Heterogeneity of rat FSH by chromatofocusing: studies on serum FSH, hormone released in vitro and metabolic clearance rates of its various forms

Neuroendocrine, autocrine, and paracrine control of follicle-stimulating hormone secretion

Follicle-stimulating hormone (FSH) is a glycoprotein hormone produced by gonadotropes in the anterior pituitary that plays a central role in controlling ovarian folliculogenesis and steroidogenesis in females. Moreover, recent studies strongly suggest that FSH exerts extragonadal actions, particularly regulating bone mass and adiposity. Despite its crucial role, the mechanisms regulating FSH secretion are not completely understood. It is evident that hypothalamic, ovarian, and pituitary factors are involved in the neuroendocrine, paracrine, and autocrine regulation of FSH production. Large animal models, such as the female sheep, represent valuable research models to investigate specific aspects of FSH secretory processes. This review: (i) summarizes the role of FSH controlling reproduction and other biological processes; (ii) discusses the hypothalamic, gonadal, and pituitary regulation of FSH secretion; (iii) considers the biological relevance of the different FSH isoforms; and (iv) summarizes the distinct patterns of FSH secretion under different physiological conditions.

Profile of follitropin alpha/lutropin alpha combination for the stimulation of follicular development in women with severe luteinizing hormone and follicle-stimulating hormone deficiency

A severe gonadotropin deficiency together with chronic estradiol deficiency leading to amenorrhea characterizes patients suffering from hypogonadotropic hypogonadism. Administration of both follicle-stimulating hormone (FSH) and luteinizing hormone (LH) to these patients has been shown to be essential in achieving successful stimulation of follicular development, ovulation, and rescue of fertility. In recent years, the availability of both recombinant FSH (rFSH) and recombinant LH (rLH) has provided a new therapeutic option for the stimulation of follicular growth in hypopituitary–hypogonadotropic women (World Health Organization Group I). In this article, we review the data reported in the literature to highlight the role and the efficacy of using recombinant gonadotropins, rFSH and rLH, in the treatment of women with severe LH/FSH deficiency. Although the studies on this issue are limited and the experiences available in the literature are few due to the small number of such patients, it is clearly evident that the recombinant gonadotropins rFSH and rLH are efficient in treating patients affected by hypogonadotropic hypogonadism. The results observed in the studies reported in this review suggest that recombinant gonadotropins are able to induce proper follicular growth, oocyte maturation, and eventually pregnancy in this group of women. Moreover, the clinical use of recombinant gonadotropins in this type of patients has given more insight into some endocrinological aspects of ovarian function that have not yet been fully understood.

Partially deglycosylated equine LH preferentially activates beta-arrestin-dependent signaling at the follicle-stimulating hormone receptor

Deglycosylated FSH is known to trigger poor Galphas coupling while efficiently binding its receptor. In the present study, we tested the possibility that a deglycosylated equine LH (eLHdg) might be able to selectively activate beta-arrestin-dependent signaling. We compared native eLH to an eLH derivative [i.e. truncated eLHbeta (Delta121-149) combined with asparagine56-deglycosylated eLHalpha (eLHdg)] previously reported as an antagonist of cAMP accumulation at the FSH receptor (FSH-R). We confirmed that, when used in conjunction with FSH, eLHdg acted as an antagonist for cAMP accumulation in HEK-293 cells stably expressing the FSH-R. Furthermore, when used alone at concentrations up to 1 nM, eLHdg had no detectable agonistic activity on cAMP accumulation, protein kinase A activity or cAMP-responsive element-dependent transcriptional activity. At higher concentrations, however, a weak agonistic action was observed with eLHdg, whereas eLH led to robust responses whatever the concentration. Both eLH and eLHdg triggered receptor internalization and led to beta-arrestin recruitment. Both eLH and eLHdg triggered ERK and ribosomal protein (rp) S6 phosphorylation at 1 nM. The depletion of endogenous beta-arrestins had only a partial effect on eLH-induced ERK and rpS6 phosphorylation. In contrast, ERK and rpS6 phosphorylation was completely abolished at all time points in beta-arrestin-depleted cells. Together, these results show that eLHdg has the ability to preferentially activate beta-arrestin-dependent signaling at the FSH-R. This finding provides a new conceptual and experimental framework to revisit the physiological meaning of gonadotropin structural heterogeneity. Importantly, it also opens a field of possibilities for the development of selective modulators of gonadotropin receptors.

