PubMed Health⌕ Search

Biomedical subjects

M Knecht

Publications and source records attributed to M Knecht.

At least 73 records · Page 4Linked to original sources
PubMed1983

Granulosa cell differentiation in vitro: induction and maintenance of follicle-stimulating hormone receptors by adenosine 3',5'-monophosphate.

Granulosa cell differentiation is stimulated in vitro by FSH and other agents that increase cAMP production. To determine if alterations in FSH receptors are associated with cAMP-mediated granulosa cell maturation, FSH-binding sites were measured during culture of undifferentiated granulosa cells from hypophysectomized diethylstilbestrol-implanted rats. FSH receptors decreased rapidly in the absence of stimulatory ligands, with loss of 75% and 90% of the FSH-binding activity from freshly prepared cells after 24 and 48 h, respectively. The decline in FSH receptors during culture was accompanied by a corresponding decrease in cAMP responses to added FSH. In cells cultured with FSH, the available FSH receptor content fell to 15% after 8 h, then rose to 25% of the initial receptor levels from 24-48 h of culture. Cells treated with 8-bromo-cAMP or choleragen for 48 h retained about 40% and 90%, respectively, of their initial FSH-binding activity. Although choleragen did not prevent the 60-70% fall in FSH binding during the first 6 h of culture, it increased receptors 2.5-fold from 12-48 h. Also, the addition of choleragen after 3, 6, or 12 h of culture elevated FSH receptors at 48 h in proportion to the amount of cAMP produced. The FSH receptors induced by choleragent treatment were functionally active, as shown by their ability to mediate FSH-stimulated cAMP production. A GnRH agonist prevented the choleragen-induced rise in FSH receptors and cAMP accumulation from 24-48 h of culture. Scatchard analysis revealed a single population of FSH receptors after all treatments, with association constant of 5 X 10(9) M-1. Freshly prepared cells contained approximately 1600 FSH binding sites/cell, while treatment with choleragen or FSH for 48 h restored receptor levels to 1150 and 500 sites/cell, respectively. These results indicate that the expression of functional FSH receptors during granulosa cell maturation is mediated by cAMP.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1982

GnRH receptors in cultured rat granulosa cells: mediation of the inhibitory and stimulatory actions of GnRH.

The regulatory actions of FSH and the GnRH agonist [D-Ala6]des-Gly10-GnRH N-ethylamide (GnRHa) upon ovarian GnRH receptors were studied in granulosa cells obtained from ovaries of hypophysectomized diethylstilbestrol-treated rats. When granulosa cells were cultured for 48 h in the presence of FSH (5-250 ng/ml) the binding of 125I-GnRHa to granulosa cell receptors was increased in a dose-dependent manner, to a maximum of 3-4 fold above the control value. Addition of FSH (100 ng) also caused a dose-dependent increase of more than 100-fold in the accumulation of cAMP and progesterone in the culture medium. In freshly prepared cells, Scatchard analysis of GnRHa binding data revealed an equilibrium constant (Ka) of 1.1 x 10(10) M-1 and GnRH receptor concentration fo 401 fmoles/mg protein. Granulosa-cell GnRH receptors decreased during culture without FSH, but were maintained in the presence of 100 ng FSH at 580 femoles/mg protein, with Ka of 0.8 x 10(10) M-1. This action of FSH on GnRH receptors was significantly reduced by 10(-8) M GnRHa. Also, GnRHa concentrations of 10(-10) and 10(-8) M caused inhibition of FSH-induced cAMP and progesterone accumulation. In cells cultured with GnRHa alone, there was a slight enhancement of GnRH receptors by GnRHa concentrations up to 10(-8) M, and a decrease below control levels with higher amounts. Also, GnRHa concentrations from 10(-8) to 10(-5) M caused a 3-4-fold increase in cAMP accumulation in the absence of FSH. These results demonstrate that FSH maintains GnRH receptors in cultured granulosa cells, and that GnRHa attenuates this effect, as well as the other actions of FSH on granulosa cell maturation. It is also evident that GnRHa itself can slightly stimulate cAMP production and partially maintain GnRH receptors, but at high concentrations causes loss of the homologous receptor sites. These findings also emphasize the ability of GnRH agonists to exert both positive and negative direct effects on rat granulosa cell function.

