Blunting of atrial natriuretic factor response to volume expansion by benazepril in hypertensive patients

The effects of medications on circulating levels of cardiac natriuretic peptides

Circulating cardiac natriuretic peptide levels are being used increasingly in a range of clinical circumstances. Since it is evident that drugs used in the treatment of cardiovascular disorders can modulate natriuretic peptide levels, we here review the literature documenting these effects. Diuretics, blockers of the renin-angiotensin system, vasodilator agents, dopamine-like agonists, amiodarone, and perhaps allopurinol and statins suppress natriuretic peptide levels, most obviously in heart failure. Beta-blockers stimulate natriuretic peptide concentrations in hypertensive subjects, whereas in heart failure they have little effect or are stimulatory in the short term and inhibitory with sustained therapy. Digitalis compounds and aspirin tend to increase natriuretic peptide levels, and calcium channel blocking agents have varying effects depending on the individual drug and duration of administration. The effects of other drugs are less clear. Additional information is needed regarding the effects of medications along with dissection of the role of altered cardiac secretion versus changes in plasma clearance as explanation for drug-induced perturbations in natriuretic peptide concentrations. In the meantime, clinicians need to consider the known effects of medications when interpreting plasma levels of the cardiac natriuretic peptides.

Combined inhibition of neutral endopeptidase and angiotensin-converting enzyme by sampatrilat in essential hypertension

BACKGROUND

The antihypertensive response to angiotensin-converting enzyme (ACE) inhibitors may be attenuated by a compensatory decrease in atrial natriuretic factor production. If so, inhibition of atrial natriuretic factor breakdown by neutral endopeptidase (NEP) may enhance the antihypertensive effects of ACE inhibition. We compared effects of the combined ACE-NEP inhibitor sampatrilat, lisinopril, and placebo on blood pressure, plasma ACE, and renin activity and urinary cyclic guanosine monophosphate (cGMP) of patients with hypertension.

METHODS AND RESULTS

After a 4-week placebo run-in period, 124 patients with a mean blood pressure of 162/102 mm Hg were randomized in a double-blind parallel-group design to 1 of 5 treatments, given once daily for 10 days: 50 mg, 100 mg, or 200 mg sampatrilat; 20 mg lisinopril; or placebo. The first dose of sampatrilat did not lower clinic or ambulatory blood pressure. Lisinopril had an immediate antihypertensive effect that differed significantly from all doses of sampatrilat. After 10 days of treatment, sampatrilat lowered clinic and ambulatory blood pressure significantly at all doses, with a trend toward a dose response for systolic ambulatory blood pressure. Sampatrilat inhibited plasma ACE in a dose-dependent fashion but significantly less so than lisinopril on days 1 and 10 of treatment. Lisinopril but not sampatrilat significantly increased plasma renin activity, whereas sampatrilat but not lisinopril significantly increased urinary cGMP excretion.

CONCLUSION

The increasing efficacy of sampatrilat compared with lisinopril over 10 days could not be attributed to an increase in plasma ACE inhibition, suggesting that the NEP inhibitor activity of sampatrilat may have contributed to its antihypertensive action. NEP inhibition may enhance the antihypertensive effect of ACE inhibition.

Low dose of ACE-inhibitor enhances sodium excretion in volume expanded patients with borderline hypertension

The purpose of the present study was to separately investigate the effects of two different dosages of captopril on pressor, vascular and humoral response to acute extracellular volume expansion in patients with borderline hypertension (BHT). Thirty-five patients were randomly allocated in two groups undergoing acute saline infusion (0.40 ml/min/kg for 45 min and 0.15 ml/min/kg for 75 min)before and after a 7-day period of treatment with either placebo or captopril at the dose of 12.5 (LD-CAP) or 50 mg (HD-CAP) twice a day. At baseline the effects of LD-CAP were limited to an increase in PRA and to a decrease in plasma aldosterone whereas HD-CAP decreased systolic and diastolic blood pressure (SBP, DBP), forearm vascular resistance (FVR) and increased venous distensibility (VV(30)) as well. After saline loading patients treated with HD-CAP showed an increase in SBP, DBP not observed in patients allocated to LD-CAP. Urinary sodium excretion in response to NaCl loading was selectively enhanced by LD-CAP (+25%) whereas HD-CAP did not (+6.3%). The present data suggest that low-doses of ACE-inhibitors acting through a selective blockade of RAA not associated with hemodynamic changes can enhance the natriuretic response to acute volume expansion in borderline hypertensives.

Atrial natriuretic factor response to acute volume expansion in borderline hypertension. Role of ACE-inhibition and changes in peripheral venous tone

Abnormalities in the response of atrial natriuretic factor (ANF) to volume expansion have been reported in hypertensive-prone animals and men as well as in hypertensive patients undergoing ACE-inhibition. To investigate some of the mechanisms affecting ANF release in borderline hypertensive patients (BHT) we have studied 16 subjects by assessing their neuro-humoral and hemodynamic response to a two-hour isotonic i.v. NaCl infusion carried out during short-term administration of either placebo or captopril. ACE-inhibition increased baseline venous distensibility (VV30:1.4 vs 1.6 ml/100 ml; p < .05) and reduced the prompt (45') ANF response to saline loading (10.3 +/- 13 vs 42.7 +/- 15%; p < .05)) without affecting the overall ANF release (120':92 +/- 25 vs 65.8 +/- 20%; NS)). A significant pressor increase in response to NaCl loading was observed exclusively after ACE-inhibition (SBP: 5.2 +/- 2 vs 2.4 +/- 1%; p < .05--DBP: 7.1 +/- 3 vs 2 +/- 3%; p < .025) and occurred along with a peripheral arterial and venous constriction and with an increase in plasma levels of an endogeneous Na+/K+ATPase inhibitor (8.8 +/- 4 vs -2 +/- 4%; p < .05). We conclude that the ANF response to saline infusion is delayed by ACE-inhibition in borderline hypertensives. The abnormalities observed in ANF response could follow the changes in peripheral venous distensibility and contribute to the pressor and neuro-humoral derangements described in borderline hypertensives during volume expansion.