Effects of adenosine agonists on ventilation during hypercapnia, hypoxia and hyperoxia in rhesus monkeys

This study characterized in rhesus monkeys the effects of selected adenosine agonists on ventilation during normal atmospheric conditions and during conditions of hypercapnia, hypoxia and hyperoxia. In seated, unanesthetized monkeys prepared with a head plethysmograph, ventilation during exposure to air, CO2 (3, 4 and 5%) mixed in air (hypercapnia), 10% O2 mixed in N2 (hypoxia) and 100% O2 (hyperoxia) was measured during cumulative dosing with each drug. The nonselective (A1/A2) agonist, 5'-N-ethylcarboxamidadenosine (NECA), the peripherally active, A2-selective agonist, CGS 21680 [2-(carboxyethylphenylamino)adenosine-5'-carboxamide], and the A1-selective agonists, N6-cyclohexyladenosine and N6-cyclopentyladenosine, increased respiratory frequency (f), but had no significant effect on minute volume (VE) during exposure to air. The relative potencies for increasing f corresponded closely with their potencies for binding at A2 receptors. NECA and CGS 21680 increased f in a dose-dependent manner during exposure to 3% CO2, but proportional increases in f were less pronounced as the concentration of CO2 increased. NECA and CGS 21680 also increased f during hypoxia, but neither had a significant effect on f during subsequent hyperoxia. The highest dose of CHA and CPA decreased f below control values during exposure to 5% CO2 and decreased f and VE during hyperoxia. In contrast, the adenosine antagonist, caffeine, and the selective phosphodiesterase inhibitor, rolipram, increased f and VE under all conditions. During hypercapnia, the magnitude of the increases in f was similar at each concentration of CO2 studied. Caffeine and rolipram increased f and VE during hypoxia, and f and VE remained elevated during hyperoxia.(ABSTRACT TRUNCATED AT 250 WORDS)