Variable content of Fel d 1 variants in house dust and cat extracts may have an impact on allergen measurement.

BACKGROUND: The major cat allergen, Fel d 1, is a tetrameric glycoprotein composed of 2 heterodimers. Polymorphisms in this allergen are well documented. Recent work shows that Fel d 1 samples can contain core fragments of variable immunoreactivity. OBJECTIVES: Our objective was to compare Fel d 1 polymorphism in cat extracts and house dust, which is used as an indicator of allergen exposure and to understand how the combination of individual Fel d 1 variants can affect cat allergen measurement. METHODS: Natural Fel d 1 allergens were water-extracted from house dust and from the chest area and anal sacs of a cat. Recombinant Fel d 1 was provided commercially. The samples were analyzed by immunoblotting; variants were isolated using gel electrophoresis and tested using enzyme-linked immunosorbent assay. RESULTS: Four Fel d 1 variants of 40, 30, 19-21, and 14-16 kDa were consistently identified in Fel d 1 samples. Fel d 1 patterns found in house dust and the chest area wash were similar. Dimers were shown to be the major variant, while intact or truncated tetramers and core fragments were found in variable amounts. Intact and truncated dimers of Fel d 1 displayed similar antibody binding. Conversely, the intact tetramer-but not the core tetramer-was found to bind twice the antibody amount as the dimers and core fragments. CONCLUSIONS: Despite a common pattern of Fel d 1 variants in cat extracts and house dust, variations in the tetramer-to-dimer ratio among samples may introduce major discordances in cat allergen measurements using immunoassays. Our findings indicate the need for further harmonization of allergen immunoassays.

[Indications of primary cesarean deliveries in a regional teaching hospital and reasonable strategies for reducing them]. / Indications des premières césariennes dans un centre hospitalo-universitaire régional et stratégies raisonnables pour les diminuer.

OBJECTIVES: To characterize the indications of primary cesarean sections and discuss the various possibilities to reduce them. MATERIALS AND METHODS: Retrospective study, carried out over a period of 1 year in a university hospital having a level 3 perinatal activity, including the 499 primary cesarean sections of 2013. Two groups were defined by parity: nulliparous patients (group 1) and multiparous patients who had never previously been delivered by cesarean section (group 2). We have assessed the indication of every primary cesarean section and health status of newborns in each group. RESULTS: Groups 1 and 2 respectively included 369 and 130 patients. The cesarean section rate in 2013 was 24.7% with a primary cesarean section rate of 17%. Seventy-four percent of the primary caesarean deliveries were performed on nulliparous women and 26% on multiparous (P<0.001). Sixty-three percent of the primary caesarean deliveries were performed on nulliparous women with a singleton fetus in cephalic presentation. The most common indications for primary cesarean delivery were non-reassuring fetal heart rate tracing (47.1%), failure to progress (24.8%) for which nulliparous women were more involved (29% vs. 13%, P<0.001) and fetal malpresentation (9.6%). CONCLUSION: Further analysis of fetal heart rate during labor, a larger use of second line means to evaluate the fetal status during labor, using 6cm as the cut off for active labor, and encouraging vaginal operative delivery constitute the best way to decrease the primary cesarean section rate.

Evidence for mannolipids as intermediates in mannose transfer to thyroid rough microsomal glycoproteins.

Thyroid rough microsomes catalyzed the transfer of mannose from GDP-mannose to endogeneous glycoprotein(s) and to glycolipids comprising a recently described dolichol phosphomannose extractable with usual organic solvents and a material tentatively identified as an oligosaccharide lipid. The labeling of the two lipids was consistent with a role in mannose transfer to glycoprotein(s). When partially purified dolichol phospho[14C] mannose was incubated with rough microsomes, a part of the label appeared in the second lipid, suggesting a role as intermediate, and less rapidly in glycoprotein(s). Sodium dodecyl sulfate/polyacrylamide gel electrophoresis did not allow to ascertain whether or not the glycoproteins receiving label from these sugar lipids comprised thyroglobulin precursors.

Cell-free labeling in thyroid rough microsomes of lipid-linked and protein-linked oligosaccharides. I. Mannosylated units.

