Glucagon and canine mesenteric hemodynamics: Effects on superior mesenteric arteriovenous and nutrient capillary blood flow

Abstract

The objective of this investigation was to define the splanchnic hemodynamic effects of parenterally administered glucagon in a canine model. Measurements in six dogs at baseline and at 10, 20, and 30 min during constant intravenous infusion of glucagon at 1 μg/kg/min included: Cardiac output (CO), mean arterial pressure, total peripheral vascular resistance (TPR), superior mesenteric artery flow (SMAQ), portal venous pressure (PVP), superior mesenteric artery vascular resistance (SMAR), percentage SMA flow through arteriovenous anastomoses (AVA%) determined by 99mTc microsphere technique, as well as volume flow through AVA (AVAQ), and volume flow through the SMA nutrient capillary circulation (NCQ). SMAQ rose significantly and disproportionately compared to the rise in CO. SMAQ more than doubled from a mean of 448 ± 124 cc at baseline to a mean of 921 ± 321 cc at 10 min, and remained elevated throughout drug infusion. SMAR and TPR both decreased significantly. Although percentage shunt was low at baseline, 1.79 ± 0.94%, and did not change, both AVAQ and NCQ increased significantly during drug infusion. The increase in AVAQ was transient, but NCQ remained elevated throughout infusion. PVP increased significantly, and the change in PVP correlated significantly with the change in AVAQ at 30 min, a time when AVAQ was not elevated significantly above baseline levels. Nutrient capillary flow comprised ≥98% of total SMAQ during the experiment and, along with total SMAQ, doubled and remained elevated throughout drug infusion. Although glucagon may increase PVP by slightly increasing the absolute volume of mesenteric shunt flow, its primary action is that of a potent mesenteric arterial dilator, increasing NCQ strikingly more than AVAQ.