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

Unlike unmodified dissociable bovine hemoglobin (UHb), cross-linked hemoglo bins do not dissociate into dimers, do not cross the glomerular filter, and are retained in the plasma for a longer time. Renal peritubular capillarie s, which are different from the glomerulus, allow the passage of molecules as large as albumin into the renal interstitium. Cross-linked hemoglobins s hould pass across these capillaries, enter the renal interstitium, and drai n through the renal lymphatics. The present experiments were done in anesth etized rats to determine the appearance of UHb, an intramolecularly cross-l inked tetrameric hemoglobin (DECHb), and a polymerized bovine hemoglobin (P Hb) 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 compar ison. After exchange, the initial plasma concentration of each of the prote ins 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 r enal hilar lymph and reached concentrations at least 30% that of plasma. PH b had a significantly smaller lymph clearance (in microliters per minute) a nd longer plasma half-time than the other nondissociable proteins, These fi ndings indicate that DECHb and PHb, although not filtered, pass across peri tubular capillaries and readily enter the renal interstitial space, The pas sage of the larger molecularsized PHb may be hindered relative to the other proteins in passage across peritubular and other systemic capillaries.