Ovarian stimulation protocols based on follicle-stimulating hormone glycosylation pattern: impact on oocyte quality and clinical outcome

OBJECTIVE

To evaluate the impact of follicle-stimulating hormone (FSH) with different glycosylation patterns on oocyte quality and clinical outcomes in an in vitro fertilization (IVF) treatment program.

DESIGN

Prospective randomized, open-label, clinical study.

SETTING

Assisted reproduction center.

PATIENT(S)

One hundred eighty-eight infertile couples undergoing assisted fertilization treatment.

INTERVENTION(S)

All participants underwent a standard down-regulation with a gonadotropin-releasing hormone (GnRH) analogue. The patients were randomized into three groups: 63 patients received combined sequential acidic and less-acidic FSH, 65 patients received only less-acidic FSH (recombinant FSH), and 60 received only acidic FSH (human-derived FSH).

MAIN OUTCOME MEASURE(S)

Number of mature metaphase II oocytes, embryo quality, clinical pregnancy rates, and implantation rates.

RESULT(S)

The pregnancy and implantation rates were statistically significantly lower in the less-acidic recombinant FSH alone group than in the combined sequential acidic hFSH/less-acidic recombinant FSH, and acidic hFSH alone groups (33.3%, 43.5%, 39% and 17.3%, 24.5%, 20.4%, respectively). Metaphase II oocytes and grade 1 embryos were statistically significantly higher in favor of the combined sequential acidic hFSH/less-acidic recombinant FSH group compared with the less-acidic recombinant FSH alone group.

CONCLUSION(S)

The glycosylation patterns of the two types of FSH implemented for ovarian stimulation have different impacts on oocyte quality and clinical outcome. A sequential combined protocol using both acidic and less-acidic FSH for ovarian stimulation improves oocyte maturity and embryo cleavage, and increases pregnancy and implantation rates.

Efficacy of a combined protocol of urinary and recombinant follicle-stimulating hormone used for ovarian stimulation of patients undergoing ICSI cycle

PURPOSE

To evaluate the efficacy of using both urinary and recombinant FSH in a combined protocol for ovarian stimulation in an IVF treatment program.

METHOD

A total of 119 infertile couples undergoing ICSI treatment were randomized prospectively in this study. After a standard down-regulation with GnRH analogue, the patients were randomized in 2 groups 58 received combined urinary and recombinant FSH, starting with uFSH and then rFSH, and 61 controls received only recombinant FSH.

RESULT(S)

Pregnancy and implantation rates were significantly higher in the combined uFSH/rFSH group than the control (rFSH) group (43.9% vs 22.1% and 27.5% vs 13.2% respectively). Metaphase II oocyte and grade 1 embryos were significantly higher in favour of combined uFSH/rFSH group than the recombinant FSH group.

CONCLUSION(S)

This study shows that using a combination of both urinary and recombinant FSH for ovarian stimulation improves oocyte maturity and embryo cleavage, and increases pregnancy and implantation rates.

