Secretion of glycoprotein hormone alpha-subunit by pituitary tumors

Serum glycoprotein hormone alpha-subunit levels were determined in 165 patients with pituitary adenomas. Elevated serum alpha-subunit levels were found in 17 patients (acromegaly, 5 of 58; prolactinoma, 6 of 56; nonfunctioning adenoma, 5 of 32; and ACTH-producing adenoma, 1 of 19), most of whom had normal serum TSH and gonadotropin levels. When TRH (0.5 mg) was injected iv in the 6 prolactinoma patients with elevated serum alpha-subunit levels, serum PRL and alpha-subunit levels increased in only 1 patient. Four acromegalic patients with high serum alpha-subunit levels received TRH; serum GH and alpha-subunit increased in 1 patient and did not change in 2, and only serum GH increased in the remaining patient. Oral administration of bromocriptine (5 mg), on the other hand, consistently decreased serum alpha-subunit and PRL levels in 2 patients with prolactinoma and alpha-subunit and GH levels in 1 acromegalic patient. When serum from 3 patients was subjected to Sephadex G-100 gel filtration, immunoreactive alpha-subunit eluted in a single peak, which emerged in fractions corresponding to [125I]TSH alpha. Concanavalin A (Con A) affinity chromatography revealed that the major portion of immunoreactive alpha-subunit was retained to Con A. A pituitary adenoma removed at surgery from a patient with acromegaly was studied in monolayer cell culture. Secretion of both alpha-subunit and GH from cultured adenoma cells was stimulated by TRH and suppressed by dopamine in a dose-dependent manner. Immunohistochemistry of the pituitary adenomas removed from patients with prolactinoma and acromegaly who had high serum alpha-subunit levels demonstrated alpha-subunit-containing cells as well as PRL- or GH-containing cells. These results suggest that elaboration of glycoprotein hormone alpha-subunit occurs without concurrent production of glycoprotein hormones in a substantial number of patients with pituitary adenomas and that alpha-subunit responses to stimuli in such adenomas are generally parallel with those of the concomitantly produced hormones.     

GLYCOPROTEIN HORMONE ALPHA-SUBUNIT AND PROLACTIN RELEASE BY CULTURED PITUITARY ADENOMA CELLS FROM ACROMEGALIC PATIENTS: CORRELATION WITH GH RELEASE

In-vitro data of pituitary adenoma cells from 28 acromegalic patients were evaluated. In addition to GH, PRL was produced by 16 adenomas (57%) and alpha-subunit by 15 adenomas (54%) while there was a significantly higher incidence of tumours producing PRL and alpha-subunit simultaneously. From 26 pituitary adenomas enough cells were obtained in order to perform secretion studies. Percentage basal hormone release (medium: (medium + intracellular hormone)) x 100% of GH and alpha-subunit by 11 adenomas showed a close correlation while such a correlation for GH and PRL was present only in a subgroup of 10 of 13 adenomas. The responses of GH and alpha-subunit release to 10nM SMS201-995, 10nM bromocriptine, 100 nM TRH and 10nM GHRH were closely related in that a response or an absent response of GH release to the four secretagogues was virtually always attended with a response or an absent response respectively of alpha-subunit release. Such a relationship was less evident with respect to the effects of SMS201-995, bromocriptine. TRH and GHRH on GH and PRL release. We conclude that basal and secretagogue-induced alpha-subunit release by cultured pituitary adenoma cells from acromegalic patients closely follows the pattern of GH release while such a relationship for GH and PRL is present only in a subgroup of the adenomas secreting GH and PRL simultaneously.     

Growth hormone (GH) and prolactin responses to repetitive administration of GH-releasing hormone in acromegaly

