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T Ranta

Publications and source records attributed to T Ranta.

At least 55 records · Page 3Linked to original sources
PubMed1984

GnRH agonist-induced inhibitory and stimulatory effects during ovarian follicular maturation.

The in vivo regulation of ovarian gonadotropin and prolactin receptors and adenylate cyclase activity by FSH, and the potent GnRH agonist [D-Ala6]des-Gly10-GnRH N-ethylamide (GnRHa), was studied in immature hypophysectomized diethylstilbestrol-implanted rats. During FSH treatment over a 48 h period, FSH receptors increased 2-fold with the maximum response during the first 12 h, whereas LH and prolactin receptors increased by 10-fold and 6-fold with the maximum response from 12 to 48 h. Administration of GnRHa at any time during the 48 h period of FSH treatment inhibited the subsequent development of gonadotropin and PRL receptors. In contrast, administration of a single dose of 10 micrograms GnRHa after 48 h of FSH treatment stimulated follicular luteinization and caused increases in basal adenylate cyclase activity, ovarian weight and PRL receptor content, and concomitant decreases in gonadotropin receptors and adenylate cyclase responses. In the immature follicles of animals not primed with FSH, GnRHa caused progressive inhibition of FSH-sensitive adenylate cyclase activity, with a decrease in FSH receptors, but increased both basal and GMP-P(NH)P-stimulated adenylate cyclase activities. These results demonstrate that GnRHa causes marked inhibition of gonadotropin receptor expression in the basal and FSH-stimulated ovary. This decrease in gonadotropin receptors is an important component of the mechanism by which GnRH agonists inhibit ovarian gonadotropin-sensitive adenylate cyclase activity. In addition, these peptides exert stimulatory effects upon ovarian weight and basal adenylate cyclase activity, and cause an increase in PRL receptors and luteinization of mature ovarian follicles.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenylyl Cyclases↗
PubMed1984

Inhibitory actions of adenosine on follicle-stimulating hormone-induced differentiation of cultured rat granulosa cells.

To determine the effects of adenosine on follicle-stimulating hormone (FSH)-induced differentiation, granulosa cells isolated from the ovaries of diethylstilbestrol-treated immature rats were cultured with increasing concentrations of the nucleoside and modulators of adenosine action. Although adenosine had no effect on basal granulosa cell function during 48 h of culture, concentrations of the nucleoside from 10 microM to 1 mM progressively inhibited FSH-induced responses, including progesterone production and expression of FSH and luteinizing hormone (LH) receptors. Adenosine had biphasic effects on FSH-stimulated cAMP accumulation, causing inhibition of cAMP production at 10 to 100 microM and stimulation at higher concentrations. The enhancement of cAMP production by 1 mM adenosine occurred during the first 24 h of culture, while both 100 microM and 1 mM adenosine reduced FSH-stimulated cAMP production from 24 to 48 h. The inhibitory effects of adenosine were prevented by adenosine deaminase and dipyridamole, an inhibitor of adenosine transport, and were antagonized by 1-methyl-3-isobutylxanthine. The inhibition of cAMP and progesterone production by adenosine was partially overcome when cells were washed and reincubated with forskolin, but not with FSH. Adenine, guanosine, and inosine at concentrations of 100 microM did not modify FSH-induced cAMP formation or LH receptor induction. These results indicate that adenosine exerts predominantly inhibitory actions on hormone-induced granulosa cell differentiation, as manifested by prominent reductions in steroidogenesis and gonadotropin receptor expression.

1-Methyl-3-isobutylxanthine↗
PubMed1984

Induction of granulosa cell differentiation by forskolin: stimulation of adenosine 3',5'-monophosphate production, progesterone synthesis, and luteinizing hormone receptor expression.