Breed differences in clearance of porcine FSH in hypophysectomized rats

Extracts of anterior pituitary (AP) glands were infused i.v. into hypophysectomized male rats followed by sequential sampling of blood for 120 min. Determination of follicle-stimulating hormone (FSH) concentrations established that FSH from Chinese Meishan males decreased in the circulation of rats more slowly than FSH in extracts of AP from crossbred occidental pigs (P<0.003). Additionally, FSH from AP extracts of castrated males disappeared somewhat more slowly (P<0.06) than FSH from extracts of boars. Evaluation of FSH by bioassay and radioimmunoassay yielded similar concentrations in AP from Meishan and crossbred boars. Serum testosterone concentrations increased with time through 90 min after infusion of AP, but the rate of increase of testosterone was not related to amount of luteinizing hormone (LH) that was administered indicating LH receptor saturation. Unexpectedly, the rate of increase in testosterone was more rapid with AP extracts from boars than with extracts from castrated males. Observations from the current study imply structural alterations of FSH in the AP of Meishan males relative to crossbred males allowing sustained concentrations in the circulation, and this FSH possesses similar activation of the FSH receptor. The amount of LH in the AP extracts saturated the LH receptors of the hypophysectomized male rats, but some factor in extracts of boars differed from those of castrated males.

Development and characterization of a long-acting recombinant hFSH agonist

BACKGROUND

Fusion of the carboxyterminal peptide (CTP) of hCG to FSH results in a follitropin agonist with an extended half-life, presumably due to the four O-oligosaccharides on the CTP. Alternatively, an rhFSH analogue containing additional N-linked carbohydrate is described in this report.

METHODS

A DNA sequence containing two N-oligosaccharide signal sequences was ligated into a vector containing hFSHbeta- and alpha-subunit encoding cDNA, and expressed in CHO-K1 cells. In-vitro bioactivity of the single-chain hormone was assessed in CHO cells expressing the hFSH receptor. Pharmacokinetic values were derived from serial serum assays of the analogue in immature female rats following a single i.v. injection. In-vivo bioactivity was assessed by measuring ovarian weight gain 3 days post-injection.

RESULTS

rhFSH-N2 and native rhFSH induced comparable levels of cAMP in vitro. t(1/2) for native rhFSH, rhFSH-CTP and rhFSH-N2 were 3.7, 7.1 and 7.3 h respectively. Rats receiving rhFSH-N2 had a mean +/- SD ovarian weight 3 days post-i.v. injection (22 +/- 3.6 mg) significantly greater than rats receiving rhFSH and saline (16.7 +/- 1.5 and 15.3 +/- 0.47 mg respectively, P < 0.05).

CONCLUSIONS

rhFSH-N2 has prolonged half-life and increased bioactivity compared with native rhFSH. This rhFSH agonist, and other analogues containing additional N-oligosaccharides may have important clinical applications.

A biological, immunological and physico-chemical comparison of the current clinical batches of the recombinant FSH preparations Gonal-F and Puregon

The immunopotency and in-vitro biopotency of clinical batches of Gonal-F((R)) and Puregon((R)) (recombinant human follicle stimulating hormones) were compared and their carbohydrate chains investigated for charge heterogeneity and internal carbohydrate complexity. Immunopotency (IU/pmol) for both Gonal-F and Puregon was 0.35 +/- 0.01 and biopotency (ED(50), pmol/l) was similar, being 7.3 +/- 0.6 and 5.4 +/- 0.2 respectively. Charge distributions were essentially the same with no difference either in median isoelectric point (pI) (between 4.26 and 4.50), or in the bulk of material fractionated between pI 4 and 5 (66.0 +/- 1.8% Gonal-F and 72.0 +/- 1.8% Puregon). However, there were minor differences in charge at extremes of pI, Gonal-F being slightly more acidic: 18.2% Gonal-F versus 9.8% Puregon at pI 3.5-4.0 (P: = 0.03) and 6.7% Gonal-F versus 10.7% Puregon at pI 5.0-5.5 (P: = 0.03). Carbohydrate complexity was the same: 9.3 versus 10.9 (complex), 76.6 versus 78.6 (intermediate) and 14.1 versus 10.5% (simple). In summary, Gonal-F and Puregon have similar immunopotency, in-vitro biopotency and internal carbohydrate complexity, differing slightly in charge heterogeneity, Gonal-F having more acidic glycoforms. We conclude them to be intrinsically very similar, expecting no difference in clinical efficacy on the basis of respective structure.

