Angiotensin II infusion during beta-adrenergic stimulation by isoproterenol. Effects on hepatic, splenic and cardiac blood volumes and on the magnitude and distribution of cardiac output in the dog

Angiotensin II induces insulin resistance independent of changes in interstitial insulin

We set out to examine whether angiotensin-driven hypertension can alter insulin action and whether these changes are reflected as changes in interstitial insulin (the signal to which insulin-sensitive cells respond to increase glucose uptake). To this end, we measured hemodynamic parameters, glucose turnover, and insulin dynamics in both plasma and interstitial fluid (lymph) during hyperinsulinemic euglycemic clamps in anesthetized dogs, with or without simultaneous infusions of angiotensin II (ANG II). Hyperinsulinemia per se failed to alter mean arterial pressure, heart rate, or femoral blood flow. ANG II infusion resulted in increased mean arterial pressure (68 +/- 16 to 94 +/- 14 mmHg, P < 0. 001) with a compensatory decrease in heart rate (110 +/- 7 vs. 86 +/- 4 mmHg, P < 0.05). Peripheral resistance was significantly increased by ANG II from 0.434 to 0.507 mmHg. ml(-1). min (P < 0.05). ANG II infusion increased femoral artery blood flow (176 +/- 4 to 187 +/- 5 ml/min, P < 0.05) and resulted in additional increases in both plasma and lymph insulin (93 +/- 20 to 122 +/- 13 microU/ml and 30 +/- 4 to 45 +/- 8 microU/ml, P < 0.05). However, glucose uptake was not significantly altered and actually had a tendency to be lower (5.9 +/- 1.2 vs. 5.4 +/- 0.7 mg. kg(-1). min(-1), P > 0.10). Mimicking of the ANG II-induced hyperinsulinemia resulted in an additional increase in glucose uptake. These data imply that ANG II induces insulin resistance by an effect independent of a reduction in interstitial insulin.

Angiotensin II increases glucose utilization during acute hyperinsulinemia via a hemodynamic mechanism

To determine whether hemodynamic changes can modulate insulin action in vivo, we administered angiotensin II (AII) to normal men under three separate, euglycemic conditions. First, in the presence of physiological hyperinsulinemia (approximately 115 microU/ml), infusion of AII at rates of 2, 10, and 20 ng/min per kg caused significant elevations of blood pressure, whole-body glucose clearance, and plasma insulin concentrations in an AII dose-dependent manner. Second, in the presence of plasma insulin concentrations that stimulate glucose transport maximally (approximately 5,000 microU/ml), AII infusions increased whole-body glucose clearance without enhancing glucose extraction across the leg. Third, in the presence of basal insulin concentrations (approximately 13 microU/ml), AII infusions had no effect on whole-body glucose turnover or leg glucose extraction. Thus, AII enhanced whole-body glucose utilization without directly stimulating glucose transport in a major skeletal muscle bed. To evaluate a possible hemodynamic mechanism for the effects of AII on glucose utilization, we measured blood flow to two areas that differ in their sensitivity to insulin: the kidneys and the leg. We found that AII redistributed blood flow away from the predominantly insulin-independent tissues of the kidney and toward the insulin-sensitive tissues of the leg during both sham and hyperinsulinemic glucose clamps. The redistribution of flow had no effect on whole-body glucose turnover when leg glucose uptake was unstimulated (sham clamps). However, when leg glucose uptake was activated by insulin, the redistribution of flow caused a net increase in whole-body glucose utilization. Our findings indicate that hemodynamic factors can modulate insulin action in vivo. Furthermore, our results suggest that variable activity of the renin-angiotensin system may contribute to inconsistencies in the association between insulin resistance and hypertension.

Reduced splanchnic vasoconstriction to angiotensin II in conscious rats with biliary cirrhosis

Decreased pressor reactivity to angiotensin II has been demonstrated in portal hypertension due to cirrhosis. The present study investigated the respective roles of portal hypertension and cirrhosis and the hemodynamic mechanisms of the depressor response in different models of portal hypertension in conscious rats. Dose-pressor curves were studied in sham-operated, portal vein stenosed (portal hypertension without cirrhosis) and biliary cirrhotic rats following angiotensin II administration. Decreased pressor response was observed in cirrhotic rats but not in portal vein stenosed rats. The hemodynamic effects of angiotensin II administration (11 ng.100 g-1 body wt.min-1, i.v.) were studied in conscious sham-operated and biliary cirrhotic rats (radioactive microsphere method). The percentage of change from basal values following angiotensin II administration were significantly more marked in sham-operated rats than in cirrhotic rats for mean arterial pressure (+34 vs. +6%), cardiac index (-36 vs. -22%), systemic vascular resistance (+117 vs. +40%). After angiotensin II, portal tributary and hepatic artery blood flows significantly decreased in sham-operated rats (-31 and -14%, respectively) but not in cirrhotic rats (+1 and +23%), whereas changes in renal blood flow were not significantly different between the two groups (-44 vs. -34%). In conclusion, in biliary cirrhotic rats, decreased pressor response to angiotensin II depends on the presence of liver disease rather than on portal hypertension or basal hemodynamic alterations. It also depends on the decreased vasoconstrictive effect which predominates in the splanchnic vascular bed.

Influence of angiotensin on total intravascular capacity in the anaesthetized pig

The present study examined the influence of angiotensin on total intravascular capacity. In eight anaesthetized pigs, splenectomy, carotid sinus denervation and cervical vagotomy were performed. Blood was drained from the venae cavae to an extracorporeal reservoir and returned to the right atrium at a constant rate so that changes in total intravascular volume could be recorded as the inverse of changes in reservoir volume. Angiotensin administration at 0.2 microgram kg-1 min-1 i.v. for 5 min was associated with a decrease in total intravascular volume of 57 +/- 6 ml (P less than 0.05) and an increase in aortic pressure from 96 +/- 5 to 119 +/- 6 mmHg (P less than 0.05). With subsequent angiotensin administration in five of the animals, the responses were not attenuated. In five of the animals, angiotensin was associated with a decrease in intravascular volume of 72 +/- 8 ml (P less than 0.05) before abdominal evisceration and 33 +/- 13 ml (P less than 0.05) after evisceration. These responses were significantly different from each other. In four of these eviscerated animals, angiotensin was associated with a decrease in intravascular volume of 35 +/- 17 ml (P less than 0.05) before ligation of all four limbs and a decrease of 36 +/- 4 ml (P less than 0.05) after limb ligation. Thus, angiotensin acts directly to decrease total intravascular volume. The decrease is due to decreases in both splanchnic and extrasplanchnic volume. The extrasplanchnic volume decrement is not due to decreases in skeletal muscle or cutaneous tissue intravascular capacity in the limbs.