EFFECT OF CHANGES IN RATE OF VASCULAR PERFUSION ON RELEASE OF SUBSTANCES INTO THE EFFLUENT FROM THE BRAIN OF THE RABBIT

The cerebral vasculature of five anaesthetised rabbits was perfused wi th a perfluorocarbon emulsion via the internal carotid arteries, and t he effluent from the jugular veins analysed for ATP, substance P (SP), endothelin (ET) and arginine vasopressin (AVP). Viability of the prep aration was monitored periodically by the electrocorticogram, oxygen u ptake, carbon dioxide release and perfusion pressure. The basal rate o f infusion of 7.8+/-1.26 ml-min-1 resulted in an infusion pressure of 114.0+/-22.1 mmHg and when increased first to 10.5+/-1.53 ml.min-1 and then to 15.0+/-1.87 ml.min-1, rose to 163.0+/-33.1 mmHg and to 170.0/-33.2 mmHg, respectively. Between each 3-min period of increased flow the rate was returned to the basal rate for 6 min. Of the four vasoac tive substances, ET was released at the largest rate during the initia l period of basal flow, 65.3+/-10.7 pmol.min 1. This increased further when the infusion rate rose to 10.5 ml.min-1, but was significant onl y when the infusion rate was increased to 15.0 ml.min-1. ATP was relea sed at 41.5+/-11.5 pmol.min-1 during the initial period of basal flow. Its release significantly increased with flow and peaked at 15.0 ml.m in-1. SP was released at a rate of 13.3+/-8.2 pmol.min-1 during the in itial period of basal flow. Its rate of release was increased signific antly the second time the flow was increased to 10.5 ml.min-1 and incr eased even further when the flow was increased to 15.0 ml.min-1. AVP w as detected in one third of the samples collected during the initial p eriod of basal flow, being released at a rate of 0.65+/-0.47 pmol.min- 1. Only in the period following the 15.0 ml.min-1 rate of flow was the re a sustained increased release of AVP. These results are consistent with the view that ATP, SP, ET and AVP are released from vascular endo thelial cells during changes in flow, and may contribute to the adjust ments in local cerebrovascular tone.