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Intravenous infusion of l‐NG‐nitro‐arginine, an inhibitor of endothelial nitric oxide (NO) synthesis, produced vasoconstriction in the coronary, cerebral, renal and duodenal vascular beds of the conscious rabbit. In this study, using radiolabelled microspheres, we provide in vivo evidence for a basal NO‐dependent vasodilator tone in the coronary vascular bed.

Two procedures are described for the detection of inhibitors of angiotensin converting enzyme (ACE). The first is a new agar-plate method useful as a screening tool. Two ACE inhibitors produced by culture A58365 were discovered using this plate test. The second method is a modification of a previously reported spectrophotometric procedure.Both procedures utilize p-nitrobenzyl-oxycarbonylglycyl-(S-4-nitrobenzo-2-oxa-1,3-diazole)-L-cysteinylglycine as substrate.Angiotensin converting enzyme, ACE, (dipeptidyl carboxypeptidase EC 3.4.15.1) catalyzes the release of dipeptide from the carboxyl terminus of angiotensin I to yield the octapeptide angiotensin II, a potent vasoconstrictor.The same enzyme inactivates the vasodilator, bradykinin, by the hydrolytic release of one or more carboxyl-terminal dipeptide residues. Although the use of ACE inhibitors is well established in treatment of hypertension and congestive heart failure, there were no known fermentation derived inhibitors of ACE at the time this screening program was initiated. There is, however, ample precedent for screening for enzyme inhibitors in fermentation broths

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