The Significance of a Smooth Muscle Component in Hemostasis.

Currently accepted theories on the control of bleeding in oozing blood postulate two main but quite distinct mechanisms: formation of blood clots and agglutination of platelets to form a plug in this region. In both instances a mechanical stopper is visualized and hemostasis is interpreted as a phenomenon entirely dependent on blood components, particularly the disintegrative processes concerned with these. Several observations have been presented (1,2,3,4) which were extremely difficult to resolve in terms of the classical theories noted above. It was then suggested that hemostasis is a function of active metabolic events and that the local area of injury, rather than blood itself, plays the most important role in the control of bleeding. Methods. The results presented here were carried out by a method developed in our laboratory. A small area of keratinized epidermis in a rat tail is removed with a razor blade and the ensuing bleeding stops in 1 to 2 minutes. When mechanical trauma (such as strong scouring with gauze) is subsequently inflicted on such scarified skin and the tail immersed, in a vertical position, in different fluids at 37°C, the bleeding in each vessel (arteriole or venule) can be observed through a dissecting microscope (30 to 50 × magnification) until hemorrhage completely ceases. Table I shows that this method is quite consistent, the range of bleeding time (B.T.) varying between 40 to 90 seconds (Table I). Results. Direct visual observation. Bleeding from arterioles never stopped abruptly. There was always a progressive decrease in the diameter of the falling column of blood until a very thin stream was observed just before the end of bleeding. Repeated mechanical stimulation. When mechanical trauma was applied at about 10-minute intervals, B.T. remained fairly constant for a period of about 2 hours (average for 12 determinations — 56″ with a range of 20″–93″). When, however, the trauma was applied as soon as the bleeding stopped, then, after from 5–10 such stimulations, the scarified skin failed to bleed even though subjected to the most violent mechanical stimulus.