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Biomedical subjects

C Magnusson

Publications and source records attributed to C Magnusson.

At least 55 records · Page 3Linked to original sources
PubMed1986

Oxygen consumption by the mouse blastocyst at activation for implantation.

When activated from delayed implantation by an oestrogen injection, mouse blastocysts rapidly increase their oxygen consumption and degree of cytochrome oxidase staining. In the present study, oxygen consumption was augmented to a similar extent also in vitro using a culture system known to permit trophoblast outgrowth. To see whether the increase of oxidative phosphorylation needs the synthesis of new protein or just activation of enzyme precursors, different anti-metabolites were added to the cultures. Inhibitors of transcription (cytosine arabinoside and alpha-amanitin) and RNA translation in the mitochondria (chloramphenicol) were all without effect, whereas blocking cytoplasmic translation by cycloheximide inhibited the increase in oxygen consumption after blastocyst culture. The results suggest that the trophoblast control of oxidative phosphorylation lies post-transcriptionally, and that activation of oxygen consumption involves translation of preformed RNA templates in the cytoplasm.

Animals↗
PubMed1985

Gonadotropin-induced inhibition of oxygen consumption in rat oocyte-cumulus complexes: relief by adenosine.

In the cumulus-oocyte complex (COC), as well as in the whole ovarian follicle, gonadotropins stimulate glycolysis, measured as lactate accumulation. In contrast to this, COC oxygen consumption is decreased by gonadotropins. One possible explanation for this inhibition is a competition for a limited supply of cofactors, common for both the glycolytic pathway and the respiratory chain. In the present study, addition of adenosine to COCs cultured with gonadotropins restored the oxygen consumption to basal levels. This effect was specific for metabolizable adenosine. Other nucleosides or non-metabolizable 2-chloro-adenosine had no effect. Adenosine also increased ATP and decreased lactate accumulation by the COC. The nucleoside transport inhibitor dipyridamol abolished the effects of adenosine on oxygen consumption and ATP accumulation. Taken together, these results support the hypothesis that a relative lack of adenosine-derived cofactors is probably involved in the decrease of oxygen consumption in vitro by gonadotropin-stimulated cumulus cells.

Adenosine↗
PubMed1985

Oocyte maturation as regulated by follicular factors.

Follicular fluid (FFl), obtained from 24 women treated with clomiphene/hCG in an in vitro fertilization program, was characterized with respect to steroid hormone levels and oocyte maturation inhibitor (OMI) activity. Three FFl samples apparently were derived from cystic follicles and contained low steroid levels and no OMI activity in an in vitro rat oocyte assay. The remaining 21 follicles contained normal preovulatory steroid levels and mature and generally fertilizable oocytes. In 7 of these follicles the FFl (at 50% concentration) significantly inhibited rat oocyte meiosis, while 14 exerted no OMI activity. The results confirm earlier work on porcine and human FFl, suggesting that the putative OMI activity declines with follicular maturation.

Animals↗
PubMed1984

Stimulation and inhibition of rat oocyte meiosis by forskolin.

The adenylate cyclase activator forskolin was used to study the role of cAMP for oocyte meiosis and follicular steroid secretion. Follicular and cumulus cAMP production was stimulated dose-dependently by forskolin, as was the follicular secretion of progesterone, testosterone and estradiol. Forskolin induced meiosis in follicle-enclosed oocytes with a maximal effect at 1 microM, with lower and higher concentrations being less effective. The spontaneous resumption of meiosis in isolated cumulus-enclosed oocytes was dose-dependently retarded by forskolin. Meiosis of cumulus-free oocytes was also retarded but only slightly. These data support the earlier hypothesis that a limited increase in follicular cAMP levels triggers meiosis, whereas sustained levels of cAMP in the oocyte itself prevent meiosis.

Animals↗
PubMed1984

Effect of a GnRH analogue on rat granulosa cell lactate production in vitro.

The effect of a GnRH analogue [D-Ala6, des-Gly10-NH2)-GnRH-ethylamide,GnRHa) on granulosa and cumulus cell glycolysis in presence or absence of FSH was studied. Cumulus complexes and granulosa cells from PMSG-treated rats were cultured in Eagle's minimal essential medium (MEM) for a period of 72 h. Media were changed at 24 and 48 h and lactate content was assayed by fluorimetry. GnRHa alone stimulated lactate production in granulosa cells. GnRH combined with FSH increased lactate production in granulosa cells during the 0-24 h period and decreased it during the 48-72 h period as compared to FSH alone. GnRHa did not stimulate lactate production in cumulus complexes during 72 h culture in MEM, while FSH did. In a less complex culture medium, BMOC, GnRHa caused a small increase in lactate production and slightly enhanced the FSH effect. In conclusion, GnRHa has a direct stimulatory effect on granulosa cell glycolysis. GnRHa also modulates the FSH stimulation of granulosa cells biphasically, i.e. early enhancement (0-24 h) and late inhibition (48-72 h). GnRHa has no consistent direct effects on cumulus cell glycolysis.

