In vitro addition of glutathione to blood from zinc-deficient rats corrects platelet defects: Impaired aggregation and calcium uptake

Zinc deficiency in rats impairs platelet aggregation, and this defect is associated with the failure of platelets to take up external calcium. Recent data show that the red cell plasma membrane from zinc-deficient rats contains a lower than normal concentration of protein sulfhydryl groups, a defect that can be corrected readily in vivo by zinc repletion. The purpose of this study was to determine the effect of zinc deficiency on sulfhydryl concentration of platelet membrane proteins and to determine if impaired platelet function can be corrected in vitro by treatment of blood with glutathione (GSH), a physiological reducing agent. Immature male rats were fed low zinc diets based on egg white or EDTA-treated soy protein (<1 mg/kg Zn) and the same diets supplemented with 100 mg/kg Zn (control). For membrane analysis, rats were fed soy-based diets for 3 weeks; for reversal experiments they were fed egg white-based diets for 2 weeks. Compared with controls, rats fed the low zinc diets had approximately 15% lower concentration of membrane protein sulfhydryls and their platelets exhibited impaired aggregation coupled with decreased calcium uptake when stimulated with ADP. Treatment of whole blood from deficient rats with 0.2 mM GSH restored aggregation and calcium uptake of washed platelets to control levels. The presence of red cells was essential for the reversal process in as much as treatment of platelet-rich-plasma or washed platelets with GSH had no effect. Treatment of control blood with GSH did not affect platelet aggregation, but decreased calcium uptake. The lower calcium uptake by controls suggests that a feedback mechanism in deficient platelets was not corrected by GSH treatment. The results show that selective sulfhydryl groups in platelet membranes are lost during zinc deficiency and that platelet function can be restored to normal by treatment of blood with GSH. There seems to be an association of oxidation-susceptible thiol groups with a calcium channel and that these groups are protected by normal physiological levels of zinc.