SYMPATHETIC NEUROTRANSMISSION IN THE TAIL ARTERY OF AGING RATS

1 Age-related changes in noradrenergic neurotransmission in the tail a rteries of three rat strains: outbred Wistar (WI/Ico), inbred Wistar ( WAG/Rij) and inbred Fischer (F344) have been compared in the present s tudy. 2 The arterial noradrenaline content varied from 5 to 10 ng mg(- 1) wet weight amongst young (3 to 6-month old) representatives of each strain, but did not change with age. As protein content increased in senescent rats (24-month old) by 30-40%, arterial tissue growth would not appear to receive a concomitant increase in sympathetic growth lea ding to relative, age-related, structural sympathectomy in all strains , 3 The vasoconstrictor response to transmural electrical stimulation was diminished in adult and senescent rats of all strains. 4 As far as could be judged from the increase in noradrenaline release following perfusion with the alpha-adrenoceptor antagonist, phentolamine (1 mu M ), the presynaptic alpha(2)-adrenoceptor-mediated inhibition of noradr enaline release was intact in old representatives of all strains. 5 Wi th blockade of the two main systems which control noradrenaline releas e in the rat tail artery, viz, neuronal reuptake with cocaine (4 mu M) and presynaptic alpha(2)-adrenoceptors with phentolamine (1 mu M), st imulation-evoked release of noradrenaline was similar at all ages and in all strains. This suggests that in the rat tail artery the basic me chanism of neuronal release of noradrenaline is not functionally modif ied by aging. 6 We conclude that as sympathetic nerve terminals are ap parently intact in all three strains of senescent rats used, the age-a ssociated deficit of alpha-adrenergic control of vascular function is postsynaptic in nature.