Extraction of soluble gonadotrophin receptors from rat testis

Solubilization, gel filtration and sedimentation behaviour of prolactin receptors from human ovarian tissue

Receptors for 125I-labelled human prolactin have been identified in the crude membrane fraction isolated from human ovarian tissue. The non-ionic detergent Triton X-100, has been used to solubilize the membrane fraction. The presence of the receptor in the detergent extract was demonstrated by gel filtration and sucrose density gradient centrifugation. The binding was time-temperature dependent, being maximal at 23 degrees C after 15 h of incubation. Large amounts of other peptide hormones did not inhibit the binding of 125I-labelled human prolactin. The binding Scatchard analysis demonstrated that the affinity of the soluble receptor (Ka 1.13 +/- 0.15 X 10(10) M-1) for the labelled hormone was slightly greater than that of the crude membrane fraction (Ka 0.91 +/- 0.12 X 10(10) M-1). The binding capacity of the solubilized receptor was also significantly greater than that seen in the particulate before solubilization. The apparent Stokes radius of the solubilized receptor was estimated to be 57 A and that the hormone-receptor complex 60 A. The sedimentation coefficient of the solubilized receptor was 7.0 +/- 0.1 s, whereas that of the hormone-receptor complex was 7.5 +/- 0.2 s.

Particulate and solubilized LH receptor in the pig and bull testis

Particulate and Triton X-100 solubilized receptors for luteinizing hormone (LH) in the pig and bull testis were studied. In some of the experiments tissue from the rat testis was included for comparison. LH receptors in the bull and pig revealed very similar association and dissociation kinetics, affinity (Kd = 1.2-1.8 x 10(-10) M), stability and physicochemical properties. Binding capacity was higher in the pig (73 fmol/mg protein) than in the rat (33 fmol/mg protein) and bull (17 fmol/mg protein). Hormone binding stabilized the receptor against thermal denaturation and temperature stability decreased upon solubilization. It is concluded that the properties of the testicular LH receptor of the pig and bull are very similar to those previously described from the rat.

Regulation of ovulation number in mammals. A follicle interaction law that controls maturation

The assumption that developing follicles communicate through circulating hormones has been used to obtain a class of interaction laws that describe follicle growth. A specific member of this class has been shown to control ovulation number. Although all interacting follicles obey the same growth law and are given initial maturities that are chosen at random from a uniform distribution, ovulatory and atretic follicles emerge. Changing the parameters in the growth law can alter the most probable ovulation number values, anovulatory states are also admitted as possible solutions of the growth law. The behavior of the model is examined for interacting follicle populations of different size. Methods are suggested for identifying growth laws in particular mammals. These can be used to test the model from experimental data.

Isolation of mRNA from bovine pituitary. The cell-free synthesis of the alpha and beta subunits of luteinizing hormone

RNA derived from bovine steer pituitary was translated in wheat germ cell-free extracts containing [35S]methionine. Antisera generated against purified denatured alpha and beta subunits of lutropin were used to demonstrate the synthesis of both proteins in vitro. The immunoprecipitated products of the cell-free system were resolved on sodium dodecyl sulfate/polyacrylamide gels and it was observed that the molecular weight of the immunoprecipitated alpha subunit protein was approximately 14,000, while that of the beta protein was estimated to be 16,000. Since the molecular weights of authentic alpha and beta subunits are 10,600 and 14,000 respectively, the cell-free products presumably represented their pre-protein forms. The ratio of the immunoprecipitated subunit pre-proteins was dependent on the magnesium concentration in the translation mixtures; at 2.1 mM, translation of lutropin alpha and beta mRNAs was comparable. RNA isolated from cow pituitary tissue directed the synthesis of fivefold less of the alpha and beta immunoprecipitated proteins than did steer RNA. Since the blood levels of gonadal steroids are higher in the cow, the results supported the hypothesis that lutropin alpha and beta mRNA biosynthesis is repressed by these steroids. The data also suggest that synthesis of lutropin alpha and beta subunits is coordinately expressed in certain physiological situations.

Studies on the stability of rat testis membrane receptors for hLH, hCG and hFSH

Receptor preparations from rat testes were stored at 4 C with various protease inhibitors and chemicals, at -20 C and -80 C, in freeze-dried form as well as at 4 C and 37 C after reconstitution in various media. Each preparation was tested for stability in terms of binding capacity of human luteinizing hormone (hLH), human chorionic gonadotropin (hCG) and human follicle-stimulating hormone (hFSH). The freeze-dried samples were stable for at least six months, although once reconstituted and stored at 4 C, they were less stable than fresh ones. Furthermore, Na azide and Na azide with diisopropylfluoro-phosphate (DIFP) prolonged the stability of the fresh samples. The samples stored at -20 C or -80 C were stable for at least 90 days and repeated freezing and thawing (15 times) did not change the binding capacity of either the hCG/hLH or hFSH receptors.

HCG-dependent regulation of gonadotropin receptor sites: negative control in testicular Leydig cells

A single injection of human chorionic gonadotropin (hCG 500 IU) to prepubertal male rats increases plasma testosterone level and decreases hCG receptors in the testicular Leydig cells for more than 120 h. Injected hCG, measured in plasma using a specific radioreceptor assay for gonadotropins, is maximal at 2 h and decreases thereafter with an apparent half-life of 16 h. Plasma testosterone exhibits a rapid increase (30-40 ng/ml) within 1h after hCG injection. A delayed paradoxical increase (20-30 ng/ml) is observed between 48 and 120 h after the injection. The number of hCG binding sites in the isolated Leydig cells membranes decreases to less than 10% of the control value within 10 h and remains almost undetectable until 96 h after hCG injection. Reappearance of the binding sites is observed around 120 h. Similar, but less pronounced effects are found after the injection of 10 IU hCG. Since receptor occupancy cannot explain such a phenomenon, it is concluded that hCG is exerting a negative control on its own receptors in the Leydig cells.

Presence in normal human testes of a chorionic-gonadotropin-like substance distinct from human luteinizing hormone

The high rate of human chorionic gonadotropin production by testicular tumors caused us to investigate the possibility that normal human testes contain small amounts of that substance. Extracts of human testes obtained at autopsy demonstrated parallel inhibition curves to the human chorionic gonadotropin standard in a radioimmunoassay specific for the hormone. The immunoreactive material was adsorbed onto concanavalin A, a reaction characteristic of glycoproteins, and was eluted within the chorionic gonadotropin range on Sephadex G-100 column chromatography. Solubilized receptor proteins for the hormone could not be identified in the extracts. The demonstration that the normal human testes contain a glycoprotein similar or identical to human chorionic gonadotropin suggests that the fetal genome responsible for production of the hormone during pregnancy is not completely suppressed in the adult. Excessive productton of this glycoprotein may account for the high levels of human chorionic gonadotropin reported in the serum of patients with germ-cell tumors of the testes.

Effect of RNA synthesis on the binding of 3H-cortisol to nuclear ribonucleoprotein particles from rat liver carrying DNA-like RNA in vivo

3H-cortisol was found to associate with rat liver nuclear 30S ribonucleoprotein particles carrying D-RNA in vivo. No interaction was detectable when RNA synthesis was inhibited by alpha-amanitine. The association appears to be specifically for RNP carrying RNA synthesized after the administration of cortisol to adrenalectomized rats. The DNA/protein/RNA ratio of rat liver nuclei was not effected by alpha-amanitine under our conditions. However, the drug caused a 5-10 fold decrease in nuclear uptake of cortisol. The results are discussed in relation to a supposed transfer of cortisol-receptor complexes from the chromatin template to the nascent RNA chains.