Comparison of Afferent Activity of Canine Aortic and Sinus Nerves

Abstract

Pressure-dependent changes in afferent activity in the aortic and the sinus nerves were studied in 17 anesthetized dogs that were artificially ventilated with oxygen. Systemic arterial blood pressure was varied either continuously or in steps over the range of mean aortic blood pressure from 220 to 50 mm Hg with a pressurized reservoir connected to the abdominal aorta. Multifiber preparations from 20 aortic and 8 sinus nerves were used, and stimulusresponse curves were defined by measuring the mean impulse frequency at the various levels of pressure. Heart rate and pulse pressure were similar during recordings from both nerves. The two curves were S-shaped, with that for the aortic nerve being to the right of that for the sinus nerve. The change in activity was approximately linear from 200 to 120 mm Hg (mean aortic blood pressure) in the aortic nerve and from 180 to 80 mm Hg in the sinus nerve; there was no significant change in impulse frequency below mean blood pressures of 100 and 70 mm Hg, respectively. The threshold systolic blood pressure was 95 ± 3 (SE) mm Hg for the aortic receptors and 62 ± 4 mm Hg for the carotid sinus receptors. Thus, in the dog, the aortic baroreceptors are involved mainly in the control of high blood pressure, whereas at lower pressures the major control occurs through the carotid sinus baroreflex.

Effects of the Head-Down Tilt Posture on Postnatal Development of the Aortic Baroreflex in the Rabbit.

“…According to reports by Thoren et al [22] and Brown et al [33,34], the regularly discharged myelinated fibers tend to respond well to the peak pressure of the sine wave and may be of major importance to cardiovascular control during decreases in arterial pressure. The pressure-aortic nerve discharge curves in systole of the present study showed an s-shape, remarkable changes during decreases in arterial pressure in all 3 groups, and were similar to results in canine aortic nerves that were obtained by depressing pressure from the maximal level to the threshold level in the study of Pelletier and colleagues [35]. The pressure-aortic nerve discharge curve in the HDT group did not fit that of the other 2 groups at threshold level, and the maximal decrease of aortic nerve activity in the HDT group was less than in both groups.…”

Effects of dynamic and static neck suction on muscle nerve sympathetic activity, heart rate and blood pressure in man.

“…5) suggests that in man extracarotid baroreceptors influence sympathetic activity at normal blood pressure levels. This would be in contrast to findings in dogs, in which the aortic arch receptors seem to be brought into action mainly when blood pressure is higher than normal (Donald & Edis, 1971;Edis, 1971;Pelletier, Clement & Shepherd, 1972).…”

Effects of vagotomy on drinking in the rat.

“…In particular, vagotomy partially interrupts aortic arch baroreceptor firing; however, given the relative importance of aortic compared with carotid sinus baroreceptors in circulatory regulation at non-hypertensive pressures (Donald & Edis, 1971;Edis, 1971;Dampney, Taylor & McLachlan, 1971;Pelletier, Clement & Shepherd, 1972) it seems probably that aortic arch afferents have only a minor role to play in the changes seen.…”