The effects of forskolin on the acquisition of differentiated functions in cultured ovarian granulosa cells were compared with the actions of FSH and prostaglandin E2 (PGE2). In 48-h granulosa cell cultures from immature diethylstilbestrol-treated rats, 100 microM forskolin caused a 45-fold increase in cAMP accumulation and stimulated progesterone production from undetectable levels (less than 0.2 ng/ml) to 80 ng/ml. The forskolin-induced increase in cAMP was similar to the maximum response to FSH, and progesterone production was about 50% of that elicited by FSH. PGE2 also enhanced cAMP and progesterone production in a concentration-dependent manner, with a maximum 8-fold increase in cAMP accumulation and an increase in progesterone to 5.6 ng/ml when the PGE2 concentration was 10 micrograms/ml. The time course of forskolin-stimulated cAMP production was notable for its rapid rise to the maximum level during the first 24 h of culture, followed by a plateau for up to 72 h. This contrasted with FSH-stimulated cAMP production, which increased progressively for up to 72 h when measured at 24-h intervals. LH receptor levels were low in untreated cells and after exposure to the various stimuli for 24 h, but increased 9- to 11-fold after culture with FSH or forskolin for 48-72 h. PGE2-induced LH receptor formation was about 20% of that seen after FSH stimulation. Forskolin enhanced cAMP and progesterone production in response to FSH and choleragen, but impaired the effects of these ligands on LH receptor formation. Exposure of the cultured cells to a potent GnRH agonist inhibited forskolin-induced progesterone and LH receptor synthesis, but did not influence forskolin-stimulated cAMP production. These results demonstrate the ability of forskolin to serve as a nonhormonal stimulator of granulosa cell differentiation and indicate the importance of cAMP in this process, as well as the ability of GnRH agonists to exert inhibitory effects on post-cAMP steps in cellular maturation.

Animals↗
PubMed1984

Estrogens enhance the adenosine 3',5'-monophosphate-mediated induction of follicle-stimulating hormone and luteinizing hormone receptors in rat granulosa cells.

The effects of estrogens on cAMP-induced FSH and LH receptor expression were studied in granulosa cells isolated from immature diethylstilbestrol-implanted rats. Although estradiol alone had negligible effects on granulosa cell maturation, estradiol concentrations from 10(-11)-10(-8) M progressively enhanced cAMP production and gonadotropin receptor formation in choleragen-stimulated cells. During 48 h of culture, estradiol augmented cAMP levels by 2-fold, LH receptors by 4- to 6-fold, and FSH receptors by 20-40%. Estradiol also enhanced the extent of LH and FSH receptor formation by other cAMP-inducing ligands, including FSH, prostaglandin E2, and forskolin. The stimulatory action of 8-bromo-cAMP on gonadotropin receptors was also increased by estradiol, indicating that part of the estrogenic effect was exerted on cAMP-activated processes. Scatchard analyses indicated that estradiol increased the number of choleragen-induced FSH receptors from 2,600 to 3,200/cell and of LH receptors from 13,000 to 86,000/cell with no changes in receptor binding affinity. Choleragen-stimulated cAMP accumulation was enhanced by estradiol during the later stages of culture (after 30 h), while increased LH receptors were detected by 30 h and FSH receptors by 43 h. The stimulatory effects of estradiol were not due to increased cellular proliferation and were also exerted by other estrogens, including estrone and diethylstilbestrol. Androgens, including testosterone and androstenedione, also amplified choleragen action. This effect was largely through conversion to estrogens, since dihydrotestosterone, a nonaromatizable androgen, did not markedly enhance LH receptor formation by choleragen. In contrast, progestins and pregnenelone had no facilitative effect on choleragen-induced responses. Although cortisol and dexamethasone increased choleragen-induced cAMP accumulation, only cortisol elevated LH receptors, and dexamethasone inhibited FSH receptor formation. These results demonstrate that estrogens enhance both ligand-induced cAMP production and cAMP-activated responses during granulosa cell differentiation. In particular, estrogens exert a major effect on the levels of gonadotropin receptors expressed in response to FSH and other cAMP-inducing ligands.

