Gut permeability in paediatric cardiac surgery.

BACKGROUND: Intestinal mucosal ischaemia can occur in infants and children during and after cardiac surgery. Severe decreases in mucosal perfusion may cause complications such as necrotizing enterocolitis and postoperative mortality. We investigated gut permeability in paediatric patients undergoing cardiac surgery using the dual sugar permeability test and absorption of two other saccharides. METHODS: Thirty-four patients undergoing palliative or corrective surgical procedures with and without cardiopulmonary bypass were investigated. Intestinal permeability was measured using 3-O-methyl-D-glucose, D-xylose, L-rhamnose and lactulose, given orally after induction of anaesthesia and 12 and 24 h later. RESULTS: Lactulose/rhamnose ratios were raised from the outset [median 0.39 (confidence interval 0.07-1.8 for patients undergoing operations without cardiopulmonary bypass and 0.30 (0.02-2.6) with cardiopulmonary bypass]. The highest lactulose/rhamnose ratios were recorded 12 h after surgery 0.32 (0.07-6.9), when cardiopulmonary bypass was used. This is approximately seven times the value expected in healthy children. There was an improvement in patients not undergoing cardiopulmonary bypass: 0.22 (0.03-0.85) 12 h and 0.11 (0-0.48) 24 h after induction of anaesthesia. Patients undergoing repair of aortic coarctation showed the fastest recovery: 0.09 (0.03-0.31) 12 h and 0.07 (0.04-0.35) 24 h after induction of anaesthesia. CONCLUSIONS: Patients with congenital heart defects have abnormal gut permeability when compared with healthy children of similar age. Cardiopulmonary bypass seems to affect the intestinal barrier morphologically (lactulose and rhamnose absorption) and functionally (3-O-methyl-D-glucose and D-xylose absorption).

Not prostacyclin synthase but prostaglandin endoperoxide synthase increases with human placental development.

Prostaglandin endoperoxide synthase (i.e. cyclooxygenase; PGH synthase) and prostacyclin synthase (PGI synthase) were quantitated with specific immunoradiometric assays in microsomes from human placentae (n = 20) obtained from 7 up to 17 weeks of gestation. Over that period, wherein trophoblastic invasion of the uterine spiral arteries occurs, the placentae showed a significant increase in concentrations of PGH synthase (r = 0.73, p less than 0.001; n = 20), but not in those of PGI synthase. While the variation between individual placentae was much larger for PGI synthase than for PGH synthase concentrations, there was no evidence for a large excess of PGI synthase over that of PGH synthase in any of these early placentae. The data indicate, first, that the developing placenta contains PGI synthase, but in amounts which are relatively small and do not appear to increase with advancing gestation. Second, they seem to indicate that the capacity for bioconversion of arachidonic acid into prostaglandin endoperoxides increases markedly with placental development.

Distribution of prostaglandin endoperoxide synthase and prostacyclin synthase in the late pregnant uterus.

Prostacyclin (PGI2) synthase and prostaglandin endoperoxide synthase (cyclo-oxygenase; PGH synthase) were measured with specific immunoradiometric assays in myometrial microsomes from different areas of a primigravid uterus at 34 weeks gestation. PGH synthase concentrations increased significantly from fundus toward lower segment (P less than 0.005), but that trend did not apply to PGI2 synthase concentrations, which were significantly higher on the placental than on the non-placental side of the uterus (P less than 0.005). PGI2 synthase concentrations showed no further increase with increasing proximity to the placental bed. In myometrium underneath the placental bed there was an inverse relation between the PGH and PGI2 synthase concentrations (r = 0.86; P less than 0.01) which did not apply to other regions of the uterus. The data suggest that local rather than general mechanisms control uterine PGH and PGI2 synthase concentrations, and that uterine prostaglandin and PGI2 production strongly depend on anatomical relations that have been neglected in previous studies on uterine prostaglandin biosynthesis.

Does or can human placenta produce prostacyclin?

In order to resolve contradictory data on the capacity of the human placenta to produce prostacyclin (PGI2), we have quantified PGI2 synthase in 12 placentae obtained in the first trimester of pregnancy. Using a specific immunoradiometric assay and two monoclonal antibodies against the enzyme, we found PGI2 synthase to be present in the microsomal fraction of all placentae investigated, albeit in concentrations that were 1000-fold lower than in bovine aortal microsomes and 100-fold lower than in both pregnant and non-pregnant myometrium. Comparison of these data with previous reports on placental PGI2 production suggests that the contradictions between previous data are more apparent than real. We conclude that the human placenta possesses the potential for PGI2 production, that it therefore 'can' produce PGI2, but that it remains uncertain whether the placenta actually 'does' or 'does not' produce PGI2 in vivo.

Increase in placental 15-hydroxy-prostaglandin dehydrogenase in the first half of human pregnancy.

