Prostaglandins and thromboxane in the delayed phase of shock induced by Serratia marcescens endotoxin

Investigation of the prostaglandin E (EP-) receptor subtype mediating relaxation of the rabbit jugular vein

1. Prostaglandin E2 (PGE2) relaxes circular smooth muscle of the rabbit isolated jugular vein at very low concentrations (mean pIC50 against histamine-induced contraction = 9.34). This effect is not blocked by the EP1-receptor antagonist, AH 6809 (2 microM). 2. From a group of prostaglandin E analogues examined, 16,16-dimethyl PGE2, misoprostol, 11-deoxy PGE2-1-alcohol and 11-deoxy PGE1 were highly potent relaxant agents, whereas 17-phenyl-omega-trinor PGE2, MB 28767 and butaprost had low potency and sulprostone and oxoprostol were virtually inactive. 3. Comparison of the jugular vein data with published data for inhibitory agonist potencies on the cat trachea (EP2 preparation) and the field-stimulated guinea-pig vas deferens (EP3) indicates that the EP-receptor in the rabbit jugular vein is closest to the EP2 subtype. However, the correlation is not entirely convincing. For example, butaprost, 16,16-dimethyl PGE2 and 11-deoxy PGE1 are of similar potency on the cat trachea, whereas butaprost is about 300 times less potent than the other two analogues on the jugular vein. The existence of more than one EP2-receptor appears possible. 4. It was felt that the activity of butaprost required further investigation in view of the claim that it is a specific EP2-receptor agonist. We have shown that butaprost has very low inhibitory activity on the guinea-pig vas deferens, a very sensitive EP3-receptor containing preparation. However, on the chick ileum, the original EP3 preparation, butaprost showed potent contractile activity (pEC25 approximately 8.0).In addition, its maximum response was lower than that of PGE2; lower maxima were also found for sulprostone, MB 28767 and oxoprostol, but not for ICI 80205, 16,16-dimethyl PGE2 and 17-phenyl-omega-trinor PGE2. The maximal response to a combination of either sulprostone and butaprost or sulprostone and PGE2 was similar to that achieved by PGE2 alone. Analysis of the interaction between sulprostone and PGE2 appears to exclude a partial agonist action for sulprostone. Furthermore neither sulprostone nor butaprost appear to have inhibitory activity on the ileum. AH 6809 at 2 pM produced only a small shift of the PGE2 log concentration-response curve.5. It is likely that contraction of the longitudinal smooth muscle of the chick ileum is mediated by (at least) two EP-receptor subtypes; activation of only one receptor system does not induce the maximum response (i.e. the acetylcholine maximum) of the preparation. One receptor could be an EP3 subtype, at which sulprostone exerts a selective agonist action. The other receptor is unlikely to be an EP, subtype, because of the high agonist potency of butaprost, the low agonist potency of iloprost, and the low antagonist potency of AH 6809. An alternative hypothesis is that the chick ileum contains a novel EP-receptor subtype in addition to an EP3-receptor.

Thromboxane and prostacyclin release after endotoxin infusion in the rat

To determine in the rat whether pulmonary artery hypertension accompanies thromboxane release, we sequentially monitored pulmonary and systemic artery pressures and cardiac output. We measured pulmonary and aortic plasma levels of TxB2 as well as 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) in awake unrestrained adult male Sprague-Dawley rats given a single infusion of endotoxin at the relatively high dose commonly administered to this endotoxin-resistant species. At 40 min after endotoxin infusion, both pulmonary and aortic TxB2 and 6-keto-PGF1 alpha levels increased nine-fold and seven-fold above baseline, respectively. In the pulmonary artery, 40 min after infusion, both mediator levels differed significantly from baseline (p less than 0.05), whereas in the aorta, because of marked variance in the response of different animals, only the 6-keto-PGF1 alpha levels achieved significance (p less than 0.05). These changes were associated with a fall in systemic blood pressure and cardiac output, but no demonstrable rise in pulmonary artery pressure (PAP). Despite ultrastructural evidence of vascular injury, these data indicate that in the rat thromboxane and prostacyclin release following a single infusion of endotoxin is not associated with pulmonary hypertension and that increased prostacyclin production may contribute to systemic hypotension.

Pulmonary intravascular macrophages in domestic animal species: review of structural and functional properties

In dogs, laboratory animals, and man, the clearance of bacteria and particulates from blood occurs predominantly in hepatic Kupffer cells and splenic macrophages. In contrast, removal of blood-borne particulates in calves, sheep, goats, cats, and pigs occurs predominantly in pulmonary intravascular macrophages (PIMs). Review of recent studies indicates that PIMs are a resident cell population, junctionally adherent to the capillary endothelium of lungs and morphologically similar to hepatic Kupffer cells. PIMs are a pulmonary constituent of the mononuclear phagocyte system with respect to secretory, endocytic, and functional properties. Differentiated PIMs are rare in newborn pigs, and the majority of cells closely apposed to capillary endothelium consists of monocytes, which are occasionally in mitosis. In 7-day-old and older pigs, most cells apposed to capillary endothelium have characteristics of differentiated PIMs. This suggests a monocytic origin of PIMs in pigs. Perinatal colonization of lung capillaries by monocytes and their subsequent differentiation into PIMs represent a component of postnatal lung development. Estimates of relative PIM numbers in ovine and porcine lung parenchyma suggest cell densities similar to that of rat hepatic Kupffer cells. Apart from phagocytic properties, PIMs participate in the removal and disintegration of aged and impaired blood cells. After phagocytic stimulation, isolated PIMs secrete oxygen radicals, which are essential for microbicidal function. Similarly, by secreting bioactive lipids, stimulated PIMs may contribute to regulation of pulmonary hemodynamics. After receiving minute amounts of bacterial endotoxin, pulmonary injury is pronounced in sheep, calves, pigs, and cats, but not in laboratory animals and dogs. This presumably is related to the secretion of bioactive lipids by PIMs.

Regional variation in the sensitivity of longitudinal smooth muscle to histamine at H1-receptors in guinea-pig ileum and colon

The sensitivity of the distal ileum, proximal colon, medial colon, and distal colon of the guinea-pig to histamine has been evaluated. The rank order of sensitivity was ileum greater than medial colon greater than proximal colon approximately equal to distal colon. The mean -logEC50 values at receptors in the ileum, medial, proximal, and distal colon were 6.74, 6.18, 5.79, and 5.72, respectively. The apparent dissociation constant for the interaction of histamine with receptors in the various regions was determined. The -log Kd values at receptors in the ileum, proximal colon, medial colon, and distal colon were 4.68, 4.65, 4.62, and 4.44, respectively. The mean apparent -log Kd values for the antagonism of histamine by mepyramine were 9.0, 9.0, 9.1, and 8.9 for receptors on the ileum, proximal, medial, and distal colon, respectively. The results of these experiments provide no evidence that histamine receptors in the colon are distinguishable from H1-receptors as characterized on the ileum. The differences in sensitivity to histamine in the various regions of the intestine may be due to differences in the density of H1-receptors.