Influence of primary prostaglandins, prostacyclin and arachidonic acid on mesenteric hemodynamics in the pig

Mesenteric traction syndrome in pigs: A single-blinded, randomized controlled trial

Background

Mesenteric traction syndrome is commonly observed in patients undergoing upper abdominal surgery and is associated with severe postoperative complications. A triad of hypotension, tachycardia, and facial flushing seems provoked by prostacyclin (PGI2) release from the gut in response to mesenteric traction. The administration of nonsteroidal anti-inflammatory drugs (NSAID) inhibits PGI2 release, stabilizing the hemodynamic response. Here, we examined the effect of mesenteric traction on splanchnic blood flow in pigs randomized to NSAID or placebo treatment.

Materials and Methods

Twenty pigs were allocated to either ketorolac or placebo treatment. Five minutes of manual mesenteric traction was applied. Plasma 6-keto-PGF1α, a stable metabolite of PGI2, hemodynamic variables, and regional blood flow (laser speckle contrast imaging) to the liver, stomach, small intestine, upper lip, and snout (laser Doppler flowmetry) were recorded prior to traction and 5 and 30 minutes thereafter.

Results

Both groups of pigs presented a decrease in systemic vascular resistance (P = .01), mean arterial blood pressure (P = .001), and blood flow in the gastric antrum (P = .002). Plasma 6-keto-PGF1α did not increase in either group (P = .195), and cardiac output, heart rate, central venous pressure, and blood flow to the liver, small intestine, upper lip, and snout remained unchanged.

Conclusion

Mesenteric traction resulted in cardiovascular depression, including reduced blood flow in the gastric antrum. Plasma 6-keto-PGF1α did not increase, and ketorolac administration did not alter the response to mesenteric traction. Furthers studies are needed to identify which substance is responsible for eliciting the cardiovascular response to mesenteric traction in pigs.

Effects of systemic prostaglandin E1 on splanchnic and peripheral haemodynamics in control subjects and in patients with cirrhosis

Prostaglandins of the E series showed metabolic and clinical effects in patients with liver disease; changes in splanchnic haemodynamics might be involved. Blood flow in femoral and mesenteric artery and in the portal vein was measured by echo-Doppler in 10 controls and 14 cirrhotic patients, in response to the systemic infusion of a PGE1 analogue (30 micrograms/h for 2-6 h) or saline, performed in random order. Intraparenchymal resistive and pulsatility indices in the liver, spleen and kidney were also measured. In both groups PGE1 increased femoral artery flow by 40%, irrespective of infusion time. Heart rate increased slightly, whereas mean arterial pressure decreased. There were no changes in mesenteric artery and portal vein flow, as well as in resistance indices. Saline infusion increased femoral artery flow by 4%. PGE1 infusion does not produces significant effects on Doppler-assessed splanchnic hemodynamics in controls and in cirrhotic patients, in spite of significant effects on peripheral circulation.

Role of prostacyclin in hemodynamic alterations in conscious rats with extrahepatic or intrahepatic portal hypertension

Although prostaglandins are thought to be involved in the hyperdynamic circulation of portal hypertension, the role of this substance has not been elucidated. Dose-response curves, the hemodynamic effects of prostacyclin (20 micrograms/kg) and its inhibitor indomethacin and measurements of plasma and urinary levels of 6-keto-prostaglandin F1 alpha were compared in three groups of six rats each: normal, with portal vein stenosis and with secondary biliary cirrhosis. Plasma and urinary levels of 6-keto-prostaglandin F1 alpha were higher in rats with portal vein stenosis and cirrhotic rats than in normal rats. Dose-response curves showed similar maximal decreases in arterial pressure in the three groups, whereas the maximal increase in portal pressure was less marked in cirrhotic rats than in normal rats and rats with portal vein stenosis. In normal rats, prostacyclin increased cardiac output by 21% and portal pressure by 41%. Similar increases were observed in rats with portal vein stenosis. In contrast, prostacyclin did not affect cardiac output and portal pressure in cirrhotic rats. Indomethacin induced a more marked vasoconstrictive effect in normal rats than in cirrhotic rats. This study shows that prostacyclin plays a role in the hemodynamic alterations in portal hypertension. Moreover, the hyporeactivity observed in cirrhotic rats suggests that prostacyclin plays a major role in the circulatory changes of portal hypertension due to chronic liver disease.

Role of prostacyclin in the splanchnic hyperemia contributing to portal hypertension

To determine the possible role of prostacyclin (PGI2) as a mediator of the splanchnic hyperemia seen with portal hypertension, the portal and mesenteric hemodynamics in normal and portal hypertensive rabbits were studied before and after cyclo-oxygenase blockade. Three weeks after partial portal vein ligation, splenic pulp pressure was elevated from 4.3 +/- 0.9 to 9.8 +/- 0.8 mmHg (p less than 0.01). Mesenteric blood flow increased from 77.0 +/- 4.7 ml.min-1.100 g-1 to 99.1 +/- 5.19 ml/min-1/100 g-1. Mesenteric vascular resistance fell from 0.82 +/- 0.6 mmHg/ml-1/min-1 to 0.49 +/- 0.07 mmHg/ml-1/min-1 (p less than 0.01). These hemodynamic changes were associated with a 27.3 +/- 0.2% rise in systemic arterial levels of PGI2 (p less than 0.01) and were substantially ameliorated by cyclo-oxygenase blockade with indomethacin. The effects of indomethacin blockade were reversed by exogenous PGI2. Moreover, in normotensive rabbits, infusion of PGI2 reproduced the splanchnic hyperemia and caused a very small but significant increase in portosystemic shunting. These findings support the previously proposed concept that splanchnic hyperemia may contribute to the maintenance of chronic portal hypertension. Furthermore, they suggest that this effect may be partially mediated by splanchnic PGI2 production.