In order to evaluate the possibility in a pig thyroid rough microsomal system of a transfer of pre-assembled sugar cores from sugar-lipids to protein, we have examined after incubation with GDP-[14C]Man the compounds bearing labeled saccharides and have determined some properties of their released saccharide moieties. The [14C]Man material specifically soluble in CHCl3/CH3OH/H2O, 10:10:3, behaved on DEAE-cellulose and when treated with hot alkali and alkaline phosphatase as a lipid pyrophosphate (sometimes accompanied by some dolichol-P-[14C]Man). Its saccharide moiety, released by mild acid, exhibited properties (molecular size, sensitivity to alpha-mannosidase, affinity for concanavalin A and charge modification introduced by a strong reductive alkaline treatment) pointing to a polymannosylated N,N'-diacetylchitobiose containing an average of nine monosaccharide units (from six to twelve). The [14C]mannosylated glycoproteins have represented all the polymeric label remaining after lipid extraction. From the susceptibility of their pronase glycopeptides to a differential reductive alkaline hydrolysis, it was concluded that their label belonged mainly to N-glycosidically linked units. Released saccharides exhibited the same properties as those from lipids, a result substantiating the possibility raised from previous studies of a transfer of pre-assembled moieties.

Transfer of glucose in the biosynthesis of thyroid glycoproteins. II. Possibility of a direct transfer of glucose from UDP-glucose to proteins.

When thyroid rough microsomes are incubated with labeled UDPglucose, extensive labeling occurs on endogenous protein. The present study reports various time-course experiments of glucose incorporation from UDPglucose either into endogenous acceptors or into exogenous synthetic peptide, whether or not conditions are used which depress dolichol-P-glucose synthesis. The results are not compatible with the presently accepted idea of oligosaccharide lipids as sole donors of labeled glucose to proteins. Some structural properties of glucose-labeled oligosaccharides released from proteins by endo-beta-N-acetylglucosaminidase H were also investigated. They appeared to be of a single species and less degradable by alpha-mannosidase than their lipid-linked counterpart. Since glucose-labeled glycopeptides were found susceptible to a beta-glucosidase, it is proposed that some labeled glucose residues are involved in beta-linkages. The possibility is raised that glucose might be directly transferred from UDPglucose to endogenous glycoproteins.

Transfer of glucose in the biosynthesis of thyroid glycoproteins. I. Inhibition of glucose transfer to oligosaccharide lipids by GDP-mannose.

Thyroid rough microsomes catalyzed the synthesis of glucose-containing oligosaccharide lipids which were compared to those extracted from labeled thyroid cells and were found to be largely similar. Glucose transfer to these oligosaccharide lipids in the microsomal system was shown to be markedly depressed by an addition of GDPmannose. This sugar nucleotide, already at 1 microM, blocked dolichol-P-glucose synthesis, thus restraining further glucosylation of oligosaccharide lipids. Using this concentration of radioactive GDPmannose in the incubation medium lead to the detection of three glucose containing mannose-labeled oligosaccharide lipids. Double labeling experiments suggested a precursor-product relationship between them. Previously labeled oligosaccharide lipids, containing glucose or not were compared in their efficiency to act as donors of their oligosaccharide chain to an exogenous synthetic Asn-X-Thr containing peptide. It was found that the presence of glucose did not significantly influence the transfer. Free glucose was released during the reaction when using the glucose-labeled oligosaccharide lipid.

Carbohydrate processing of thyrotropin differs from that of free alpha-subunit and total glycoproteins in microsomal subfractions of mouse pituitary tumor.

We have determined the structures of high mannose (Man) oligosaccharide units of TSH, free alpha-subunit, and non-TSH-related total glycoproteins (TP) within microsomal subfractions of mouse thyrotropic tumor. Tumor minces were incubated with D-[2-3H]Man, homogenized, and subfractionated into rough endoplasmic reticulum (RER) as well as proximal and distal smooth endoplasmic reticulum/Golgi apparatus. TSH subunits and TP were precipitated from these fractions, and high Man units released by endoglycosidase H were analyzed by paper chromatography. Glc3Man9GlcNAc2 (Glc = glucose; GlcNAc = N-acetylglucosamine) was not detected in TSH subunit precursors in any fraction, but was detected in TP. Glc1Man9GlcNAc2 accumulated in TSH with chase, but only small amounts were detected in free alpha-subunit and TP. Trimming of Man9GlcNAc2 to Man8GlcNAc2 began in RER before 1 h for all species, but the rate of Man trimming was rapid for free alpha-subunit, moderate for TSH, and slow for TP. Man8GlcNAc2 was a rate-limiting step in processing for all species in the RER. Man5GlcNAc2 was a second major rate-limiting step in processing of free alpha-subunits only and accumulated in distal smooth endoplasmic reticulum/Golgi apparatus. Other studies in progress suggest that a function of the thyrotroph is to modulate the structure of TSH oligosaccharide units during biosynthesis to achieve mature hormone with physiologically appropriate metabolic clearance and intrinsic biological activity. The present study supports this notion, since we found that the qualitative nature and kinetics of processing differ for oligosaccharide units of TSH, free alpha-subunit and TP within the microsomes.

