Techniques for testing isolated blood vessels.

There are many different techniques described for studying isolated blood vessels, either human or animal. 1. For postsynaptic responses, spiral strip preparations using isometric tension monitoring probably allow the greatest flexibility for drug concentration-effect relationships. Isotonic tension may be monitored if extreme sensitivity is necessary and ring preparations probably better mimic the situation in vivo, but are harder to use. 2. Minor differences in salt solutions, pH, temperature and degree of oxygenation are probably not important except in special situations such as pH alterations when studying cerebral vessels and pO2 alterations when studying pulmonary or umbilical vessels. It is most important that the calcium concentrations remain constant as altered contractile effect may occur with small alterations in the calcium concentration of the physiological salt solution. 3. Electrical stimulation is necessary for studying presynaptic mechanisms. Most commonly, vessels are canulated and perfused through their lumen and superfused to remove the transmitter which has overflowed from the perivascular nerve stimulation. Neurotransmitter is then measured after preloading with tritiated noradrenaline. Electrical stimulation can also be performed on spiral strips which are immersed in small volume tissue baths allowing rapid changes in the bathing fluid, and although this method allows better monitoring of the postsynaptic responses associated with the electrical stimulation, it is more difficult to perform than perfusion and superfusion.