Abstract
A new riboflavin derivative, 2', 3'-di-o-nicotinoyl riboflavin-4'(5')-phosphate (DNRP) had the constrictory effect on renal artery and the dilatory effect on other arteries as described in the previous paper. In this study, following four experiments were employed to determine the pharmacological correlation among DNRP, dipyridamole (Dip) and adenosine (Ade). (1)The isolated guinea-pig uterus was not contracted by Dip, but was done by DNRP and Ade. Both DNRP and Ade induced contractions in isolated guinea-pig uterus, which being antagonized by aminophylline (Ami). Ade-induced contraction of the uterus was enhanced by Dip, unaffected by DNRP. (2)The contractile response of isolated guinea-pig ileum to transmural electrical stimulation (0.1 cps, 0.6 msec, 50 V) was inhibited by DNRP, Dip and Ade. The inhibitory effect of these three compounds was antagonized by Ami. (3) The effect of Ade on cardiovascular system (the decrease of heart rate, myocardial contractile force and blood pressure) was enhanced by DNRP and Dip in the open-chest dogs. (4) The increase of coronary blood flow induced by either Ade or reactive-hyperemia was enhanced by Dip in dogs, and only the former was enhanced by DNRP. The following suggestion was obtained from these observations, that although DNRP and Dip had enhancing effect on Ade-induced responses, DNRP seemed to have a different mechanism from Dip.
