Summary
Human platelets exposed to hypotonicity undergo regulatory volume decrease (RVD),
controlled by a potent, yet labile, lipoxygenase product (LP). LP is synthesized and
excreted during RVD affecting selectively K+ permeability. LP is assayed by its capacity to reconstitute RVD when lipoxygenase
is blocked. Centrifugation for preparing washed platelets (1,550 × g, 10 min) is sufficient to express LP activity, with declining potency in repeated
centrifugations, indicating that it is not readily replenish-able. When platelet suspension
flows in a vinyl tubing (1 mm i.d.), at physiological velocity, controlled at 90–254
cm/s, LP formation increases as a function of velocity but declines as result of increasing
the tubing length. Stirring the platelets in an aggregometer cuvette for 30 s, yields
no LP unless the stirring is intermittent. No associated platelet lysis or aggregation
are observed following the mechanical stress applications. These results demonstrate
that although mechanical stresses result in LP production, the mode of its application
plays a major role. These results may indicate that LP is synthesized under pathological
conditions and could be of relevance to platelets behavior related to arterial stenosis.
