DISTRIBUTION OF ESTRADIOL BETWEEN SERUM AND RED CELLS

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Abstract
The solubility of estradiol in aq. soln. at 37.5[degree]C and ionic strength of 0.115 is (9.0 [plus or minus] 0.3) X 10-6 moles/l. A shift of pH from 7.0 to 8.6 is without influence, indicating complete hydrolysis and the absence of salt formation with the weakly acid phenolic group. The heat of soln. of estradiol in water in the temp. range 25.0[degree]C to 37.5[degree]C, at ionic strength 0.155, is 4300 calories/mole. The solubility of estradiol in 3% bovine albumin at 37.5[degree]C, ionic strength 0.155 and pH range 5.5 to 6.9 is (2.0 [plus or minus] 0.1) X 10-4 moles/l. Correcting for solubility in water, dispersing power of bovine albumin toward estradiol is one mole estra-diol/2.2 moles albumin. The heat of dispersion in 3% albumin is 13,700 calories/mole. The solubility of estradiol in rabbit serum may be roughly apportioned to the following constituents: albumin 75%, globulin 15% and lecithin 10%. The distribution coefficients of estradiol between red cells and either saline, albumin soln. or serum are inversely proportional to the solubilities of estradiol in these solutes. On re-equilibration of red cells, which have extracted estradiol from saline or serum solution, with the same respective solutes, the distribution coefficient remains the same. Estradiol is removed from albumin soln. by collodion or by sesame oil. The expts. demonstrate rather conclusively that the distribution of estradiol in blood is governed solely by the forces which govern its solubility. There is no indication of compound formation or inactivation. To it, the red cell is freely permeable. The solubility of estradiol in albumin soln. is markedly lessened by competition with testosterone. The effect of progesterone under similar conditions is less than that of testosterone.
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