Removal of the endothelial layer in perfused mesenteric vascular bed of the rat

cGMP release in rat mesenteric arterioles and in conduit mesenteric artery

1. Relaxing factors were studied in two perfused preparations of the same vascular area in the rat: resistance mesenteric arterioles and conduit mesenteric artery. 2. In both preparations, an acetylcholine (ACh) infusion inhibited noradrenaline (NA) vasoconstrictor effects but at a ten-times greater concentration in conduit artery than in resistance arterioles. 3. Endothelium destruction with hypotonic Krebs solution did not change basal perfusion pressure, but increased NA responses and suppressed ACh inhibitory effects in arterioles and arteries. Likewise, L-NAME abolished the ACh effect in mesenteric arterioles but only reduced it in mesenteric artery. 4. Basal release of cyclic GMP was significantly greater in mesenteric artery than in resistance arterioles. By contrast, ACh-induced cGMP release was higher in mesenteric arterioles. Endothelium removal did not change basal release of cGMP in mesenteric arterioles but reduced it in mesenteric artery. 5. These results suggest that in basal conditions several relaxing factors are present in higher concentrations in conduit mesenteric artery than in resistance mesenteric arterioles. However, although it releases higher basal amount of cGMP, this vessel has a reduced role in vascular control than do smaller arteries.

Studies of human airways in vitro: a review of the methodology

The pathophysiology of human airway narrowing is only partly understood. In order to gain more insight in the mechanisms of human lung diseases and potential beneficial therapeutic agents, adequate models are needed. Animal airway models are of limited value since lung diseases such as asthma and chronic obstructive pulmonary disease (COPD) are unique to humans and because the mechanisms of airway narrowing differ between species. Therefore, it is important to perform studies on human isolated airways. We describe the models that have been developed to study airway function in vitro, emphasizing human airway preparations. The easily prepared airway strip and ring preparations are described first. The potential damage during preparation and the interference with airway structure are important drawbacks in these preparations. Lung parenchymal strips, described next, were designed in order to study responsiveness of small airways. However, parenchymal strips are anatomically complex, and responsiveness is determined by the relative amounts of airway and vascular smooth muscle. The lack of reproducibility between species and even within one animal limits their usefulness. Airway tube preparations, in which luminal and serosal stimulation can be separated, enable us to study the modulatory role of the airways epithelium in vitro. Furthermore, airway compliance can be measured. In the isolated perfused lung preparation, relationships between the airways and the vascular system are preserved and the interaction between these two systems can be studied. Weight gain due to fluid extravasation is a problem in this model which has not been used yet to study human lungs in vitro. Next, methodological aspects such as tissue handling and storage, recording of responses, removal of the epithelium, and electrical field stimulation are discussed in some detail. Although animal airways tissue can be studied immediately after removal, human tissue is often obtained with some delay. However, this seems tenable since electron microscopy of lung tissue obtained at autopsy showed that recovery of the preparation occurs during incubation of carbogenated Krebs-Henseleit (K-H) buffer. Dissected airways can be stored overnight in cooled K-H buffer until up to 55 hr after resection without losing viability. Commonly used physiological salt solutions which bath the tissue contain osmotic molecules, ions important for contractility, glucose as a substrate, and a bicarbonate-carbon dioxide buffer.(ABSTRACT TRUNCATED AT 400 WORDS)

Cardiac endothelial cells modulate contractility of rat heart in response to oxygen tension and coronary flow

The aim of this study was to determine if endothelial cells in the heart release substances into the coronary perfusion medium that modify the contractility of myocardial cells. To assay the effects on the contractility of cardiac muscle of fluid that has passed through the coronary vasculature, a new method has been developed based on the cascade principle used to study vascular smooth muscle function. The coronary venous effluent from an isolated perfused working heart was collected periodically, and after reoxygenation it was used as the bathing medium for trabeculae isolated from the endocardial surface of another heart. The coronary venous effluent changed the contraction of the isolated trabeculae. The amplitude and the direction of the change depended on the degree of oxygen saturation of the coronary effluent before it was reoxygenated and the rate of coronary flow at the time the effluent was collected. The response of the trabecula to the coronary effluent was substantially altered by damaging the endocardial endothelium with a 1-second exposure to 0.5% Triton X-100 in Krebs' solution. It was completely eliminated by damaging endothelial cells in both the perfused heart producing the effluent and the trabecula on which the effluent was assayed. Therefore, endothelial cells are required for the presence of cardioactive substances in the coronary effluent. The production of a labile endothelium-derived upregulating (positively inotropic) factor and a more stable endothelium-derived downregulating (negatively inotropic) factor has been demonstrated and appears to account for all of the changes in myocardial contractility produced by the coronary effluent. Neither of the endothelium-derived substances demonstrated in the isolated perfused heart is nitric oxide or endothelin. The concentration of the endothelium-derived upregulating factor is sensitive to oxygen tension, whereas the concentration of the endothelium-derived downregulating factor is sensitive to the rate of coronary flow but not oxygen tension. The coronary effluent appears to contain substances that stimulate secretion by the endothelial cells (preendothelial factors) as well as substances that have been produced by the endothelial cells (endothelial factors). The results indicate that during the passage of perfusion medium through the coronary vasculature upregulating and downregulating factors are added to the perfusate in relative concentrations that depend at least in part on local tissue PO2 and the rate of coronary flow. In the intact heart, this mechanism could operate to maintain balance between energy supply and work performed.