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The binding characteristics of glucocorticoids to cytoplasmic and nuclear fractions of the adenohypophysis were determined and an attempt was made to correlate steroid uptake with physiological action. Binding was of high affinity and exhibited a limited number of acceptor sites for dexamethasone (Dx). It was shown that the steroid-receptor complex dissociated rapidly at 37 °C, but was stable at low temperatures. An inverse relationship was detected between the plasma corticosterone (B) titer and the capacity of receptors to combine ³H-Dx. Shortly after stress or injection of physiological doses of B, 50 to 70% of the acceptor sites were saturated. Progressive desaturation of the occupied receptors appeared to depend upon time and the plasma B concentration. Some evidence was also provided supporting a possible correlation between the extent of Dx inhibition of in vitro ACTH secretion and the degree of binding sites’ occupancy. These results suggest that glucocorticoid binding to pituitary receptors may be correlated with the physiological action of the steroids on ACTH release.

The inOuence of transcortin-binding capacity on corticosterone tissue uptake and degradation in the infant rat were studied. It was shown that the T 4-induced increase of plasma transcortin level did not alter the corticosterone half-life, but caused areduction oe the virtual volume oe distribution and, as a consequence, oe the hormone metabolie c1earance rate.From a comparison between in vivo and in vitro tissue uptake oe the steroid, it was concluded that plasma transcortin binding sites strongly compete with tissue binding sites. In addition, some oe the fmdings would suggest that the liver may not store transcortin, as a moleeule exhibiting the same characteristics as the plasma counterpart.Horm. Metab. Res.: 2: 292-297 (1970) K e y -W 0 r d s: PlaSmtl Transeortin -Corticosterone Half-Life, Distribution Volume and Metabolie Clearanee Rate -Corticosterone Tissue Binding.

The occurrence of at least two types of binders could be demonstrated: one exhibited high affinity for both natural and synthetic glucocorticoids (component D), while the .other bound only the natural steroid. The latter closely resembled plasma transcortin (Koch, Lutz, Briaud and Mialhe 1975, 1976, DeKloet and McEwen 1976), whose concentration is known to be higher in female than in male rats (Labrie 1967). In the present paper we report a similar sexual difference at the level of the pituitary and, in addition, suggest a possible function for the transcortin-like (TL) component. Methods Binding studies were performed as previously described (Koch et al. 1974. 1975), using pituitaries from I-day post-operative adrenalectomized rats, killed under Nembutal anesthesia by perfusion of ice-cold saline through the heart.

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