Rapid resetting of rabbit aortic baroreceptors and reflex heart rate responses by directional changes in blood pressure

• Published in: The Journal of physiology Vol. 378; no. 1; pp. 391 - 402
• Main Authors: Burke, S L, Dorward, P K, Korner, P I
• Format: Journal Article
• Language: English
• Published: Oxford The Physiological Society 01-09-1986; Blackwell
• Subjects: Animals; Aorta - innervation; Biological and medical sciences; Blood Pressure; Fundamental and applied biological sciences. Psychology; Heart Rate; Hemodynamics. Rheology; Pressoreceptors - physiology; Rabbits; Reflex - physiology; Time Factors; Vertebrates: cardiovascular system; Heart rate; Vertebrata; Regulation(control); Mammalia; Rabbit; Blood pressure; Circulatory system; Baroreceptor; Hemodynamics; Lagomorpha; Hysteresis
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.1986.sp016226

In both anaesthetized and conscious rabbits, perivascular balloon inflations slowly raised or lowered mean arterial pressure
(M.A.P.), at 1-2 mmHg/s, from resting to various plateau pressures. Deflations then returned the M.A.P. to resting. 'Steady-state'
curves relating M.A.P. to unitary aortic baroreceptor firing, integrated aortic nerve activity and heart rate were derived
during the primary and return pressure changes and they formed typical hysteresis loops. In single units, return M.A.P.-frequency
curves were shifted in the same direction as the primary pressure changes by an average 0.37 mmHg per mmHg change in M.A.P.
Shifts were linearly related to the changes in M.A.P. between resting and plateau levels for all pressure rises and for falls
less than 30 mmHg. They were established within 30 s and were quantitatively similar to the rapid resetting of baroreceptor
function curves found 15 min-2 h after a change in resting M.A.P. (Dorward, Andresen, Burke, Oliver & Korner, 1982). Unit
threshold pressures were shifted within 20 s to the same extent as the over-all curve shift to which they contributed. In
the whole aortic nerve, return M.A.P.-integrated activity curves were shifted to same degree as unit function curves in both
anaesthetized and conscious rabbits. Simultaneous shifts of return reflex M.A.P.-heart rate curves were also seen in conscious
rabbits within 30 s. During M.A.P. falls, receptor and reflex hysteresis was similar, but during M.A.P. rises, reflex shifts
were double baroreceptor shifts, suggesting the involvement of other pressure-sensitive receptors. We conclude that hysteresis
shifts in baroreceptor function curves, which follow the reversal of slow ramp changes in blood pressure are a form of rapid
resetting. They are accompanied by rapid resetting of reflex heart rate responses. We regard this as an important mechanism
in blood pressure control which produces relatively high-gain reflex responses, during slow directional pressure changes,
over a wider range of absolute pressure levels than would otherwise be possible.