Animals↗
PubMed1981

Gonadotropin-releasing hormone: regulation of adenosine 3',5'-monophosphate in ovarian granulosa cells.

The antigonadal effects of gonadotropin-releasing hormone in ovarian granulosa cells are due to attenuation of the adenosine 3',5'-monophosphate (cyclic AMP) response to follicle-stimulating hormone. Agonists of gonadotropin-releasing hormone progressively inhibit adenylate cyclase and stimulate phosphodiesterase activities in cultured granulosa cells, indicating that blockade of gonadotropin action is attributable to the combined effects of decreased production and increased degradation of cyclic AMP.

Animals↗
PubMed1981

Gonadotropin-releasing hormone inhibits cyclic nucleotide accumulation in cultured rat granulosa cells.

Ovarian granulosa cells obtained from hypophysectomized, diethylstilbestrol-treated rats were cultured in the presence of ovine follicle-stimulating hormone (FSH) and gonadotropin-releasing hormone (GnRH). FSH stimulated the production and accumulation of both cAMP and cGMP, as well as progesterone, during a 48-h incubation period. Addition of GnRH or an agonist analog, [D-Ala6]des-Gly10-GnRH N-ethylamide (GnRHa), did not influence the cyclic nucleotide response to FSH in the first 6 h of incubation, but caused dose-dependent inhibition of the FSH-induced rise in cyclic nucleotide production from 24 to 48 h of incubation. Cellular production of both cyclic nucleotides and progesterone was decreased by GnRHa concentrations as low as 10(-12) M, with maximum inhibition at 10(-9) M GnRHa. These results suggest that the in vitro antigonadal actions of GnRH and related peptides are expressed through inhibition of cyclic nucleotide production.

Animals↗
PubMed1981

Hormonal regulation of cytodifferentiation and intercellular communication in cultured granulosa cells.

Granulosa cells from immature hypophysectomized diethylstilbestrol-treated rats displayed pronounced intracellular and intercellular changes after 48 hr of exposure to follicle-stimulating hormone (FSH) in vitro. As determined by light and electron microscopy, most of the FSH-treated cells became highly aggregated and grew in multilayered clusters. Numerous gap junctions were seen between cells, indicating the presence of significant intercellular communication. Microvilli densely covered the surface of the hormone-stimulated cells, which contained enlarged mitochondria with convoluted cristae, characteristic of steroidogenic cells. Luteinizing hormone receptors, identified by autoradiography with 125I-labeled human chorionic gonadotropin, were mainly associated with aggregated cells, whereas single cells were usually free of the labeled hormone. Addition of a gonadotropin-releasing hormone agonist prevented the appearance of luteinizing hormone receptors and markedly impaired cyclic AMP and progesterone production, as well as the morphological changes induced by FSH. The majority of the granulosa cells grown in the absence of either hormone assumed a flattened, and smooth shape and grew primarily in monolayers. The maintenance of cellular aggregation and intercellular communication by FSH, and its inhibition by gonadotropin-releasing hormone, may play an important role in the cytodifferentiation of ovarian granulosa cells.

Animals↗
PubMed1981

[Hyperinsulinaemia and impaired glucose tolerance in chronic inflammatory liver disease (author's disease)].

In 64 patients suffering from chronic inflammatory liver disease (alcoholic hepatitis, chronic active hepatitis, chronic persistent hepatitis) significantly increased values of blood glucose and insulin, free fatty acids and C-peptide were observed during a 100 g oral glucose load. Fasting values of blood glucose, free fatty acids and C-peptide were also increased, while serum growth hormone remained unchanged. In patients with chronic active hepatitis the C-peptide/insulin-ratio, a measure for hepatic insulin degradation, was significantly lowered after glucose uptake. During oral load there were no discernible differences between the different types of chronic inflammatory liver disease concerning blood glucose, serum insulin and free fatty acids. In normal weight and in overweight patients suffering from liver disease blood glucose and serum insulin values were increased to the same extent. As it is known from the liver cirrhosis chronic inflammatory liver disease lead to an insulin resistance, to which elevated free fatty acid levels contribute. Increased body weight has no influence on the insulin resistance observed in chronic liver inflammation. From the changes of the C-peptide and the C-peptide/insulin-ratio it can be deduced, that the hyperinsulinism in patients with chronic inflammatory liver disease is due to both insulin hypersecretion and diminished hepatic insulin degradation.

