Age-related alterations in ?1- and ?-adrenoceptors mediated responsiveness of rat aorta

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Abstract
We have examined the responsiveness of α- and β-adrenoceptors in aortae from 1.5, 3, 6 and 24 month old rats. The isometric contraction to phenylephrine was antagonised competitively by prazosin with a pA2 value of 9.45, suggesting that the receptor is an α1-adrenoceptor. The potency of phenylephrine was significantly reduced in 24 months old as compared with all younger rats combined. The maximum contraction to phenylephrine was unaltered in 24 month old rats. The maximum contraction to potassium chloride was significantly less than that to phenylephrine only in 1.5 months old rats. In tissues contracted by potassium chloride, isoprenaline produced a marked relaxation in 1.5 months old animals, but there was a progressive loss with increasing age of the β-adrenoceptor-mediated relaxation which was markedly reduced by 6 months and abolished in 24 months old. It is concluded that, in the rat aorta, there is a decrease in α1-adrenoceptor responsiveness in senescence, and a loss of β-adrenoceptor-mediated responses in maturation.