Angiotensin converting enzyme inhibition in plasma and tissues

Novel molecular angiotensin converting enzyme and angiotensin receptor imaging techniques

Angiotensin II (AII), an octapeptide member of the renin-angiotensin system (RAS), is formed by the enzyme angiotensin converting enzyme (ACE) and exerts adverse cellular effects through an interaction with its type 1 receptor (AT1R). Both ACE inhibitors and angiotensin receptor blockers (ARB) mitigate the vasoconstrictive, proliferative, proinflammatory, proapoptotic, and profibrotic effects of AII and are widely used as effective anti-remodeling agents in clinical practice. Prediction of individual response to these agents, however, remains problematic and is influenced by many factors including race, gender, and genotype. In addition, systemic and tissue RAS activity do not correlate closely. This report summarizes the results of on-going attempts to noninvasively determine tissue ACE activity and AT1R expression using novel nuclear tracers. It is hoped that the availability of such imaging techniques improve treatment of heart failure through more selective pharmacologic intervention and better dose titration of available drugs.

Acute and chronic effects of angiotensin-converting enzyme inhibitors on tissue angiotensin-converting enzyme

1. The effects of angiotensin-converting enzyme (ACE) inhibitors on the tissue ACE were assessed by quantitative in vitro autoradiography after acute and chronic administrations of the drugs. 2. Following acute administration of lisinopril, perindopril or benazepril, ACE was markedly inhibited in the lung, kidney and blood vessels but not in the testis. In the brain, ACE was inhibited mainly in structures with a deficient blood brain barrier. 3. High doses of perindopril progressively inhibited ACE in other brain structures. Tissue ACE inhibition persisted after serum levels of the enzyme had returned to control levels. In the case of perindopril, the time course of tissue ACE inhibition correlated with the inhibition of the pressor responses to exogenous angiotensin I. 4. After chronic administration of lisinopril or perindopril for 14 days, a similar pattern of ACE inhibition was observed in the kidney, lung and blood vessels. In the lung, however, lisinopril was found to increase total ACE by 30%, while plasma ACE was increased two-threefold by both lisinopril and perindopril. Testicular ACE remained unaltered by chronic lisinopril treatment. 5. Overall, the changes in tissue ACE after the administration of inhibitors more closely parallel the drugs' biological effects than changes in plasma ACE or drug levels. ACE in the testis and brain is protected by permeability barriers that limit access of the drugs.

Tissue and plasma angiotensin converting enzyme and the response to ACE inhibitor drugs

1. There is a body of circumstantial and direct evidence supporting the existence and functional importance of a tissue based RAS at a variety of sites. 2. The relation between circulatory and tissue based systems is complex. The relative importance of the two in determining haemodynamic effects is unknown. 3. Despite the wide range of ACE inhibitors already available, it remains unclear whether there are genuine differences related to tissue specificity. 4. Pathological states such as chronic cardiac failure need to be explored with regard to the contribution of tissue based ACE activities in generating acute and chronic haemodynamic responses to ACE inhibitors. 5. The role of tissue vs plasma ACE activity may be clarified by study of the relation between drug concentration and haemodynamic effect, provided that the temporal dissociation is examined and linked to circulating and tissue based changes in ACE activity, angiotensin peptides and sympathetic hormones.

Endocrinologic Warfare: The Role of Angiotensin-Converting Enzyme Inhibitors in Congestive Heart Failure

The angiotensin-converting enzyme (ACE) inhibitors represent the gold standard of vasodilator therapy for congestive heart failure through blunting of the endocrinologic manifestations of heart failure. The future role of these agents may be in the asymptomatic and mild stages of heart failure. ACE inhibitors have been shown to decrease morbidity and mortality with the natural history of this disease being altered. The future will bring many new ACE inhibitors to market, with the challenge for physicians and pharmacists to understand the important distinctions of each specific agent. © 1990 by W.B. Saunders Company.

Perindopril. A review of its pharmacokinetics and clinical pharmacology

Perindopril is an orally active, non-thiol angiotensin-converting enzyme (ACE) inhibitor, which in doses of 4 to 8mg is effective in the control of essential hypertension. As monotherapy it is as effective as once-daily atenolol and possibly more effective than twice-daily captopril. A synergistic response has been noted when perindopril is combined with a thiazide diuretic. Maximal pharmacodynamic effects (ACE inhibition, increase in plasma renin activity and angiotensin I, reduction in aldosterone and angiotensin II and blood pressure) are seen 4 to 6 hours after dosing, with substantial effects still present at 24 hours. Perindopril is a prodrug which requires de-esterification to perindoprilat for useful ACE inhibition. Maximal plasma perindoprilat concentrations are reached 2 to 6 hours after oral administration of perindopril, and 70% of the active metabolite is cleared by the kidneys. The other major metabolite of perindopril is an inactive glucuronide. Ageing is associated with increased serum perindoprilat concentrations, which are probably caused by a combination of enhanced conversion to the active metabolite and diminished renal clearance. Compensated cirrhosis does not appear to have an independent effect. There is little published experience of the use of perindopril in patients with cardiac failure or other cardiac disease, but preliminary evidence would support the general value of this class of agent as adjunctive therapy.