NAD-dependent 15-hydroxy-prostaglandin dehydrogenase (PGDH) activity was measured in homogenates of 25 human placentae obtained between 7 and 17 weeks of gestation. PGDH activity, expressed in nanomoles PGF2 alpha metabolized per min, ranged from 0.2 to 5.4 nmoles per mg placental protein and from 1.5 to 80 nmoles per g wet weight. PGDH activity per mg protein and per g weight increased significantly in function of gestational age (p less than 0.001). Between 7-8 weeks' gestation and 15-16 weeks mean values increased tenfold from 0.4 to 3.0 nmoles per mg protein and from 2.7 to 36.6 nmoles per g wet weight. Per unit of weight these early placentae contained less PGDH activity than term controls, but this related mainly to their high water content. Per mg placental protein PGDH activities already equalled values found at term before the end of the first trimester. The data indicate that the development of terminal villi and the migration of trophoblast into the maternal spiral arteries is associated with a substantial increase in the placental capacity for prostaglandin metabolism.

Control of prostacyclin synthesis in pregnancy-induced hypertension.

Uterine prostacyclin synthase (PGI synthase) and prostaglandin endoperoxide synthase (PGH synthase) concentrations, measured by specific immunoradiometric assays, did not differ between patients with severe pregnancy-induced hypertension (syn. pre-eclampsia; n = 5) and normotensive gravidae (n = 6) with comparable gestational ages (34 - 38 weeks). Myometrial microsomes from pre-eclamptic women contained ten times more PGI synthase than PGH synthase and the ratio of PGI synthase to PGH synthase (mean +/- SD; 10.1 +/- 3.9) was not different from that in normotensive pregnancies. None of the pre-eclamptic patients had myometrial enzyme levels that were more than one standard deviation below the mean established previously for pregnancies ranging from 32 to 42 weeks of gestation. These findings indicate that the commonly observed association between deficient PGI2 production and pregnancy-induced hypertension cannot be explained in terms of a generalized lack of immunoassayable prostacyclin or prostaglandin endoperoxide synthases.

Immunohistochemical localisation of prostaglandin endoperoxide synthase and prostacyclin synthase in pregnant human myometrium.

The localisation of prostaglandin endoperoxide synthase and prostacyclin synthase in pregnant human myometrium was examined by indirect immunocytofluorescent staining using monoclonal antibodies raised against these enzymes. Both enzymes were demonstrated to be present in myometrial smooth muscle cells. Staining associated with prostacyclin synthase, however, was more intense throughout the myometrium and less circumscript than that associated with prostaglandin endoperoxide synthase. The findings indicate that the uterine smooth muscle cells themselves possess the enzymes necessary for producing prostacyclin from arachidonic acid and that this capacity is not limited to the uterine macro- and microvasculature.

An easy method for preparing radioactive methyl esters of eicosanoids suitable as ligands in radioimmunoassays.

A rapid and convenient method is described for methylating prostanoids and other arachidonic acid metabolites. With 3H-methyl iodide of high specific activity, tracers for radioimmunoassay can be produced at a cost which is only a fraction of that of labeled compounds currently available. In radioimmunoassays for PGE2, TXB2 and 6-keto-PGF1 alpha, labeled methyl esters gave results which were comparable to those obtained with the use of tritiated free acids as radioligands.

Increase in concentrations of prostaglandin endoperoxide synthase and prostacyclin synthase in human myometrium in late pregnancy.

Concentrations of prostaglandin endoperoxide synthase (i.e. cyclooxygenase; PGH synthase) and prostacyclin synthase (PGI synthase) were quantified with specific radioimmunometric assays in human myometrium during the last trimester of pregnancy (n = 23) and in non-pregnant controls (n = 8). Pregnant myometrium contained 3 times more PGH synthase per mg microsomal protein than non-pregnant myometrium (p less than 0.01) but there was no increase with increasing gestational age in the third trimester nor with the onset of labor. In pregnancy, as compared to the non-pregnant state, there was no significant change in the PGI synthase content of myometrial microsomes, but significantly more PGI synthase was recovered in other subcellular fractions (p less than 0.01). This suggests that pregnancy affects preferential changes in the subcellular distribution of PGI synthase in myometrial cells. Relative to its PGI synthase content pregnant myometrium contained twice as much PGH synthase as non-pregnant myometrium (p less than 0.01). This may offer further evidence that PGH synthase rather than PGI synthase itself is the rate limiting factor in myometrial PGI2 production. On the other hand, the much larger increase in PGH synthase than in PGI synthase in pregnant as compared to non-pregnant myometrium, may serve to promote preferential synthesis of prostaglandins that are potent myometrial stimulants and of critical importance in human parturition.

An improved method for separation of thromboxane B2 by reversed phase liquid chromatography.

Column efficiency for thromboxane B2 (TXB2) is 10 times lower than for prostaglandins when chromatographed on octadecyl-silica columns. We described the use of a new non-silica reversed phase support which brings the column efficiency for TXB2 in the range of the prostaglandins.