Interaction of the autonomic nervous system with intrinsic cardiac rate regulation in the guinea-pig, Cavia porcellus

In the denervated mammalian heart a change in right atrial pressure will st ill alter heart rate (intrinsic rate response, IRR). We have examined the I RR in isolated right atria of the guinea-pig maintained in oxygenated Krebs -Henseleit solution at 37 degreesC, to compare with and extend studies in o ther species, and to determine whether the guinea-pig is a suitable model f or electrophysiological studies of the IRR. Baseline diastolic transmural p ressure was set at 2 mmHg. A 6-mmHg increase in right atrial pressure (RAP) caused an increase in atrial rate that reached a steady value of 15 min(-1 ) after 1-2 min. This response was enhanced by carbamylcholine and attenuat ed by isoprenaline. The influence of RAP on the rate response to vagal stim ulation was examined. With RAP set at 8 mmHg, the reduction in atrial rate following vagal stimulation was 72 +/- 5% of that at 2 mmHg (n = 6, mean S. E., P < 0.005). Continuous vagal stimulation produced a sustained bradycard ia, and the effect of this bradycardia on the IRR was examined. When atrial rate was reduced 6% by vagal stimulation, the IRR was augmented to 202 +/- 21% of the control (n = 6, P < 0.005). This augmentation was larger (P < 0 .05) than that seen when atrial rate was reduced 8% by carbamylcholine (130 +/- 8% of control; n = 7, P < 0.05). Overall, the IRR in the guinea-pig is similar to that in the rabbit, and shows similar interactions with the aut onomic nervous system. (C) 2001 Elsevier Science Inc. All rights reserved.