Animals↗
PubMed1983

In vitro inhibition of rat oocyte meiosis by human follicular fluid fractions.

We studied the effect of low molecular weight fractions of human follicular fluid (FF1) on rat oocyte meiosis and progesterone secretion by the granulosa cells. Steroid-free FF1 extracts were filtered through Sephadex G50 gel. One highly retarded fraction was obtained (GF-3), which was either used for testing or further purified by filtration on Sephadex G10, the G10-3 fraction of which was used for experiments. The GF-3 and G10-3 fractions of FF1 inhibited (in a dose-dependent and reversible manner) meiosis of isolated rat oocytes during a 4-h culture. Similarly treated fractions of serum had no effect. The inhibition was not abolished by ether extraction, trypsin treatment, heating to 56 degrees C for 1 h or boiling for 5 min, whereas heating to 105 degrees C for 18 h decreased the effect. Gonadotropin-stimulated progesterone secretion by cumulus and mural granulosa cells was also dose-dependently and reversibly inhibited by the GF-3 fractions. Our results confirm those obtained in earlier studies on porcine oocyte maturation inhibitor (OMI).

Animals↗
PubMed1983

Biphasic effect of gonadotropin releasing hormone on progestin secretion by rat granulosa cells.

The effect of an agonistic gonadotropin releasing hormone (GnRH)-analog (D-Ala6, des-Gly10-NH2-GnRH-ethylamide, GnRHa) on granulosa cell steroidogenesis in the presence or absence of follicle-stimulating hormone (FSH) or luteinizing hormone (LH) was studied. Granulosa cells, isolated from preovulatory follicles of pregnant mare's serum gonadotropin (PMSG)-treated immature rats or from the less mature follicles of untreated immature rats, were cultured for a period of 72 h with daily changes of medium, and progesterone and its metabolite, 20 alpha-dihydro-progesterone (20 alpha-OHP), were assayed in the medium. In granulosa cells from preovulatory follicles, LH and FSH caused a much greater stimulation of steroidogenesis than did GnRHa. There appeared to be no interaction between GnRHa and FSH during the first 10 h, but at 24 h and later the presence of GnRHa clearly inhibited the steroidogenic response to LH and FSH. Steroidogenesis in granulosa cells from immature rats was considerably lower and the effects of GnRHa and FSH alone less pronounced. In these cells, FSH-stimulated progesterone secretion was inhibited by GnRHa only at 72 h. In contrast, 20 alpha-OHP secretion in the same cultures was potentiated by the combined presence of FSH and GnRHa. In conclusion, it seems as though the effects of GnRHa on granulosa cell steroidogenesis varies with exposure time, the initial response being stimulatory and the later inhibitory. Furthermore, the response is also to some extent determined by the maturational stage of the granulosa cells.

20-alpha-Dihydroprogesterone↗
PubMed1983

Gonadotrophins stimulate lactate production by rat cumulus and granulosa cells.

Oocyte-cumulus complexes and mural granulosa cells, respectively, isolated from pre-ovulatory rat follicles and cultured in lactate-free medium showed a continuous accumulation of lactate during a 1 to 7 h incubation. Lactate production was stimulated by gonadotrophins, both when administered in vivo and in vitro, with the exception that LH given in vivo did not affect granulosa cell lactate production. Since the oocyte is known to have specific demands on energy substrate, it is suggested that the lactate produced is important for the growing and maturing oocyte.

Animals↗
PubMed1983

Oxygen consumption by rat oocytes and cumulus cells during induced atresia.

Oxygen consumption was measured in denuded oocytes and oocyte-cumulus complexes isolated from atretic rat follicles. Adult cyclic rats or immature PMSG-treated rats were used, and follicular atresia was induced by hypophysectomy on the morning of pro-oestrus or by repeated pentobarbitone injections beginning on the day of pro-oestrus. The later stages of atresia were accompanied by meiosis-like changes in the oocytes. Oxygen consumption by oocytes that had resumed meiosis (germinal vesicle breakdown, GVB) was higher than in oocytes with an intact germinal vesicle, a change similar to that observed in oocytes maturing in healthy follicles. This may indicate that the meiotic process in the atretic follicles is similar to that in normal ones. Oxygen consumption by the cumulus cells was not altered during pentobarbitone-induced atresia. Hypophysectomy led to a rapid and marked increase in cumulus oxygen consumption in cyclic rats but there was no change in PMSG-treated young animals. Since both pentobarbitone-treatment and hypophysectomy result in follicular atresia, but changes in cumulus respiration occurred only in hypophysectomized adult rats, it is concluded that an increase in cumulus respiration is not inherent to the atretic process.

