Effects of aging on alpha 1-adrenoceptor mechanisms and the inhibitory effect of diltiazem on noradrenaline maximum response in isolated rat aortic preparation

The effects of aging on alpha 1-adrenoceptor mechanisms in aortic preparations isolated from 3-, 6-, 10-, 18-, and 40-week-old rats were studied and compared with serotonin receptor mechanisms in the same preparations. The potency (pD2 value) of noradrenaline increased with age from 3 to 10 weeks, but decreased thereafter with age from 10 to 40 weeks. The affinity (pKA value) of noradrenaline and of prazosin (pA2 value) did not alter with aging. The change in potency or the pD2 value of noradrenaline was proportional to receptor reserve (pD2-pKA value) for noradrenaline, suggesting that the change of potency of noradrenaline with age was due to a change of receptor reserve, but not to change of drug affinity to alpha 1-adrenoceptors. The potency (pD2 value) and affinity (pKA value) of serotonin, and the affinity (pA2 value) of ketanserin, did not alter with aging, suggesting that serotonin receptor mechanisms in rat aorta did not change with age. The inhibitory effect of diltiazem on noradrenaline maximum response decreased with age from 3 to 10 weeks, but increased with age from 10 to 40 weeks. An inverse relationship between changes of diltiazem inhibition and receptor reserve of noradrenaline was found. Diltiazem's inhibitory effect on serotonin maximum response did not alter with aging.