Expression of a mammalian alpha 2,6-sialyltransferase gene in Pichia pastoris

Terminal sialic acid on oligosaccharides of glycoproteins shows several biological functions of the glycoproteins. The yeast Pichia pastoris normally does not contain sialic acid on the oligosaccharides of glycoproteins. A sialyltransferase (ST) gene was transfected into P. pastoris to assess the possibility of using yeast cells as a host to produce sialoglycoproteins. The expression vectors pPIC3.5 and pPIC9 were used as carriers. The recombinant P. pastoris harbouring ST-pPIC3.5 and ST-pPIC9 had sialyltransferase activity of 1.1 and 10.2 mU l(-1) respectively. The ability of the recombinant ST-pPIC3.5 and ST-pPIC9 to transfer the fluoresceinyl-NeuAc into the cell glycoproteins was 36.9 and 20.9 pmol mg -1 protein respectively.

Isoforms of human recombinant follicle-stimulating hormone: comparison of effects on murine follicle development in vitro

The effects of three isoforms derived from recombinant human FSH on ovarian follicle development in vitro were characterized for the first time. The three subfractions comprised discrete pI ranges of 3. 6-4.6 (acid), 4.5-5.0 (mid), and 5.0-5.6 (least acidic). Follicular growth, estradiol secretion, and antral formation were assessed for each fraction of isoforms in a range of concentrations over a 5-day culture period. Least acidic FSH produced, at and above 1.5 ng/ml, a high percentage of follicles growing above the size threshold necessary for antral formation, whereas mid and acid FSH induced similar growth only at higher concentrations (7.5 ng/ml and 50 ng/ml, respectively). Least acidic FSH specifically induced the most rapid growth of follicles during preantral development. Acid FSH at all concentrations stimulated estradiol-17ss secretion later during culture and antral formation in a lower proportion of follicles than did least acidic and mid FSH. It can be concluded 1) that the least acidic isoform induced fastest preantral growth, producing the largest antral follicles at the lowest dose of all three fractions and 2) that the less and mid acidic isoforms had more impact on stimulation of estradiol production and antral formation than the acid isoform.

Neither castration nor steroid-replacement change the apparent molecular size of FSH in the sheep pituitary

Gonadal steroids alter the apparent molecular size of intrapituitary Follicle-Stimulating Hormone (FSH) in rats and monkeys as well as increase the percentage of acidic FSH isohormones in sheep. Hence, we hypothesized that the molecular size of ovine (o) FSH would be increased by gonadal steroids. Extracts of pituitaries from rams and wethers, as well as, from wethers which had been implanted with dihydrotestosterone (DHT), 17 beta-estradiol (E2) or both steroids (n = 4-6 per treatment group) were subjected to analytical gel permeation chromatography using Sephadex g-100 Superfine. FSH concentrations in chromatographic fractions were determined by radioimmunoassays. Although FSH in pituitaries of non-implanted wethers eluted slightly earlier (i.e. larger) than FSH in pituitaries from E2-implanted wethers as evaluated by distribution coefficients (Kds) during chromatography (P < 0.05), gonadal steroids did not consistently increase Kds but tended to decrease them. When Kds were extrapolated to apparent molecular weights using a series of standard proteins (bovine serum albumin (bSA), ovalbumin (OA), carbonic anhydrase (CA) and cytochrome c (CC)) that were included in each chromatogram, the differences between treatment groups were not statistically significant (P > 0.05). Thus, in contrast to rats and monkeys, neither castration nor steroid-replacement appears to alter the molecular size of FSH in the sheep pituitary as evaluated by analytical gel permeation chromatography.

