Varagic, V.M. (7006591279)V.M. (7006591279)VaragicProstran, M. (7004009031)M. (7004009031)Prostran2025-06-122025-06-121986https://www.scopus.com/inward/record.uri?eid=2-s2.0-0022924303&partnerID=40&md5=4e03710fd1c76bf9c641d7a0a793c050https://remedy.med.bg.ac.rs/handle/123456789/20411. The effect of L-N6-phenylisopropyladenosine (L-PIA) on the maximum tension developed (Td) and the maximum rate of rise of tension (dT/dt max) of the isolated hemidiaphragm of the rat was investigated during direct electrical stimulation. 2. L-PIA itself (0.07-5.5 μmol l-1) did not produce significant changes in either Td or dT/dt max. 3. In the presence of a standard concentration of dipyridamole (26.4 μmol l-1), L-PIA produced a significant and concentration-dependent increase in both Td and dT/dt max. 4. In the presence of a standard concentration of aminophylline (640 μmol l-1), L-PIA produced a small and insignificant, but concentration-dependent decrease of both Td and dT/dt max. 5. In the presence of both dipyridamole (26.4 μmol l-1) and of aminophylline (640 μmol l-1), L-PIA (0.07-5.5 μmol l-1) produced a small and insignificant potentiation of the isometric contraction of the isolated hemidiaphragm. 6. It is concluded that antagonistic action between L-PIA and aminophylline probably takes place at A1-receptors. The inhibitory action of L-PIA, observed after blockade of adenosine receptors by aminophylline, is presumably realized through some other mechanism(s) independent of adenosine receptor sites.