Comparative mapping of human thyrotropin, gonadotropins, and free subunits with antipeptide antibodies.

To compare the structural topology of the human TSH to that of the structurally related gonadotropins, 10 peptides covering the entire primary sequence of the alpha- and beta-subunits of TSH were synthesized and used as antigens for the preparation of polyclonal antibodies. The alpha-subunit was synthesized as 4 nonoverlapping peptides (1-25, 26-51, 49-73, 72-92) while the beta-subunit was segmented in 6 overlapping sequences (2-18, 10-38, 31-51, 53-76, 77-96, 92-112). Most of the peptide sequences were predicted to contain a putative antigenic determinant. All antipeptide antisera were found to bind to the corresponding synthetic sequence in an enzyme-linked immunosorbent assay as well as to denatured TSH subunits after Western blotting. The N-terminal half of the alpha-subunit was found differentially accessible in TSH and gonadotropins compared to the free subunit: antipeptide-alpha 1-25 antibodies exhibited variable affinity for the four glycoprotein hormones whereas anti-alpha 26-51 displayed a remarkable recognition of free alpha-subunit. Four peptides proved to be accessible in the TSH beta-subunit: the N-terminal peptide (beta 2-18) elicited antibodies that bound to free TSH-beta and poorly to the dimer while antibodies against the C-terminal sequence (beta 92-112) recognized equally well free beta-subunit and TSH. Antipeptide-beta 31-51 antibodies proved to be specific for TSH while the beta 53-76 contiguous peptide appeared accessible in both TSH and gonadotropins. The current findings therefore demonstrate that most of the sequences predicted to contain antigenic sites in the alpha- or the beta-subunits are indeed accessible at the surface of these proteins. Additionally, both subunits appear to contain amino acid sequences that are differentially expressed in TSH and gonadotropins as well as in free and combined subunits.

Immunoreactive and bioactive isoforms of human thyrotropin.

Isoforms of intrapituitary human TSH were separated by gel isoelectrofocusing, and their immunoreactivity analyzed by subsequent immunoblotting using polyclonal and monoclonal antibodies. Under these conditions, TSH polymorphism could be resolved as seven major isoforms (pI 8.6, 8.3, 8.0, 7.5, 7.0, 6.5, and 6.0) by both silver staining of the gels and binding to anti-TSH polyclonal antibodies. The distribution pattern of these forms appeared totally distinct from that of individual TSH alpha (pI 8.8, 8.4, 8.2, 7.6, 7.4, 6.8, 6.6, 5.8, and 5.4) and TSH beta (pI 8.7, 8.1, 7.2, 6.8, 6.2, and 5.8) subunits. While most anti-TSH polyclonal antibodies recognized neutral and alkaline isoforms of TSH (pI 8.6, 8.3, 8.0, 7.5, 7.0, 6.5, and 6.0) through beta determinants, they displayed a variable potency to bind acidic forms of the hormone (pI 5.8, 5.5, 4.8, and 4.5), in contrast to anti-TSH alpha antisera, which enlighted the broadest spectrum of isoforms. Monoclonal antibodies of various specificities largely reproduced this distribution, indicating that at least five distinct epitopes are coexpressed in the neutral and alkaline forms of TSH, but only two are expressed in the acidic ones. All of the forms were found to induce cAMP production and stimulate growth of FRTL-5 rat thyroid cells, although neutral forms proved to be definitely less potent than the others. We therefore, conclude that TSH isoforms differ in the expression of both their immunoreactive and bioactive domains and that the bioactive/immunoreactive ratio is not an accurate index for the biopotency of the hormone.

Polymorphism of prolactin secreted by human prolactinoma cells: immunological, receptor binding, and biological properties of the glycosylated and nonglycosylated forms.

