Renal nerve and alpha 2-adrenergic action during acute volume expansion inthe anaesthetized rats

1. The effects of renal denervation and alpha(2)-adrenoceptor blockade on d iuresis and natriuresis in response to acute volume expansion (VE) were inv estigated in anaesthetized rats. 2. In normal rats, a 30 min int avascular VE of up to 7.5% of bodyweight ca used a significant diuresis and natriuresis. 3. Denervation enhanced the diuretic effect of VE by 39%, while cut blockad e by 12 mu mol/kg per h rauwolscine significantly inhibited the response by 61% in innervated kidneys and 43% in denervated kidneys. 4. Similar results were found for natriuresis in both innervated and denerv ated kidneys. 5. The results demonstrate that renal sympathetic nerve activity inhibits p art of the increase in sodium and water excretion caused by VE, since dener vation increased excretion under these conditions. The contribution of rena l nerves to the control of renal function, however, decreases during the re sponse to VE. 6. alpha(2)-Adrenoceptor action enhanced the diuretic and natriuretic effec ts of VE by mechanisms otherwise unrelated to renal nerve activity: