Chromium excretion in the dog

¹ Department of Physiology and Pharmacology, Michigan State University, East Lansing, Michigan

Renal clearance of chromium decreases exponentially with time after a single intravenous injection of Cr⁵¹Cl₃ from 2.5 or 3 ml/min/m² at 1 hr to less than 1 ml/min 8 hr post-injection. Equilibrium dialysis measurements showed similar results for plasma dialyzable chromium. These observations lead to the determination of a dialyzable chromium clearance (C_d-cr) in which the concentration in dialyzable chromium replaced total plasma chromium in the clearance formula. The mean and standard deviation for C_d-cr of 36.6 ± 11.6 ml/min/m² was relatively unaffected by time after chromium administration, plasma concentration of dialyzable chromium, or rate of urine flow. Values of C_d-cr determined repeatedly in two dogs intravenously infused with Cr⁵¹Cl₃ for over 7 hr also remained stable. Glomerular filtration and tubular reabsorption are involved in renal excretion of chromium. The lack of a reduction of C_d-cr at high plasma levels of dialyzable chromium favors the conclusion that tubular excretion is of minor importance. Simultaneous creatinine and PAH clearances were normal, indicating that renal function was not impaired by the doses of chromium used.