Development of autonomic heart rate control in the kitten during sleep.

Development of cardiac rate control was studied in 34 kittens aged 4 days to 6 wk during quiet and active sleep, using atropine and propranolol to quantitatively assess the degree of tonic parasympathetic and sympathetic control, with the analysis based on the Rosenblueth and Simeone model. The order of blocking agent administration did not significantly affect the results if a correction was made for the baroreceptor-mediated heart rate change after the blockade of a single autonomic branch. During the first 4 wk, the heart rate in quiet sleep was lower than in active sleep due to a significantly higher parasympathetic tone. The heart rate decreased with age in both sleep states: the decrease in quiet sleep was accompanied by a transition from sympathetic to parasympathetic dominance. The intrinsic rate of the pharmacologically denervated heart was maximum at about 2 wk and decreased steadily thereafter. The observed changes may help explain some features of the development in heart rate previously reported for sleeping human infants.