Abstract
1. Reports that a greater natriuresis occurs after gastric rather than intravenous sodium loads suggest that a gastric sodium monitor exists which releases a humoral natriuretic factor. As vasoactive intestinal peptide (VIP) is natriuretic, it might act as this mediator. To determine whether it released from the gut in response to sodium we measured VIP levels in portal and systemic plasma of anaesthetized rabbits after a gastric sodium load. Levels of VIP in systemic plasma were also measured in conscious rabbits after gastric and portal sodium loads to determine the contributions of anaesthesia or increased sodium concentration in the portal tract to any observed rise in systemic VIP levels. 2. In the anaesthetized rabbit study portal and systemic VIP levels had both increased significantly from control values by 5 min after the sodium load in the low salt diet group (P less than 0.025, portal: P less than 0.05, systemic). By 10 min the levels in systemic and portal plasma were equal. 3. In the conscious rabbits an increase in systemic VIP levels was observed in the group on a low salt diet after a gastric but not a portal sodium load. 4. We conclude that VIP is released in response to gastric sodium loads in rabbits on low salt diets and that hepatic metabolism of VIP is reduced in this group.