Effects of prostaglandin inhibition on systemic and hepatic hemodynamics in patients with cirrhosis of the liver

The role of prostaglandins in the pathogenesis of the circulatory abnormalities of cirrhosis was investigated by studying the effects of prostaglandin inhibition with indomethacin (50 mg/8 h for 24 h) on the systemic and splanchnic hemodynamics in 13 patients with cirrhosis of the liver. Indomethacin administration significantly reduced cardiac output (from 7.44 +/- 0.7 to 6.78 +/- 0.7 L/min, p less than 0.05) and increased peripheral vascular resistance (from 990 +/- 104 to 1155 +/- 140 dyn X s X cm-5, p less than 0.05). Arterial pressure was not modified. These changes in systemic hemodynamics were associated with a significant reduction in hepatic blood flow (from 1.88 +/- 0.43 to 1.48 +/- 0.3 L/min, p less than 0.05) and with a slight decrease of portal pressure (from 18.8 +/- 1.3 to 17.5 +/- 1.4 mmHg, p less than 0.05). These results suggest that endogenous prostaglandins contribute to the increased cardiac output and diminished vascular resistance observed in cirrhosis of the liver. In addition, by promoting splanchnic vasodilation, prostaglandins may contribute to increased portal pressure in these patients.

Effects of indomethacin and prostaglandins I2 and E2 on the tone of human isolated mesenteric arteries

The actions of indomethacin (IND), PGE2 and PGI2 were studied on the tone of isolated mesenteric arteries obtained from operated patients. The cyclooxygenase inhibitors IND (3 mumol/l) and suprofen (0.58 mumol/l) increased the resting tone and potentiated the contractile responses to electrical stimulation and noradrenaline. Low concentrations of PGE2 (0.7-5.6 X 10(-9) mol/l) decreased the baseline tone and reduced the stimulation-evoked contractions whereas higher concentrations (from 5.7 X 10(-8) mol/l) increased the tone of vessels. PGI2 (0.7-10.8 X 10(-9) mol/l) also relaxed IND-treated arteries but, in contrast to PGE2, it did not produce contraction even at a concentration of 10(-6) mol/l. Prostacyclin reduced the tone evoked and sustained by a high concentration of PGE2 or PGF2 alpha, the IC50 values being 46.2 or 7.9 X 10(-9) mol/l, respectively. The contractile responses to electrical stimulation and to noradrenaline were also inhibited by PGI2 (IC50 5.6 and 6.8 X 10(-9) mol/l, respectively). These results suggest that the smooth muscle cells of human mesenteric arteries are just as sensitive to IND, PGE2 and PGI2 as are those from laboratory animals. Our observations may be of clinical importance.

Effects of indomethacin, naproxen and paracetamol on regional blood flow in rabbits: a microsphere study

Ulcerogenic side-effects and prostaglandin-synthesis-inhibiting capacity are well documented in indomethacin treatment. According to recent works, indomethacin reduces gastrointestinal blood-flow. Naproxen and paracetamol, claimed to be prostaglandin-synthesis-inhibitors, have few ulcerogenic side effects. In an attempt further to study the indomethacin effects and to reveal whether naproxen and paracetamol have similar effects, the labelled microsphere technique was used. The regional blood flow determinations were made before, and 12-15 min. after, the injection of the drugs. Indomethacin 3 mg/kg, reduced gastrointestinal blood flow and increased arterial blood flow to the liver. Naproxen, 10 mg/kg, and paracetamol, 25 mg/kg, had no effects except for a very small decrease in liver blood flow with paracetamol. The results strongly suggest that, at least under light general anaesthesia, prostaglandins influence resting blood flow in the gastrointestinal tract, the liver and parts of the brain. The results more raise doubts whether naproxen and paracetamol inhibit prostaglandin synthesis in these tissues. These data offer a plausible explanation as to why naproxen and paracetamol are usually well tolerated in the gastrointestinal tract. None of the drugs tested influenced resting blood flow in muscles, tendons, bones, joints or synovial membranes.

Histamine H1- and H2-receptors in the mesenteric vascular bed of the pig

In order to study whether both histamine H1- and H2-receptors are present in the pig mesenteric vascular bed, natural histamine, 2-(2-pyridyl) ethylamine and 4-methylhistamine, as well as mepyramine and metiamide, were infused directly into the superior mesenteric artery. The results indicate that histamine H1- and H2-receptors, both inducing vasodilation, are present in the mesenteric circulation of the pig. Jejunal motility proved to be influenced by H1-receptor stimulation only.

Substance P: a powerful intestinal vasodilator in the pig

In anaesthetized young pigs the influence of intra-arterial infusions of Substance P (SP) on mesenteric vascular resistance is studied, both before and after serotoninergic and nervous conductivity blockade by dihydroergotamine (DHE) and tetrodotoxin (TTX). SP has a strong dilator effect on pig mesenterial vessels, which is not significantly modified by DHE or TTX; presumably SP acts directly on the vascular smooth muscle. By comparing the threshold level of SP with that of other intestinal vasdodilators, it may be concluded that SP is the most powerful intestinal vasodilator so far extperimented in the pig.