Sympathetic neurotransmission in the rabbit isolated central ear artery is affected as early as one week following a single dose of X-irradiation

Abstract

1 The short-term effect of a single dose of 4500 rad X-irradiation on sympathetic neurotransmission (involving both noradrenergic and purinergic components) was assessed in the rabbit central ear artery, 1, 4 and 6 weeks post-irradiation. 2 Neurally mediated contractions were reduced as early as 1 week post-irradiation, with responses to lower frequency stimulation being initially most affected. This suggests that the purinergic component of the contractile response is affected earlier than the adrenergic component. 3 There was no change in the amplitude or sensitivity of treated preparations to the cumulative application of noradrenaline when compared with untreated preparations. In contrast, contractions to α,β-methylene ATP (1 μM), a P2-purinoceptor agonist, were significantly increased at 4 and 6 weeks post-irradiation, although not at 1 week post-irradiation. 4 There were no apparent changes in the pattern of catecholamine fluorescence as a result of irradiation. However, the tissue content of noradrenaline was significantly reduced 6 weeks post-irradiation when compared with control preparations. 5 It is concluded that damage to sympathetic cotransmission is one of the early effects of irradiation, with initial impairment predominantly of the purinergic component.