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Y Combarnous

Publications and source records attributed to Y Combarnous.

At least 37 records · Page 2Linked to original sources
PubMed1984

Induction of pituitary lactotrope differentiation by luteinizing hormone alpha subunit.

Addition of gonadotropin releasing hormone to cultures of fetal rat pituitary induced differentiation of lactotropes as revealed by immunocytochemistry. Antiserum to luteinizing hormone (LH) (recognizing native LH), but not antiserum to LH-beta (recognizing both native LH and its beta subunit), inhibited this induction. Further addition of highly purified LH-alpha subunit in culture medium also induced lactotrope differentiation. Thus, the alpha subunit may have a specific biological activity of its own with probable practical use in clinical investigations.

Animals↗
PubMed1984

Reevaluation of lipolytic activity of growth hormone in rabbit adipocytes.

The lipolytic activities of porcine pituitary fractions and purified growth hormone (GH) from human (h), porcine (p), ovine (o) and rabbit (Rb) origin as well as ovine placental lactogen (oPL), were compared to that of ACTH on rabbit adipocytes. All the GH preparations and oPL were equivalent in inhibiting the binding of labelled oGH to liver plasma membranes from pregnant rabbits. ACTH, and to a lesser extent porcine pituitary fractions and hGH, stimulated free fatty acid production by isolated adipocytes. The sensitivity of the adipocytes to these factors was increased when adenosine deaminase was added to the incubation medium. But, RbGH, pGH, oGH and oPL had no effect. We conclude that GH is not directly involved in the control of lipolysis in rabbit adipocytes and that the effect of hGH is rather due to a contamination of this preparation by other pituitary factors.

Adipose Tissue↗
PubMed1984

Comparison of in vitro follicle-stimulating hormone (FSH) activity of equine gonadotropins (luteinizing hormone, FSH, and chorionic gonadotropin) in male and female rats.

Not only equine FSH (eFSH) but also equine LH (eLH) and equine CG (eCG/PMSG) exhibit FSH activity in the rat. The concomitant loss of LH and FSH activities upon dissociation at acidic pH of eLH demonstrates that its FSH activity is intrinsic to the molecule and not due to contamination by FSH. Indeed, this latter hormone dissociates at a much higher pH. The binding activity as well as the in vitro biological activity of the equine gonadotropins were determined on rat gonadal cells from both male and female rats using the homologous hormone rat FSH as a reference. In the female, the biological activity of all of the gonadotropins is strictly related to their binding activity. In the male, this is true for all hormones except eFSH. Indeed, the biological activity of eFSH on rat Sertoli cells is higher than expected from its binding activity. Moreover, the FSH from other species (rat, ovine, and porcine) as well as eLH and eCG inhibit the response elicited by a submaximal dose of eFSH. These data indicate that eFSH acts as a superagonist of rat FSH in rat Sertoli cells, since it triggers cell activation at a much lower concentration than expected from its relative binding activity.

Animals↗
PubMed1984

Highly specific antisera against native ovine follitropin (oFSH) obtained from crude antisera by affinity chromatography on solid-phase undissociable lutropin (LH) column.

Antibodies recognizing determinants of the alpha-subunit, which is common to all glycoprotein hormones, were eliminated from antisera against native oFSH by affinity chromatography. Since the free alpha-subunit is immunologically different from the alpha-subunit in the intact hormone, we did not use an alpha-subunit affinity column. Instead, the antisera were applied to an LH affinity column. However, because intact LH dissociates in the conditions used to elute the purified antibodies, we prepared an LH derivative with covalently-linked subunits and coupled it to gel matrix. By this method oFSH antisera were freed from their non-specific antibodies. The cross-reaction of ovine lutropin in the oFSH radioimmunoassay (RIA) was lowered from 2% to less than 0.1%. Moreover, as the columns can be used repeatedly over long periods with no apparent loss of efficiency, large volumes of antiserum can be treated in this manner.

Animals↗
PubMed1984

[Origin of the FSH + LH double activity of equine chorionic gonadotropin (eCG/PMSG)].

