Relationships between mammary estrogen receptor and estrogenic sensitivity. Molecular properties of cytoplasmic receptor and its binding to deoxyribonucleic acid.

The cytoplasmic estrogen receptors (ER) from mammary glands of estrogen-responsive nulliparous and estrogen-resistant lactating mice have been studied to delineate various relationships between the molecular properties of ER and estrogenic sensitivity. These studies indicate that there are essentially no differences in the hydrodynamic parameters of native ER isolated in hypotonic buffer; the ER from both tissues have a stokes radius of 80-85 A, sedimentation coefficient of 9-10S, and mol wt of 300,000-340,000. However, while 60-80% of the total ER in mammary glands of nulliparous mice, upon exposure to 400 mM KC1 is able to bind to DNA, under identical experimental conditions only approximately 20% of total ER from lactating mammary glands binds to DNA. Analyses of ER in buffers containing 400 mM KC1 reveal that the ER in lactating mammary glands have a larger mol wt (100,000-130,000) as compared to ER in mammary glands of nulliparous mice (70,000). The ER in lactating mammary glands also appear to be more acidic when analyzed by diethylaminoethyl cellulose chromatography. Experiments performed with mixed cytosol reveal that lactating mammary cytosol contains factors which can impede the ability of ER to bind to DNA subsequent to exposure to KC1. The possible significance of the observed differences in the properties of ER from estrogen-responsive and unresponsive mammary glands has been discussed.

A comparison of the cytoplasmic estrogen receptors of mammary gland from virgin and lactating mice.

Recent studies suggest that the mammary cytoplasmic estrogen receptor of virgin mice sediment predominantly as 45 species on low ionic strength sucrose gradients. In the present studies we show that the mammary cytoplasmic estrogen receptor from both the intact and ovariectomized virgin and lactating mice sediment at 9S on sucrose gradients prepared in low ionic strength buffers. However, the receptor from the virgin mice is susceptible to cleavage, resulting in the appearance of 3-4S forms of the receptor. If, however, phosphate buffers or buffers containing sodium molybdate are used in the preparation of cytosol and its analysis, it preserves the integrity of the native 9S estrogen receptor.

Comparative in vitro biological activity of 1-34 N-terminal synthetic fragments of human parathyroid hormone on bovine and porcine kidney membranes.

1-34 N-terminal fragments of human parathyroid hormone with sequences according to Brewer et al (hPTHB) and to Niall et al (hPTHN) were synthesized and compared for their ability to activate bovine and porcine kidney cortex membrane adenylate cyclase. Results show that these two hormone sequences are able to activate these membranes but at least in this in vitro assay, hPTHN is about 10 times more active than hPTHB on bovine as well as on porcine membranes. These "apparent potencies" with respect to the potency of bPTH 1-34 in bovine and porcine membrane assay systems are respectively 4% and 11% for hPTHB and 39% and 156% for hPTHN. These relative potencies may be interpreted as corresponding to species specificity of the hormone receptor structural relationships.

Liquid scintillation counting for measurement of tritiated uptake in lymphocyte transformation in vitro: a new direct-suspension procedure.

Liquid scintillation counting of trichloracetic acid extracts of [3H] TdR-labelled lymphocytes has been studied by a direct suspension method without previous solubilization. In this new method, mixing of the labelled powder in water suspension with Scintillator Emulsifying Mixture (SEM) results in a firm gel whose mechanical properties provide an heterogeneous sample ready for counting. Counting efficiency and stability of such samples are related to the amount of labelled cells. Comparative studies with standard hyamine procedure have shown that this simple and rapid method gives reliable results.