Multiple forms of PRL differing in their physicochemical and biological characteristics have been described. We have analyzed the molecular forms of human (h) PRL released in culture by pure hPRL-secreting tumors with a particular attention to glycosylated hPRL. The prolactinoma cells from six different tumors released, in serum-free conditions, 10-28 mg hPRL. The combination of polyacrylamide gel electrophoresis and immunoblotting techniques using a [125I]anti-hPRL monoclonal antibody allowed qualitative and quantitative analysis of the hPRL variants. The ratio of the glycosylated 25,000-mol wt form (G-hPRL) to the 23,000-mol wt nonglycosylated monomeric hPRL (NG-hPRL) varied from 0.13 to 0.25. Under the conditions of our studies, cleaved forms of the hormone (19,000 and 15,000 mol wt) accounted for less than 5% of the total immunoreactivity. G- and NG-hPRL were subsequently purified by gel filtration and lectin affinity chromatography. G-hPRL appeared fully sensitive to endoglycosidase F digestion, further supporting the presence of a freely accessible N-linked carbohydrate chain. When assayed for their ability to react with polyclonal antibodies directed against hPRL in a competitive RIA, G-hPRL was 3 times less immunoreactive than NG-hPRL. However, both types of hPRL exhibited superimposable displacement curves when tested in an immunoassay using an anti-hPRL monoclonal antibody. In binding studies using crude rabbit mammary gland membranes G-hPRL was half as potent as NG-hPRL. In stimulating the growth of the Nb2 lymphoma cell line, G-hPRL was 50% less active than NG-hPRL. Thus 1) under basal conditions, hPRL undergoes partial and variable glycosylation; 2) glycosylation of the hormone may modulate its immunoreactivity; 3) glycosylation of hPRL not only lowers its mammary gland receptor binding capacity but also its growth-promoting activity.

Variable carbohydrate structures of circulating thyrotropin as studied by lectin affinity chromatography in different clinical conditions.

Carbohydrate structures of intrapituitary and circulating TSH were studied by Concanavalin-A (Con A) and ricin lectin chromatography under different clinical conditions. Con A permits the separation of molecules differing in the extent of their carbohydrate branching, whereas ricin gives an estimation of the degree of their sialylation. Intrapituitary TSH was more retained on Con A and less sialylated than circulating hormone, suggesting that carbohydrate chains of intrapituitary molecules are less mature than those present in the circulation. A greater proportion of TSH firmly bound to Con A, compared to control values, was found in sera from fetuses and patients with uremia, TSH-secreting adenomas, and central hypothyroidism. In primary hypothyroid patients, TSH binding to Con A was similar to that found in controls, but a greater percentage of sialylated forms was seen. In central hypothyroidism patients, TSH released in response to TRH was less sialylated. Interestingly, no sialylated TSH was found in normal fetuses. In conclusion, the present data show that both TSH carbohydrate branching and sialylation may vary in different clinical conditions. As some of the above clinical conditions are known to be accompanied by variations in the bioactivity of circulating TSH, the finding of changes in TSH carbohydrate structures further supports the view that glycosylation modulates the expression of TSH biological activity.

Concanavalin A affinity chromatography of human serum gonadotropins: evidence for changes of carbohydrate structure in different clinical conditions.

We have studied the carbohydrate of circulating human gonadotropins (FSH and LH) in different clinical conditions using Concanavalin A (Con A) affinity chromatography. This technique permits separation of molecules differing in the extent of carbohydrate branching. The proportion of molecules that does not bind to Con A was greater in circulating FSH than in LH, reflecting a higher content of multiantennary and/or bisected biantennary complex carbohydrate structures in serum FSH. No significant difference in gonadotropin binding pattern to Con A was found between normal controls and patients with chronic uremia or gonadotropin-secreting pituitary adenomas. On the contrary, sera from postmenopausal women and fetuses contained a greater proportion of FSH and LH that bound to Con A, indicating a shift from multiantennary and/or bisecting structures to hybrid and/or high mannose forms, i.e. to the secretion of less mature forms. International Reference Preparations, derived from pituitary extracts, were more retained on Con A than circulating hormones, suggesting that carbohydrate chains of the intrapituitary hormone stock are less mature than those present in the circulation. Less mature forms were also found in FSH, but not in LH, from normal controls after GnRH injection. Finally, a higher proportion of unbound forms, i.e. complex carbohydrate chains, was found in healthy subjects presenting with an immunologically anomalous variant of LH. In conclusion, the current data show that the hormonal status of the individual may differently affect carbohydrate branching of gonadotropins. Alteration in glycosylation is likely to be involved in masking at least one epitope specific for intact LH dimer, thus indicating that it may modulate the tertiary structure of glycoprotein hormones.

Dual activity of human pituitary thyrotrophin isoforms on thyroid cell growth.

