BLEEDING-TIME IN LABORATORY-ANIMALS .2. COMPARISON OF DIFFERENT ASSAY CONDITIONS IN RATS

Two techniques for measurement of bleeding times on the tails of unanaesthetized male rats were compared in various experimental conditions. The first technique consisted in producing a standardized incision on the dorsal part of the tail by means of a 'template' device. The second consisted of a 'free-hand' full transection of the tail tip with a disposable surgical blade. The position of the tail, the environment in which it was placed and the temperature were variably associated in four different experimental groups. In all cases the times obtained with the transection were significantly longer than with the template. For both techniques bleeding times were longer when the tail was vertical instead of horizontal, when it was placed in isotonic saline instead of room air and when the temperature of the bathing solution was 23°C instead of 37°C. Tail blood flow was significantly greater at 37°C than at 23°C. These data indicate that 'tail bleeding time' in rats is markedly influenced by the methodology applied. This makes it difficult to compare the results obtained in different laboratories and could be a major reason for the conflicting findings reported by various Authors on the effect of aspirin in this test. © 1979.