Cytoplasmic 17 beta-[3H]estradiol binding in rat adipose tissues

Area of Science:

• Endocrinology
• Adipose Tissue Biology
• Hormone Action

Background:

• Ovarian hormones, especially 17 beta-estradiol, influence body fat in rats.
• The precise mechanism of estrogen's effect on adiposity (direct vs. indirect) remains unclear.

Purpose of the Study:

• To investigate whether 17 beta-estradiol directly affects various fat depots in rats.
• To identify estrogen-specific binding sites within adipose tissues.

Main Methods:

• Used radiolabeled 17 beta-[3H]estradiol to detect binding in cytoplasmic fractions of adipose tissue from ovariectomized rats.
• Performed saturation analysis to determine binding affinity (Kd) and specificity.
• Tested inhibition of binding with various unlabeled hormones and enzymes (pronase, DNase, RNase).

Main Results:

• High-affinity, estrogen-specific macromolecular binding of 17 beta-[3H]estradiol was identified in rat adipose tissue cytoplasm.
• Binding affinity (Kd) was 7.4 X 10(-10) M, specific to 17 beta-estradiol and R2858, and inhibited by pronase, suggesting a protein receptor.
• Binding was observed in abdominal, subcutaneous, and brown fat, with highest concentrations in parametrial fat pads and isolated adipocytes.

Conclusions:

• Adipose tissues in rats possess estrogen-specific binding sites, indicating they are potential estrogen target tissues.
• Estrogenic effects on body weight and composition may be partly mediated by direct actions on adipose tissue.