Alkaline (pI 8.6-7.5) and neutral (pI 7.0-6.0) isoforms of human TSH have been isolated from a highly purified intrapituitary preparation by isoelectric focusing and compared for their respective actions on thyroid cell proliferation. Both TSH isoforms displayed the same ability to bind to porcine thyroid membranes as the original hormone preparation, indicating a similar recognition at the receptor sites. Alkaline forms showed a higher potency in inducing either cyclic AMP (cAMP) production or [3H]thymidine incorporation in FRTL-5 cells (half-maximal effective doses (ED50 values) = 0.25 and 0.29 nM respectively) compared with their neutral counterparts (ED50 values = 0.66 and 0.70 nM respectively). Increasing the concentration of alkaline forms in the presence of a half-maximal concentration of neutral TSH resulted in a profound inhibition of cell growth without a significant change in cAMP. Conversely, increasing the amount of neutral forms in the presence of a half-maximal dose of alkaline TSH resulted in an additive response for cAMP production but not in cell proliferation. To assess whether glycosylation might be responsible for the variation in hormone action, both alkaline and neutral TSH isoforms were tested for recognition of their carbohydrate chains by concanavalin A (Con A) and ricin. No major difference was found in binding to Con A, indicating that the contribution of carbohydrates to changes in hormone pI was not related to core branching. Very few galactose residues were accessible in either hormone fraction since little binding to ricin was observed. Isoelectric focusing of TSH forms before and after neuraminidase treatment revealed that neutral forms had a higher sialic acid content than alkaline TSH. In conclusion, the current findings show that TSH isoforms differentially affect cAMP production and cell growth. TSH fractions with a high sialic acid content and a low mitogenic activity behave as antagonists to the more active forms for cell proliferation. It is suggested that physiological control of TSH action at the thyroid gland may reside in the respective amounts of various TSH forms which, once bound to their receptor, can induce variable activation of post-receptor events while controlling cell proliferation.

Carbohydrate-dependent epitope mapping of human thyrotropin.

To probe possible effects of carbohydrate chains in the conformation of pituitary glycoprotein hormones, two radiolabeled derivatives of human thyroid-stimulating hormone (hTSH), either partially deglycosylated in the beta-subunit or fully deglycosylated in both the alpha- and beta-subunits, were compared to the native hormone for binding to monoclonal as well as polyclonal antibodies. Monoclonal antibodies were screened for their ability to bind the intact hormone (anti-hTSH), hTSH and its free alpha-subunit (anti-alpha) or its free beta-subunit (anti-beta). A panel of 14 monoclonal antibodies directed against at least eight out of the 12 epitopes known to be present in the hormone was tested in solid-phase assays for their capacity to bind intact and deglycosylated forms of hTSH. All of them displayed identical recognition of native and partially deglycosylated 125I-hTSH. In contrast, binding of fully deglycosylated 125I-hTSH to anti-hTSH and anti-beta antibodies was dramatically lost while that of anti-alpha was preserved. This clearly indicates that most of the epitopes specific for subunit association as well as those present on the beta-subunit are glycosylation dependent. No alteration was found in antibody recognition following deglycosylation of free individual subunits, indicating that the carbohydrate effect can only occur in the combined dimer. Using polyclonal antisera raised against the International Reference Preparations, we found that the deglycosylated hormone could be bound by the anti-beta antiserum although at a much lower dilution than the native antigen, suggesting the presence of at least one glycosylation-independent epitope in the beta-subunit. Competitive binding assays revealed that deglycosylated hTSH is 5 times less immunoreactive toward the anti-beta compared to the anti-alpha antiserum. The current data thus demonstrate the presence of the glycosylation-independent epitopes in the alpha-subunit of hTSH and the localization of most of the glycosylation-dependent domains in the beta-subunit.

Differential effect of glycosylation on the expression of antigenic and bioactive domains in human thyrotropin.

