Effects of haemorrhagic hypotension on carotid chemosensory discharge in the kitten.

Hypotension is known to affect the rate of carotid chemosensory activity in the adult cat, but the relationship between arterial blood pressure and carotid sinus nerve discharge has not been established in the kitten. The purpose of this study was to determine the response of carotid chemosensory afferents to hypotension induced in normoxia and in hyperoxia in eight kittens aged 1 to 25 days. Hypotension was obtained by a gradual decrease in blood volume. The activity of a few chemosensory fibres was recorded from one carotid sinus nerve. Baseline steady-state mean arterial blood pressure and carotid chemosensory activity were, respectively, 70.0 +/- 4.3 mmHg and 7.6 +/- 1.9 impulse/s (mean +/- SEM) in normoxia and 56.3 +/- 6.7 mmHg and 0.58 +/- 0.2 impulse/s in hyperoxia. Lowering arterial blood pressure below 37.5 +/- 3.5 mmHg in normoxia and 26.8 +/- 2.3 mmHg in hyperoxia was associated with a consistent increase in the rate of chemosensory discharge. Above this threshold, blood pressure variations had little effect on carotid chemoreceptor activity. These data are qualitatively similar to those of adult cats and provide evidence that, in newborn kittens, changes in arterial blood pressure will not influence carotid chemosensory discharge unless these changes are out of the physiological range.