Corticosteroid binding by plasma proteins and the effects of oestrogens in the marsupial brush-tailed opossum, Trichosurus vulpecula (Kerr).

Using the techniques of equilibrium dialysis at 36 degrees C and gel filtration at 4 degrees C, a high-affinity, transcortin-like, corticosteroid binding system has been demonstrated in the blood plasma of the marsupial Trichosurus vulpecula. The affinity constant for non-albumin binding was 4-018 +/- 1-032 X 10(7) (S.C.) 1/mol for males and 4-046 +/- 0.981 X 10(7) for females. The concentration of non-albumin binding sites was 1-82 +/- 0.76 X 10(-7) mol/1 in males and 1-86 +/- 0-57 X 10(-7) mol/1 for females. Oestrogen administration, sufficient to cause marked hypertrophy of the genital tract in the femlaes, had no effect on the affinity constant or the concentration of the non-albumin binding sites in either males or females. The general condition of the animals deteriorated during oestrogen administration and there were significant falls in the concentrations of albumin and cortisol in the blood plasma. In one animal which died during oestrogen treatment, the adrenal glands were significantly hypertrophied.