Growth hormone dynamics in acromegaly

Growth hormone increase by luteinizing hormone-releasing hormone reflects gonadotroph-related characteristics in acromegaly

PURPOSE

We previously showed the clinical characteristics of acromegaly with a paradoxical growth hormone (GH) response to oral glucose or thyrotropin-releasing hormone. However, the clinical characteristics of acromegaly with an increased GH response to luteinizing hormone-releasing hormone (LHRH responders) remain unclear. The aim of the present study was to evaluate the clinical characteristics, especially gonadotroph-related characteristics of LHRH responders in acromegaly.

METHODS

The clinical characteristics of 33 LHRH responders and 81 LHRH nonresponders were compared.

RESULTS

No differences in age, sex or basal serum levels of GH, insulin-like growth factor-1 (IGF-1), and gonadotropin were observed between the two groups. Steroidogenic factor 1 (SF-1), gonadotropin-releasing hormone receptor (GnRHR), and LH expression was more frequently observed in LHRH responders (P < 0.05). In addition, a greater increased rate of GH after LHRH loading, and the proportion of GnRHR and gonadotropin expression was observed in pituitary tumor with SF-1 expression than that without the expression (P < 0.01). LHRH responders showed a greater GH decrease in the octreotide test and a greater IGF-1 decrease after first-generation somatostatin ligand than LHRH nonresponders (P < 0.05). Furthermore, the proportion of hypointense pituitary tumors on T2-weighted magnetic resonance imaging and tumors with densely granulated type was higher in LHRH responders than in LHRH nonresponders, respectively (P < 0.05). No difference between the two groups was observed in either somatostatin receptor 2 or 5 expression.

CONCLUSIONS

The increased GH response to LHRH is associated with the gonadotroph-related characteristics. This response may reflect the biological characteristics of somatotroph tumors.

Paradoxical GH increase during oral glucose load may predict overall remission in acromegalic patients

BACKGROUND

The nadir growth hormone (nGH) during the oral glucose tolerance test (OGTT) is the gold standard method for diagnosing acromegaly. A paradoxical growth hormone (GH) response to oral glucose (OG) in acromegaly can be observed. The role of the paradoxical GH response on how the patients with acromegaly respond to the treatment has been addressed in few studies. The aim of this study was to investigate the association between glucose-dependent growth hormone results and and the responses of acromegalic patients to surgical and/or medical therapy following surgery.

MATERIAL AND METHODS

This retrospective cohort study included patients with acromegaly who underwent surgery (n = 189) or received primary medical treatment (n = 9). The mean age was 50.44 ± 12.81 years (M/F: 84/114). The patients were grouped into paradoxical (GH-P) and non-paradoxical (GH-nP) according to GH response to OG and were compared in terms of clinical and pathological features, pituitary tumor size, invasiveness, biochemical profiles, and how they responded to the treatment.

RESULTS

The mean age, gender distribution, and basal tumor diameter were all similar in both groups (p &gt; 0.05). The GH-P group had a higher remission rate in response to medical therapy followed by surgery (83% vs. 55%; p = 0.026). Although a higher surgical remission rate in favor of GH-P was observed, it did not reach statistical significance (63% vs. 48%; p = 0.059). Overall treatment response rates were also higher in the GH-P group compared to the GH-nP group (89% vs. 71%; p = 0.005).

CONCLUSION

A paradoxical GH response to OG load may help to predict the response to medical treatment in patients with acromegaly.

Through veiled mirrors: Fish fins giving insight into size regulation

Faithful establishment and maintenance of proportion is seen across biological systems and provides a glimpse at fundamental rules of scaling that underlie development and evolution. Dysregulation of proportion is observed in a range of human diseases and growth disorders, indicating that proper scaling is an essential component of normal anatomy and physiology. However, when viewed through an evolutionary lens, shifts in the regulation of relative proportion are one of the most striking sources of morphological diversity among organisms. To date, the mechanisms via which relative proportion is specified and maintained remain unclear. Through the application of powerful experimental, genetic and molecular approaches, the teleost fin has provided an effective model to investigate the regulation of scaling, size, and relative growth in vertebrate organisms. This article is categorized under: Establishment of Spatial and Temporal Patterns > Regulation of Size, Proportion, and Timing Adult Stem Cells, Tissue Renewal, and Regeneration > Regeneration Comparative Development and Evolution > Regulation of Organ Diversity.