We investigated the pattern of GH secretion in response to repetitive GH-releasing hormone (GHRH) administration in patients with active acromegaly and in normal subjects. Twelve acromegalic patients (nine women and 3 men; aged 21-76 yr) were studied. Eight had never been treated, whereas four had undergone neurosurgery but still had active disease. All patients and eight normal subjects received three doses of 50 micrograms GHRH, iv, at 2-h intervals. Seven patients were retested 6-8 weeks after transsphenoidal removal of a pituitary adenoma. There was a marked serum GH rise in acromegalic patients and normal subjects after the first GHRH dose [area under the curve, 2070 +/- 532 (+/- SE) vs. 1558 +/- 612 ng/min X ml, respectively; P = NS]. Successive GHRH doses stimulated GH release only in acromegalic patients (second dose, 1123 +/- 421 ng/min X ml; third dose, 2293 +/- 1049 ng/min X ml). In normal subjects, the GH response to the second and third GHRH doses was blunted (second dose, 86 +/- 32 ng/min X ml; third dose, 210 +/- 63 ng/min X ml; P less than 0.01). PRL secretion did not change in normal subjects, whereas 6 of 12 acromegalic patients had PRL release after each GHRH dose (PRL responders to GHRH). Transsphenoidal surgery led to normalization (less than 5 ng/ml) of the preoperatively elevated GH levels in all but 2 patients, who, however, had reduction of somatomedin-C levels. The amount of GH released in the postoperative test was significantly lower than that released preoperatively (first dose, 722 +/- 209 vs. 2945 +/- 743 ng/min X ml; second dose, 358 +/- 117 vs. 1737 +/- 633 ng/min X ml; third dose, 320 +/- 144 vs. 1776 +/- 676 ng/min X ml, respectively; P less than 0.05 in all instances). Thus, patients with active acromegaly, but not normal subjects, respond to repetitive GHRH administration at 2-h intervals with an increase in GH levels. This increase may be due to a larger releasable GH pool and/or faster GH turnover in the adenomatous cell.     

Serum alpha-subunit levels in patients with pituitary adenomas

OBJECTIVE: We investigated preoperative and postoperative serum alpha-subunit levels and the alpha-subunit response to TRH in patients with various types of pituitary tumour and correlated the data with histological findings in order to clarify the significance of alpha-subunit measurement in pituitary adenomas. PATIENTS: We examined 59 patients with pituitary tumours (22 with GH cell adenomas, 30 with clinically nonfunctioning adenomas and seven with other tumours) treated at Toranomon Hospital between 1996 and 1998. RESULTS: The basal alpha-subunit level was supranormal in six out of 22 (27%) patients with a GH cell adenoma and in nine out of 30 (30%) patients with a nonfunctioning adenoma. A paradoxical alpha-subunit response to TRH was found in seven out of 22 (32%) patients with a GH cell adenoma. These seven patients also showed a paradoxical GH response to TRH administration. In addition, paradoxical response to TRH was found in eight out of 30 (27%) patients with a clinically nonfunctioning adenoma. In contrast, patients with other types of pituitary tumour showed neither a supranormal alpha-subunit level nor a paradoxical response to TRH. The supranormal alpha-subunit level and the abnormal response to TRH were normalized in both GH cell adenoma and nonfunctioning adenoma patients after successful surgery. Immunohistochemical studies showed alpha-subunit positive cells in 51% of GH cell adenomas or nonfunctioning adenomas and there was a good concordance with the serum alpha-subunit levels in both GH cell adenoma and nonfunctioning adenoma patients. CONCLUSIONS: These findings suggest that supranormal serum alpha-subunit levels are mainly due to hypersecretion by the tumour itself, while the paradoxical alpha-subunit response to TRH is an associated phenomenon in patients with a GH cell adenoma or nonfunctioning adenoma. The alpha-subunit level and the response to TRH may be useful indicators for assessing the operative outcome, especially in nonfunctioning adenoma patients who have no other definite endocrine markers.     

Glycoprotein hormone alpha-subunit secretion in patients with pituitary adenomas: influence of TRH, LRH and bromocriptine

Twelve patients with pituitary adenomas and increased serum concentration of the glycoprotein hormone alpha-subunit were studied. Eight patients were acromegalic and one had a FSH producing tumour. The adenomas in 9 patients had undergone subtotal operative removal and/or external irradiation but no patient was studied within 3 months of these treatments. Many of the acromegalic patients, with moderately elevated alpha-levels, showed marked increases in alpha-concentration after TRH and/or LRH, compared with controls. The non-acromegalic patients, with the highest alpha-levels, showed poor responses to releasing hormones. These results suggest that excessive alpha-subunit secretion in acromegalic patients is often under hypothalamic control whereas in non-acromegalic patients it is often autonomous. Seven patients, 4 with acromegaly, were then given oral bromocriptine, 5 mg over 3 h. There was a significant fall in log mean alpha-level at 4 and 5 h (P less than 0.02). Six patients took bromocriptine for 1--2 months. Log mean alpha-concentration was significantly reduced at the end of treatment (P less than 0.02) and then recovered to basal levels after stopping treatment for one week. alpha-Subunit hypersecretion in some patients with pituitary adenomas is therefore modulated by dopaminergic control mechanisms.     

