Biomedical subjects

K M Menon

Publications and source records attributed to K M Menon.

At least 55 records · Page 3Linked to original sources

PubMed1989

Evidence for monomeric and oligomeric hormone-binding domains in affinity-purified gonadotropin receptor from rat ovary.

Rat ovarian lutropin/choriogonadotropin receptor was purified from a Triton X-100-solubilized membrane preparation by affinity chromatography with Affi-Gel 10 coupled to purified human choriogonadotropin. The affinity-purified receptor preparations contained a single class of high-affinity binding sites for 125I-labeled human choriogonadotropin, with an equilibrium dissociation constant (Kd) of 2.5 x 10(-9) M, which is comparable to the Kd values for membrane-bound and solubilized receptors. The purified receptor appeared as two dominant bands with molecular weights of 135,000 and 92,000 after sodium dodecyl sulfate/polyacrylamide gel electrophoresis (SDS/PAGE) under nonreducing conditions. These two bands were also detected in subsequent direct ligand blotting analysis when the purified receptor was electrophoretically transferred to a nitrocellulose membrane after SDS/PAGE under nonreducing conditions. When the individual affinity-purified receptor bands were electroeluted from the gel and analyzed again by SDS/PAGE under nonreducing conditions, both the Mr 92,000 and the 135,000 proteins retained their original molecular form even when 8 M urea was included in the gel. However, when the electrophoretically purified Mr 92,000 and 135,000 bands were subjected to SDS/PAGE under reducing conditions, the Mr 135,000 species was almost completely converted to a Mr 92,000 band, but the Mr 92,000 species did not undergo any alteration in molecular weight. The results suggest that the lutropin/choriogonadotropin receptor from rat ovary exists in two molecular forms, and the higher molecular weight form appears to be composed of disulfide-linked Mr 92,000 subunit, which comprises the hormone-binding domain.

Animals↗

PubMed1989

Cholesterol flux between high density lipoproteins and cultured rat luteal cells.

Although high density lipoprotein (HDL) is a promoter of cholesterol efflux from peripheral cells, in steroidogenic tissues it has been shown to provide cholesterol for steroid synthesis. The present study examines the dynamics of cholesterol exchange between HDL particles and rat luteal cells. Cholesterol influx was measured by following the uptake of label from HDL particles labeled with [3H]cholesterol or [3H]cholesteryl linoleate. The efflux of cholesterol was simultaneously measured by incubating [3H]cholesterol-labeled luteal cells with unlabeled HDL. Conversion of endogenous and lipoprotein-derived steroids to progestins was also determined. The results showed that HDL promotes both influx and efflux of cholesterol in those cells. The amount of influx exceeds efflux, thus resulting in a net uptake of cholesterol from HDL by rat luteal cells. The relative utilization of endogenous vs. HDL-derived cholesterol for steroid synthesis was also examined. The results show that only a fraction of the HDL-derived cholesterol was converted directly to steroids. The fraction that was converted depended on the HDL concentration and had no apparent relation to the incubation time. These results show that although cholesterol flux in luteal cells is bidirectional in the presence of HDL, the influx exceeds the amount of efflux, and the internalized cholesterol is diluted with the endogenous cholesterol pool before it is converted to steroids.

Animals↗

PubMed1989

Regulation of rat luteal cell high density lipoprotein receptors: up-regulation in response to changes in intracellular cholesterol concentration.

High density lipoprotein (HDL)-derived cholesterol is preferentially utilized by rat luteal cells for steroid synthesis. This process is mediated, at least in part, by the HDL receptor. The regulation of the HDL receptor by intracellular cholesterol concentration in the ovary was assessed in the present study. Superovulated rats were treated with 4-aminopyrozolo [3, 4-d] pyrimidine (4-APP), which inhibits lipoprotein synthesis by the liver, to determine the effects of reduced levels of intracellular cholesterol on HDL receptor expression. Pseudopregnant rats were treated with 4-APP or the vehicle on days 3, 4, and 5 of pseudopregnancy. On day 6 rats were killed and ovarian membranes isolated for binding studies. Treatment with 4-APP resulted in almost a 50% decrease in serum cholesterol level 24 h later. A similar effect was observed on the level of ovarian esterified cholesterol. The binding of apolipoprotein E-free HDL to ovarian plasma membranes increased up to 34%. The effects of increased intracellular cholesterol on HDL receptor binding was then determined. Pseudopregnant rats received two injections of aminoglutethimide or vehicle on day 5 of pseudopregnancy at 10 h intervals for a period of 20 h. Rats were decapitated 10 h after the second injection of aminoglutethimide, and [125I] HDL binding studies were performed in ovarian plasma membranes. The treatment increased ovarian free and esterified cholesterol 27% and 70%, respectively. The number of binding sites for HDL in ovarian membranes increased up to 31% in response to the treatment. The evidence suggests that the HDL receptor may play a dual role in HDL metabolism. The receptor may increase to promote influx of cholesterol when intraovarian cholesterol stores are reduced and to promote cholesterol efflux when stores of intraovarian cholesterol are increased. Thus, HDL receptor appears to play a crucial role in the regulation of ovarian cholesterol level.

Adenine↗

PubMed1989

Serum bioactive follicle-stimulating hormone-like activity increases during pregnancy.

It is presently accepted that high circulating steroid levels during pregnancy suppress pituitary immunoreactive FSH (I-FSH) secretion from early pregnancy to term. In this study we tested the hypothesis that bioactive FSH (B-FSH) in the sera of pregnant women would likewise be suppressed. Serum samples were obtained from one woman daily for 21 days after the I-LH surge, and in a second, every 10 min for 10 h on days 10, 20, and 27 after the I-LH surge. Single serum samples were also obtained from women at 2-41 weeks of gestation. In all samples, I-LH/hCG, I-FSH, B-FSH, progesterone (P), and estradiol (E2) were measured. In the first woman, serum I-FSH levels were suppressed from days 9-21 after the LH surge (0.2 +/- 0.04 ng/mL; 1.9 +/- 0.3 IU/L), whereas serum B-FSH increased linearly from 1.7 ng/mL (5.3 IU/L) on day 9 post-I-LH surge to 6.0 ng/mL (18.6 IU/L) on day 17 (r = 0.91; P less than 0.01) and remained elevated through day 21. In the second woman, the mean +/- SE of the serum I-FSH concentrations were 0.7 +/- 0.04, 0.1 +/- 0.01, and 0.1 +/- 0.01 ng/mL (5.5 +/- 0.3, 0.9 +/- 0.1, 1.1 +/- 0.1 IU/L) on days 10, 20, and 27 post-I-LH surge, respectively. The mean serum B-FSH concentrations increased from 3.1 +/- 0.2 ng/mL (9.6 +/- 0.7 IU/L) on day 10 to 7.5 +/- 0.6 ng/mL (23.2 +/- 1.7 IU/L) on day 27. Using the DETECT pulse analysis method at the 0.01 confidence level, the serum I-FSH pattern was relatively nonpulsate, while serum B-FSH averaged 8, 7, and 10 pulses/10 h on post-LH surge days 10, 20, and 27. Incremental peak amplitudes were 3.5 +/- 0.7, 4.6 +/- 0.4, and 8.0 +/- 1.3 ng/mL (10.9 +/- 2.2, 14.3 +/- 1.2, and 24.8 +/- 4.0 IU/L), respectively. In the cross-sectional study, serum I-FSH levels remained low, while serum B-FSH concentrations increased from 4.2 +/- 0.8 ng/mL (13.2 +/- 2.5 IU/L) during the early first trimester to 59.3 +/- 2.9 ng/mL (183.8 +/- 9.0 IU/L) by the late third trimester. There was no correlation between serum B-FSH and hCG levels. Incubates of term placentae secreted B-FSH in preference to I-FSH (i.e. B-FSH, 33.0 +/- 9.6 ng/h/g placental tissue; I-FSH, 0.7 +/- 0.1 ng/h/g).(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1988

Differential uptake and metabolism of free and esterified cholesterol from high-density lipoproteins in the ovary.

Rat luteal cells utilize high-density lipoproteins (HDL) as a source of cholesterol for steroid synthesis. Both the free and esterified cholesterol of HDL are utilized by these cells. In this report, we have examined the relative uptake of free and esterified cholesterol of HDL by cultured rat luteal cells. Incubation of the cells with HDL labeled with [3H]cholesterol or [3H]cholesteryl linoleate resulted in 4-6-fold greater uptake of the free cholesterol compared to esterified cholesterol. The increased uptake of free cholesterol correlated with its utilization for progestin synthesis: utilization of HDL-derived free cholesterol was 3-6-fold higher than would be expected from its concentration in HDL. The differential uptake and utilization of free and esterified cholesterol was further examined using egg phosphatidylcholine liposomes containing cholesterol or cholesteryl linoleate as a probe. Liposomes containing free cholesterol were able to deliver cholesterol to luteal cells and support steroid synthesis in the absence of apolipoproteins, and the addition of apolipoprotein A-I (apo A-I) moderately increased the uptake and steroidogenesis. Similar experiments using cholesteryl linoleate/egg phosphatidylcholine liposomes showed that inclusion of apo A-I resulted in a pronounced increase in the uptake of cholesteryl linoleate and progestin synthesis. These experiments suggest that free cholesterol from HDL may be taken up by receptor-dependent and receptor-independent processes, whereas esterified cholesterol uptake requires a receptor-dependent process mediated by apolipoproteins.

Animals↗

PubMed1988

Characterization of rat Leydig cell gonadotropin receptor structure by affinity cross-linking.

The present study was intended to examine the structure of the rat Leydig cell gonadotropin receptor. Leydig cell suspensions were prepared by either collagenase digestion or mechanical disruption of the testes. The cells were incubated with 125I-human chorionic gonadotropin (hCG) following which the bound 125I-hCG was covalently cross-linked to the cell surface receptor using a cleavable (dithiobis(succinimidyl propionate] and a noncleavable (disuccinimidyl suberate) cross-linking reagent. The extracted cross-linked membrane proteins were resolved on sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing and nonreducing conditions and subjected to autoradiographic analysis. Under nonreducing conditions, three radiolabeled bands, in addition to intact hCG and its alpha-subunit, were detected with apparent molecular weights of 184,000, 136,000, and 103,000. However, under reducing conditions, three radiolabeled bands migrated on the gel corresponding to molecular weights of 144,000, 106,000, and 75,000. The binding of 125I-hCG to the receptor was inhibited by hCG and luteinizing hormone, but not by a number of other peptides or proteins. The radiolabeled bands were not detectable in hCG down-regulated Leydig cells. Furthermore, a similar autoradiographic pattern of 125I-hCG-linked complexes was seen when the 125I-linked receptor complex was subjected to immunoprecipitation with anti-hCG antibodies followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In addition, evidence was obtained indicating that these three labeled bands were derived from the same molecular species. The data suggests that the hCG receptor in Leydig cell is probably an oligomeric complex with a molecular weight of about 250,000, which is composed of three polypeptide chains of molecular weights 121,000, 83,000, and 52,000 held together through noncovalent forces. Additionally, collagenase treatment of Leydig cells does not appear to alter the autoradiographic pattern of the 125I-hCG-linked receptor.

Animals↗

PubMed1988

Studies on the mechanism of action of prostaglandin F2 alpha induced luteolysis in rats.