Recombinant technique and gonadotropins production: new era in reproductive medicine

OBJECTIVE

To review current knowledge regarding recombinant DNA technology and its safety and efficacy in relation to recombinant gonadotropin production.

DATA IDENTIFICATION AND SELECTION

Studies that relate specifically to recombinant DNA technology, method of laboratory production, and the clinical aspects of using recombinant gonadotropins were identified through literature and Medline searches.

RESULTS

Recent developments in recombinant DNA technology have resulted in a rapidly expanding range of new diagnostic and therapeutic opportunities. This technology paves the way to the identification, isolation, cloning, and production of specific proteins. Recently, recombinant human gonadotropins became available for clinical use. The pharmacokinetics, receptor availability, pharmacodynamics, and safety were studied extensively and the drugs were found to be identical if not superior to urinary gonadotropins that have been used in reproductive medicine for the last 30 years. It is clear today that the use of recombinant human gonadotropins is expected to provide better batch-to-batch consistency, steady supply, and most importantly, a purified compound with high specific activity, which accounts for >99% of the preparation's protein content, allowing SC administration.

CONCLUSION

There is no doubt that recombinant gonadotropins produced by genetic engineering technology are here to stay and will represent an important treatment modality in various fertility disturbances.

Comprehensive pharmacokinetics of urinary human follicle stimulating hormone in healthy female volunteers

PURPOSE

The study determined the pharmacokinetics of urinary human follicle stimulating hormone (u-hFSH) in 12 down-regulated healthy female volunteers.

METHODS

Following pituitary desensitization, baseline FSH serum levels were measured over a 24-hour period. Then each subject received, in random order, single doses of u-hFSH (Metrodin), 75 IU, 150 IU and 300 IU iv, and 150 IU im on four occasions separated by washout periods of one week. Blood and urine samples were collected at preset times. FSH levels were measured by a immuno-radiometric assay and an in vitro rat granulosa cells aromatase bioassay.

RESULTS

All doses of u-hFSH were well tolerated. After an iv bolus, the pharmacokinetics of FSH were well described by a two-compartment open model. Immunoassay data showed that the total exposure to FSH was proportional to the administered dose. Mean total clearance of FSH was approximately 0.5 L.h-1 and renal clearance was 0.14 L.h-1. The volume of distribution at steady-state was around 8 liters. The distribution half-life was 2 h and the terminal half-life nearly one day. After im injection, almost two thirds of the administered dose was available systemically. The in vitro bioassay confirmed this pharmacokinetic analysis.

CONCLUSIONS

The estimation of the elimination half-life of around one day indicates that the maximal effect of a given dose of u-hFSH administered daily cannot be observed until 3 to 4 days of repeated administration. This indicates that, on a pure pharmacokinetic basis, physicians should wait at least 4 days to assess the efficacy of a given dose of u-hFSH and that they should not modify dosage too frequently.

Application of a sensitive HPLC-based fluorometric assay to determine the sialic acid content of human gonadotropin isoforms

The human pituitary gonadotropins, follitropin (hFSH) and lutropin (hLH) are glycoproteins which are microheterogeneous in terms of their charge and molecular size, as well as their in vitro and in vivo bioactivities. The aim of this study was to determine the contribution of variations in sialic acid (N-acetyl neuraminic acid) content to the structural heterogeneity of these glycoproteins. Sialic acid (Neu5Ac) was released by partial acid hydrolysis (0.1 M TFA, 80 degrees C, 1 h) and derivatised with the fluorescent label DMB (1,2-diamino-4,5-methylenedioxybenzene) in conjunction with an internal standard (N-glycoyl-neuraminic acid). The derivatives were then separated by reversed-phase HPLC. This method allowed quantitation of the sialic acid content over a range of 5-100 pmol with between assay variation of < 6% for sialic acid released from approximately 100 ng (3 pmol) of hFSH or hLH. Comparison of the sialic acid contents of standard sialylated glycoproteins by either DMB-derivatisation or high-performance anion-exchange chromatography with pulsed amperometric detection yielded similar results, confirming the reliability of the fluorescence detection method. The sialic acid contents of 9 hFSH isoforms varied between 1.5-13.7 mol Neu5AC/mol FSH, whilst a range of 1.1-9.1 mol Neu5AC/mol LH was observed for 12 hLH isoforms. The sialic acid content of the hFSH isoforms was also observed to be related to the hormonal specific activity in a radioreceptor assay, confirming that alterations in the carbohydrate structure can influence the FSH-receptor interaction. In contrast, the sialic acid content of the hLH isoforms was found to be not related to specific activity at the receptor level.

