CARDIAC AFFERENTS PLAY THE DOMINANT ROLE IN RENAL NERVE INHIBITION ELICITED BY VOLUME EXPANSION IN THE RABBIT

In the rabbit, vagotomy combined with arterial baroreceptor denervatio n abolishes the renal sympathoinhibition elicited by volume expansion. However, the effect of removing cardiopulmonary afferents alone has n ot been investigated. The aim of the present study was to determine th e role of the cardiac afferents in the renal sympathetic response elic ited by volume expansion in the normal conscious rabbit. Four experime ntal groups were used in which rabbits were administered 1) volume exp ansion (Haemaccel, 1.9 ml/min for 60 min), 2) volume expansion + bolus intrapericardial procaine (20 mg) to block cardiac afferents, 3) volu me expansion + intravenous procaine (20 mg bolus), and 4) intrapericar dial procaine alone (20 mg bolus). Volume expansion did not significan tly affect mean arterial pressure or heart rate but produced a profoun d fall in renal sympathetic nerve activity (similar to 50%). Intraperi cardial procaine administered 30 min after the start of volume expansi on markedly reversed the renal sympathoinhibition to within 20% of the pre-volume expansion level, an effect that wore off over 25 min. In c ontrast, intravenous procaine lowered renal sympathetic nerve activity slightly further. The results suggest that cardiac afferents play the dominant role in the renal sympathoinhibition in response to volume e xpansion in the normal conscious rabbit.