The role of platelets in mesangial localization: carbon uptake in thrombocytopenic rats.

The role of platelets in mesangial localization has been studied in Lewis rats following a single intravenous injection of colloidal carbon 32 mg/100 g body weight. Following carbon injection there was an abrupt thrombocytopenia (peripheral platelet count at 10 min 165 +/- 107 X 10(3)/mm3). Temporary sequestration of platelets in lung, liver and spleen was demonstrated using quinacrine-labelled platelets. Carbon was quantitated in blood, lung, liver and spleen by digestion and spectrophotometry and in glomerular mesangium by particle counting of histological sections under oil-immersion microscopy. In thrombocytopenic rats (busulphan 17.5 mg/kg weight) blood carbon levels (up to 1 h after injection) were higher than normal controls (P less than 0.01) and mesangial carbon content at 24 h was significantly increased (P less than 0.01). No significant alteration in mononuclear phagocytic function was detected at 24 h. In platelet-restored thrombocytopenic rats, (busulphan-treated, infused with homologous platelets) blood and mesangial carbon levels were decreased towards normal values. These findings show that (1) platelets are involved in the initial removal of carbon from the blood (2) mesangial localization is related to blood levels and (3) platelet numbers affect both these parameters. The finding of increased mesangial deposition in thrombocytopenic rats may have significance for immune complex glomerulonephritis where platelet numbers may be low due to persistent platelet activation.