A novel, nonradioactive in vivo bioassay of thyrotropin (TSH)

A new and simple in vivo bioassay suitable for routine testing of pituitary and recombinant TSH preparations was developed. Male Albino Swiss CF-1 mice were given T3 in their drinking water to suppress endogenous TSH. T3, 3.0 micrograms/mL, given to mice for a period of 4 days decreased plasma total T4 (TT4) level to less than 10% of the nonsuppressed (control) level. Various doses of exogenous pituitary and recombinant TSH preparations were injected intraperitoneally and blood samples were obtained from the orbital sinus 6 h later. The TT4 level, measured by radioimmunoassay, served as the assay end-point. The assay required injection of approximately 3.0 micrograms of pituitary human TSH (phTSH), 1.0 microgram recombinant human TSH (rhTSH), 0.2 microgram bovine TSH (bTSH), and 0.1 microgram rat TSH (rTSH) to attain half-maximal response. The maximal level of TT4 after TSH stimulation was similar to that observed in normal, nonsuppressed mice. The procedure developed is relatively easy to perform, economical, and, unlike earlier TSH bioassays, does not require the use of radionuclides. This bioassay showed acceptable sensitivity and reliability in structure-function studies of pituitary TSH from different species as well as rhTSH.

Developmental patterns of bioactive and immunoreactive FSH in the female rabbit: effects of ovariectomy

A longitudinal study was performed to determine the relationship between immunoreactive and biologically active FSH in the serum of sham-operated and ovariectomized female rabbits. Twenty-two-day-old female rabbits, 8 per group, were sham-operated or bilaterally ovariectomized on day 23. Blood was taken every 3-4 days from each rabbit until they achieved a weight of 3 kg or age 100 days. Sera were analysed by radioimmunoassay for LH and FSH or for bioactive FSH. In sham-operated animals, immuno-FSH levels showed a 10-fold increase from 0.36 +/- 0.04 ng/ml to greater than 35 ng/ml between days 45 and 80. By contrast, bio-FSH levels increased more gradually from a baseline of 5.4 +/- 0.4 ng/ml to about 8 ng/ml. Bilateral ovariectomy resulted in a significant increase in both bio-FSH, 5.5 +/- 0.4 ng/ml to 12.6 +/- 1.5 ng/ml and immuno-FSH levels from 0.4 ng/ml to 5.2 +/- 1.4 ng/ml 24 h later. These levels of FSH remained elevated throughout the sampling period in both groups of animals and then decreased after day 100. Peripheral LH levels showed much more variation but were 2-fold higher in ovariectomized rabbits, 0.4-1.4 ng/ml in sham-operated vs. 0.8-2.4 ng/ml in ovariectomized rabbits. These results emphasize the marked variations in FSH levels according to the method of analysis. They also suggest that extra-ovarian factors may play a role in inhibiting gonadotropin release especially LH.

