Investigation on the thermostability of steroid hormone receptors in lyophilized calf uterine tissue powder.

Powdered calf uteri were lyophilized and sealed in a vacuum. The effects of lyophilization and the thermostability of the binding activity of uterine steroid hormone receptors were studied. The lyophilized powder was analyzed for its ability to bind estrogen, progestin, androgen, and glucocorticoid steroids. Lyophilization had no deleterious effects on the binding activity. Storage of the lyophilized powder at +20 C for more than 14 days did not reduce the binding activity. No reduction of the binding capacity was also observed when the storage temperature was at +30 C for 16 hours. However, a slight loss of specific binding sites was observed for 17 beta-estradiol (-12%) at the storage temperature of +40 C, but the other steroid binding proteins were more stable. When the storage temperature was at +60 C for 16 hours, a loss of about 24% was observed for the specific estrogen binding sites, whereas the binding capacity of progestin, androgen, and glucocorticoid receptors was reduced by only less than 10%. Storage at the high temperature of +80 C for 16 hours resulted in a loss of only 36% for the estrogen binding capacity and less than 30% loss for the other binding proteins. The freeze-dried uterine powders can be useful quality control specimens for steroid receptor assays.