Appearance of dissociable and cross-linked hemoglobins in the renal hilar lymph

Unlike unmodified dissociable bovine hemoglobin (UHb), cross-linked hemoglobins do not dissociate into dimers, do not cross the glomerular filter, and are retained in the plasma for a longer time. Renal peritubular capillaries, which are different from the glomerulus, allow the passage of molecules as large as albumin into the renal interstitium. Cross-linked hemoglobins should pass across these capillaries, enter the renal interstitium, and drain through the renal lymphatics. The present experiments were done in anesthetized rats to determine the appearance of UHb, an intramolecularly cross-linked tetrameric hemoglobin (DECHb), and a polymerized bovine hemoglobin (PHb) of larger molecular size into the renal hilar lymph. Renal hilar lymph samples were obtained before and after an isovolemic exchange of 2 mL/100 g rat weight of a 6% solution of each hemoglobin for blood. The behavior of a 5% solution of Evan's blue-labeled albumin was also determined for comparison. After exchange, the initial plasma concentration of each of the proteins was in excess of 20 mg/mL. UHb appeared both in urine and lymph. DECHb, PHb, and albumin were absent from the urine but appeared promptly in the renal hilar lymph and reached concentrations at least 30% that of plasma. PHb had a significantly smaller lymph clearance (in microliters per minute) and longer plasma half-time than the other nondissociable proteins, These findings indicate that DECHb and PHb, although not filtered, pass across peritubular capillaries and readily enter the renal interstitial space, The passage of the larger molecularsized PHb may be hindered relative to the other proteins in passage across peritubular and other systemic capillaries.