Síndrome de Turner con isocromosoma X: diagnóstico tardío / Turner' s syndrome with isochrome X: delayed diagnosis

No disponible

Mechanism of action of pituitary adenylate cyclase-activating polypeptide (PACAP) in human nonfunctioning pituitary tumors.

Several evidence suggest that pituitary adenylate cyclase activating polypeptides (PACAP-38 and -27) could function as hypophysiotropic factors. Both peptides interact with either the type I receptor, which preferentially binds the two PACAPs and has a much lower affinity for vasoactive intestinal polypeptide (VIP) or the type II receptor, which binds the two PACAPs and VIP with a nearly equal affinity. In addition to the stimulation of adenylyl cyclase (AC) activity, in different cell types PACAP causes an increase of cytosolic calcium levels ([Ca2+]i), consequent to phospholipase-C activation. In the present study, we investigated the effect of PACAP on cAMP formation and [Ca2+]i levels in 16 human nonfunctioning pituitary adenomas (NFPA). PACAP-38 increased cAMP formation in all tumors; the peptide stimulated either AC activity in membrane preparations from 26 +/- 10 to 214 +/- 179 pmol/mg prot/min (P < 0.01) or cAMP efflux from 12 +/- 5.4 to 73.2 +/- 32 pmol/well (P < 0.01) in cultured cells. The effect, detectable at concentrations higher than 1-10 pM, was maximal at 0.1-10 nM. While PACAP-38 and PACAP-27 were nearly equally effective and potent, 100-fold higher concentrations of VIP were required to obtain similar AC activation. GHRH and CRH were ineffective in any NFPA. The PACAP effect was not antagonized by a VIP antagonist, while PACAP fragment 6-27 amide partially reduced the stimulatory effects of both PACAP-27 and VIP in 2 out of 3 tumors tested. PACAP-38 caused a [Ca2+]i rise in cells obtained from 7 NFPA (from 110 +/- 34 to 151 +/- 40 nM [Ca2+]i, P < 0.05) while in the remaining 7 the peptide was ineffective at any concentrations tested (from 1 nM to 10 microM). In the responsive tumors, PACAP-38 effect was not consequence of phospholipase-C activation since removal of extracellular Ca2+ as well as blockade of L-type Ca2+ channels by dihydropyridine antagonists abolished [Ca2+]i increase triggered by the peptide. These data indicate that PACAP is by far the most potent activator of cAMP formation in NFPA and suggest a possible modulatory action of this peptide on cell growth.

Serum levels of beta-subunit of chorionic gonadotropin in patients with pituitary tumors.

Many studies have shown that normal and tumoral pituitary is able to synthesize chorionic gonadotropin (CG). The aim of the present work was to investigate the circulating levels of free beta-subunit of CG (CG-beta) in a large number of patients with pituitary tumors in basal conditions and after thyrotropin-releasing hormone (TRH) injection. The study includes 27 healthy subjects, 23 patients with prolactinoma, 20 with growth hormone-secreting adenoma and 77 with non-functioning pituitary adenoma (NFPA). The CG-beta was evaluated using a new one-step immunometric assay employing two monoclonal antibodies directed against epitopes present only on the free CG-beta and showing a detection limit of 0.04 U/l and a cross-reactivity with complete CG < 0.01%. In basal conditions, serum CG-beta was undetectable in healthy subjects and in the majority of patients, while in seven patients with NFPA and four with prolactinoma the CG-beta values ranged between 0.05 and 0.72 U/l. In these 11 patients serum levels of intact CG were found within the normal range (normal range < 5 U/l), while two patients with NFPA and one with prolactinoma had levels of free alpha-subunit inappropriately high with respect to gonadotropins and thyrotropin. Injection of TRH caused CG-beta to increase in two out of 16 patients with NFPA, whereas it was ineffective in 12 healthy subjects and 10 patients with prolactinoma. The present data indicate that detectable level of CG-beta not associated with hypersecretion of the intact CG molecule may be observed in about 10% of patients with NFPA or prolactinoma, while abnormal CG-beta responses to TRH are observed infrequently in individual patients with NFPA.

Abnormal transduction of dopamine signal in human nonfunctioning pituitary adenomas.

