ADENOSINE STIMULATES CANINE RETINAL MICROVASCULAR ENDOTHELIAL-CELL MIGRATION AND TUBE FORMATION

Purpose. To evaluate the effects of adenosine and related substances o n events that occur during vasculogenesis and angiogenesis, using in v itro assays. Methods. Adenosine (ADO), inosine (INO), an adenosine cat abolite), and 5'-(N-ethylcarboxamido) adenosine (NECA, an adenosine ag onist) were evaluated for their effect on the proliferation of canine retinal microvascular endothelial cells (DRME), using a cell count ass ay. Also, these substances and ADO receptor selective agonists and ant agonists were evaluated in an assay for DRME chemokinesis by measuring random migration into a wound made in a confluent cellular monolayer. Finally, the effects of these substances on DRME cord formation were evaluated in a 3-dimensional collagen gel. Bovine retinal extract (RE) was used as a positive control for all assays. Results. There was no effect on proliferation of DRME by any of the substances related to ad enosine, but VEGF yielded a 30% stimulation of proliferation. Retinal extract, 10 mu M ADO and 1.2 nM VEGF stimulation of DRME migration was 2- to 2.5-fold greater than 10 mu M INO yielded. In addition, a combi nation of 1.2 nM VEGF with 10 mu M ADO exceeded the stimulation in mig ration by ADO only and VEGF only. The total length of tubes formed in the presence of 10 mu M ADO was comparable to that formed in the prese nce of RE and was 11-fold greater than with 10 mu M INO. Tube length w ith a combination of VEGF plus ADO was 36% greater than with retinal e xtract. Use of selective ADO receptor antagonists suggested that tube formation and the migration response may be mediated through both aden osine A(1) and A(2) receptors, but use of selective ADO agonists sugge sts that A(2) receptors may be mon important than A(1) for endothelial cell migration. Conclusions. This in vitro analysis suggests that ade nosine may stimulate retinal vasculogenesis, an event which involves m igration of angioblasts and their assembly into vascular cords, prior to canalization.