AGE-RELATED-CHANGES IN ADENOSINE IN RAT CORONARY RESISTANCE VESSELS

1. The vasodilator effects of adenosine receptor agonists, isoprenalin e and histamine were examined in perfused heart preparations from youn g (4-6 weeks) and mature (12-20 weeks) rats. 2. Adenosine induced a bi phasic concentration dependent decrease in KCI (35 mM) raised coronary perfusion pressure in hearts from young and mature rats, suggesting t he presence of both high- and low-affinity sites for adenosine recepto rs in the two age groups tested. In heart preparations from mature rat s, vasodilator responses to adenosine were significantly reduced compa red with responses observed in young rats. 3. Responses to 5'-N-ethylc arboxamidoadenosine (NECA) and thyl)phenethylamino-5'-N-ethylcarboxami doadenosine hydrochloride (CGS-21680) were reduced in preparations fro m mature rats, whereas the vasodilator actions of N-6-cyclopentyladeno sine (CPA) and N-6-2-(4-aminophenyl)ethyladenosine (APNEA) did not cha nge with age. 4. The results presented in this study suggest that seve ral adenosine receptor subtypes mediate vasodilator responses in the c oronary circulation of the rat and that a reduction in response to ade nosine with age may be due to changes in the high-affinity receptor si te. (C) 1998 Elsevier Science Inc.