Androgens↗
PubMed1984

Dependence of cyclic nucleotide production and luteinizing hormone receptor formation upon ribonucleic acid synthesis in cultured rat granulosa cells.

The role of newly synthesized RNA in the differentiation of granulosa cells isolated from diethylstilbestrol-treated immature rats was studied during culture with actinomycin D. Choleragen-induced LH receptor formation and cGMP production at 48 h were completely inhibited by actinomycin D (greater than or equal to 100 ng/ml) added as late as 20 h after the initiation of culture and were partially reduced by addition of the antibiotic from 30-48 h. In contrast, addition of actinomycin D to freshly prepared cells enhanced choleragen-stimulated cAMP accumulation during the 48-h culture period. This effect was caused by both elevation of adenylate cyclase activity at 3 and 6 h of culture and inhibition of choleragen-induced phosphodiesterase activity during culture. The increase in cAMP production by actinomycin D was confined to the first few hours of culture, since the antibiotic did not enhance cAMP levels when added after 3 h and significantly reduced cAMP accumulation when added from 20-48 h of culture. Actinomycin D inhibited choleragen-stimulated incorporation of [3H]uridine into RNA of freshly prepared cells by 65% and reduced both RNA synthesis and incorporation of [3H]leucine into protein at 20 and 48 h of culture by approximately 90%. In untreated cells, RNA and protein synthesis and phosphodiesterase activity increased to a larger extent from 20-48 h than after choleragen treatment, but did not lead to elevated cAMP levels or LH receptors. These results suggest that the cAMP-induced syntheses of RNA and protein that are specific for increases in cGMP production and LH receptor formation occur predominantly during the second day of granulosa cell culture. In contrast, cAMP production can be markedly altered by changes in RNA and protein syntheses during the first hours of culture.

Adenosine Triphosphate↗
PubMed1983

gamma-Glutamyl transpeptidase in human amniotic fluid and in fetal tissues.

The activity of gamma-glutamyl transpeptidase (GGT) was measured in 360 amniotic fluid samples from second and third trimester pregnancies with fetal and maternal disorders. The enzyme level was within the normal range in all but one of the 18 second trimester pregnancies with congenital malformations. On cellulose acetate electrophoresis, GGT fractionated as an alpha 1-band in all mid-trimester samples tested. Highly elevated GGT values were found in five samples from the third trimester gestations with fetal gastroschisis, hydrops fetalis and Meckel's syndrome. The enzyme in these samples showed alpha 1-mobility while most of the third trimester amniotic fluids contained GGT with beta-mobility. Considerable GGT activity was observed in several fetal tissues that are in contact with the amniotic fluid. Highest levels were found in meconium and bile from a second trimester fetus. The total activity and electrophoretic mobility of GGT in late amniotic fluid and in urine from newborns was similar.

Amniotic Fluid↗
PubMed1983

Hormonal regulation of a plasma membrane phosphodiesterase in differentiating granulosa cells. Reciprocal actions of follicle-stimulating hormone and a gonadotropin-releasing hormone agonist on cAMP degradation.