The LH and FSH activities of equine choriogonadotropin (eCG) have been compared in several species with those of the highly purified homologous pituitary gonadotropins. The molar FSH/LH activity ratio of eCG determined by RRA is 0.20 in the pig, 0.25 in the rat and 0 in the horse. These data demonstrate the LH monospecificity of eCG in its own species as it is the case for hCG. We have also shown that equine LH exhibited a FSH-activity similar to that of eCG in the pig and in the rat but not in the horse. In the female rat, the binding activity to FSH receptors and the in vitro FSH activity of eCG are similar (about 0.005 X eFSH). In the male rat, the binding activity of eCG to FSH receptors is much higher (0.15 X eFSH) than its in vitro FSH activity (0.007 X eFSH). The behaviour of equine LH is similar to that of eCG in the four systems. Our data clearly indicate that the double activity of eCG is not unique to this molecule. Moreover, the double activity is not intrinsic to the eCG molecule since it depends on the species and the sex of the animal used as well as on the system used (RRA) or in vitro biological assay).

Animals↗
PubMed1983

The release of plasminogen activator by rat granulosa cells is highly specific for FSH activity.

The release of plasminogen activator by rat granulosa cells in vitro has been shown to be dependent on the concentration of FSH, and it has thus been proposed as a good assay for this hormone. However, it has been recently claimed that relaxin was also able to trigger the release of plasminogen activator by the same cells. In order to check the specificity of the assay, we studied the behavior of a large number of hormones and we found that it was strictly specific for FSH activity.

Animals↗
PubMed1982

[Role of seminal plasma in the in vitro survival of goat sperm].

The in vitro survival of ejaculated and epididymal goat sperm was measured in a milk diluent while being incubated at + 37 degrees C and after having been exposed to seminal plasma or to its components. Non-breeding season seminal plasma had a negative effect on sperm survival whether the cells were cooled to + 20 degrees C, chilled to + 4 degrees C or deep-frozen (- 196 degrees C) before being incubated at + 37 degrees C. Bulbo-urethral gland secretions also had a deleterious effect on the survival of washed ejaculated and epididymal sperm cooled to + 20 degrees C. The deleterious effect of the bulbo-urethral secretions on sperm survival and motility was significantly inhibited by the vesicular secretions. Non-breeding season seminal plasma contained bulbo-urethral but little or no vesicular secretions. The non-inhibition of their negative effect(s) may explain that of non-breeding season seminal plasma. Breeding season and non-breeding season washed ejaculated sperm had a better survival and a better motility than those incubated with breeding season seminal plasma. The mild washing procedure used may be responsible for the incomplete removal of seminal plasma from the sperm environment, namely that of the negative factors of the bulbo-urethral secretions. Breeding season seminal plasma would thus simply inhibit the effect of these negative factors or the factors themselves. This hypothesis is supported by the fact that breeding season seminal plasma had no effect on the survival of epididymal sperm.

Animals↗
PubMed1981

[Original hypothesis on the specificity of the binding of glycoprotein hormones to their receptors].

From the data we have obtained in the last few years concerning the interaction of gonadotropins with their receptors in vitro we develop a coherent model of the mechanism responsible for the binding specificity of these hormones. In this model we postulate that there is structural separation between the sites responsible for the high affinity of this class of hormones for their receptors and the sites responsible for the specificity of binding of these hormones. The high affinity site would be common to all the glycoprotein hormones and would be mainly formed by the alpha subunit which is common to all these hormones. The specific sites would act by inhibiting the binding of each hormone to the receptors of the others. These sites would be borne mainly by the specific beta subunits. We have introduced the term "negative specificity" to describe this mechanism.

Animals↗
PubMed1981

Equine follicle-stimulating hormone. Purification, acid dissociation, and binding to equine testicular tissue.

A simple method of purification of equine follicle-stimulating hormone is described by which two forms of the hormone are obtained. The acid dissociation of the most active preparation was studied and a pKa of 5.8 was determined at 37 degrees C. This value is 2 pH units higher than that observed for pregnant mare serum gonadotropin suggesting that the binding areas between subunits are not identical in the two hormones. We also describe an homologous radioreceptor assay of equine follicle-stimulating hormone which is highly specific for this hormone in contrast to the heterologous systems described so far. The analysis of the properties of equine gonadotropins in homologous and heterologous radioreceptor assays suggests that all glycoprotein hormones share a common high affinity binding site and that specificity of binding is due to binding prohibition sites preventing fixation of each hormone to the receptors of the other glycoprotein hormones. This specific hindering is defined as "negative specificity."

