Age, endothelium and aortic reactivity to calcium in Wistar rat.

The influence of age from (9 to 72 weeks) was investigated on contractions elicited by calcium in Wistar rat aortic rings with and without endothelium. The arteries were either depolarized by KCl or exposed to Bay K 8644 and concentration-effect curves to cumulative additions of CaCl2 were constructed. Whether the endothelium was present or not, the potency of CaCl2 but not its maximal effect decreased with age. The same decrease in potency was obtained with Bay K 8644, in the presence of which the maximal contractions were increased at 72 weeks. In K+ depolarized arteries, nitrendipine (10(-10) and 10(-9) M) markedly decreased maximal contraction elicited by CaCl2 and it moderately displaced to the right the concentration-effect curves. The endothelium did not modify the responses to CaCl2 of depolarized arteries, in the absence of nitrendipine. However it markedly enhanced the depressor effect of nitrendipine in these preparations, and it impaired contractions elicited by calcium in the presence of Bay K 8644. These effects of the endothelium were both less at 72 weeks than at younger ages. These experiments show a possible impairment of the inhibitory effect of the endothelium in 72 week old rats in the presence of both agonist and antagonist dihydropyridines.