The blood-bathed organ technique has made it possible to estimate the release, distribution, and uptake of catecholamines directly and continuously without extracting and purifying them from samples of blood. The technique has been used to measure the release of catecholamines and of angiotensin during haemorrhage (21); the release of catecholamines induced by peptides (24), histamine (25), tyramine (29), and nerve stimulation (17, 18). The technique has the advantage that the results are immediate and continuous, so that they can be used to direct the further course of an experiment. Furthermore, it has the advantage, common to other bioassay procedures, of being relatively inexpensive.
It is difficult to foresee what place bioassay procedures will have in catecholamine research in 5 to 10 years. Certainly, the fact that they are relatively inexpensive will continue to make them attractive to some laboratories, just as the increasing number of pharmacologists primarily trained in biochemistry will encourage the use of chemical methods in others. These, however, are not the only factors influencing the choice of biological vs. chemical method of assay. With many people, psychological factors also are important. Some find a biological assay is more pleasing aesthetically. Furthermore, biological methods by their very nature, constantly remind the investigator of the subtleties and intricacies of living organisms, whereas chemical methods may well allow him to forget them.