Assay for thrombopoietin: a comparison of time of isotope incorporation into platelets and the effects of different strains and sexes of mice.

Several workers have used mice for thrombocytopoiesis-stimulating factor (TSF) assays, but the methods have differed. In quest of the optimum TSF assay conditions, we investigated the effects of interval between isotope injection and measurement of 35S incorporation into platelets, different mouse strains and sexes of mice. The 35S incorporation into platelets of mice increased with increase of the interval after isotope injection. However, the greatest difference in radioactivity between control and TSF-injected mice occurred at 16-40 h for normal mice and 24 h for rebound-thrombocytotic mice. When C3H, BALB/c or B6D2F1 mice were injected with platelet specific antisera, similar degrees of thrombocytopenia and rebound-thrombocytosis occurred. After injection of a standard dose of TSF, C3H and B6D2F1 mice showed greater isotopic incorporation levels, compared to suitable controls, than did BALB/c mice. Female and male mice exhibited essentially the same response to a standard dose of TSF. The data show that the mouse strain and isotopic incorporation time influence the sensitivity of the TSF assay but sex of test animals does not.