Effects of theophylline infusion on the growth hormone (GH) and prolactin response to GH-releasing hormone administration in acromegaly

Since theophylline has been shown to blunt the GH response to growth hormone-releasing hormone (GHRH) in normal subjects, we investigated whether the same effect of theophylline administration could be reproduced in patients with active acromegaly. Ten acromegalic patients received on two different days 100 micrograms GHRH iv alone and the same GHRH dose during a constant infusion of theophylline (3.56 mg/min), beginning 2 h before GHRH administration. In the whole group theophylline did not affect basal GH secretion significantly (from a mean of 44.6 +/- 14.4 at 0 min to 41.8 +/- 13.5 ng/ml at 120 min). However, the amount of GH released after GHRH stimulation was lower when theophylline was concomitantly infused (7525 +/- 3709 ng min/ml vs. 12038 +/- 6337 ng min/ml; p less than 0.05). The inhibitory effect of theophylline was not homogeneous, since either marked or minimal reductions of the GHRH-stimulated GH secretion occurred. Serum PRL levels increased after GHRH administration in 6 patients and theophylline infusion had no influence upon this response. Peak GHRH levels were not different in both studies (14.9 +/- 1.7 and 17.1 +/- 4.0 ng/ml, respectively). Free fatty acid levels rose progressively during theophylline administration (from 0.66 +/- 0.10 at 0 min to 1.04 +/- 0.10 mEq/l at 240 min) and were significantly higher than after GHRH stimulation alone from 180 min up to the end of the test. Our results demonstrate that in active acromegaly theophylline blunts the GH response to GHRH, though this effect is not uniformly seen in all patients.(ABSTRACT TRUNCATED AT 250 WORDS)     

Glycoprotein hormone alpha-subunit in pituitary adenomas.

Elevated serum glycoprotein hormone alpha-subunit (alpha-subunit) levels are seen in about one of six patients bearing pituitary adenomas. This finding has particular clinical significance in patients with nonfunctioning pituitary adenomas. Moreover, the measurement of alpha-subunit along with the calculation of the molar ratio between alpha-subunit and TSH, LH, or FSH is helpful in the diagnosis of glycoprotein hormone-secreting pituitary adenomas. Since serum alpha-subunit levels may vary greatly in several physiologic and pathologic conditions, care has to be taken to differentiate abnormal from normal states of alpha-subunit hypersecretion as well as to exclude causes of alpha-subunit overproduction only casually associated with the presence of pituitary tumors.     

Heterogeneity of pituitary adenoma cell subpopulations from acromegalic patients obtained by Percoll density gradient centrifugation

Pituitary adenoma cells from 6 acromegalic patients were separated on continuous Percoll density gradients according to differences in their density. Two adenomas produced GH only in culture, the other 4 adenomas produced either GH and PRL (one adenoma) or GH and alpha-subunit (one adenoma) or GH, PRL and alpha-subunit (2 adenomas). The cell subpopulations obtained by this technique differed in the amount of hormone production per 10(5) cells: GH release decreased from the low density fractions to the higher density fractions in 5 of 6 adenomas. Intracellular GH levels completely followed this profile. In the mixed GH/alpha-subunit adenomas the alpha-subunit profile completely paralleled the GH profile, whereas in the mixed GH/PRL adenomas the PRL profile showed a pattern different from that of GH (and alpha-subunit). In neither of the adenomas did we find any differences between the subpopulations with respect to the responsiveness of GH, PRL or alpha-subunit release to GHRH, TRH and the somatostatin analogue SMS 201-995. Conclusions: 1. Within pituitary adenomas from acromegalic patients heterogeneity exists with respect to hormone production per cell. 2. The cell subpopulations obtained by density gradient centrifugation are not different in their responsiveness to SMS 201-995, GHRH or TRH. 3. Because GH and alpha-subunit release by the fractions from the mixed GH/alpha-subunit secreting adenomas were completely parallel, further evidence for co-release of GH and alpha-subunit by the same tumoural cells is provided.     

