Effects of Free Fatty Acids on Free Form Fraction of Steroids in Human Serum [in Japanese]

Sadao Watanabe

Kanagawa Prefectural Public Health Laboratory, 1-1-1 Nakao-cho, Asahi-ku, Yokohama 241-0815, Japan

Steroids are transported in free forms and also in bound forms with beta-globulin and/or with albumin in serum, and bind to with an intracellular specific‘receptor' protein after permeation through the cell membrane of target cell. Albumin and globulin cannot permeate through the cell membrane, so it has been generally assumed that the concentration of steroids in free forms determines the uptake rate and its bioavailability. In this report, the effects of the addition of such free fatty acids as palmitic acid, oleic acid and linoleic acid to the fractions of free beta-estradiol and testosterone in serum were examined in vitro. It was found that the concentration of free steroids did not vary at the normal levels (when the range of the molar ratios of free fatty acid/albumin in serum was from 0.5 to 2) in men and women, but when the molar ratios of free fatty acid/albumin exceeded 3 the concentration of free steroids increased by the addition of free fatty acids. The effects of free fatty acids on the increase of the concentration of free steroids fraction were in the following order : linoleic acid, oleic acid>palmitic acid. These results suggest that the elevation of the concentration of free fatty acids in serum, amplified by high fat consumption, obesity and stress, may cause the increases of physiologically active beta-estradiol and testosterone.