Isolation and structure determination of the intact sialylated N-linked carbohydrate chains of recombinant human follitropin expressed in Chinese hamster ovary cells

Biologically active recombinant human follitropin has been expressed in Chinese hamster ovary cells. The carbohydrate chains of the recombinant glycoprotein hormone were enzymatically released by peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase F. The oligosaccharides were separated from the N-deglycosylated protein by gel-permeation chromatography on Bio-Gel P-100, and fractionated by a combination of FPLC on Mono Q and HPLC on Lichrosorb-NH2. The structures of the carbohydrate chains were determined by 500- or 600-MHz 1H-NMR spectroscopy. The following types of carbohydrates occur: monosialylated diantennary (10%), disialylated diantennary (43%), disialylated tri-antennary (5%), trisialylated tri-antennary (13%), trisialylated tri'-antennary (8%), and tetrasialylated tetraantennary (12%) N-acetyllactosamine type of carbohydrate chains, all bearing exclusively alpha 2-3-linked N-acetylneuraminic acid (Neu5Ac). Previously, for pituitary follitropin mono-, di-, tri-, tri'-, and tetra-antennary oligosaccharides containing alpha 2-3- as well as alpha 2-6-linked Neu5Ac residues were reported. The bisecting GlcNAc residues present in native follitropin were not detected in the recombinant glycoprotein. Of the oligosaccharides 29% have an alpha 1-6-linked Fuc residue at the asparagine-bound GlcNAc, whereas this amount is about 50% in pituitary follitropin. In some of the tri-, tri'- and tetra-antennary oligosaccharide fractions small amounts (less than 5%) of compounds were detected having one or more additional N-acetyllactosamine units.

The charge characterization of native and deglycosylated thyrotropin

Chromatofocusing was used to characterize the charge microheterogeneity of crude pituitary, highly purified native bovine (b) and deglycosylated (dg) thyrotropin (TSH) preparations. Greater than 90% of crude pituitary TSH and native bTSH-I-1 bound to concanavalin-A (conA) columns while dgbTSH was excluded from the column. Extracts of ovine (o) pituitaries contained at least nine species (isohormones) of immunoreactive TSH when chromatofocused on pH 7.5-4 gradients. Highly purified native bTSH-I-1 displayed a similar elution profile. In contrast, dgbTSH eluted as a single homogeneous species with an apparent pI greater than 7.5. When subjected to chromatofocusing on a pH 10.5-7 gradient, 68% of crude pituitary oTSH and 96% of native bTSH-I-1 was bound to the column but could be eluted with NaCl indicating acidic species, while at least three peaks of dgbTSH could be resolved having apparent pI's of 9.12, 9.03 and 8.98. These data suggest that although removal of the carbohydrate moieties markedly alters the isohormone pattern of TSH, chemical deglycosylation does not completely eliminate the charge microheterogeneity of bTSH.

Pituitary glycoprotein hormone oligosaccharides: structure, synthesis and function of the asparagine-linked oligosaccharides on lutropin, follitropin and thyrotropin

Luteinizing hormone (LH), follicle-stimulating hormone (FSH) and thyroid-stimulating hormone (TSH) from pituitary and chorionic gonadotropin (CG) from placenta are a family of closely related glycoproteins. Each hormone is a heterodimer, consisting of an alpha- and a beta-subunit. Within an animal species, the alpha-subunits of all four glyco-protein hormones have an identical amino acid sequence, whereas each beta-subunit is distinct and confers hormone-specific features to the heterodimer. LH and FSH are synthesized within the same cell, the gonadotroph of the anterior pituitary, but are predominantly stored in separate secretory granules. We have characterized the asparagine-linked oligosaccharides on bovine, ovine and human LH, FSH and TSH. The various pituitary hormones were found to contain unique sulfated oligosaccharides with the terminal sequence SO4-4GalNAc beta 1----4GlcNAc beta 1----2Man alpha, sialylated oligosaccharides with the terminal sequence SA alpha Gal beta GlcNAc beta Man alpha, or both sulfated and sialylated structures. Despite synthesis of LH and FSH in the same pituitary cell, sulfated oligosaccharides predominate on LH while sialylated oligosaccharides predominate on FSH for all three animal species. We have examined the reactions leading to synthesis of the sulfated oligosaccharides to determine which steps are hormone specific. The sulfotransferase is oligosaccharide specific, requiring only the sequence GalNAc beta 1----4GlcNAc beta 1----2Man alpha. In contrast, the GalNAc-transferase appears to be protein specific, accounting for the preferential addition of GalNAc to LH, TSH, and free (uncombined) alpha-subunits compared with FSH and other pituitary glycoproteins. The predominance of sulfated oligosaccharide structures on LH may account for sorting of LH and FSH into separate secretory granules. Differences in sulfation and sialylation of LH, FSH and TSH may also play a role in the regulation of hormone bioactivity.