Bromocriptine does not alter growth hormone (GH) responsiveness to GH-releasing hormone in acromegaly

GHRH (100 micrograms) and TRH (200 micrograms) were administered to 24 active acromegalic patients before and during chronic bromocriptine (Br) treatment (Br, 10-15 mg/day for 3-5 months) to evaluate the possible effects of the dopamine agonist on GH release induced by these releasing hormones. Mean daily plasma GH levels were reduced by Br treatment from 34 +/- 40 (SD) to 16 +/- 19 ng/ml (P less than 0.01). No significant changes were found when comparing the GH response to GHRH as mean area under the response curve (nanograms per min/ml above the basal) (pretreatment, 5453 +/- 7843; during Br, 7017 +/- 12763 ng/ml . min), and as mean individual peak GH values (pretreatment, 130 +/- 148; during Br, 126 +/- 187 ng/ml) before and during treatment. The percentage GH increase (pretreatment, 340 +/- 354; during Br, 617 +/- 539%) was however significantly higher during Br. Br treatment significantly reduced the GH response to TRH in terms of mean of individual peak levels (from 136 +/- 134 to 60 +/- 52 ng/ml; P less than 0.01) and area under the response curve (from 3142 +/- 3998 to 1331 +/- 1646 ng/min . ml; P less than 0.01). However, the percentage GH increase was not significantly different (pretreatment, 486 +/- 729; during Br, 1059 +/- 1862%). When the patients were divided into Br responders, i.e. mean daily GH reduction during Br of at least 50% below baseline, and nonresponders, the initial response to GHRH was significantly higher in the latter group, but was unaffected by Br treatment in either group. On the contrary, the response to TRH, statistically significant initially only in the Br responder group, was reduced by Br treatment. We suggest that cells sensitive to Br and TRH but not to GHRH (lactotroph-like) and cells sensitive to GHRH but not to Br (pure somatotrophs) may coexist in GH-secreting adenomas.     

Growth hormone-releasing hormone infusion in patients with active acromegaly

To determine GH-releasing hormone (GHRH)-stimulated GH secretion in patients with active acromegaly, nine patients received a 50-microgram GHRH-(1-44) bolus dose followed by a 2-h infusion with 100 micrograms GHRH/h, after which a second 50-microgram GHRH bolus dose was given. Serum GH, PRL, and immunoreactive GHRH levels were measured from 2 h before to 1 h after the end of the infusion and compared with hormone levels in six normal subjects subjected to the same protocol. In addition, seven of the nine acromegalic patients received 100 micrograms GHRH as an iv bolus dose, followed by a 2-h saline infusion on a different day. After the 100-micrograms GHRH bolus dose, the mean GH level increased from 55.9 +/- 18.0 (+/- SE) to 148.5 +/- 40.0 ng/ml within 15 min. Thereafter, GH levels decreased and were significantly lower at 90 and 120 min compared to the peak level 15 min after GHRH injection. After the 50-micrograms GHRH bolus dose, all acromegalic patients except two also had a clear-cut rise of GH levels, with the mean GH level increasing from 37.5 +/- 13.2 to 108.4 +/- 55.0 ng/ml at 60 min. Thereafter, elevated GH levels were sustained in the acromegalic patients throughout the GHRH infusion. In contrast, normal subjects had a significant decrease in the initially elevated GH levels, despite continuous GHRH infusion. There were no significant differences between PRL secretion and immunoreactive GHRH levels in either group. These findings suggest that patients with active acromegaly not only have elevated basal GH levels, but also have a greater ready releasable GH pool and/or accelerated GH turnover compared to those of normal subjects, which cannot be exhausted by a 2-h GHRH infusion.     

