An investigation of age-related changes in pre- and postjunctional alpha-adrenoceptors in human saphenous vein.

The responsiveness of prejunctional alpha 2-, postjunctional alpha 1- and postjunctional alpha 2-adrenoceptors was examined in human isolated saphenous veins from male patients in the age range 37-70. There was no age-related alteration in the prejunctional potency of the alpha 2-adrenoceptor agonist xylazine for inhibiting the stimulation-evoked overflow of tritium in tissues preincubated with [3H]noradrenaline. The alpha 2-adrenoceptor antagonist yohimbine (0.01-1 microM) and the alpha 1-adrenoceptor antagonist prazosin (0.1-1 microM) significantly reduced stimulation-evoked contractions in a concentration-dependent manner. There was no significant age-related correlation for the potency of prazosin but there was a significant negative correlation between the potency of yohimbine and age (r = 0.70, n = 11, P less than 0.05), i.e. the potency of yohimbine decreased with increasing age. The decreased postjunctional potency of yohimbine may reflect a loss of alpha 2-adrenoceptors with increasing age.