Mesoatrial shunt hemodynamics

Hemodynamic profiles were obtained for patients with portal hypertension secondary to the Budd-Chiari syndrome who underwent mesoatrial shunting procedures. In contrast to the well-known hyperdynamic, low-resistance state of chronic cirrhosis, patients with the Budd-Chiari syndrome had normal cardiac index and systemic vascular resistance values before anesthesia and surgery. Opening the mesoatrial shunt produced a 46% (p less than 0.01) increase in cardiac index and a 38% (p less than 0.01) decrease in overall systemic vascular resistance. Right atrial pressure and pulmonary capillary wedge pressures were sharply increased--by 5.3 mm Hg and 4.7 mm Hg, respectively (p less than 0.01). A mathematical model was developed to assess the cause of the observed changes in systemic vascular resistance. The model suggests that the hemodynamic changes seen with shunt opening are unlikely to be the result of shunt effects alone and that dilatation of peripheral vascular beds is probable. Thus shunting converts the normal systemic vascular resistance and cardiac index of patients with the Budd-Chiari syndrome to the high-output, low-resistance state seen in patients with chronic cirrhosis. Although the physiology is complex, we conclude that the data are consistent with release, by the shunting process, of a systemic vasodilator.

Use of cultured cells to study the relationship between arachidonic acid and endothelium-derived relaxing factor

We have used mixed- and co-cultures of endothelial and vascular smooth muscle cells to investigate the role of phospholipase activation and arachidonic acid metabolites in the production of endothelium-derived relaxing factor (EDRF). Inhibition of phospholipase A2 with para-bromophenacyl bromide, dexamethasone or quinacrine, alone or in combination, blocked arachidonate release by 50%-60% but had no effect on EDRF production as assessed by cyclic GMP accumulation in mixed- or co-cultures of endothelial and vascular smooth muscle cells. Inhibition of the phospholipase C-diacylglycerol (DAG) lipase pathway of arachidonate release by the DAG lipase inhibitor RHC-80267 also caused partial inhibition of arachidonate release and had no effect on EDRF. When both phospholipase A2 and phospholipase C pathways for arachidonate mobilization were inhibited (dexamethasone + RHC 80267), arachidonate release was totally inhibited while EDRF release remained intact. We conclude that neither phospholipase activation nor arachidonate mobilization is required for EDRF release from cultured bovine endothelial cells.

Potassium-free solution prevents the action but not the release of endothelium-derived relaxing factor

Exposure to a K+-free solution reversibly inhibited the acetylcholine-induced relaxation in perfused canine femoral artery segments with endothelium and in superfused bioassay femoral artery rings without endothelium. Infusion of 6.7 mM K+ into the K+-free perfusate downstream of the perfused artery restored the acetylcholine-induced relaxation in the bioassay ring, whereas no relaxation was observed in the perfused segment still exposed to the K+-free solution. These data demonstrate that the K+-free solution depresses the endothelium-dependent relaxation to acetylcholine in femoral arteries by preventing the action, but not the production, of endothelium-derived relaxing factor.

Vasodilatation and the discovery of endothelium-derived relaxing factor

Whether endothelium-derived relaxing factor (EDRF) is important in the physiology and pathology of vascular reactivity must await the discovery of the nature of the factor and an appropriate antagonist substance. Nevertheless the demonstration that EDRF is powerful, short-lived and can be released by a wide variety of stimuli adds a new dimension to our knowledge of the control of the circulation. The macroenvironment of the vessel wall is influenced by nerves, blood-borne factors and the architecture of the wall. The discovery of a role of the endothelial cell has for the first time forced pharmacologists to consider cell-cell interactions in the micro-environment of the blood-vessel wall. This is a potentially important target for new therapy.

Inhibitors of acyl-coenzyme A:lysolecithin acyltransferase activate the production of endothelium-derived vascular relaxing factor

