Decreased follistatin gene expression in gonadotroph adenomas

What growth factors are involved in the pathogenesis of gonadotroph adenomas is not yet known. Activin is one possible candidate because it stimulates growth and differentiation in many cells, including the gonadotroph cell, and it stimulates FSH secretion, characteristic of gonadotroph adenomas. As activin beta B-subunit is expressed in gonadotroph adenomas, we sought to determine whether activin receptor II and follistatin are also expressed. Total ribonucleic acid (RNA) was extracted from 10 gonadotroph adenomas that did not express pit-1 and was reverse transcribed. The resulting complementary DNAs for human activin receptor II and follistatin were amplified by PCR. All 10 adenomas expressed activin receptor II messenger RNA (mRNA), as did nonadenomatous pituitary tissue. Only 2 of the 10 gonadotroph adenomas expressed detectable follistatin mRNA, although all 4 nonadenomatous pituitaries did. Quantitation of follistatin mRNA by competitive reverse transcription-PCR showed that none of the 10 gonadotroph adenomas expressed as much follistatin mRNA as did the 4 nonadenomatous pituitaries, and 8 of the 10 expressed less than 10% as much. Immunospecific staining showed follistatin in the cytoplasm of the gonadotroph cells of all 5 nonadenomatous pituitaries studied, but only faintly in 1 gonadotroph adenoma and not at all in the other 9. These results suggest that pit-1-negative gonadotroph adenomas express less follistatin mRNA and follistatin peptide than do nonadenomatous gonadotroph cells. A consequence could be less binding, and thereby enhanced effectiveness, of activin, contributing to adenoma growth.

Expression of activin/inhibin subunit messenger ribonucleic acids by gonadotroph adenomas

As an initial step in determining whether activin could play a role in the development of gonadotroph adenomas, we attempted to determine if activin/inhibin subunit messenger ribonucleic acids (mRNAs) are expressed by these pituitary tumors. We selected 19 pituitary adenomas that had been excised by transsphenoidal surgery and determined by immunocytochemical criteria to be gonadotroph adenomas. Total RNA was extracted from these adenomas and reverse transcribed. The resulting pit-1 complementary DNA, expected to be present only in somatotroph, lactotroph, and thyrotroph cells, was amplified by the polymerase chain reaction to test the possibility that the adenoma tissue was contaminated by normal pituitary tissue. Only the 10 adenomas that did not express pit-1 mRNA were subjected to further analysis by polymerase chain reaction amplification of the adenoma reverse transcriptase products for the activin/inhibin beta B-, beta A-. and alpha-subunits. All 10 adenomas expressed beta B-subunit, none of the 10 expressed the beta A-subunit, and 6 of the 10 expressed the alpha-subunit. We conclude that gonadotroph adenomas express mRNAs for activin/inhibin beta B- and alpha-subunits. The relationship of beta B expression to the pathogenesis of gonadotroph adenomas remains to be determined.

Identification of gonadotroph adenomas in men with clinically nonfunctioning adenomas by the luteinizing hormone beta subunit response to thyrotropin-releasing hormone

Because of the recent finding that a majority of clinically nonfunctioning pituitary macroadenomas in women could be identified as of gonadotroph origin by their LH beta-subunit responses to TRH, we evaluated in this study the value of the LH beta-subunit response to TRH in identifying gonadotroph adenomas in men with clinically nonfunctioning macroadenomas. Thirty-eight consecutively studied men with clinically nonfunctioning macroadenomas were given TRH iv, and intact FSH and LH and LH beta- and alpha-subunits were measured every 15 min for 90 min before and 90 min after. TRH tests were also performed on 15 healthy, age-matched control men and on 12 men with adenomas secreting GH or PRL. Of the 38 men with clinically nonfunctioning macroadenomas, basal values were supranormal in 10 for FSH and in 6 each for alpha- and LH beta-subunits. Responses to TRH were elevated, compared to the healthy, age-matched controls, in 14 for LH beta-subunit and in 5 each for intact FSH and LH. None of the men with adenomas secreting GH or PRL exhibited supranormal responses to TRH. Of the 38 clinically nonfunctioning adenomas, 35 were established in dispersed cell culture, and 29 secreted readily detectable amounts of intact FSH, LH, and LH beta-subunit, strongly suggesting that these adenomas were of gonadotroph cell origin. We conclude that the LH beta-subunit response to TRH can identify gonadotroph adenomas in men with clinically nonfunctioning adenomas better than can basal concentrations of intact FSH and alpha-subunit, alone or combined, but not as well as it can in women.

Recognition of gonadotroph adenomas in women

BACKGROUND

Pituitary adenomas that arise from the gonadotroph cells are being recognized with increasing frequency in men, but they are still rarely recognized in women. This rarity could be the result of an actual difference in occurrence or of greater difficulty in recognition. The tumors are usually recognized in men more than 50 years old, but elevated serum gonadotropin levels in women of that age could be produced by normal gonadotroph cells.

