Characteristics of single carotid sinus baroreceptor fibers and whole nerve activity in the normotensive and the renal hypertensive dog.

Abstract

Carotid sinus baroreceptor nerve activity was examined in 8 renal hypertensive dogs with a duration of hypertension of 5-82 days and a mean blood pressure of 148 .+-. 0.5 mm Hg. These results were compared with those from 13 normotensive dogs. Whole carotid sinus nerve activity and single fiber activity were recorded in the isolated carotid sinus preparation in response to controlled static and pulsatile pressures. Stimulus-response curves were constructed. Single fiber adapted (5 s) threshold pressure under static pressure conditions increased from 104 .+-. 3.2 mm Hg in the normotensive dogs to 128 .+-. 3.9 mm Hg in the hypertensive dogs. Inflection pressure and plateau pressure were higher in hypertension. Impulse frequency at the inflection pressure was reduced from 39 .+-. 2.3 impulses/s in normotensive dogs to 32 .+-. 1.7 impulses/s in hypertensive dogs and, at the plateau pressure, from 43 .+-. 2.1 impulses/s to 34 .+-. 1.9 impulses/s. Whole nerve recordings showed significantly higher threshold, inflection and plateau pressures in the hypertensive dog. In response to pulsatile pressure, the single fiber sensitivity decreased from 0.17 .+-. 0.01 to 0.11 .+-. 0.01 impulses/cycle per mm Hg. Continuous nerve activity under these conditions occurred at a mean pressure of 166 .+-. 3.5 mm Hg for the normotensive dogs, compared with 188 .+-. 0.4 mm Hg for the hypertensive dogs. Hypertensive dogs showed an impulse frequency identical to that of normotensive dogs at pressures equivalent to each dog''s unanesthetized mean blood pressure. Baroreceptor resetting was not seen before 5 days of hypertension. It was possible to reverse the resetting by lowering the blood pressure in 1 dog which was hypertensive for 47 days.