Studies on the response of growth hormone (GH) secretion to GH-releasing hormone, thyrotropin-releasing hormone, gonadotropin-releasing hormone, and somatostatin in acromegaly

The plasma GH response to GH-releasing hormone (GHRH), TRH, or GnRH administration was examined in 25 acromegalic patients. Plasma GH levels increased in 21 patients after GHRH, in 19 after TRH, and in 4 after GnRH. The four GHRH nonresponders had had acromegaly longer than had the GHRH responders. No specific combination of GH responsiveness to these 3 releasing hormones was found among the patients. Infusion of 1 mg GHRH for 150 min gradually increased plasma GH levels, with some fluctuations, from the beginning to the end of infusion in normal subjects and in 7 patients who were GHRH responders, but a bolus injection of 100 micrograms GHRH at the end of the infusion did not further elevate plasma GH levels. These results suggest that desensitization to GHRH occurred in the normal subjects and acromegalic patients. However, in 5 acromegalic patients who responded to both GHRH and TRH, a bolus injection of 500 micrograms TRH given at the end of the 150-min infusion of 1 mg GHRH evoked a further plasma GH rise. In 5 normal subjects and 2 patients who were responders to GHRH but not TRH, a bolus injection of 500 micrograms TRH did not cause plasma GH elevation at the end of 150-min infusion of 1 mg GHRH. These results imply that TRH and GnRH stimulate GH secretion from the adenoma cells in vivo through receptors different from those for GHRH. In vitro studies using cultured pituitary adenoma cells from 2 patients revealed that the responses of GH secretion to GHRH were similar to those in vivo. These data, therefore, suggest that the responsiveness of GH secretion to stimuli is determined by the specificity of the receptors on adenoma cells. The action of somatostatin-28 was more potent than that of somatostatin-14 in the suppression of GH secretion from adenoma cells.     

Pulsatile growth hormone secretion in patients with acromegaly and normal men: the effects of growth hormone-releasing hormone infusion

Twenty-four GH secretory patterns were studied before and during continuous infusions of GHRH in six patients with active acromegaly and in six normal adult men. GH release was episodic in both groups. Control subjects showed a normal diurnal variation in GH release, with the majority of GH released at night (2200-0800 h); mean levels were 1.5 +/- 0.4 (SE) ng/mL (day) and 4.2 +/- 0.8 ng/mL (night). Acromegalics had no diurnal variation in GH; levels were 45.3 +/- 13.7 ng/mL (day) and 39.8 +/- 12.2 ng/mL (night). Acromegalics demonstrated an increased frequency of GH pulses compared to normals (11.8 +/- 0.8 vs. 2.2 +/- 0.3/24 h). During continuous 24-h infusions of GHRH, the normal subjects continued to show a diurnal variation in GH release, but GH pulse frequency increased to a rate (11.7 +/- 1.4 pulses/24 h) very similar to that of the patients with acromegaly. In contrast, GHRH infusion did not alter the GH pulse frequency in the acromegalics. GHRH increased the mean levels of GH in both groups (patients 80.2 +/- 20.3 vs. 41.0 +/- 12.1 ng/mL, x +/- SE. P less than 0.05; controls 10.2 +/- 2.0 vs. 3.33 +/- 0.5 ng/mL, P less than 0.01). Some of the patients with acromegaly showed a progressive decline in GH levels during the infusion period, suggesting desensitization or exhaustion of releaseable stores; however, GH levels remained above basal values in all patients. After the 24-h GHRH infusions, the GH response to a bolus of GHRH was diminished in the normal subjects (2.1 +/- 0.9 vs. 16.8 +/- 5 ng/mL, x +/- SE; P less than 0.01) but not in the acromegalic patients (30.2 +/- 8.9 vs. 35.5 +/- 12.5 ng/mL; NS). These results indicate that GH release is episodic under basal conditions and during continuous GHRH infusion in both acromegalic and normal subjects, indicating the importance of other modulators of GH release, such as somatostatin, which may remain pulsatile even in acromegaly.     

Glycoprotein hormone alpha-subunit production in somatotroph adenomas with and without Gs alpha mutations.

