The glomerular mesangium: uptake and transport of intravenously injected colloidal carbon in rats.

Collodial carbon, 70 mg/100 g, was injected into rats which were sacificed for histologic study of the kidneys at intervals of five minutes to seven weeks. Transient thrombocytopenia and albuminuria were observed. Uptake of carbon by the mesangium of glomeruli was maximal at 32 hr and gradually decreased thereafter. Semiquantitative analysis of the distribution of carbon particles within glomeruli revealed a predominately peripheral localization during early time periods, and increased relative concentration of particles within more central zones and in the lacis area at the vascular pole of the glomerulus at two to seven weeks, indicating that one of the mechanisms for clearance of materials from the mesangium was movement of particles in the direction of the lacis area. Sequential electron microscopic studies showed that carbon particles moved through fenestrae in the endothelium covering the mesangium into channels between mesangial cells. Observations at later intervals suggested that carbon eventually reached the vascular pole by being passed on from one mesangial cell to the next. Vasoactive amines or other substances derived from platelets may play an important role in initiating the process of mesangial uptake.