Endocrinology, Vol 124, 3128-3130, Copyright © 1989 by Endocrine Society

ARTICLES

Conservation of free but not total or non-sex-hormone-binding-globulin- bound testosterone in serum from Nagase analbuminemic rats

CM Mendel, JT Murai, PK Siiteri, SE Monroe and M Inoue
Cardiovascular Research Institute, Liver Center, University of California, San Francisco 94143-0130.

Nagase analbuminemic rats have normal reproductive capacity, normal apparent libido, and normal serum concentrations of LH and FSH. Therefore, it is reasonable to assume that intracellular sex steroid hormone concentrations are normal or at least adequate to maintain normal reproductive function in these rats. To test whether intracellular testosterone concentrations in these rats are maintained by the circulating concentration of free or free-plus-weakly-bound testosterone, we measured the concentrations of total testosterone, free testosterone, and non-sex-hormone-binding-globulin-bound testosterone in sera from five adult male Nagase analbuminemic rats and from five age- and sex-matched controls. We found that the analbuminemic rats had markedly decreased serum concentrations of total and non-sex-hormone-binding-globulin-bound testosterone, but normal serum concentrations of free testosterone. These results suggest that intracellular concentrations of testosterone in biologically relevant organs of the rat are maintained by the concentration of free rather than free-plus-weakly-bound testosterone in plasma, in accord with the free hormone hypothesis.