The effects of prostaglandin F2 alpha (PGF2 alpha) administration on the utilization of low density lipoprotein (LDL) and progesterone secretion were examined in dispersed luteal cells from rat ovaries. Immature rats were rendered pseudopregnant with administration of pregnant mare serum gonadotropin and human chorionic gonadotropin. Animals were sacrificed at different times after PGF2 alpha (5 mg/kg) or vehicle administration on day-5 of pseudopregnancy. Administration of PGF2 alpha in vivo decreased human chorionic gonadotropin (hCG) binding to luteal cell membranes in vitro but enhanced binding of LDL. Utilization of labelled cholesterol for steroid synthesis from reconstituted LDL [(3H)-CL-LDL] by dispersed luteal cells was enhanced following PGF2 alpha administration. This suggests that the LDL pathway is not suppressed during prostaglandin induced luteolysis. Progesterone and total progestin secretion in response to N6-2'-0-Dibutyryladenosine 3'5'-cyclic monophosphate (cAMP) was decreased at 2, 4 and 24 hours following PGF2 alpha administration demonstrating a post-cAMP defect in steroidogenesis. Addition of the hydroxylated sterols, 20 or 25-OH cholesterol as substrate stimulated progesterone secretion in vehicle treated rats in a dose dependent fashion with 20-OH cholesterol being more potent. Progesterone secretion in response to stimulation with luteinizing hormone (LH) and cAMP from vehicle treated rats was less than that observed with 20 or 25-OH cholesterol, indicating that endogenous substrate may be a limiting factor in steroid synthesis. The maximal capacity of luteal tissue to produce progestins following PGF2 alpha administration was determined with 20-OH cholesterol as the substrate. The results suggest that the post-cAMP defect at 4 hours following PGF2 alpha administration may be due to failure of the cells to mobilize endogenous cholesterol. However at 24 hours following PGF2 alpha administration the decreased ability of luteal cells to convert cholesterol to pregnenolone may contribute to decreased progesterone synthesis.

Animals↗

PubMed1988

Estrogen increases precursor for pregnenolone synthesis with temperature-sensitive occupancy of P-450scc in mitochondria of rabbit corpus luteum.

To examine the mechanism of estrogen's direct stimulation of steroidogenesis in the rabbit corpus luteum, we tested the hypothesis that the effect of estrogen on progestin production occurs at the site of processing of the precursor for pregnenolone (i.e. cholesterol) in the mitochondrion. For this purpose, we manipulated a model of estrogen stimulation by 1) removing sc estradiol-filled polydimethylsiloxane capsules from superovulated rabbits on day 9 of pseudopregnancy or 2) leaving the capsules in place to preserve a chronic estrogen stimulus. In the estrogen-deprived rabbits, the serum progesterone level fell precipitously in vivo within 24 h, but in rabbits with chronic estrogen stimulation, serum progesterone levels remained high. Our results show that the loss in progestin production caused by estrogen deprivation could not be attributed to loss of the mitochondrial cytochrome P-450 side-chain cleavage enzyme (P-450scc), a common rate-limiting step in progestin synthesis in many steroidogenic tissues. In addition, we confirmed that there was no loss in the catalytic activity of this enzyme. Treatment with aminoglutethimide in vivo followed by electron paramagnetic resonance spectroscopic analysis of mitochondria (prepared in aminoglutethimide-free buffers) showed that incubation of isolated mitochondria at 37 C and pH 6.2 caused an increased high spin state (g = 8.2 signal) and a concomitant decreased low spin state. This shift from low to high spin states, which is indicative of cholesterol-P-450scc complex formation, occurred in the luteal mitochondria from both estrogen-deprived and estrogen-stimulated rabbits. In further studies to localize estrogen's regulatory point, we determined that the initial (first minute) rate of production of pregnenolone (per mg protein or per U P-450scc) from endogenous precursor proceeded equally fast in mitochondria from estrogen-deprived and those from estrogen-stimulated rabbits. However, the rapid pregnenolone production in the estrogen-deprived group lasted for a shorter time and, after 30 min, yielded less pregnenolone per mg protein or per U P-450scc than did mitochondria from estrogen-stimulated rabbits. Addition of 25-hydroxycholesterol did not increase the initial rate of pregnenolone formation, indicating that precursor availability is not limiting during the initial period. In aggregate, these observations suggest that the effect of estrogen on progestin production in the rabbit corpus luteum is not regulation of the movement of cholesterol to the catalytic site on the inner mitochondrial membrane, even though this is a step in the regulation of protein hormone-stimulated steroidogenesis.(ABSTRACT TRUNCATED AT 400 WORDS)

Aminoglutethimide↗

PubMed1988

Modulation of progesterone synthesis and cytochrome P450 levels in rat luteal cells during human chorionic gonadotropin-induced desensitized state.