Activating mutations of the Gs alpha subunit have been identified in a subset of somatotroph adenomas. The mutant form of the Gs alpha subunit causes persistent activation of adenylyl cyclase and consequently results in high intracellular levels of cAMP. Because cAMP is known to stimulate the synthesis of the glycoprotein hormone (GPH) alpha-subunit as well as GH, we examined somatotroph tumors with and without Gs alpha mutations for GPH alpha-subunit production. GPH alpha-subunit production was assessed in vivo by measuring serum hormone levels and in vitro by analyzing hormone secretion by cultured pituitary tumor cells. DNA was extracted from the pituitary tumors of 26 acromegalic patients. The Gs alpha gene was amplified by the polymerase chain reaction and screened for mutations at codons 201 and 227 using oligonucleotide specific hybridization. Nine of the 26 tumors (35%) had point mutations at Arg 201. Seven of these tumors contained a CGT to TGT mutation (Arg to Cys) and 2 contained a CGT to CAT mutation (Arg to His). No mutations were detected at codon 227. There were no significant differences in age, sex distribution, tumor size, or serum levels of GH or insulin-like growth factor-1 between the groups of patients with or was Gs alpha mutations. The mean serum level of the free GPH alpha-subunit was 1.9-fold higher in the group with Gs alpha mutations (0.48 +/- 0.37 micrograms/L) than in patients without mutations (0.25 +/- 0.17) (P less than 0.05). In pituitary tumor cell culture, 75% of somatotroph tumors with Gs alpha mutations secreted free GPH alpha-subunit into the media compared with 45% of tumors without Gs alpha mutations. The amount of GPH alpha-subunit secretion was 12-fold greater in the group of tumors containing the Gs alpha mutation (P less than 0.05). Immunocytochemical detection of the free GPH alpha-subunit was similar in the two groups of patients with 75% positive for the GPH alpha-subunit in tumors with Gs alpha mutations and 67% positive in tumors without mutations (P = 0.69). We conclude that GPH alpha-subunit production occurs in somatotroph tumors with and without Gs alpha mutations. The increased levels of GPH alpha-subunit secretion in vivo and in vitro suggest that the Gs alpha mutation may increase the amount of preexisting GPH alpha-subunit biosynthesis in the tumors, perhaps via activation of the cAMP pathway.     

Effect of galanin on the growth hormone response to growth hormone-releasing hormone in acromegaly.

Galanin enhances growth hormone (GH)-releasing hormone (GHRH)-stimulated GH secretion in normal man. In acromegaly, circulating GH levels are increased and the GH response to GHRH may be exaggerated. Galanin has been recently shown to decrease circulating GH levels in acromegaly. The aim of our study was to investigate the effects of galanin on the GH response to GHRH in acromegalic subjects. Five acromegalic patients (three men and two women) and seven healthy adult subjects (five men and two women) were studied. GHRH-induced GH secretion was evaluated during a 40-minute intravenous (IV) infusion of saline (100 mL) or porcine galanin (12.5 micrograms/min in 100 mL saline). In normal subjects, delta GH levels after GHRH+porcine galanin administration (47 +/- 7.5 micrograms/L) were significantly higher in comparison to levels obtained with GHRH+saline (21.7 +/- 3.5 micrograms/L, P < .05). In acromegalic patients, GH responses to GHRH (delta GH, 18.8 +/- 8.6 micrograms/L) were not altered by galanin infusion (delta GH, 17.6 +/- 5 micrograms/L). Our results give the first evidence that the same dose of galanin that induces a significant enhancement of the GH response to GHRH in normal subjects has no effect on the GH response to GHRH in acromegalic patients. It can be hypothesized that galanin may interact at the pituitary level with its own receptors expressed by somatotropes independent of GHRH. Failure of galanin to enhance GH response to GHRH in acromegalic patients could be due to a change in function of the galanin receptor on GH-secreting adenomatous cells.     

Endocrine and immunohistochemical studies on thyrotropin (TSH)-secreting pituitary adenomas: responses of TSH, alpha-subunit, and growth hormone to hypothalamic releasing hormones and their distribution in adenoma cells.

