Cyclosporin A abolishes renal reserve capacity.

Renal functional reserve (RFR) was investigated in a group of renal transplant recipients taking cyclosporin A (CyA) immunosuppressive therapy. Nine patients received a 93 g oral protein load containing 5983 mg of glycine. GFR and ERPF were measured using isotope infusions of 51Cr EDTA and 125I OIH, respectively, before and for 3 h after the meal. Patients studied demonstrated a wide range of baseline GFRs (20.9-89.5 mL/min, mean 50.09 mL/min). However, few patients demonstrated an individual RFR, regardless of original level of function. Overall, no significant change in either GFR or ERPF was demonstrated after the protein stimulus. CyA is known to alter intrarenal prostanoid synthesis in favor of vasoconstriction and RFR is thought to be mediated by prostanoids. Therefore a mechanism for the absence of RFR in patients receiving CyA therapy is suggested.