Down-regulation of hCG receptors and a steroidogenic lesion in progesterone production were observed in isolated luteal cells after 24-h treatment of pseudopregnant rats with 50 IU hCG. The luteal cells from hCG-desensitized rats exhibited a complete loss of steroidogenic response to lipoproteins in both the absence and presence of hCG. This loss of response was not overcome by the addition of 25-hydroxycholesterol. To examine if the loss of steroidogenic response is due to a transient loss of steroidogenic enzymes or inadequate delivery of substrate cholesterol, cholesterol side-chain cleavage enzyme (P450scc) activity was measured in the isolated mitochondria. No differences appeared in enzyme activity between control and hCG-treated groups. Furthermore, electron paramagnetic resonance spectra of mitochondrial cytochrome P450scc from control and hCG-treated groups exhibited no appreciable differences in low spin electron paramagnetic resonance signal (g = 1.9, 2.2, and 2.4) or high spin EPR signal (g = 8.2), suggesting that the binding of the substrate to P450scc was not impaired. Additionally, the iron sulfur protein signal (g = 1.95 and 2.03) of the reduced mitochondria remained unchanged in the desensitized group. These data were supported by immunoblotting analysis which revealed no difference in the relative amounts of iron sulfur protein or cytochrome P450scc between the two groups. Moreover, the inner mitochondrial membranes, the locus of cytochrome P450scc, showed an identical cholesterol content in control and desensitized mitochondria, indicating that the availability of cholesterol substrate is not impaired during desensitization. These results suggest that the intramitochondrial transfer of cholesterol and cholesterol side-chain cleavage enzyme activity are unaffected in the desensitized state, but an inhibitory substance might be responsible for the lack of steroidogenic response.

Animals↗

PubMed1988

Comparison of peripheral, uterine and cord estrogen and progesterone levels in laboring and nonlaboring women at term.

Although a direct effect of steroid hormones on the initiation of labor has been shown in animals, conclusive data on human parturition are lacking. To elucidate steroid changes associated with human labor, venous serum samples were obtained at cesarean section from the maternal peripheral and uterine veins and umbilical cord vein of seven laboring and seven nonlaboring women at term. Assays of estradiol (E2), estriol (E3) and progesterone (P) revealed that: (1) there is a major concentration difference in all the steroids between peripheral and local values, (2) labor is associated with a significant rise in systemic and local E2 but no change in P, and (3) the increased production of E2 does not appear to be from a fetoplacental source. These data strongly support a modulating role for alterations in steroid hormones at the onset of human labor. The results demonstrate an increase in estrogen, rather than the classic "withdrawal", as the prime factor in E2:P ratio changes associated with labor and suggest that the source of the estrogen increase may be maternal rather than fetal.

Adult↗

PubMed1987

Metabolism of high-density lipoproteins in cultured rat luteal cells.

The uptake of cholesterol from high-density lipoproteins (HDL) labeled with 125I and [3H]cholesterol was examined in cultured rat luteal cells. Luteal cells were incubated with labeled HDL, following which the metabolic fate of the apolipoproteins and cholesterol moieties of the receptor-bound HDL were examined. About 50% of the originally bound HDL apolipoproteins were released into the medium in 24 h by a temperature-dependent process while only 5% of the HDL cholesterol was released unmetabolized. Inclusion of unlabeled HDL in the chase incubation resulted in increased release of apolipoprotein-derived radioactive products without significant change in the release of unmetabolized cholesterol. 60% of the apolipoprotein-derived radioactivity could be precipitated with trichloroacetic acid; the remaining trichloroacetic acid-soluble radioactive fraction was identified as [125I]iodotyrosine. Gel filtration chromatography of the chase-released material showed that the trichloroacetic acid-precipitable products, which contained no detectable amounts of cholesterol, eluted over a range of molecular sizes (9-80 kDa). No intact HDL was retroendocytosed. About 80% of trichloroacetic acid-precipitable products could be immunoadsorbed on anti-apolipoprotein A-I antibody immobilized on CNBr-activated Sepharose, suggesting the presence of fragments containing apolipoprotein A-I. This material was also capable of reassociating with native HDL. Lysosomal inhibitors were partially effective in inhibiting the amount of trichloroacetic acid-soluble products formed. The lysosomal degradation appeared to have no role in the uptake of HDL-derived cholesterol. These studies demonstrate preferential and total uptake of HDL cholesterol by luteal cells, with concomitant degradation of the lipoprotein.