The activity of a plasma membrane cAMP-phosphodiesterase in cultured ovarian granulosa cells was regulated by follicle-stimulating hormone (FSH) and the gonadotropin-releasing hormone (GnRH) agonist [D-Ala6]des-Gly10-GnRH N-ethylamide (GnRHa). Degradation of cAMP was similar in cultures treated with FSH alone or FSH plus GnRHa when the labeled cyclic nucleotide was added from 24 to 42 h of culture. However, at 48 h and subsequent times of incubation, cAMP phosphodiesterase activity was significantly higher in cells incubated with FSH plus GnRHa. Phosphodiesterase activity was progressively increased by GnRHa concentrations between 10(-13) and 10(-10) M, and was maximally stimulated by 10(-9) M GnRHa. In comparison with control cells, FSH lowered the Vmax of cAMP catabolism by the high (1 microM cAMP substrate) and the low (50 microM) affinity phosphodiesterase, while GnRHa raised enzyme activity toward control levels. These actions of FSH and GnRHa were specific for a plasma membrane phosphodiesterase that was accessible to extracellular cAMP, since extracellular substrate was hydrolyzed, no intracellular uptake of [3H]cAMP was observed, and only a small fraction (10%) of cAMP was catabolized in the incubation medium in the absence of cells. Further, the actions of FSH and GnRHa on the membrane enzyme were the opposite of those observed when total phosphodiesterase activity was measured in cellular sonicates. Hormonal changes in phosphodiesterase activity were not due to leakage of the enzyme from damaged cells since a constant percentage of cAMP hydrolysis in the medium was observed during culture. Analysis of cAMP catabolites in granulosa cells indicated that the phosphodiesterase reaction product, 5'-AMP, was rapidly converted to adenosine by a plasma membrane 5'-nucleotidase, independent of the cellular hormonal status. These results indicate that the opposing actions of FSH and GnRHa upon granulosa cell differentiation include modulation of cAMP degradation at the plasma membrane level.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1983

Alkaline phosphatase activity in amniotic fluid in pregnancies with fetal disorders.

Alkaline phosphatase (ALP) activity was determined in 255 amniotic fluid samples collected by amniocentesis between 15 and 39 weeks of gestation. The samples were originally used for chromosomal analysis and/or alpha-fetoprotein measurements. The mean ALP activity in early amniotic fluid from pregnancies with fetal trisomy 18 and 21 syndromes was half of that found in the controls. Highly elevated ALP activity (over 10 times the median level) was found in 14 samples. Two of these pregnancies had normal outcome. Three samples were from pregnancies with intrauterine fetal death. Fetal disorders, including abdominal wall defect (four cases), Meckel's syndrome (two), hydrops fetalis syndrome (two) and genital anomaly (one), were observed in nine cases. Moderately elevated ALP activity (over three times the median) was found in 10 cases, including five pregnancies with a preterm labour shortly after the sample collection. The results indicate that elevated ALP activity in the third trimester amniotic fluid is often associated with fetal disorders.

Alkaline Phosphatase↗
PubMed1983

Accumulation of prolactin in human seminal vesicles as revealed by immunohistochemical studies.

The immunoperoxidase technique was used to identify PRL in human seminal vesicles. PRL reactivity was seen as a strong, specific, perivascular staining in the venous plexuses of the invaginations between the folds in the seminal vesicle walls as well as a diffuse staining in the subepithelial stroma. The immunohistochemical staining methods used in this study do not allow any conclusive speculation on the mechanisms by which high concentrations of PRL in the seminal plasma arise, because no distinct cells could be identified as actively producing and secreting PRL by the current techniques.

Humans↗
PubMed1983

Inhibitory actions of a gonadotropin-releasing hormone agonist on ovarian follicle-stimulating hormone receptors and adenylate cyclase in vivo.