Animals↗
PubMed1983

Aspects concerning the role of prostaglandins for ovarian function.

The present review briefly summarizes the current view of the mechanisms whereby prostaglandins (PGs) may act to modulate ovarian function. Particular concern is devoted to the aspects of ovarian function which are under current investigation by the authors, namely follicular maturation and rupture, granulosa cell and oocyte maturation, and the formation and maintenance as well as the regression of the corpus luteum (CL). PGs are formed in the granulosa cells of the preovulatory follicle in response to gonadotropin action and are at their highest levels around the time of ovulation. PGs are believed to be obligatory for follicular rupture, but their mechanism of action is still unknown. In the process of oocyte maturation PGs can mimic the stimulatory effects induced by LH or hCG, but are probably not obligate mediators of these effects. The importance of PGs for CL formation and maintenance is so far unsettled, and PGs may be regarded more as modulators than as inducers for these processes. The most well-documented effect of PGs is the induction of CL regression. Evidence is presented that PGs may have this effect also in the human.

Alprostadil↗
PubMed1982

Ovulation induced by a gonadotropin releasing hormone analog in hypophysectomized rats involves prostaglandins.

A potent analogue of gonadotropin releasing hormone [D-Ala6- Des-Gly10-NH2]-GnRH ethylamide (GnRHa) caused oocyte maturation and ovulation when injected in the afternoon of proestrus in immature PMSG-treated female rats, hypophysectomized on the morning of proestrus. This action of GnRHa was accompanied by a marked increase in ovarian PGE levels. Furthermore, the pretreatment of the animals with a prostaglandin synthetase inhibitor (indomethacin) completely inhibited this PGE increase and ovulation. These data suggest a role for prostaglandins in GnRHa induced ovulation.

Animals↗
PubMed1982

A gonadotrophin-releasing hormone (GnRH) antagonist inhibits GnRH- but not LH-induced meiosis in follicle-enclosed rat oocytes in vitro.

Previous studies have shown that gonadotrophin-releasing hormone (GnRH) can induce resumption of meiosis in follicle-enclosed rat oocytes. In the present study a GnRH antagonistic analogue ([D-pGlul,D-Phe2,-D-Trp3,6]LRF) was found to effectively abolish the stimulatory effect of a GnRH agonist upon resumption of meiosis and lactate accumulation in isolated pre-ovulatory rat follicles but the have no effect on LH stimulation of these parameters. It is concluded that although LH and GnRH can evoke a similar response they act through separate receptor sites and that it is unlikely that GnRH mediates the effect of LH on meiosis or glycolysis.

Animals↗
PubMed1982

Comparison between the progestin secretion responsiveness to gonadotrophins of rat cumulus and mural granulosa cells in vitro.

Several studies have shown differences in gonadotrophin receptor content between different granulosa cell (gc) populations within the ovarian follicle, but little is known about the gonadotrophin sensitivity in gc from different parts of the follicle. This study is an investigation of progestin synthesis and responsiveness to highly purified human and partly purified rat gonadotrophins. It involves short-term culture of rat cumulus and mural gc obtained from preovulatory follicles of PMSG-treated immature rats. The responsiveness to FSH in terms of progestin accumulation was similar in the two gc populations, whereas the responsiveness to LH was greater in the mural gc than in the cumulus. The morphological response in the cumulus cells (mucification) correlated with the steroidogenic response. The pattern of progestin synthesis differed between the two gc populations. In the cumulus gc progesterone was dominant, whereas 20 alpha-dihydroprogesterone was the main progestin secreted in the mural gc. The difference in responsiveness to gonadotrophins correlates well with the reported differences in receptor content in the two gc populations.

20-alpha-Dihydroprogesterone↗
PubMed1981

Further studies on the gonadotrophin-induced inhibition of respiration in the preovulatory rat cumulus oophorus.

It has been shown earlier that LH decreases the oxygen consumption of the rat cumulus oophorus cells, i.e. the granulosa cells immediately surrounding the follicular oocyte. The decrease occurs in the preovulatory period at the time when the oocyte resumes and completes meiosis. This study examines in more detail the time-course of LH-induced inhibition of cumulus respiration. The results show that when isolated cumuli were exposed to LH during in vitro culture a significant inhibition of respiration occurred within one hour. When follicle-enclosed cumuli were exposed to LH, in vivo or in vitro, the decrease in respiration was not evident until 4 hours after the hormone exposure. By this time oocyte maturation was already in progress. The results suggest that the decrease in cumulus respiration may not be directly linked to the onset of oocyte meiosis.

Animals↗