enalapril and cilazaprilat

The principle of enzyme radioinhibitor binding displacement was developed to measure the concentration of angiotensin converting enzyme (ACE) inhibitors in rat serum. 125I MK351A, a tyrosyl derivative of enalaprilic acid, and a potent ACE inhibitor, bound in a concentration and time dependent manner to ACE. Binding of 125I MK351A to rat serum ACE was reduced in a concentration dependent manner in vitro by the ACE inhibitors MK521 (lisinopril), S9780, and Ro 31-3113-000 (Cilazapril diacid). This relationship was used to measure MK521 and S9780 in rat serum four hours after oral gavage with MK521, S9490-3 the prodrug ester of S9780, at 1, 2 and 4 mg/kg, or 1/2 hour after intraperitoneal injection of Ro 31-3113-000 (0.0125-0.7 mg/kg). Serum MK521 concentrations, estimated by radio inhibitor binding displacement, and radioimmunoassay, correlated well (r = 0.94, N = 9, P less than 0.001). Serum MK521, S9780 and Ro 31-3113-000 concentrations measured by radioinhibitor binding displacement assay were dose related, and inversely related to serum ACE enzymatic activity. The radioinhibitor binding displacement assay method using 125I MK351A as a ligand for ACE has application to the measurement of any competitive inhibitor of ACE.

Topics: Angiotensin-Converting Enzyme Inhibitors; Animals; Cilazapril; Dipeptides; Enalapril; Female; Iodine Radioisotopes; Lisinopril; Peptidyl-Dipeptidase A; Pyridazines; Rats; Rats, Inbred Strains