In a previous study (Wang, W., J. S. Chen, and I. H. Zucker. Circ. Res. 68: 1294-1301, 1991), we showed a depression in baroreflex gain in dogs with pacing-induced heart failure. This depression was not accompanied by a decrease in the central gain (carotid sinus nerve stimulation vs. renal nerve activity). These previous experiments were carried out on animals that were vagotomized and aortic denervated. In the present study these experiments were repeated, and the data were analyzed both in the intact and vagotomized state. Dogs were cardiac paced at 250 beats/min until heart failure was noted. Sham dogs were used as controls. The carotid sinuses were isolated, and the aortic nerves were sectioned. Activity from a renal sympathetic nerve (RSNA) was recorded with arterial pressure and carotid sinus pressure (CSP) during bilateral step increases in CSP from 25 to 300 mmHg. Mean arterial pressure (MAP) and RSNA responses to carotid sinus pressurization and to carotid sinus nerve stimulation were tested before and after bilateral vagotomy, and curves describing these relationships were constructed. Before vagotomy, the peak response relating stimulation frequency to MAP was significantly depressed in dogs with heart failure (-18.3 +/- 4.7 vs. -37.0 +/- 2.2%, P < 0.001). In addition, the CSP-MAP curves were depressed in dogs with heart failure. Frequency-RSNA curves were not altered in heart failure. There were no significant changes in the baroreflex gain responses to pressurization or electrical stimulation after vagotomy in either sham or heart failure groups.(ABSTRACT TRUNCATED AT 250 WORDS)