The influence of age from (9 to 72 weeks) was investigated on contract
ions elicited by calcium in Wistar rat aortic rings with and without e
ndothelium. The arteries were either depolarized by KCl or exposed to
Bay K 8644 and concentration-effect curves to cumulative additions of
CaC2 were constructed. Whether the endothelium was present or not, the
potency of CaCl2 but not its maximal effect decreased with age. The s
ame decrease in potency was obtained with Bay K 8644, in the presence
of which the maximal contractions were increased at 72 weeks. In K+ de
polarized arteries, nitrendipine (10(-10) and 10(-9) M) markedly decre
ased 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 elic
ited by calcium in the presence of Bay K 8644. These effects of the en
dothelium were both less at 72 weeks than at younger ages. These exper
iments show a possible impairment of the inhibitory effect of the endo
thelium in 72 week old rats in the presence of both agonist and antago
nist dihydropyridines.