Vasoactive intestinal polypeptide potentiates the hypoxemia-induced decrease in splanchnic circulation in the rat.
The effects of acute infusion of vasoactive intestinal polypeptide (VIP) and hypoxemia on splanchnic circulation were examined in 35 awake Sprague-Dawley rats. Indwelling catheters were placed in the superior vena cava and the proximal aorta via the internal jugular vein and internal carotid artery, respectively, while the rats were under ether anesthesia. Four hours later, when the rats were awake and active, VIP (molecular lot 3226) was infused intraarterially for 30 minutes. The distribution of cardiac output was measured at the end of VIP infusion using 125I-labeled microspheres. VIP was administered at a low (1.5 ng/min) and a high infusion rate (44.1 ng/min) for 30 minutes. The effect of hypoxemia on circulatory response to VIP was examined only in the high VIP infusion group, by placing the rat in a 10% oxygen environment. Appropriate control experiments were performed with each group. The high-dose VIP resulted in a marked reduction in distribution of cardiac output to the splanchnic circulation. This effect was potentiated by hypoxemia, particularly in the distal ileum and colon. The metabolic clearance rate of VIP increased with the rate of VIP infusion and was decreased by hypoxemia. It was concluded that only in high concentration does VIP have any effect on splanchnic circulation. However, in the presence of hypoxemia, VIP may have an important role in cardiovascular compensatory response and may contribute to the development of ischemic bowel injury.