This paper examines the effects of freezing and thawing on steroid receptor concentrations in the brain and pituitary of the rat. Storage at -70°C for 1-2 weeks had no detectable effect on levels of cytoplasmic estrogen receptors. However, freezing and thawing resulted in measurable losses of cytoplasmic androgen, progestin and glucocorticoid receptors. Cell nuclear receptors were measured by exchange assay after in vivo administration of non-radioactive steroids. Nuclear estrogen, androgen and progestin receptor concentrations were all reduced by freezing compared to the levels in fresh tissue. In all cases except that of cytoplasmic glucocorticoid receptors, these losses could be prevented by freezing the tissue in 10% aqueous dimethylsulfoxide.
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