Endocrine and immunohistochemical studies were performed in two cases of TSH-secreting pituitary adenomas. The patients had elevated serum TSH and alpha-subunit concentrations despite high serum thyroid hormone levels. In addition, one patient (no. 1) had elevated serum GH levels with clinical evidence of acromegaly. GH-releasing hormone infusion increased serum levels of TSH, alpha-subunit and GH in the two patients. TRH injection increased serum TSH levels in both patients and, concomitantly, serum alpha-subunit and GH levels in patient 1. Basal TSH levels and their responses to TRH changed reciprocally to changes in serum thyroid hormone levels, although TRH-induced GH release did not. The administration of GnRH also increased serum TSH, alpha-subunit, and GH levels in patient 1. In accordance with these in vivo results, pituitary adenoma cells in culture obtained from patient 1 responded to GH-releasing hormone, TRH, or GnRH to secrete TSH, alpha-subunit, and GH. Incubation of cells with dexamethasone resulted in inhibition of TSH and stimulation of GH secretion without a significant change in alpha-subunit secretion. On the basis of light microscopic and electron microscopic double gold immunohistochemistry, the tumor from patient 1 was a bimorphous adenoma composed of two separate cell types: cells with TSH beta-subunit (TSH beta) and alpha-subunit, and those with GH and alpha-subunit. The remainder consisted mainly of cells with TSH beta and alpha-subunit. The coproduction of the unusual combination of two hormones such as GH and alpha-subunit in a single-type of adenoma cell and the coexistence of thyrotrophs and somatotrophs in one pituitary adenoma along with the aberrant responses of TSH beta, alpha-subunit, and GH to multiple hypothalamic hormones suggest the dedifferentiation of pituitary cells to multipotential progenitor cells by neoplastic transformation.     

Effect of cholinergic muscarinic receptor blockade on human growth hormone (GH)-releasing hormone-(1-44)-induced GH secretion in acromegaly and type I diabetes mellitus

In 10 patients with type I diabetes mellitus, 9 acromegalic patients, and 8 normal subjects, serum GH levels after an iv injection of 1 microgram/kg BW human GH-releasing hormone-(1-44) (GHRH) with and without cholinergic muscarinic receptor blockade (1 mg atropine, im, 15 min before GHRH) were measured. The GH increase after GHRH treatment in type I diabetic patients did not differ significantly from that in normal subjects. Pretreatment with atropine almost completely blocked the GH response to GHRH in patients with type I diabetes and normal subjects, but did not suppress the GH response to GHRH in acromegalic patients. These data indicate that cholinergic muscarinic receptors modulate GH secretion in normal man as well as in patients with type I diabetes mellitus, whereas acromegalic patients have a defect of cholinergic control of GH secretion.     

The GH-releasing hormone (GHRH) test in acromegaly before and after adenomectomy

The GHRH test may represent a new tool in the study of GH dynamics in acromegaly. GH responsiveness to GHRH 1-40 (50 micrograms iv) has been studied in 21 acromegalic patients. Nineteen out of 21 had active disease. Five patients were also studied 1-12 months after neurosurgery. Two apparently cured acromegalics were studied 1-2 yr after surgery. GH secretion has been evaluated in all patients by means of TRH, bromocriptine and insulin hypoglycemia tests, too. GH response to GHRH has also been performed in 14 normal subjects. In acromegaly, GH responses after GHRH (p less than 0.01 vs placebo) were variable. The GH peak ranged from 8 to 445 ng/ml in patients with active disease. Maximum GH increase after GHRH (calculated as peak/basal value ratio) was significantly reduced in acromegaly (2.9 +/- 0.5 ng/ml; mean +/- SE) in comparison to controls (34.1 +/- 10.9 ng/ml; p less than 0.01). No significant differences in GH pattern after GHRH were found between untreated and previously treated patients with active disease. A significant correlation was found between GH basal levels and GH incremental area (p less than 0.05) and between GH basal and peak levels (p less than 0.01) after GHRH. A significant increase in PRL secretion was observed in acromegalic patients after GHRH (p less than 0.01 vs placebo). No discernable variation was found in the other pituitary hormones pattern after the peptide administration. A positive correlation was observed between GH increase after GHRH and insulin hypoglycemia (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Gonadotropin release by clinically nonfunctioning and gonadotroph pituitary adenomas in vivo and in vitro: relation to sex and effects of thyrotropin-releasing hormone, gonadotropin-releasing hormone, and bromocriptine

