[Hypoxia-induced increase in nerve activity of rabbit carotid body mediated by noradrenaline].

The responses of 39 hypoxia-sensitive units of chemoreceptive afferent in sinus nerve to noradrenaline (NA) and its antagonist were recorded in carotid body-sinus nerve preparations from 30 rabbits. The results are as follows. (1) Discharges of the units increased from 0.13 +/- 0.06 to 0.25 +/- 0.12 imp/s (P < 0.001, n = 19) upon lowering PO2 of modified Tyrode solution. (2) Adding NA (10(-6) mol/L) to the perfusate led to an increase in the unit discharge from 0.14 +/- 0.08 to 0.23 +/- 0.13 imp/s (P < 0.01, n = 19). (3) Prazosin (10(-6) mol/L) did not alter the basal frequency of chemosensory unit discharges under normoxic conditions (P > 0.05, n = 4). (4) Yohimbine (10(-6) mol/L) did not alter the basal frequency of chemosensory unit discharges under normoxic conditions (P > 0.05, n = 6). (5) Chemosensory responses to hypoxia were not altered after pretreatment with prazosin. (6) Chemosensory responses to hypoxia were inhibited by pretreatment with yohimbine. The present results suggest that (1) NA is not mainly concerned with spontaneous discharges of chemoreceptor sensitive to hypoxia, but does elicit an increase in spontaneous discharges, and (2) the increase of chemosensory unit discharges produced by hypoxia can be inhibited by yohimbine. It is likely that the excitatory action of hypoxia on chemoreceptive process is mediated by NA.