Clinical Characteristics of Acromegalic Patients With Paradoxical GH Response to Oral Glucose Load

CONTEXT

A paradoxical GH response to oral glucose (OG) is often found in acromegaly. However, the clinical characteristics of patients with acromegaly and a paradoxical GH response to OG (OG responders) remain unclear.

OBJECTIVE

The aim of the present study was to define the clinical characteristics of OG responders with acromegaly.

DESIGN

Retrospective study.

SETTING

Hospitalized care at Osaka University Hospital.

PATIENTS AND METHODS

Of 63 patients with acromegaly admitted to our hospital from January 2006 to January 2017, 19 were classified as OG responders and 44 as nonresponders. The clinical characteristics of these groups were compared.

RESULTS

Before surgery, OG responders had substantially greater IGF-1 SD scores than nonresponders (P < 0.05), although no difference was found in basal GH levels between the two groups (P = 0.46). Regarding glucose metabolism, 120-minute plasma glucose and immunoreactive insulin after OG administration and hemoglobin A1c were significantly greater in OG responders than in nonresponders (P < 0.01, P < 0.05, P < 0.05, respectively). GH levels during octreotide or bromocriptine testing were decreased more significantly in OG responders than in nonresponders (P < 0.05, P < 0.05, respectively). The proportion of pituitary tumors with hypointensity on T2-weighted MRI was significantly greater in OG responders than in nonresponders (P < 0.05). The difference in IGF-1 and parameters of glucose metabolism described disappeared between the two groups after surgery.

CONCLUSIONS

The paradoxical GH response reflected the clinical characteristics, especially IGF-I level, glucose metabolism, and drug efficacy in acromegaly. A paradoxical GH response, in addition to the nadir GH levels, to OG load is potentially useful for evaluation of the clinical characteristics of acromegaly.

Multiple aberrant hormone receptors in Cushing's syndrome

The mechanisms regulating cortisol production when ACTH of pituitary origin is suppressed in primary adrenal causes of Cushing's syndrome (CS) include diverse genetic and molecular mechanisms. These can lead either to constitutive activation of the cAMP system and steroidogenesis or to its regulation exerted by the aberrant adrenal expression of several hormone receptors, particularly G-protein coupled hormone receptors (GPCR) and their ligands. Screening for aberrant expression of GPCR in bilateral macronodular adrenal hyperplasia (BMAH) and unilateral adrenal tumors of patients with overt or subclinical CS demonstrates the frequent co-expression of several receptors. Aberrant hormone receptors can also exert their activity by regulating the paracrine secretion of ACTH or other ligands for those receptors in BMAH or unilateral tumors. The aberrant expression of hormone receptors is not limited to adrenal CS but can be implicated in other endocrine tumors including primary aldosteronism and Cushing's disease. Targeted therapies to block the aberrant receptors or their ligands could become useful in the future.

Growth hormone/insulin-like growth factor I axis, glucose metabolism, and lypolisis but not leptin show some degree of refractoriness to short-term fasting in acromegaly

Starvation exerts critical influence on somatotroph and leptin secretion. Fasting enhances GH levels in normal subjects, but not in GH hyposecretory states, while it always inhibits leptin secretion. We aimed to clarify the GH/IGF-I and metabolic response to short-term fasting in a GH hypersecretory state such as acromegaly. To this goal, in 8 active acromegalic (ACRO) and in 7 normal women (NS) we evaluated mean GH (mGHc), leptin (mLEPc), insulin (mINSc), glucose (mGLUc) concentrations as well as IGF-I, IGF binding protein (IGFBP)-3, IGFBP-1, and free fatty acid (FFA) levels before and after 36-h fasting. Before fasting, mGHc, IGF-I, mINSc, mGLUc, and FFA levels in ACRO were higher (p<0.01) than in NS. IGFBP-3, IGFBP-1, and mLEPc were similar in ACRO and in NS. Fasting clearly (p<0.02) increased mGHc in NS only. After 36-h fasting, significant IGF-I reduction was recorded in NS only (p<0.03). IGFBP-3 did not change both in ACRO and NS. IGFBP-1 significantly increased (p<0.05) after fasting in both groups but in ACRO were lower (p<0.03) than in NS. Fasting decreased (p<0.03) mLEPc, mGLUc, and mINSc in ACRO as well as in NS; mINSc and mGLUc after fasting in ACRO persisted higher (p<0.005) than in NS. FFA levels were increased by fasting in NS (p<0.02), but not in ACRO. This study shows that GH/IGF-I axis, glucose metabolism, and lypolisis but not leptin display some degree of refractoriness to short-term fasting in acromegaly. The lack of any GH response to fasting in acromegaly would likely reflect neuroendocrine alterations secondary to the GH hypersecretory state. On the other hand, the lack of somatotropic response and the peculiarly blunted metabolic reaction to short-term fasting would partially reflect the delayed adaptation of insulin resistance to starvation.

