Altered sedimentation behaviour and ultrastructure of platelets in hyperlipidemia

The influence of hyperlipidemia on platelet sedimentation behavior and ultrastructure was studied in samples of plasma obtained from 22 normal subjects, 7 patients with Type II and 12 patients with Type IV hyperlipoproteinemia, all fasting; also from 11 normal subjects prior to and at intervals up to 6 hr following ingestion of a meal containing 65 g of fat. Platelet counts were made on mixed platelet rich plasma after centrifugation of whole blood at 1,000 rpm, on top plasma layers after high speed centrigufation (10,000 rpm), and on the sediments resuspended in imidazole buffer. The mean ± SE number of platelets per mm³ in top layer among normal, Type II and Type IV plasmas were 4,090 ± 405; 9,000 ± 70, and 21,500 ± 1,950, respectively. The rise and subsequent fall in plasma triglycerides in response to fat ingestion in normal subjects paralleled those of platelets in the top layers. No such correlation was found with plasma cholesterol. The presence of platelets in the top layers of plasma was demonstrated further by electron microscopy. The buoyant platelets revealed the presence of osmophilic (lipid) particles within their open canalicular system, and pseuodopod formation. The sedimented platelets from normal subjects had a smooth contour, whereas those from patients with hyperlipidemia displayed a striking formation of pseudopods. The data suggest that the sedimentation behavior of platelets and their normal structure are altered significantly as they interact with abnormal concentrations of plasma lipoproteins.