Synthesis and biological activity of ketomethylene-containing nonapeptide analogues of snake venom angiotensin converting enzyme inhibitors.

Two ketomethylene-containing nonapeptide analogues were synthesized to determine if ketomethylene analogues of the nonapeptide venom inhibitors of angiotensin converting enzyme (ACE) would have oral ACE inhibition activity. Both ketomethylene-containing nonapeptides 18 and 19 were potent inhibitors of rabbit lung ACE with I50s of 3.4 and 8.0 nM, respectively, compared to 340 nM for their parent nonapeptide and 450 nM for captopril. Peptide 18 was rapidly cleaved by trypsin, but 19 was reasonably stable to all enzyme degradation systems tested with maximum degradation of 50% by pepsin in 3 h. Both 18 and 19 when given iv to normotensive rats were between 3 and 10 times more potent than captopril in inhibiting an angiotensin I induced blood pressure increase. Peptide 19 showed no ACE inhibition activity in unanesthetized normotensive rats when administered orally at doses of 10 or 100 mg/kg. Experiments were conducted to determine whether 19 is adsorbed from the gastrointestinal track following oral administration. These experiments indicated that 19 is adsorbed. It is concluded that the lack of oral activity of 19 is probably due to its rapid excretion, probably into the bile.

Influence of various antihypertensive agents on lifespan of renal hypertensive rats.

1 Daily treatment of two-kidney clipped renal hypertensive rats with hydrallazine, hydrochlorothiazide (HCTZ) and a new orally active inhibitor of the angiotensin-converting enzyme, captopril (SQ14,225), was correlated with survival rates for up to 9 months. 2 The groups of rats given captopril alone or captopril plus intermittent or chronic HCTZ had the best survival rate, whereas HCTZ alone or hydrallazine did not benefically affect survival. 3 Survival rates correlated well with control of BP in these animals.

Chronic antihypertensive effects of captopril (SQ 14,225), an orally active angiotensin I-converting enzyme inhibitor, in conscious 2-kidney renal hypertensive rats.

Indirect systolic blood pressure (SBP) was monitored in 9 groups of 15 male conscious 2-kidney renal hypertensive rats (RHR) for over 6 months. Daily oral dosing with captopril (SQ 14,225, D-3-mercapto-2-methylpropanoyl-L-proline, 30 mg/kg), an orally active angiotensin I-converting enzyme inhibitor, lowered SBP 30--50 MM Hg during this period. Withdrawal of captopril for 5 days at 1, 3 and 6 months resulted in gradual return of SBP to control levels without overshoot. Resumption of dosage with captopril again decreased SBP. Daily oral dosing with hydrochlorothiazide (HCTZ, 6 mg/kg/day) alone for 6 months had little or no effect on SBP, but increased the antihypertensive effect of captopril. Daily oral dosing with hydralazine (6 mg/kg) caused an initial marked antihypertensive effect greater than that of captopril but almost complete tolerance developed within 4 weeks of dosing. Highest survival rates occurred in RHR treated with captopril plus HCTZ. In four other similarly treated groups of RHR and normotensive rats (NR), least cardiac hypertrophy and highest plasma renin activity occurred in captopril-treated animals compared with vehicle-treated controls. Plasma renin activity was about 2 to 4 fold higher in the rats dosed with captopril compared with vehicle-treated rats. Heart weight/body weight ratios, initially higher in the two RHR groups compared to NR, decreased only in the captopril treated group to or near those of the NR groups. These results indicate that chronic treatment with captopril decreased SBP and cardiac weights of RHR, and that HCTZ, or possibly other diuretics, can augment the antihypertensive effect of captopril while having little or no effect by themselves.