Renal nerve and alpha 2-adrenergic action during acute volume expansion in the anaesthetized rat

1. The effects of renal denervation and alpha 2-adrenoceptor blockade on diuresis and natriuresis in response to acute volume expansion (VE) were investigated in anaesthetized rats. 2. In normal rats, a 30 min intravascular VE of up to 7.5% of bodyweight caused a significant diuresis and natriuresis. 3. Denervation enhanced the diuretic effect of VE by 39%, while alpha 2 blockade by 12 mumol/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 denervated kidneys. 5. The results demonstrate that renal sympathetic nerve activity inhibits part of the increase in sodium and water excretion caused by VE, since denervation increased excretion under these conditions. The contribution of renal nerves to the control of renal function, however, decreases during the response to VE. 6. alpha 2-Adrenoceptor action enhanced the diuretic and natriuretic effects of VE by mechanisms otherwise unrelated to renal nerve activity.