EDRF RELEASED FROM MICROVASCULAR ENDOTHELIAL-CELLS DILATES ARTERIOLES INVIVO

Microvascular endothelial cells (MECs) from rat epididymal fat pad were isolated and cultured in vitro on Cytodex 3 microcarrier beads. In Krebs-suffused cremaster muscle of pentobarbital-anesthetized rats arteriolar diameters (mean control diam 20.9 +/- 0.9-mu-m) were measured using image shearing video microscopy. Two lines of suffusate (1.5 ml/min each) were established; one contained a column of microcarrier beads only (no cells in line; NC) the other contained a 1-ml column of MECs grown on beads (through cells; TC). The muscle preparation and the MECs were first treated with indomethacin (Indo; 28-mu-M). Indo treatment blocked arteriolar dilation to A23187 (1-mu-M) and arachidonic acid (AA; 0.25-mu-M) administered into the NC line. A 4.0 +/- 0.6-mu-m increase in arteriolar diameter was observed, however, when A23187 (but not AA) was infused through the TC line containing Indo-treated MECs on beads. The A23187-elicited dilation was abolished by the introduction of N(G)-monomethyl-L-arginine (L-NMMA; 200-mu-M) into the TC line. Administration of atropine (2-mu-M) onto the cremaster muscle via the NC line inhibited the dilations in response to acetylcholine (ACh; 2.7-mu-M) given through the NC line. Infusion of ACh through the TC line onto the atropine-treated cremaster muscle, however, elicited a 5.8 +/- 1.3-mu-m increase in arteriolar diameter, a response that was blocked by prior administration of L-NMMA into the TC line. Arteriolar dilation induced by adenosine (0.5-mu-M) or sodium nitroprusside (0.5-mu-M) applied via the NC or TC line was unaffected by L-NMMA. Results of our experiments suggest that cultured microvascular endothelial cells are able to release in basal conditions and upon stimulation by agonists, a non-prostaglandin vasodilator principle that has the attributes of endothelium-derived relaxing factor.