The platelet response to hypotonic shock. Its value as an indicator of platelet viability after storage.

The nature of the platelet response to osmotic shock and its relationship to platelet viability were studied. Light absorbancy changes of human platelet concentrates exposed to hypotonic shock were measured in a spectrophotometer: a sudden drop of light absorbancy was followed by a reversal of light absorbancy towards normal (reversal reaction). It was confirmed that the reversal reaction is a complex phenomenon dependent on the integrity of biochemical and enzymatic functions of the platelets. It was suppressed by glycolytic inhibitors and by SH-blocking agents. Ouabain had no immediate effect, but with prolonged incubation it depressed the reaction. Suspension of the platelets in a protein-free medium caused a rapid loss of the reversal reaction. Disappearance of the marginal bundle of microtubules by exposure to colchicine did not change the reaction leading to the hypothesis that microfibrils rather than the microtubules may have been responsible for the reversal reaction. The conclusion was derived that the reversal reaction is due to cell volume contraction for which integrity of the platelet contractile protein and energy availability are essential. Platelet storage at 4 degrees C or at 22 degrees C caused a progressive depression of the reversal reaction which was more severe in platelets preserved at 4 C than in those preserved at 22 degrees C, and paralleled the loss of the platelet capacity to survive in vivo. Cryoprotective agents (DMSO, DMAC and glycerol) partially inhibited the reversal reaction. Freezing with these agents caused a more severe depression of the reaction. The least depression was observed with 5 per cent DMSO. The results demonstrated that the reversal reaction is a valid and accurate in vitro indicator of in vivo platelet viability when the results to be compared are limited to a single method of storage. Usefulness of the reversal reaction is reduced when results obtained with different methods of storage are compared.