been examined on aortic ring preparations from young (2 months) and aged (greater than 24 months) rats. The potency (neg log IC50) values for pinacidil in relaxing K+ (20 mM)-contracted preparations were in the range expected for its K+ channel opening (hyperpolarizing) effects but were not significantly different between young (6.34) and aged (6.31) rats. Thus, ageing does not affect the drug's potency as a K+ channel opening drug. The more marked depression of the maximum response to noradrenaline by pinacidil (10 microM) in aged rats (85% reduction) compared with young rats (43% reduction), reflected a reduced alpha-adrenoceptor reserve for noradrenaline in preparations from aged rats. Pinacidil, in concentrations greater than 10 microM, was able to relax preparations contracted with 80 mM K+ suggesting that it may have a second mechanism which does not involve hyperpolarization. It was more potent in producing this effect on the preparations from aged rats.