Animals↗

PubMed1987

Induction of high-density-lipoprotein receptors in rat corpus luteum by human choriogonadotropin. Evidence of protein synthesis de novo.

The present studies investigated the specific binding of 125I-labelled high-density lipoprotein (125I-HDL) to plasma membranes. Golgi, rough endoplasmic reticulum and mitochondria/lysosomes, prepared from ovaries of rats injected with human choriogonadotropin (hCG) or 0.9% NaCl. Treatment in vivo with hCG resulted in 2-3-fold induction of 125I-HDL binding activity in all the subcellular organelles. The specific binding of HDL to various subcellular organelles was dependent on the amount of protein, lipoprotein concentration and incubation time. Equilibrium-binding studies revealed comparable Kd values (13-22 micrograms of HDL protein/ml) for HDL binding in all the subcellular organelles tested. Treatment with cycloheximide (2.0 mg/kg body wt.) before hCG administration abolished the induction of HDL receptors, suggesting the involvement of a protein-synthesis-dependent process in receptor induction. Analysis of equilibrium dissociation constants (Kd) for 125I-HDL binding in membranes from hCG-, cycloheximide-and saline-treated animals suggests that the increase in binding was due to an increase in the number of binding sites rather than a change in the affinity. Additionally, pretreatment with tunicamycin, an inhibitor of N-linked glycosylation, had no effect on hCG-mediated receptor induction, suggesting that glycosylation of the receptor may not be necessary for the interaction of HDL with its receptors.

Animals↗

PubMed1987

The effect of insulin on aromatase activity in isolated human endometrial glands and stroma.

Hyperinsulinemic states have been associated with an increased incidence of estrogen-dependent endometrial neoplasia. To study the effect of insulin on the ability of endometrium to aromatize androgens to estrogens, late proliferative endometrium was obtained from normally cycling women at the time of indicated surgery, separated into component glands and stroma, and grown to confluence. Separated gland and stromal cultures were incubated in triplicate with increasing insulin concentrations and epidermal growth factor. Aromatase activity was assayed by the production of tritiated water from tritium-labeled androstenedione. The activity was noted to increase proportionally with increasing concentrations of insulin greater than 10 U/ml, and the effect was specific. These data suggest the following conclusions: (1) Insulin stimulates aromatase activity in both endometrial glands and stroma; (2) hyperinsulinemia may predispose to endometrial neoplasia by enhancing endogenous endometrial estrogen production.

Adult↗

PubMed1987

Luteal phase dysfunction in endometriosis: elevated progesterone levels in peripheral and ovarian veins during the follicular phase.

Endometriosis has been associated with corpus luteum inadequacy and abnormalities of luteal phase progesterone (P) secretion. In this study, abnormal luteolysis, as a second factor of luteal dysfunction, was assessed in 13 women with endometriosis and 25 control patients by measurement of ovarian vein estradiol (E2) and P during the follicular phase. The results reveal that women with endometriosis have (1) significantly lower ovarian vein E2, (2) significantly higher both peripheral and ovarian vein P, and (3) threefold higher P/E2 ratios than controls during the follicular phase. These data support the concept of continued P production from an active corpus luteum well into the follicular phase of the following cycle in women with endometriosis. Failure of adequate luteolysis is a second aspect of luteal dysfunction in endometriosis and strongly supports the growing body of data confirming ovulatory asynchrony in the minimal; endometriosis infertility syndrome.

Endometriosis↗

PubMed1987

Regulation of cholesterol side-chain cleavage enzyme activity by gonadotropin in rat corpus luteum.