Considerable acyl-CoA:lysolecithin acyltransferase (LAT) activity could be demonstrated in homogenates of cultured bovine endothelial cells. This LAT activity was inhibited by thimerosal and p-hydroxymercuribenzoate in a concentration-dependent manner. Preconstricted strips of rabbit aorta were relaxed by acetylcholine or the LAT inhibitors in a concentration-dependent fashion if the endothelium was intact (maximal effect of both LAT inhibitors at 10(-5) M). In rabbit aortic strips thimerosal also induced a concentration-dependent stimulation of the formation of 6-keto-prostaglandin F1 alpha, the major cyclooxygenase metabolite of this tissue. This effect of thimerosal was more pronounced in endothelium-intact than in endothelium-denuded preparations. Inhibition of prostaglandin synthesis with indomethacin (10(-5) M) did not impair the relaxation. Thimerosal and acetylcholine-induced relaxations were abolished when the endothelium was removed or when endothelium-intact preparations were pretreated with nordihydroguaiaretic acid (3 X 10(-5) M), gossypol (5 X 10(-6) M) or dithiothreitol (3 X 10(-4) M). In contrast, mepacrine (3 X 10(-5) M), that abolished the acetylcholine response, had no effect on the thimerosal relaxation. In other experiments bovine endothelial cells were grown to confluence on microcarrier beads and packed into columns. Adding thimerosal (5 X 10(-6) M) or bradykinin (10(-10) to 10(-8) M) to the medium superfusing the columns induced the release of an unstable nonprostanoid factor (or factors) that relaxed endothelium-denuded rabbit femoral artery segments. Bradykinin induced a transient effect whereas there was a strong and long-lasting release of the factor after administration of thimerosal.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on endothelium-dependent vasorelaxation

Recent studies on endothelium-dependent vasorelaxation have been briefly reviewed and analyzed. This mechanism, which might involve the release of metabolite(s) termed "endothelium-derived relaxing factor(s)" (EDRF), could play a major role in the regulation of vascular tone.

Production of endothelium derived relaxant factor is dependent on oxidative phosphorylation and extracellular calcium

The production (synthesis or release or both) of endothelium derived relaxant factor was studied in rabbit aortic strip preparations and an aortic-coronary artery bioassay system. Production of endothelium derived relaxant factor was rapidly inhibited by agents that inhibit mitochondrial electron transport or F1-ATPase, or which uncouple oxidative phosphorylation, but was only slowly impaired by inhibition of glycolysis. It was dependent also on the presence of extracellular calcium with a rapid on-off response time. This study shows that production of endothelium derived relaxant factor appears to be dependent on both oxidative phosphorylation and extracellular calcium.

Endothelium-derived relaxing factor (EDRF)

Recent studies on endothelium-dependent vasorelaxation have been briefly reviewed and analyzed. The following processes appear to subserve this mechanism: In the endothelial cell: receptor activation, activation of phospholipases, mobilization of intracellular Ca2+, synthesis and release of 'endothelium-derived relaxing factor(s) (EDRF); In the smooth muscle cell: activation of guanyl cyclase and protein kinase, protein phosphorylation/dephosphorylation, relaxation. Alterations of this mechanism could be involved in certain cardiovascular disorders.

Paradoxical endogenous synthesis of a coronary dilating substance from arachidonate

Isolated bovine, canine, and human coronary arteries exhibited dose dependent contractions to prostaglandin (PG) E2 and F2alpha (50 ng/ml to 10mug/ml). The ED50 value for both PGE2 and PGF2alpha was 500 ng/ml in the bovine and human coronary arteries. Paradoxically, although PGE2 and gf2alpha are vasoconstrictors, administration of their precursor, arachidonate (100 ng/ml to 10 mug/ml) caused relaxation of the bovine, canine and human coronary arteries. This observation suggests that arachidonate is not being converted by the coronary PG synthetase to PGE2 or PGF2alpha. However, the arachidonate induced coronary relaxation was inhibited by pretreatment with PG synthetase inhibitors, indomethacin, meclofenemate and aspirin. Indomethacin addition to the strips previously relaxed by arachidonate caused contraction. In contrast to other PGs (E2 and F2alpha), PGE1 (10 ng/ml to 10 mug/ml) caused dose dependent relaxation of the bovine coronary arteries (ED50 = 100 ng/ml). Indomethacin induced further relaxation of the blood vessels previously relaxed by PGE1. Since PGE1 cannot arise from arachidonate, the arachidonate coronary dilation and reversal by indomethacin must be independent of PGE1 formation. Linolenate (100 ng/ml to 10 mug/ml) and oleate (100 ng/ml to 10 mug/ml) also caused relaxation of the bovine coronary blood vessels both before and after indomethacin, thereby eliminating a direct non-specific fatty acid effect as the cause of the arachidonate relaxation. These results suggest that in isolated coronaries, arachidonate undergoes a novel conversion, possibly by PG synthetase, to a dilating substance which exerts different contractile effects than exogenously administered PGE2, PGF2alpha and PGE1.

Mechanisms for the high circulatory requirements in sepsis and septic shock

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