Enzymatic deglycosylation of human thyroid-stimulating hormone (hTSH) was shown to result in a mixture of partially and fully deglycosylated forms of the hormone by gel electrophoresis, silver staining and immunoblotting. Radioiodination of the enzymatic digest, followed by gel filtration and concanavalin A-Sepharose chromatography allowed to separate two different forms of partially deglycosylated [125I]hTSH and a fully deglycosylated hormone. The final recovery was of approx. 60% for [125I]hTSH deglycosylated in its beta-subunit, of 30% for [125I]hTSH missing the oligosaccharide in beta and one in alpha but only of 10% for [125I]hTSH deglycosylated in both the alpha- and beta-subunits. Gel electrophoresis under non-denaturing conditions showed that each form migrated distinctly from free subunits and reverse-phase high performance liquid chromatography after reduction and carboxymethylation identified the presence of the two subunits. Mapping of [125I]hTSH derivatives with polyclonal, monoclonal and anti-peptide antibodies allowed to identify two novel glycosylation-independent epitopes preserved in deglycosylated hTSH while the main immunogenic determinant was lost. When assayed in a bioassay with FRTL-5 cells, the hormone deprived of its beta-linked carbohydrate chain was found to be as effective as the native hormone on cAMP production and cell growth. In contrast, the fully deglycosylated derivative proved to stimulate cAMP release but appeared to be definitely less potent on thyroid cell growth. Our findings thus demonstrate that glycosylation of the alpha-subunit but not that of the beta-subunit is essential to express the domains involved in hTSH immunoreactivity as well as those controlling the post-receptor biological activity of the hormone.

Evaluation of 29 monoclonal and polyclonal antibodies used in the diagnosis of pituitary adenomas. A collaborative study from pathologists of the Club Français de l'Hypophyse.

Fifteen polyclonal antibodies (pAbs) and 14 monoclonal antibodies (mAbs) directed against hGH, hPRL, beta hFSH, beta hLH, beta hTSH and alpha-subunit were assessed by five different laboratories on normal and adenomatous pituitary tissues. This study aims at providing pathologists with a selected panel of antisera suitable for diagnosis, and appreciating the interest of the recently introduced mAbs. All the anti-hGH Abs proved to be specific (3 pAbs and 4 mAbs); three mAb out of four gave a few false-negative reactions. Three out of six polyclonal anti-hPRL showed cross-reactivity with hGH; anti-hPRL mAbs gave a strong staining with no false-negativity detected so far. MAbs proved to be more efficient for detecting glycoprotein hormones and alpha subunit than pAbs, which, in several cases, gave widespread cross-reactivity. This lack of specificity could explain the noticeable discrepancies reported so far in the appraisal of gonadotropic and somatoprolactinic adenomas.

[Gonadotropin receptors]. / Les récepteurs des gonadotropines.

The reproductive function of both the male and female is under the control of several pituitary hormones including lutropin (LH) and follitropin (FSH). These hormones are highly homologous glycoprotein dimers sharing a common subunit. Their polymorphism mainly resides in the microheterogeneity of their carbohydrate chains that is also responsible for the variations in biological activity. In the gonads, these hormones bind to specific receptors and regulate steroidogenesis and gametogenesis. LH receptors also bind the choriogonadotropin hormone and are located in Leydig cells in testis, interstitial and medulla cells in ovary. FSH receptors are present in Sertoli cells in the male while they control follicular maturation in the female. In both sexes, their activity is coupled to that of other receptors such as that of prolactin or one able to recognize GnRH. The purification of LH receptor has been successfully achieved in several animal species and showed a significant structural homology between the receptors of both sexes.

[Biological polymorphism and functional domains of pituitary glycoprotein hormones]. / Polymorphisme biologique et domaines fonctionnels des hormones glycoprotéiques hypophysaires.

The glycoprotein hormones are a family of four proteins: LH, FSH, TSH and CG. These molecules are glycosylated dimers, sharing a common alpha-subunit and differing by their beta-subunit which confers to the hormone its immunological and biological specificity. The biological function of these hormones is mediated through the recognition of specific receptors at the target organ. Although still controversial, it appears that both subunits of the hormone are required to bind to the receptor and induce cAMP release. Furthermore, these hormones exhibit natural variability in their bioactivity and the molecular basis of this process are poorly understood at the moment. Recent data relative to the mapping of glycoprotein hormones, were obtained by site-directed mutagenesis as well as by the use of synthetic peptides. These two approaches allowed to elucidate several linear peptide sequences involved in the biologically active conformation and immunoreactivity of these molecules. Furthermore, these hormones exist in different molecular forms with a variable biological activity and immunological ratio, and this polymorphism is probably due to the glycan moities. The presence of these glycans are necessary for full expression of their biological activity as well as immunoreactivity, and both the biosynthesis and the secretion of these various glycoforms are probably under physiological regulation. We therefore propose that glycosylation may alter the expression of several domains at the surface of the hormone to modulate its plasmatic clearance as well as the action of each individual glycoform at the receptor and this will ultimately control its biological function.