The effects of modulation of prostanoid metabolism on the thoracic platelet accumulation induced by intravenous administration of collagen in the guinea-pig.

The effects of intravenously administered collagen on the circulatory platelet count, TxB2, 6-keto PGF1 alpha and 51Cr-labelled platelet accumulation in the thorax have been evaluated in the guinea-pig. Administration of collagen induced a dose-related peripheral thrombocytopenia and a concomitant increase in 51Cr-labelled platelets in the thorax. There was also a transient dose-related increase in plasma TxB2 but no change in plasma 6-keto PGF1 alpha levels. The thromboxane synthetase inhibitors tested, reduced the platelet accumulation, but only CGS 13080 significantly inhibited TxB2 production. In contrast all the cyclooxygenase inhibitors tested impaired the elevation of plasma TxB2 after collagen, but only diclofenac inhibited the 51Cr-labelled platelet accumulation. The greater effect of thromboxane synthetase inhibitors compared to cyclooxygenase inhibitors on platelet accumulation in this system cannot be completely explained by the changes measured in the circulating prostanoids.