ANTIHYPERTENSIVE ACTIVITY DURING INHIBITION OF NEUTRAL ENDOPEPTIDASE AND ANGIOTENSIN CONVERTING ENZYME

The specific neutral endopeptidase (NEP) inhibitor, SQ 29,072 (7-{2-(mercaptomethyl)-1-oxo-3-phenylpropyl]amino}heptanoic acid), was studied in conscious spontaneously hypertensive rats (SHRs) and in DOCA/salt hypertensive rats during inhibition of angiotensin-converting enzyme (ACE) activity with captopril or SQ 27,519 (the free acid of fosinopril). In the SHR, the maximal depressor responses to the combination of SQ 29,072 and captopril (-62 +/- 9 mm Hg) or the combination of SQ 29,072 and SQ 27,519 (-44 +/- 4 mm Hg) were greater than the responses to any of the inhibitors given alone (-26 +/- 5, -40 +/- 10, and -28 +/- 6 mm Hg for SQ 29,072, captopril, and SQ 27,519, respectively). In contrast, the maximal antihypertensive activities of SQ 29,072 were the same in conscious DOCA/salt hypertensive rats infused with saline, captopril, or SQ 27,519 (-54 +/- 10, -51 +/- 8, and -58 +/- 11 mm Hg, respectively), indicating a lack of synergism in this model. In agreement, SQ 28,133 {N-[2-(mercaptomethyl)-1-oxo-3-phenylpropyl]-L-leucine}, a compound that inhibits both NEP and ACE, elicited significant depressor activities in both SHR and DOCA/salt hypertensive rats. In conclusion, a selective NEP inhibitor enhanced the depressor activity of ACE inhibitors in the conscious SHR, indicating that these agents may be effectively combined for treatment of some types of hypertension.