It is known that the flow of blood through an extremity is decreased by injection of serotonin (5-hydroxytryptamine [5-HT]) into its arterial blood supply.10,12,14 This is assumed to be due to narrowing caused by spasm of the vascular conduits. Serotonin also causes marked aggregation of platelets, leukocytes, and erythrocytes both in vitro and in vivo.17 This has been observed in vivo to be accompanied by a marked slowing of the circulation in the conjunctival blood vessels and, after repeated injections of serotonin, by significant reductions in the hematocrit. These changes could be due to, or contributed to by, microembolism of the smaller blood vessels by aggregated blood cells which remain sequestered in the capillary beds. In the present paper this problem is explored, and the response of the cerebral circulation to intravascular injections of serotonin is reported.
Material and Methods
Adult mongrel dogs weighing 14.6 ± 3.2 kg were