Cardiovascular responses to adenosine in the Antarctic fish Pagothenia borchgrevinki

We have investigated the effects of adenosine on the cardiovascular system of the Antarctic fish Pagothenia borchgrevinki. Continuous measurements of ventral and dorsal aortic blood pressures, heart rate (f(H)) and ventral ao rtic blood flow (cardiac output, (Q)over dot) were made using standard cann ulation techniques and a single-crystal Doppler flowmeter, On line measurem ents of arterial P-O2 were made using an oxygen electrode connected to an e xtracorporeal loop. Adenosine (10 nmol kg(-1)) and the specific A(1)-receptor agonist N-6-cyclo pentyadenosine (CPA) elicited biphasic changes in the branchial and systemi c resistances. While there was an initial decrease in the branchial resista nce followed by an increase, the opposite was true for the systemic respons e. The resistance changes were significantly attenuated by aminophylline (a P-1-receptor antagonist) and 8-cyclopentyltheophylline (CPT; an A(1)-recep tor antagonist). In addition, adenosine induced an aminophylline-sensitive decrease in the arterial P-O2. The reduction was attenuated when pre-inject ion arterial P-O2 was low. Adenosine and CPA also caused a marked reduction in f(H), with CPA being mo re potent. The bradycardia was blocked by aminophylline and CPT, demonstrat ing an involvement of A(1) receptors in this response.