METHODS

Because the stimulation of follicle-stimulating hormone (FSH), luteinizing hormone (LH), and the beta subunit of LH (LH beta) by thyrotropin-releasing hormone (TRH) is a characteristic of gonadotroph adenomas in men, we administered TRH to 16 women with apparently nonsecreting pituitary macroadenomas and measured serum FSH, LH, LH beta, and the glycoprotein hormone alpha subunit every 15 minutes for 90 minutes before and 90 minutes after. The results were compared with the responses in 16 healthy women matched for age and in 10 women with macroadenomas secreting prolactin, growth hormone, or corticotropin. The tumors from 12 of the women with nonsecreting adenomas were cultured, and the secretion of FSH, LH, and LH beta in culture was determined.

RESULTS

Eleven of the 16 women with apparently nonsecreting adenomas had significant increases in serum LH beta in response to TRH, 3 had FSH responses, and 4 had LH responses. None of the 16 healthy women and none of the 10 women with secreting macroadenomas had LH beta, FSH, or LH responses to TRH. Ten of the 12 adenomas that were cultured secreted readily detectable amounts of FSH, LH, and LH beta, and their secretion in vitro correlated with the patients' responses to TRH in vivo.

CONCLUSIONS

Most apparently nonsecreting pituitary macroadenomas in women arise from gonadotroph cells. The majority of these can be recognized, even in postmenopausal women, by the serum LH beta responses to TRH, and some can be recognized by the responses of serum FSH and LH.

Secretion of chorionic gonadotropin by cultured human pituitary cells

To investigate the possibility that the human pituitary gland secretes CG, we used a highly specific, two-site, double monoclonal immunoradiometric assay to measure CG in the medium in which the dispersed cells of pituitary glands from human fetuses of 20-24 weeks gestation were cultured. The cross-reactivity of immunopurified human LH in the CG assay was less than 0.03%. LH was also measured by a double monoclonal immunoradiometric assay. Secretion of CG by the cultured fetal pituitary cells was readily detectable, although in gradually decreasing amounts, for the 11 days of culture. LH secretion paralleled CG secretion and was much greater in magnitude. Pituitary cells from female fetuses generally secreted more CG as well as more LH than those from male fetuses. Dilutions of the medium showed that the secreted CG exhibited parallelism with the CG standard. Chromatofocusing of the medium across a pH 6-9 gradient yielded several peaks of LH immunoreactivity between pH 6.5 and 8.5, but no peaks of CG. Chromatofocusing of the medium across a pH 3-7 gradient yielded peaks of CG, but not LH, between pH 4.0-5.5. These data indicate that CG immunoreactivity, distinct and separable from LH immunoreactivity, is secreted by the dispersed cells of fetal human pituitary glands.

Secretion of multiple forms of human luteinizing hormone by cultured fetal human pituitary cells

Previous studies of the heterogeneity of human LH have employed LH stored within the pituitary gland. In this study we characterized LH secreted by dispersed fetal human pituitary cells. Chromatofocusing across a pH 9-6 gradient of the medium in which fetal pituitary cells had been grown yielded at least eight distinct peaks of LH immunoreactivity. The more basic LH peaks bound more strongly to Concanavalin-A-Sepharose than did the more acidic ones, suggesting that the more basic LH molecules contain more hybrid oligosaccharides, in which one antenna terminates in a mannose, and that the more acidic human LH molecules contain more complex oligosaccharides, in which both antennae terminate in negatively charged groups, sialic acid and/or N-acetylgalactosamine-sulfate. The biological/immunological activity (B/I) ratios of the secreted LH varied directly and dramatically with the pI, from 8.1 at pI 8.4 to 1.1 at pI 6.3. Secreted LH, therefore, exhibits similar heterogeneity of glycosylated forms as does stored LH, raising the possibility that the hormones that control overall LH secretion could affect the secretion of some isohormones more than others and thereby influence LH biological activity to a degree not predicted by measuring total LH immunoreactivity.

Characterization of human LH isohormones from fresh pituitary tissue

The pattern of human LH (hLH) microheterogeneity was determined using freshly obtained pituitary tissue. Chromatofocusing across a pH 9-6 gradient produced several, distinct peaks of hLH immunoreactivity between pH 8.5 and 6.8, as well as a 'salt peak'. Chromatofocusing of the 'salt peak' across a pH 7-4 gradient yielded distinct peaks of hLH at pH 6.1, 5.6, and 5.4. Pituitary tissue obtained at surgery produced a virtually identical pattern. By gel filtration the elution volume of each major chromatofocusing peak was similar to that of intact hLH, rather than those of the hLH subunits. The bioactivity/immunoreactivity ratios of the major chromatofocusing peaks fell dramatically with decreasing pH, from approximately 8 at pH 8.5 to approximately 1 at pH less than 6. These results indicate that human pituitary LH exists in multiple, isomeric forms that differ markedly in charge and bioactivity. These differences appear to be inherent in the native, intact molecules and not the result of autolysis or of dissociation into subunits.

