Postsynaptic alpha 1-adrenoceptor mechanisms in rat vas deferens and ageing

Postsynaptic alpha 1-adrenoceptor mechanisms in vasa deferentia isolated from 3, 6, 18 and 40 week-old rats were studied by analysis of the concentration-response curve of noradrenaline and the Scatchard plot of specific binding of [3H]prazosin to microsomal fractions. The maximum tension developed by noradrenaline also increased with age from 3 to 18 weeks. The efficacy of noradrenaline and capacity of the maximum binding sites of [3H]prazosin increased with increasing age, while the dissociation constants of noradrenaline (KA) and prazosin (Kd) were not changed with age. The increase of the maximum tension was proportional to the increase in efficacy. The increase of efficacy for noradrenaline in the vasa deferentia from rats of different ages is due to the increase in the total concentration of postsynaptic alpha 1-adrenoceptors.