The locus of gonadotropin-induced acute stimulation of pregnenolone production by cholesterol side-chain cleavage (CSCC) enzyme containing cytochrome P450 (cytP450scc) was examined in rat corpus luteum. Mitochondria were isolated from pseudopregnant rat ovaries after treatment with different doses of human CG (hCG) (25-200 IU) for 30 min; Electron Paramagnetic Resonance (EPR) spectra of high spin cholesterol complex of cyt P450scc (type I high spin EPR signal) and the cyt P450scc activity were determined. hCG treatment increased the formation of type I EPR spectra compared to that obtained with saline-treated controls, and pretreatment with cycloheximide (30 mg/kg BW) before hCG abolished this increase. The magnitude of type I EPR signal diminished with increasing pH over the range of 6.2-7.3. The type I EPR signal increased with doses of hCG and correlated well with the pregnenolone production. Aminoglutethimide treatment (competitive inhibitor of CSCC) before hCG injection led to an increased accumulation of cholesterol in inner mitochondrial membranes with a corresponding decrease in the outer membrane cholesterol, and cycloheximide treatment inhibited this accumulation. This suggests that the transport of cholesterol to inner mitochondrial membranes from outer membranes is regulated by hCG. In addition, gonadotropin also regulates the redistribution of cholesterol within the inner mitochondrial membranes.

Animals↗

PubMed1986

Evidence that the subunit structure of gonadotropin receptor is preserved during regression of rat corpus luteum.

The level of hCG/LH receptor has been shown to undergo marked changes during the life span of rat corpus luteum. To evaluate whether these fluctuations are due to changes in the receptor subunit structure or receptor protein content, the 125I-hCG binding activity and the receptor subunit structure were determined during different time periods of pseudopregnancy. The maximum 125I-hCG binding activity was observed on day 7, after which it decreased by 20 and 45% on day 11 and day 14, respectively. The Scatchard analysis of 125I-hCG binding data showed that the decrease in binding activity was caused by a change in the number of binding sites rather than a change in the binding affinity. The LH/hCG receptor in ovarian membranes obtained on days 7, 11 and 14 were then characterized by the method of affinity cross-linking. All four subunits of the LH/hCG receptor were detected in the ovarian membranes at all stages while the intensity decreased parallel to a decrease in hCG binding from day 7 to day 14. These results suggest that the decrease in 125I-hCG binding activity in rat ovarian membranes from day 7 to day 14 of pseudopregnancy is due to a decrease in receptor concentration rather than a change in the receptor subunit structure.

Animals↗

PubMed1986

Identification of gonadotropin inducible, high density lipoprotein receptors in the solubilized membranes from rat ovary.

Specific receptors for high density lipoproteins (HDL3) were solubilized from membranes of rat corpus luteum using different detergents. Among the detergents tested, octyl-beta-D-glucoside (40 mM) was most effective with respect to recovery of binding activity. The receptor activity released into 105,000 X g supernatant, can be assayed directly or with the precipitate obtained after dilution of the soluble supernatant. The 125I-HDL3 binding activity in the precipitated extract was linear with time, proportional to the amount of protein in the incubation mixture and saturable with increasing concentrations of 125I-HDL3. The solubilized receptor has an equilibrium dissociation constant (Kd) of 21.2 micrograms/ml and the binding activity was insensitive to Ca+2, EDTA and NaCl. These properties are similar to the membrane associated receptor. Administration of gonadotropin induced the HDL3 receptor in the solubilized membranes, suggesting that this receptor represents the physiologic receptor in the ovary.

Animals↗

PubMed1986

Comparison of amniotic fluid disaturated phosphatidylcholine and the lecithin-sphingomyelin ratio in the prediction of fetal lung maturity.

Although use of the lecithin-sphingomyelin (L/S) ratio has contributed to a reduction in the frequency of respiratory distress syndrome (RDS), its accuracy in pregnancies complicated by fetomaternal disease has been questioned. Disaturated phosphatidylcholine is the major active component of surfactant and has been advocated as being a more specific indicator of fetal lung maturity. A study of 105 pregnancies in which a L/S ratio and disaturated phosphatidylcholine assay were performed on amniotic fluid was carried out to ascertain if amniotic fluid disaturated phosphatidylcholine is indeed a more accurate predictor of RDS. The results of this investigation reveal no significant difference in the reliability of these two tests in predicting neonatal RDS. Five infants developed RDS with a mature L/S ratio ranging from 2.0 to 3.36, suggesting that the disaturated phosphatidylcholine assay may be a helpful adjunctive test in instances in which the L/S ratio is less than 3.5.

Amniotic Fluid↗