We studied in vivo hormone levels and in vitro hormone and subunit release in a group of 22 patients who were operated upon because of a clinically nonfunctioning or gonadotroph pituitary adenoma. In vivo, 5 of the 22 patients, all men, had hypersecretion of FSH, LH beta, or alpha-subunit. An elevated ratio of serum alpha-subunit to LH and FSH was found in 6 of 8 women in vivo, although in all 6 women serum LH, FSH, and alpha-subunit levels were low. LH, FSH, alpha-subunit, LH beta, or a combination of these glycoprotein hormones could be demonstrated in 19 of 22 cultured adenomas. We conclude that 1) virtually all clinically nonfunctioning adenomas contain or release gonadotropins or their subunits in vitro; 2) in vivo hypersecretion of these hormones and subunits occurs infrequently, and in this series only in men; 3) an elevated ratio of alpha-subunit to LH and FSH is frequently found in women and may prove to be a useful diagnostic tool; 4) responses to TRH and bromocriptine do not depend on baseline gonadotropin levels, either in vitro or in vivo, implying that the distinction between gonadotroph adenomas and adenomas without hypersecretion of gonadotropins in vivo is absent where hormone dynamics are concerned.     

GH deficiency in patients irradiated for acromegaly: significance of GH stimulatory tests in relation to the 24 h GH secretion

BACKGROUND: Radiotherapy for pituitary adenomas frequently leads to GH deficiency (GHD). The characteristics of GH secretion in GHD induced by postoperative radiotherapy for acromegaly are not known. HYPOTHESIS: In the long term, stimulated and spontaneous GH release is not different between patients with GHD treated by postoperative radiotherapy for acromegaly or for other pituitary adenomas. DESIGN/SUBJECTS: We compared the characteristics of basal and stimulated GH secretion in patients with GHD, who had previously received adjunct radiotherapy after surgery for GH-producing adenomas (n=10) vs for other pituitary adenomas (n=10). All patients had a maximal GH concentration by insulin tolerance test (ITT) of 3 microg/l or less, compatible with severe GHD. Mean time after radiation was 17 and 18.7 years, respectively. Stimulated GH release was also evaluated by infusion of growth hormone-releasing hormone (GHRH), GHRH-arginine and arginine, and spontaneous GH by 10 min blood sampling for 24 h. Pulse analyses were performed by Cluster and approximate entropy. OUTCOMES: There were no differences between both patient groups in stimulated GH concentrations in any test. Spontaneous GH secretion was not different between both patient groups, including basal GH release, pulsatility and regularity. Pulsatile secretion was lost in two acromegalic and three non-acromegalic patients. Insulin-like growth factor-I (IGF-I) was below -2 s.d. score in nine patients in each group. CONCLUSION: Acromegalic patients treated by surgery and postoperative radiotherapy with an impaired response to the ITT do not differ, in the long term, in GH secretory characteristics from patients treated similarly for other pituitary tumors with an impaired response to the ITT. The ITT (or the GHRH-arginine test) is therefore reliable in establishing the diagnosis of GHD in patients treated for acromegaly by surgery and radiotherapy.     

Acromegaly due to ectopic growth hormone (GH)-releasing hormone (GHRH) production: dynamic studies of GH and ectopic GHRH secretion

Dynamic studies of GH and GH-releasing hormone (GHRH) secretion were performed in a man with a GHRH-producing carcinoid tumor and acromegaly. Insulin hypoglycemia stimulated and metoclopramide inhibited both GH and GHRH acutely. Bromocriptine suppressed GH both acutely and chronically without altering circulating GHRH levels and also blunted the GH response to exogenous GHRH. TRH acutely stimulated GH, but not GHRH, secretion, and iv bolus doses of synthetic GHRH-(1-40) stimulated GH release acutely. Somatostatin infusion decreased both GH and GHRH concentrations and blunted the GH responses to TRH and GHRH-(1-40). We conclude that prolonged exposure of the pituitary gland to high concentrations of GHRH is associated with chronic GH hypersecretion and may be accompanied by a preserved acute GH response to exogenous GHRH; a paradoxical response of GH to TRH may be mediated at the pituitary level, consequent to prolonged pituitary exposure to GHRH; bromocriptine suppression of GH in acromegaly is due to a direct pituitary effect of the drug; and somatostatin inhibits both ectopic GHRH secretion as well as GH responsiveness to GHRH in vivo. Since GH secretory responses in patients with somatotroph adenomas are similar to those in this patient, augmented GHRH secretion may play a role in development of the "classic" form of acromegaly.