Naturally occurring antihormones: secretion of FSH antagonists by women treated with a GnRH analog

Follicle-stimulating hormone (FSH) is a glycoprotein essential for gonadal development and steroidogenesis. Recent studies suggest that deglycosylation of FSH results in the formation of antagonistic proteins that are capable of binding to gonadal receptors but that are devoid of bioactivity. Treatment of hypogonadal women with an antagonist of gonadotropin-releasing hormone substantially decreased serum FSH bioactivity with minimal changes in immunoreactivity. Chromatofocusing and size fractionation of the serum samples indicated the secretion of immunoreactive FSH isoforms that are devoid of bioactivity but that are capable of blocking FSH action in ovarian granulosa cells. These findings provide the first demonstration of naturally occurring circulating antihormones. These FSH antagonists may play an important role in the physiology and pathophysiology of the gonads.

Tonic inhibition of adenylate cyclase in cultured hamster Sertoli cells

Sertoli cells cultured from immature hamsters respond to FSH with a dose-related increase in cAMP accumulation. Pertussis toxin acts synergistically with FSH to stimulate cAMP accumulation. This effect of pertussis toxin indicates that Sertoli cell adenylate cyclase is under tonic inhibition due to the activity of the Ni inhibitory transducer. The acetylcholine receptor antagonists atropine or tubocurarine, or the opioid antagonist naltrexone, have no effect on the FSH-induced stimulation of cAMP accumulation, suggesting that neither acetylcholine nor opioids are responsible for the inhibition of Sertoli cell cyclase. While exogenous adenosine is inhibitory, adenosine deaminase augments the ability of FSH to stimulate cAMP accumulation, but not to the level of pertussis toxin. This indicates that the Sertoli cells produce endogenous adenosine that is at least partially responsible for the tonic inhibition of adenylate cyclase. Other possibilities for the tonic inhibition of cyclase include other Sertoli cell products, germ cell products, peritubular cell products or an action of FSH itself through both stimulatory and inhibitory transducers.

Differential processing of Asn-linked oligosaccharides on pituitary glycoprotein hormones: implications for biologic function

Luteinizing hormone, follicle-stimulating hormone, and thyroid-stimulating hormone from pituitary and chorionic gonadotropin from placenta are a family of glycoproteins, each consisting of an alpha and beta subunit. Within an animal species, the alpha subunit of all four hormones contains the identical amino acid sequence, while each beta subunit is distinct and confers biologic specificity to the hormone dimer. Despite sharing common alpha subunits, these hormones bear Asn-linked oligosaccharides which differ in structure. Whereas chorionic gonadotropin contains exclusively neutral and sialylated oligosaccharides, the pituitary hormones bear neutral, sialylated, sulfated, and sialylated/sulfated structures. The sulfated oligosaccharides are unique in structure and are more prevalent on certain pituitary hormones, indicating that the synthesis of these unusual oligosaccharides is tightly regulated. The differences in oligosaccharide structures in conjunction with the highly specific endocrine responses elicited by these hormones, suggest an important functional role for the oligosaccharides, such as metabolic clearance, control of hormone response, modulation of hormone potency, and/or intracellular sorting of hormones into separate secretory granules.