The effect of vasopressin on hepatic artery flow in the rat

The effects of vasopressin on systemic and splanchnic hemodynamics and metabolism in endotoxin shock

We compared the effects of vasopressin and norepinephrine on systemic and splanchnic circulation and metabolism in endotoxin shock in pigs. Twenty-one pigs were randomized to endotoxin shock (Escherichia coli endotoxin infusion) (n = 6), endotoxin and vasopressin (VASO; n = 6), endotoxin and norepinephrine (NE; n = 6), and controls (n = 3). Endotoxin infusion was increased to induce hypotension, after which vasopressin or norepinephrine was started to keep systemic mean arterial blood pressure >70 mm Hg. Regional blood flows and arterial and regional lactate concentrations were measured. Tonometers with microdialysis capillaries were inserted into the stomach, jejunum, and colon. Systemic mean arterial blood pressure >70 mm Hg was achieved in the VASO and NE groups. Vasopressin decreased cardiac output, superior mesenteric artery, and portal vein blood flow, whereas hepatic arterial blood flow increased. Arterial lactate concentration increased from 2.0 mM (1.6-2.1 mM) to 4.7 mM (4.7-4.9 mM) (P = 0.007). Systemic and mesenteric oxygen delivery and consumption decreased and oxygen extraction increased in the VASO group. Vasopressin increased mucosal-arterial PCO(2) gradients in all three locations, whereas luminal lactate release occurred only in the jejunum. Animals in the NE group remained stable. Vasopressin reversed hypotension but decreased systemic and gut blood flow. This was associated with hyperlactatemia, signs of visceral dysoxia, and jejunal luminal lactate release.

IMPLICATIONS

Although vasopressin induces vasoconstriction in visceral region, its effects on splanchnic circulation and metabolism during septic-endotoxin shock are still poorly characterized. We evaluated the metabolic and hemodynamic effects of vasopressin and norepinephrine within the splanchnic area in porcine endotoxin shock.

Management of vasodilatory shock: defining the role of arginine vasopressin

The rationale for an arginine vasopressin (argipressin) infusion was put forward after it was discovered that patients in shock states might have an endogenous arginine vasopressin deficiency. Subsequently, several investigations impressively demonstrated that arginine vasopressin can successfully stabilise haemodynamics even in advanced vasodilatory shock. We report on physiological and pharmacological aspects of arginine vasopressin, and summarise current clinical knowledge on employing a continuous arginine vasopressin infusion in critically ill patients with catecholamine-resistant vasodilatory shock of different aetiologies. In view of presented experimental evidence and current clinical experience, a continuous arginine vasopressin infusion of approximately 2 to approximately 6 IU/h can be considered as a supplemental strategy to vasopressor catecholamines in order to preserve cardiocirculatory homeostasis in patients with advanced vasodilatory shock. Because data on adverse effects are still limited, arginine vasopressin should be reserved for patients in whom adequate haemodynamic stabilisation cannot be achieved with conventional vasopressor therapy or who have obvious adverse effects of catecholamines that result in further significant haemodynamic deterioration. For the same reasons, arginine vasopressin should not be used as a single, alternative vasopressor agent instead of catecholamine vasopressors. Future prospective studies will be necessary to define the exact role of arginine vasopressin in the therapy of vasodilatory shock.

Differential effects of neuropeptides on coeliac and superior mesenteric blood flows in conscious rats

The effects on coeliac and superior mesenteric blood flows of intravenous bolus doses of arginine-8-vasopressin (0.7 and 7.0 pmol) porcine neuromedin U-25 (0.01 and 1.0 nmol), rat alpha-calcitonin gene-related peptide (0.05 and 0.5 nmol), bombesin (0.06 and 0.6 nmol), and rat corticotropin-releasing factor (1.0 and 5.0 nmol) were investigated in conscious, Long-Evans rats chronically instrumented with pulsed Doppler flow probes. The peptides investigated were chosen on the basis of the range (vasoconstrictor-vasodilator) of their effects on superior mesenteric blood flow. With the exception of rat corticotropin-releasing factor (which increased coeliac and superior mesenteric flows) all peptides caused directionally opposite changes in coeliac and superior mesenteric blood flows. The results are consistent with the proposition that endogenous neuropeptides could influence blood flows to different abdominal viscera selectively.

Liver blood flow measurement in the rat. The electromagnetic versus the microsphere and the clearance methods

This study describes the simultaneous measurement of hepatic arterial and portal venous blood flow in the pentobarbital anesthetized rat by means of electromagnetic flowmeters. Hepatic arterial flow was 0.21 +/- 0.02 mL/min/g liver, and portal venous flow was 1.53 +/- 0.19 mL/min/g liver (n = 20). Flows remained stable for more than 3 hr. A clear advantage of the electromagnetic technique is that it allows the continuous simultaneous separate measurement of hepatic arterial and portal venous blood flow. Simultaneous measurement of hepatic blood flow by the electromagnetic method and the microsphere method yielded almost identical results. Adenosine infusion (100 micrograms/min) did not affect hepatic blood flow measured electromagnetically nor via the microsphere technique. The suitability of indocyanine green (ICG) as an indicator of hepatic blood flow was evaluated by comparing the ICG clearance at steady-state conditions to the values of liver flow obtained by direct electromagnetic measurement. ICG clearance was only 30% of the electromagnetically measured blood flow. These data strongly suggest that ICG clearance does not reflect liver flow in the rat. Intravenous infusion of the vasoactive agents phenylephrine (2, 4, 10 micrograms/min during 5 min) and adenosine (20, 40, 200 micrograms/min) did not affect portal venous nor hepatic arterial flow, measured by the electromagnetic method, although brisk effects on mean arterial blood pressure were observed. This suggests autoregulatory responses of the hepatic vascular bed. The data suggest that electromagnetic flowmeters may be used to measure portal venous and hepatic arterial flow simultaneously in anesthetized rats. The continuous measurement of both flows simultaneously offers a clear advantage over other methods of hepatic flow measurement.