Vascular development in chick embryos: a possible role for adenosine

We studied the possible role of adenosine in the development of the vasculature using 217 chick embryos. Adenosine (2-32 mumol/day), inosine (16 mumol/day), dipyridamole (0.04-0.4 mumol/day), or aminophylline (400 and 800 micrograms/day) were administered twice each day into the air space on days 11-14. Control embryos received Ringer solution. Whole body vascularity was estimated on day 15 as the whole body structural vascular resistance (SVR), i.e., the hydraulic resistance of the maximally dilated vasculature. Adenosine decreased the SVR in a dose-related manner at the lower dosage amounts but caused a maximum decrease in SVR at the higher dosage amounts averaging 30% below the Ringer control values. Equimolar amounts of adenosine and inosine decreased the SVR by the same extent. Dipyridamole, which potentiates the biological effects of endogenous adenosine, also decreased the SVR in a dose-related manner to values averaging approximately 30% below control. When the effects of endogenous adenosine were blocked by aminophylline, the SVR increased in a dose-related manner to approximately 100% above control at the highest dosage amount. These results suggest that adenosine could have a physiological role in growth regulation of the vascular system in the chick embryo.