Similar isoelectric profiles of FSH from gonadotroph cell adenomas and non-adenomatous pituitaries

Heterogeneity of intact FSH in human pituitary tissue was evaluated by the column isoelectric focusing technique, chromatofocusing. FSH was examined from three autopsy pituitaries, one piece of apparently normal pituitary obtained at surgery, three purified FSH preparation, and four gonadotroph cell adenomas. FSH from all of these sources was found to exist in multiple isoelectric forms. FSH from the gonadotroph cell adenomas exhibited chromatofocusing profiles that were similar, both in the range of pI's and the relative proportions of the FSH isohormones, to those of the non-adenomatous pituitaries. We conclude that gonadotroph cell adenomas produce a population of FSH that is qualitatively normal although quantitatively excessive.

Comparison of hormonal secretory behavior of gonadotroph cell adenomas in vivo and in culture

To determine whether pituitary macroadenomas associated with supranormal serum FSH concentrations represent gonadotroph cell adenomas or nonsecreting adenomas that selectively impair LH secretion by normal gonadotroph cells, we studied the secretory behavior in dispersed cell culture of three pituitary adenomas from patients who had supranormal serum FSH concentrations. Similar comparisons were made for 11 other adenomas, which were associated with the in vivo hypersecretion of alpha-subunit (n = 4) or PRL/GH (n = 4) or with no obvious hypersecretion (n = 3). Adenomas associated with supranormal serum FSH in vivo released more FSH in culture (5.1-27.0 ng/well . 24 h) than they did other hormones (TSH, less than 0.33; GH, less than 0.10; PRL, less than 0.14 ng/well . 24 h) and more FSH than did PRL/GH-secreting (less than 0.1-0.9 ng/well . 24 h) and nonsecreting (less than or equal to 0.5 ng/well . 24 h) adenomas. Adenomas associated with supranormal serum alpha-subunit in vivo released not only more alpha-subunit in culture (7.2-22.0 ng/well . 24 h) than did other adenomas (0.1-2.4 ng/well . 24 h), but two of them also released as much FSH (12.7 and 17.0 ng/well . 24 h) as did adenomas associated with supranormal serum FSH. The close correlation between the hormonal secretory behavior in vivo and that in culture of the three pituitary macroadenomas associated with supranormal serum FSH concentrations suggests that these are indeed adenomas of gonadotroph cells that are hypersecreting FSH. The release of relatively large amounts of FSH by cultured cells of adenomas that appeared to be hypersecreting only alpha-subunit in vivo suggests that at least some alpha-subunit-secreting adenomas are also gonadotroph cell adenomas.

Secretion of uncombined subunits of luteinizing hormone by gonadotroph cell adenomas

The nature of the LH abnormality in four men who had gonadotroph cell pituitary adenomas was studied to determine why they had supranormal serum LH concentrations but subnormal or normal serum testosterone concentrations. When basal sera from these four men were subjected to gel filtration chromatography, FSH immunoreactivity eluted principally in the position of intact FSH, but the elution patterns of LH immunoreactivity were biphasic; one peak corresponded to intact LH, and another peak corresponded to the LH subunits, LH beta and alpha. Gel filtration of sera obtained after administration of TRH showed increases in LH immunoreactivity predominantly in the subunits peak. The subunits peak in basal sera consisted principally of alpha, but the percent increase in LH beta in post-TRH sera was greater. When dispersed cells from one gonadotroph adenoma were cultured, medium LH immunoreactivity eluted with the LH subunits. LH beta release into the medium was somewhat greater than alpha initially, but declined more rapidly. We conclude that the apparent hypersecretion of immunoreactive LH of impaired biological activity by four men with gonadotroph cell adenomas represents hypersecretion of LH beta- and alpha-subunits that are uncombined, perhaps because of a structural abnormality or anatomical compartmentalization.

Characterization of pepsin-solubilized bovine heart-valve collagen

Collagens extracted from heart valves by using limited pepsin digestion were fractionated by differential salt precipitation. Collagen types were identified by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, amino acid analysis and cleavage with CNBr. Heart-valve collagen was heterogeneous in nature, consisting of a mixture of type-I and type-III collagens. The identity of type-III collagen was established on the basis of (a) insolubility in 1.7 M-NaC1 at neutral pH, (b) behaviour of this collagen fraction on gel electrophoresis under reducing and non-reducing conditions, (c) amino acid analysis showing a hydroxyproline/proline ratio greater than 1, and (d) profile of CNBr peptides on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis showing a peak characteristic for type-III collagen containing peptides alpha1(III)CB8 and alpha1(III)CB3. In addition to types-I and -III collagen, a collagen polypeptide not previously described in heart valves was identified. This polypeptide represented approx. 30% of the collagen fraction precipitated at 4.0 M-NaCl, it migrated between beta- and alpha1-collagen chains on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and its electrophoretic behaviour was not affected by disulphide-bond reduction. All collagen fractions from the heart valves contained increased amounts of hydroxylysine when compared with type-I and -III collagens from other tissues. The presence of beta- and gamma-chains and higher aggregates in pepsin-solubilized collagen indicated that these collagens were highly cross-linked and suggested that some of these cross-links involved the triple-helical regions of the molecule. It is likely that the higher hydroxylysine content of heart-valve collagen is responsible for the high degree of intermolecular cross-linking and may be the result of an adaptive mechanism for the specialized function of these tissues.