This human study characterized how Ac-SDKP is cleared, measuring plasma and urine levels in healthy subjects given a single oral dose of captopril and again after seven days of dosing. Urinary Ac-SDKP relative to creatinine rose roughly 42-fold acutely and 34-fold with repeated dosing, alongside a four to five fold rise in plasma Ac-SDKP, showing the peptide is measurable and quantifiable in human plasma and urine and that ACE governs its clearance. The effect of chronic renal failure on plasma levels was also examined. This is human pharmacokinetic evidence about clearance of the endogenous peptide, not a study of an administered product.
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ACE inhibition raises plasma and urinary Ac-SDKP 4-5x and ~40x respectively, confirming renal clearance governs this endogenous TB4 fragment in humans.