The regulation of ovarian gonadotropin-sensitive adenylate cyclase and FSH receptors was studied in hypophysectomized diethylstilbestrol-primed rats treated with FSH and/or the potent GnRH agonist [D-Ala6]des-Gly10-GnRH N-ethylamide (GnRHa). The animals were treated with 7.5 micrograms ovine FSH twice daily for 2 days, either alone or with 10 micrograms GnRHa. FSH-stimulated adenylate cyclase activity was augmented by 2.5- to 3.5-fold in the presence of 5'-guanyl-imidodiphosphate. Adenylate cyclase responses to FSH were almost completely abolished by GnRHa treatment in ovarian homogenates from control animals and rats treated with FSH. This inhibition was receptor specific, since GnRHa did not block adenylate cyclase stimulation by prostaglandin E2 or isoproterenol. No inhibition of 5'-guanyl-imidodiphosphate- or sodium fluoride-stimulated adenylate cyclase activity was noted after any hormone treatment. When GnRHa treatment was initiated at 12, 24, or 36 h during the 2-day period of FSH treatment, inhibition of both FSH- and LH-stimulated adenylate cyclase was observed in ovaries collected at 48 h. Whereas FSH treatment increased the ovarian FSH receptor concentration by more than 100%, concomitant treatment with GnRHa prevented this increase and reduced FSH receptors to 60% of the control level. Treatment with GnRHa alone caused a 65% decrease in FSH receptor levels below the untreated control values. Histological analysis of hormone-treated ovaries indicated that FSH stimulated follicle growth and antrum formation, but caused little luteinization. GnRHa did not completely prevent the effects of FSH on follicle growth, but did induce degeneration and premature cleavage of ova. GnRHa alone suppressed the diethylstilbestrol-stimulated mitotic activity, slightly increased degenerative changes in granulosa cells, and caused oocyte cleavage and premature antrum formation. These findings demonstrate that GnRHa inhibits FSH-dependent adenylate cyclase by a mechanism involving the loss of binding sites for FSH. It is also evident that only short term exposure to GnRHa is necessary for expression of the inhibitory action of the peptide upon FSH- and LH-stimulated adenylate cyclase.

Adenylyl Cyclases↗
PubMed1983

Calcium dependence of the inhibitory effect of gonadotropin-releasing hormone on luteinizing hormone-induced cyclic AMP production in rat granulosa cells.

The role of calcium in the inhibitory action of the GnRH superagonist, [D-Ala6]des-Gly10-GnRH N-ethylamide (GnRHa), on LH-stimulated cAMP production was studied in cultured granulosa cells obtained from immature hypophysectomized diethylstilbestrol (DES)-implanted rats. After culture for 48 h with FSH to induce LH receptors, cells were incubated for 2 h with LH or LH plus GnRHa. In this system, the cAMP response to LH was independent of extracellular calcium. In the presence of 0.25 to 1 mM extracellular calcium, 10(-8) M GnRHa caused a 15 to 40% inhibition of LH-stimulated cAMP production. Omission of extracellular calcium completely abolished the inhibitory effect of GnRHa upon LH-induced cAMP production. The inhibitory effects of GnRHa on prostaglandin E2 (PGE2) and isoproterenol-induced cAMP productions were also markedly reduced in the absence of extracellular calcium. Addition of the phosphodiesterase inhibitor, 1-methyl-3-isobutylxanthine (MIX), reversed the inhibitory action of GnRHa on LH-induced cAMP production. These results demonstrate that extracellular calcium is necessary for the acute inhibitory action of GnRHa upon LH-induced cAMP production in cultured rat granulosa cells, and indicate that increased degradation of cAMP may be a contributing factor for this effect of GnRHa.

1-Methyl-3-isobutylxanthine↗
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

Metabolic control and serum hormone levels in relation to retinopathy in diabetic pregnancy.

The occurrence and progression of retinopathy were related to the mean blood glucose levels and the serum concentrations of prolactin, human placental lactogen, oestradiol and progesterone in 57 pregnant insulin-dependent diabetic patients. Fifteen patients had frank retinopathy, of whom eight showed a marked increase in retinopathy. The initial blood glucose levels were significantly higher in patients whose retinopathy progressed, whereas during the second and third trimester similar blood glucose levels were achieved in all groups. Serum concentrations of progesterone and human placental lactogen were significantly increased in diabetic patients during the last trimester when compared with those in normal pregnancies, and during the second trimester, patients with retinopathy showed significantly higher concentrations than those without, but no significant difference was found in oestradiol values. The eight patients with progressive retinopathy showed progesterone, human placental lactogen and oestradiol levels at or above the upper limit of the normal range. Throughout gestation, serum prolactin concentrations were significantly lower in diabetic patients than in healthy subjects. No correlation was found between serum prolactin values and the occurrence of retinopathy.

Adult↗
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↗