The effect of pentobarbital anesthesia on “intrinsic” heart rate.

Abstract

While it is well established that pentobarbital alters cardiac autonomic regulation, the effects of this anesthetic agent on intrinsic heart rate (HRi) remain to be determined. Therefore, HRi, was measured in purpose‐bred mixed breed dogs (n = 11, 22.2 ± 0.9 kg, age 1–3 y) by means of combined adrenergic (propranolol HCl 1.0 mg/kg, i.v.) and muscarinic (atropine sulfate 50 ug/kg iv.) receptor inhibition before (Control, Con) and, at least one week later, during pentobarbital anesthesia (Pen, 30–40 mg/kg, i.v). Pentobarbital significantly (ANOVA, P<0.01) depressed the high frequency component (0.24 – 1.04 Hz, an index of cardiac parasympathetic regulation) of heart rate variability (Con, 7.2 ± 0.4 vs. Pen, 1.0 ± 0.4 ln ms2) and increased baseline heart rate (Con, 105.9 ± 8.7 vs. Pen, 139.1 ± 6.8 beats/min) but decreased HRi (Con, 148.7 ± 6.7 vs. Pen, 128.9 ± 5.3 beats/min). The nonselective adenosine antagonist aminophylline (10 mg/kg, i.v.) did not alter heart rate variability (0.4 ± 0.3 ln ms2) but restored HRi to control (i.e., without pentobarbital) values (141.5 ± 6.7 beats/min). These data suggest that pentobarbital both alters cardiac autonomic regulation and depresses intrinsic heart rate. These data further indicate that the activation of adenosine receptors may play an important role in this apparent depression of cardiac pacemaker rate.