It is well established that dopamine (DA) plays an important role in inhibiting anterior pituitary function. DA receptors present in the pituitary show the pharmacological and biochemical characteristics of the D2 receptor; in fact, they are coupled to the inhibition of both adenylyl cyclase (AC) activity and the reduction of cytosolic free Ca2+ levels ([Ca2+]i) suggesting the involvement of different G-proteins. While the DA receptors present in human PRL-omas display these characteristics, no information is available on the coupling mechanism(s) of DA receptors expressed in nonfunctioning pituitary adenomas (NF-PA). In the present study, the effect of DA on AC activity and [Ca2+]i was investigated in 8 NFPAs surgically removed by the transphenoidal route. DA, at concentrations between 0.01 and 10 mumol/l, had no effect on cAMP formation in any tumor (from 27.6 +/- 11.9 to 27.9 +/- 11.0 pmol/mg prot/min; NS). By contrast, DA was effective in reducing [Ca2+]i levels either in resting conditions or after TRH stimulation in 5 out of 8 tumors, suggesting that NFPA express DA receptors with a defective transduction mechanism. As in these tumors SRIH caused the expected inhibition of both AC activity (from 31.4 +/- 9.3 to 24.4 +/- 11.0 pmol/mg prot/min; p < 0.005) and [Ca2+]i levels, it is likely that the lack of DA action on AC activity may be due to functional/structural properties of DA receptors expressed in NFPA, instead of a defect at the level of Gi proteins. In conclusion, these data indicate that DA receptors expressed in NFPA show a defective transduction mechanism, leading to a partial inhibitory response.

Abnormal response of luteinizing hormone beta subunit to thyrotrophin-releasing hormone in patients with non-functioning pituitary adenoma.

OBJECTIVE: It has been suggested that the response of free beta-subunit of LH (LH beta) to TRH is the most useful in-vivo marker of gonadotroph adenomas in patients with non-functioning pituitary adenomas (NFPA). The aim of the present study was to investigate LH beta secretion in patients with NFPA in whom other markers of gonadotroph adenomas, such as supranormal basal concentrations or responses of intact gonadotrophins to TRH, were absent. DESIGN AND PATIENTS: Serum basal levels of LH beta LH and FSH were evaluated in 80 patients with NFPA showing normal levels of intact gonadotrophin, 20 with PRL-secreting adenomas, 25 with GH-secreting adenomas and 58 healthy subjects. Moreover, LH beta, LH, FSH and alpha-subunit (alpha-SU) were evaluated in 27 patients with NFPA in whom intact gonadotrophin responses to TRH were absent, 8 with PRL-oma, 7 with GH-oma and 17 healthy subjects before and 20, 30 and 60 minutes after the intravenous administration of either 200 micrograms TRH or placebo. A response was considered present when serum LH beta increased by at least 50% above basal levels. MEASUREMENTS: LH beta was evaluated using a new assay based on the sequestration of the combined and free alpha-SU by an anti alpha-SU biotinylated monoclonal antibody (MAb) and the subsequent measurement of the LH beta by an IFMA method employing two MAbs directed towards two different epitopes on LH beta. Intact LH and FSH were assayed with an IFMA method and alpha-SU with an IRMA method. RESULTS: In basal conditions, no significant difference in the mean values of LH beta was observed among patients with different types of tumour and normal controls. In 9 of 27 (33%) patients with NFPA, TRH caused an abnormal elevation of serum LH beta (net increase 410 +/- 403%, range 71-1300) which was completely dissociated from changes in intact gonadotrophins. Of the 5 patients who had a TRH test repeated after transsphenoidal surgery, abnormal LH beta responses disappeared in 2 and were maintained in 3. Disappearance of LH beta response occurred only in patients in whom improvement of visual field and radiological imaging after adenomectomy was observed. In contrast, in all patients with pituitary tumours other than NFPA and healthy subjects a response to TRH was absent (net increase ranging from 0 to 23%). Immunofluorescence, performed on 14 NFPA removed from patients either responsive or unresponsive to TRH, showed a variable proportion of cells positive for LH beta, without a significant difference between the two groups. CONCLUSIONS: These results indicate that measurement of basal LH beta is of poor value in the diagnosis of non-functioning pituitary adenomas and the identification of gonadotroph adenomas among non-functioning pituitary adenomas. Conversely, an abnormal response of free LH beta to TRH occurs in about a third of patients with low/normal basal gonadotrophins unresponsive to TRH stimulation.

Immunodetection of chorionic gonadotropin and its subunits in human nonfunctioning pituitary adenomas.

Human nonfunctioning pituitary adenomas (NFPA) may produce CG in addition to the classical glycoprotein hormones (LH, FSH, and TSH). The aim of the present study was to localize LH beta, FSH beta, TSH beta, alpha-subunit (alpha SU), CG, and its beta-subunit (beta SU) in NFPA using a highly specific immunohistochemical technique. Nine NFPA, obtained at surgery, were processed for both electron microscopy and immunohistochemistry. Three tumors resulted oncocytomas, and six were null cell. Using an immunofluorescence technique, all tumors were positive for at least one glycoprotein; in particular, seven adenomas were markedly positive for CG beta, whereas only two were positive for the intact CG. No association among LH beta, FSH beta, and CG beta positivity could be demonstrated in the different adenomas. In the seven tumors positive for both CG beta and alpha SU, double fluorescence labeling demonstrated that six cases localized CG beta and alpha SU in different cells, but only one tumor showed the two subunits colocalized in the same cells. These data confirm that pituitary tumors synthesize both alpha SU and beta SU of glycoprotein hormones; in particular, the present study indicates that the majority of NFPA is able to synthesize CG, particularly its beta SU. Moreover, the localization of CG beta and alpha SU in different tumoral cells might account for the preferential expression of beta SU and alpha SU instead of the intact hormonal molecules in NFPA.

