Hormone replacement therapy in the menopause: a suitable animal model.

Female CBA mice, aged 11 months, were treated cyclically with oral ethynyl oestradiol or oestrone sulphate for 3 months. The ovaries of all animals appeared to be atrophied. Target tissues throughout the genital tract showed a response to both oestrogens. Electron microscopy of both the endometrium and the urothelium demonstrated morphological changes characteristic of increased cellular metabolic activity in the treated mice. Endometrial hyperplasia developed in both treatment groups but more pronounced epithelial changes occurred with oestrone sulphate. This hyperplasia was accompanied by a doubling in the number of uterine cytoplasmic oestrogen receptors. A 50% fall in serum levels of luteinizing hormone in the treated mice revealed that the hypothalamic-pituitary system was still intact. Both oestrogens improved skeletal balance by changes in cortical-endosteal bone remodelling. The results suggest that the CBA strain of mouse is a suitable model for the study of the human climacteric and its response to hormone replacement therapy.

The incidence of cestradiol receptor sites in breast tissues.

PIP: Portions of tumors from 41 patients with benign breast disease, 105 with breast cancer, and 6 of normal breast tissue were studied. Tissues were stored up to 1 month at -20 degrees C in air-tight containers prior to assay. Of the 41 benign tumors 3 had measurable receptor sites. 69 of the 105 cancers showed receptor sites, mostly of a higher order than the benign group. There was a statistically significant difference (p= .02) between the binding site concentration in the malignant tumors from pre- and postmenopausal patients. Concentrations were greater in the postmenopausal patients. The addition of increasing concentrations of dithioerythritol (DTT) in the buffers was found to enhance progressively the affinity for binding in 4 of tumors. In the 6 normal breast tissues, 2 sowed binding with DTT but none by the standard method. Using DTT to increase the sensitivity of the method may improve the prediction of later response to hormone manipulation.^ieng

The synthesis of polyribonucleotides by cytoplasmic enzymes.

1. The possibility that the cell cytoplasm contains enzymes catalysing the biosynthesis of RNA was investigated in fractions obtained by differential centrifugation of homogenates of Landschutz ascites-tumour cells. 2. The microsomal fraction was shown to be most active in incorporating UMP residues from [alpha-(32)P]UTP into polyribonucleotide material. 3. The same fraction also incorporated [(3)H]CTP, [(3)H]ATP and [(3)H]GTP separately and independently of the presence of complementary ribonucleoside 5'-triphosphates. 4. The reaction was promoted by the addition of RNA and showed an absolute requirement for Mg(2+) ions. 5. Analysis of alkaline hydrolysates of the reaction products after the incorporation of [alpha-(32)P]UTP showed that most of the radioactivity was recovered in (2',3')-UMP residues irrespective of whether CTP, ATP and GTP were present in the reaction mixture. 6. Extraction of RNA from the reaction mixtures after the incorporation of [(3)H]ATP, [(3)H]GTP or [(3)H]CTP and analysis by sucrosedensity-gradient centrifugation showed no labelling of the ribosomal RNA. Radioactive material appeared between the 4s region and the meniscus of the sucrose gradient. In agreement with this observation, determinations of the chain length of the product showed that only short sequences of polynucleotides were synthesized. It is concluded that only homopolyribonucleotide synthesis is catalysed by the microsomal fractions and that there is little or no synthesis of RNA-like heteropolymers.

THYMIDINE TRIPHOSPHATE SYNTHESIS IN TETRAHYMENA: I. Studies on Thymidine Kinase.

The amount of thymidine-H(3) converted to thymidine-H(3) monophosphate in 30 min formed the basis for assays of thymidine kinase in cell extracts from Tetrahymena pyriformis. The optimal concentration of adenosine triphosphate is lower than that required by other cell types. Thymidine triphosphate does not exercise any feedback control of the enzyme. Other deoxyprimidine nucleotides were tested, but these also failed to exhibit any feedback inhibition. At suboptimal adenosine triphosphate levels, thymidine triphosphate and other deoxypyrimidine nucleotides stimulate the reaction, suggesting that these nucleotides may act either directly or indirectly as phosphate donors in the crude enzyme preparations. This possibility was affirmed when thymidine triphosphate and deoxycytidine triphosphate were shown to be capable of limited phosphorylation of thymidine. Comparison of enzymatic activities in logarithmically growing culture and stationary phase culture, in which nuclear DNA synthesis has virtually ceased, reveals no change in enzymatic activity. The results suggest that thymidine kinase is a constitutive enzyme in Tetrahymena.