Amino Acids↗
PubMed1981

Physico-chemical properties of pregnant mare serum gonadotropin.

Pregnant mare serum gonadotropin exhibits a dissociation at acid pH as shown by the drop of s20,w values from 3.52 S at pH 8.1 to 2.52 S at pH 2.0. The dissociation is accompanied by an absorbance change with a maximum at 287 nm and a parallel loss of both follicle-stimulating hormone (FSH) and luteinizing hormone (LH) activities as followed by radioreceptor assays. The apparent pKa of the acid transition is 3.45 with an extremely slow and temperature-dependent rate at pH 2.0 (1.8 . 10(-4) s-1 at 37 degrees C). By gel filtration the molecular weight of the active hormone is estimated to be 45 000 (rather than the previously reported 53 000-64 000). The active conformation of the hormone includes beta sheet structure (34%) as for other gonadotropin hormones with a minor but significative amount of alpha-helix. Four tyrosine residues were titrated, two of pKa = 10.3 and two of pKa = 11 out of a total of seven tyrosines. The parallel changes in FSH and LH activities during the preparation and the acid transition suggest that the two biological activities are intrinsic properties of the same molecular entity.

Animals↗
PubMed1978

Study of follitropin receptors in testis using a homologous system. Binding of porcine follitropin to plasma membranes from immature porcine testis and correlation with adenylate cyclase stimulation.

The properties of follitropin receptors in immature porcine testis were determined using highly purified porcine follitropin. 1. The characteristics of follitropin binding to a subcellular fraction rich in plasma membranes were studied using a 125I-labelled follitropin with high specific activity (75-100 Ci/g) and high binding activity. The binding is dependent on time, temperature and pH. It is specific to follitropin as demonstrated by the very low binding activity of the follitropin alpha and beta subunits and of the other glycoprotein hormones. Scatchard analysis of binding data indicated an equilibrium association constant of 2 x 10(10) M-1 and a concentration of high affinity binding sites of 500 fmol/mg membrane proteins. 2. A sensitive radio-ligand receptor assay was developed. Fifty percent inhibition of binding was obtained with as little as 2 ng of porcine follitropin. Ovine and bovine follitropins and pregnant mare serum gonadotropin gave binding inhibition curves parallel to that given by porcine follitropin. With equine and human follitropin, significantly different slopes were recorded. 3. Kinetics of dissociation of labelled follitropin from its testis receptors showed the presence of at least two compartments with fast and slow dissociation rate constants. The ratio between the sizes of the slow and fast compartments appeared dependent upon preincubation time. 4. A temporal correlation was observed between binding of follitropin to testis receptors and activation of membrane bound adenylate cyclase.

Adenylyl Cyclases↗
PubMed1976

Chemical study of the topography of porcine lutropin (LH) using dinitrofluorobenzene and dansyl chloride.

Treatment of porcine lutropin beta-subunit by increasing amounts of dansyl chloride shows that only one fluorescent group can be bound to the free subunit, namely on tyrosine beta-37. This modification prevents reassociation with native chi-subunit. In contrast to dansyl chloride, dinitrofluorobenzene reacts preferentially with tyrosine beta-59. This substitution does not interfere with the reassociation with the native chi-subunit. By using equimolar ratio of dansyl chloride and porcine lutropin chi-subunit it is possible to modify this subunit on a single site, which is found to be a tyrosine residue. The monodansylated X-subunit is still able to recombine with native B-subunit but its fluorescence is found to be markedly quenched upon binding. In addition, the O-dansyl-tyrosyl fluorescence quenching by potassium iodide is more effective on the recombined dimer than on the free chi-subunit. Both reconstituted dimers (native xhi chi dinitrophenylated beta and dansylated chi chi native beta) are without biological activity. It is not clear whether the substituted phenolic groups are essential or whether the added groups prevent the chi beta dimer from taking the active conformation. This alternative is discussed in the light of recent data from this laboratory and others.

Amino Acids↗