Differential transduction of dopamine signal in different subtypes of human growth hormone-secreting adenomas.

This article reports the effect of dopamine (DA) on adenylyl cyclase (AC) activity and intracellular free calcium concentration ([Ca2+]i) in 20 GH-secreting pituitary adenomas exclusively composed of somatotrophs (GH-omas) and 3 tumors largely constituted by mammosomatotrophs (MS-omas). DA (between 10 nmol/L and 100 mumol/L) did not reduce AC activity in any GH-omas, whereas the amine caused a significant inhibition in membranes from all MS-omas. The effect was detectable at DA concentrations higher than 0.1 mumol/L, and maximal inhibition (ranging from 24-30%) was reached at 10 mumol/L. The ergot derivative CH 29717 and l-sulpiride demonstrated potent agonist and antagonist activities, respectively. Somatostatin reduced AC activity in all tumors; the percent inhibition values (between 17-34%) were similar in GH-omas and MS-omas. In both GH-omas and MS-omas, DA (1 mumol/L) caused a significant [Ca2+]i reduction (between 17-44%) that was essentially due to the block of Ca2+ influx from the extracellular spaces. The receptors involved in this effect showed the pharmacological properties of D2 receptors. In conclusion, the DA effect in tumoral somatotrophs is defective; DA fails to exert an inhibitory action on AC activity. In mammosomatotrophs, the typical D2 receptor-effector coupling is retained, resulting in decreased AC activity in these cells.

In vitro detection of glycoprotein production and secretion by human nonfunctioning pituitary adenomas.

This study, carried out on 9 nonfunctioning pituitary adenomas, was undertaken in order to evaluate the ability of these tumors to synthesize and release gonadotropins and/or free alpha-subunit (alpha-SU) of glycoproteins. The morphological study included electron microscopy and immunofluorescence analysis while hormone release was evaluated by the reverse hemolytic plaque assay (RHPA) and measurements in culture media. By electron microscopy in all tumors (6 null cell adenomas and 3 oncocytomas), it was possible to identify rough endoplasmic reticulum, Golgi apparatus and secretory granules. By immunofluorescence, 5 of 6 tumors were immunoreactive for one or more gonadotropin subunits; in particular, 5 adenomas were positive for alpha-SU and LH-beta, and 3 for FSH-beta. By the RHPA, about 1% of cells obtained from one single tumor formed plaques for LH-beta and alpha-SU while the remaining tumors were negative. Similarly, the study of media concentrations of LH, FSH and alpha-SU in 2 h culture revealed very low amounts of released hormones. In these experimental conditions no modification was observed after the addition of stimulatory agents such as TRH, GnRH and VIP. The present study clearly indicates that although the large majority of nonfunctioning tumors are positive for gonadotropins their secretory capacity is very low in both basal and stimulated conditions.

Hypothalamic peptides modulate cytosolic free Ca2+ levels and adenylyl cyclase activity in human nonfunctioning pituitary adenomas.

The effects of hypothalamic peptides (TRH, GnRH, arginine vasopressin, vasoactive intestinal peptide, GHRH, CRH, and SRIH) on cytosolic free calcium concentrations ([Ca2+]i) and adenylyl cyclase (AC) activity were evaluated in 12 nonfunctioning pituitary adenomas. TRH, GnRH, and arginine vasopressin induced a marked [Ca2+]i rise in 10/12, 4/12, and 2/5 tumors, respectively. The transients induced by these peptides were due to both Ca2+ mobilization from the intracellular stores and Ca2+ influx from the extracellular medium. AC activity was evaluated in 10 adenomas; 1 microM vasoactive intestinal peptide induced a 2- to 6-fold stimulation of the enzyme activity in all tumors, while neither GHRH nor CRH were effective. Moreover, in 5/10 tumors 1 microM SRIH reduced both AC activity and [Ca2+]i, while in 2/10 the peptide caused a significant rise in [Ca2+]i despite the AC inhibition and in 3/10 SRIH did not modify either AC activity or [Ca2+]i. This study indicates that in nonfunctioning pituitary adenomas a wide spectrum of hypothalamic peptides modulate [Ca2+]i and AC activity. Moreover, the presence of biologically active receptors may offer a possible target for therapeutic intervention.