Circulatory changes and renin secretion in sheep in response to feeding.

1. The effect of feeding on the circulation, on renin release and on renal function has been examined in the sheep.2. There was a rapid reduction of plasma volume within 15 min of starting to eat dry feed.3. This was accompanied by an abrupt rise in systolic blood pressure and by a more gradual and prolonged elevation of heart rate.4. Within 30 min of feeding there occurred renal conservation of sodium and water which continued for at least 2-3 hr.5. Renin was released into the circulation of sheep that ate rapidly; slow feeders did not show this response.6. The rise in plasma renin concentration was inhibited by infusing a solution similar in composition to mixed saliva at a rate that prevented the change in plasma volume.7. It is concluded that the rapid transfer of sodium and water from the circulation to the rumen via the saliva during ingestion of dry feed is sufficient to activate the renin/angiotensin system.