Adult↗
PubMed1980

Effect of hCGbeta-tt immunization on ovarian morphology in hamster implanted with human choriocarcinoma.

Histological analysis of ovaries from hamsters immunized with hCGbeta-tt and implanted with human choriocarcinoma has shown that the gonadotropic activity of hCG was neutralized for 5 days of tumor growth. In control immunized hamsters, hCG secreted from the tumor induced the formation of large, cystic follicles, thecal luteinization and an increase in ovarian mass from Days 1-10 of tumor growth. In contrast, ovarian morphology in hCGbeta-tt immunized hamsters on Days 1-5 of tumor growth resembled that of non-tumor bearing hamsters. Normal follicular growth and corpora lutea formation were observed despite the secretion of hCG by the tumor. Gonadotropic stimulation, as indicated by the presence of cystic follicles, was not evident until Day 10 of tumor growth in hamsters immunized with hCGbeta-tt. hCGbeta-tt immunization did not affect ovarian structure or the normal estrus cycle in hamsters without tumors. These results indicate that the biological activity of hCG in vivo can be inhibited by active immunization with hCGbeta-tt.

Animals↗
PubMed1980

The lack of an effect of active immunization with the beta-subunit of chorionic gonadotropin coupled to tetanus toxoid on the growth of human choriocarcinoma maintained in the hamster cheek pouch.

The antitumor properties of antibodies to the beta-subunit of hCG (hCG beta) coupled to tetanus toxoid (tt) were studied in hamsters implanted with the BeWo strain of human choriocarcinoma. After active immunization with hCG beta-tt mixed in complete Freund's adjuvant, hamsters synthesized large quantities of antibodies which bound whole hCG, as measured in vitro by the binding of radiolabeled hCG to plasma. Scatchard binding analysis indicated that the total high affinity hCG-binding capacity of hCG beta-tt plasma was approximately 130 microgram/ml. However, these antibodies were devoid of any antitumor activity. Choriocarcinoma implanted into hamsters during the peak times of [125I]iodo-hCG-binding activity by plasma did not show any change in tumor volume over a 20-day period of tumor growth compared to tumors in hamsters immunized with tt alone. Active immunization with hCG beta-tt did not alter the percentage of tumors taking, the length of lag phase of tumor growth, or the initial day of grossly detectable tumor necrosis. These results suggest that active immunization with hCG beta-tt will not alter the growth of transplantable choriocarcinoma.

Animals↗
PubMed1975

Radioactive labeling and location of specific thiol groups in myosin from fast, slow and cardiac muscles.

1. Based on incorporation of radioactively labeled N-ethylmaleimide, the readily reactive thiol groups of isolated myosin (EC 3.6.1.3) from fast, slow and cardiac muscles could be classified into 3 types. All 3 myosins contain 2 thiol-1, 2 thiol-2 and a variable number of thiol-3 groups per molecule. Both thiol-1 and thiol-2 groups which are essential for functioning of the K+-stimulated ATPase, are located in the heavy chains in all 3 myosin types. 2. The variation in the incorporation pattern of N-ethylmaleimide over the 3 thiol group classes under steady-state conditions of Mg(2+) - ATP hydrolysis allowed different conformations of some reaction intermediates to be characterized. In all 3 types of myosin the hydrolytic cycle of Mg(2+) - ATP was found to be controlled by the same step at 25 degrees C. In all three cases, this rate-limiting step is changed in the same way by lowereing temperature. 3. Using the chemically determined molecular weights for myosin light chains, their stoichiometry was found on the basis of sodium dodecyl sulfate electrophoresis to be 1.2 : 2.1 : 0.8 for light chain-1: light chain-2:light chain-3 per molecule of fast myosin, 2.0 : 1.9 for light chain-1:light chain-2 per molecule of slow myosin and 1.9 : 1.9 for light chain-1:light chain-2 per molecule of cardiac myosin. This qualitative difference in light subunit composition between the fast and the two types of slow myosin is not reflected in the small variations of the characteristics exhibited by the isolated myosins, but rather seems to be connected with their respective myofibrillar ATPase activities.

Adenosine Triphosphatases↗