The coronary vasodilator mediator released by hypoxia and isoprenaline is not affected by cyclo-oxygenase inhibition

Dilation of rat diaphragmatic arterioles by flow and hypoxia: roles of nitric oxide and prostaglandins

The in vitro responses to ACh, flow, and hypoxia were studied in arterioles isolated from the diaphragms of rats. The endothelium was removed in some vessels by low-pressure air perfusion. In endothelium-intact arterioles, pressurized to 70 mmHg in the absence of luminal flow, ACh (10(-5) M) elicited dilation (from 103 +/- 10 to 156 +/- 13 microm). The response to ACh was eliminated by endothelial ablation and by the nitric oxide synthase antagonists NG-nitro-L-arginine (L-NNA; 10(-5) M) and NG-nitro-L-arginine methyl ester (L-NAME, 10(-5) M) but not by indomethacin (10(-5) M). Increases in luminal flow (5-35 microl/min in 5 microl/min steps) at constant distending pressure (70 mmHg) elicited dilation (from 98 +/- 8 to 159 +/- 12 microm) in endothelium-intact arterioles. The response to flow was partially inhibited by L-NNA, L-NAME, and indomethacin and eliminated by endothelial ablation and by concurrent treatment with L-NAME and indomethacin. The response to hypoxia was determined by reducing the periarteriolar PO2 from 100 to 25-30 Torr by changing the composition of the gas used to bubble the superfusing solution. Hypoxia elicited dilation (from 110 +/- 9 to 165 +/- 12 microm) in endothelium-intact arterioles but not in arterioles from which the endothelium had been removed. Hypoxic vasodilation was eliminated by treatment with indomethacin and was not affected by L-NAME or L-NNA. In rat diaphragmatic arterioles, the response to ACh is dependent on endothelial nitric oxide release, whereas the response to hypoxia is mediated by endothelium-derived prostaglandins. Flow-dilation requires that both nitric oxide and cyclooxygenase pathways be intact.

A new concept of the isolated perfused heart preparation with on-line computerized data evaluation

A modified perfusion apparatus for electrophysiological, hemodynamic and metabolic studies on hearts of small animal (e.g., rat, guinea pig) has been described. The apparatus consisted of two oxygenators connected to the aortic cannula of the Langendorff perfused heart, each one of which could be used on demand. The constant aortic perfusion pressure was controlled by oxygenating gas (5% CO2 in O2, usually). The perfusing medium could be changed easily and quickly without interruption. Left ventricular pressure was recorded by means of a balloon-catheter, while special suction electrodes obtained the high-amplitude, noise-free electrogram recordings. The coronary effluent partial pressure of oxygen (Po2) was continuously monitored, which enabled the calculation of myocardial oxygen consumption (MVO2). The effluent partial pressure of carbon dioxide (Pco2) and pH value were also measured simultaneously. A computerized system of data acquisition, calculation, storage, and end report has also been described. In this study, the influence of indomethacin on hypoxia-induced hemodynamic and metabolic changes in the isolated guinea pig heart was observed. The advantages and disadvantages of the described and standard Langendorff apparatus have been discussed also.

The influence of oxygen tension on membrane potential and tone of canine carotid artery smooth muscle

In vascular smooth muscle of canine carotid artery segments the decrease in oxygen tension from approximately 550 mmHg to approximately 30 mmHg leads to a dose-dependent hyperpolarization and relaxation of the vessel strip. At PO2 values below approximately 15-20 mmHg depolarization and subsequent contraction were found. All changes of the parameters investigated were reversible. Indomethacin (10(-5) M) had no significant effect on the hypoxia-dependent potential and tension changes. The hyperpolarized part of the activation curve was obtained by plotting tension versus membrane potential values.