Effect of acute pharmacological modulation of plasma free fatty acids on GH secretion in acromegalic patients

OBJECTIVES

In acromegaly GH secretion is markedly increased due in most cases to a GH secreting pituitary adenoma. GH secretion is modulated by variations in the levels of free fatty acids (FFA). Recent studies in different clinical situations, have shown that reduction in FFA with acipimox (A) modifies somatotroph cell responsiveness. The aim of the present study was to evaluate the effect of acute pharmacological reduction of plasma FFA on both basal GH levels and GHRH-mediated GH secretion in acromegalic patients.

PATIENTS

Six acromegalic patients (four female, two male) aged 57 +/- 4 years., with active disease due to pituitary adenomas were studied. Four of the patients had been treated previously by surgery and/or radiotherapy. The diagnosis of active acromegaly was established by clinical assessment, increased serum IGF-I and impaired GH suppression after oral glucose.

MEASUREMENTS

Four tests were performed: placebo, A (250 mg, orally, - 210 minutes and - 60 minutes), GHRH (100 microg, iv, 0 minutes) and GHRH plus A. The different tests on each subject were performed in random order one week apart, each subject served as their own control. Serum GH was measured by RIA at appropriate intervals. The area under the curve (AUC) was calculated by the trapezoidal

METHOD

Statistical analysis was performed by Wilcoxon test. P < 0.05 was considered significant.

RESULTS

The administration of A induced a FFA reduction during the entire test both when administered with placebo and with GHRH: AUC (mmol/l x 90 minutes): placebo plus placebo: 88.2 +/- 7.3. Placebo plus A: 23.2 +/- 4.6 (P < 0.05). Placebo plus GHRH: 85.4 +/- 6.9. A plus GHRH: 21.8 +/- 3.8 (P < 0.05). Mean peak GH level (microg/l) after placebo plus placebo was 5.0 +/- 1.8 not significantly different than after placebo plus A with a mean peak of 6.2 +/- 2 (P = ns). Mean peak GHRH-induced GH secretion was 26.0 +/- 15.4 and was not modified by previous A administration with mean peak of 24.4 +/- 11.8 (P = ns).

CONCLUSIONS

In acromegalic patients acute pharmacological reduction of FFA with acipimox did not modify basal GH levels or GHRH-induced GH secretion, suggesting that the adenomatous somatotroph cell is unresponsive to physiological signals such as FFA which act at a pituitary level. These data support the hypothesis of an intrinsic neoplastic pituitary defect for the pathogenesis of acromegaly.

Ectopic and abnormal hormone receptors in adrenal Cushing's syndrome

The mechanism by which cortisol is produced in adrenal Cushing's syndrome, when ACTH is suppressed, was previously unknown and was referred to as being "autonomous." More recently, several investigators have shown that some cortisol and other steroid-producing adrenal tumors or hyperplasias are under the control of ectopic (or aberrant, illicit, inappropriate) membrane hormone receptors. These include ectopic receptors for gastric inhibitory polypeptide (GIP), beta-adrenergic agonists, or LH/hCG; a similar outcome can result from altered activity of eutopic receptors, such as those for vasopressin (V1-AVPR), serotonin (5-HT4), or possibly leptin. The presence of aberrant receptors places adrenal cells under stimulation by a trophic factor not negatively regulated by glucocorticoids, leading to increased steroidogenesis and possibly to the proliferative phenotype. The molecular mechanisms responsible for the abnormal expression and function of membrane hormone receptors are still largely unknown. Identification of the presence of these illicit receptors can eventually lead to new pharmacological therapies as alternatives to adrenalectomy, now demonstrated by the long-term control of ectopic P-AR- and LH/hCGR-dependent Cushing's syndrome by propanolol and leuprolide acetate. Further studies will potentially identify a larger diversity of hormone receptors capable of coupling to G proteins, adenylyl cyclase, and steroidogenesis in functional adrenal tumors and probably in other endocrine and nonendocrine tumors.

The evaluation of hypothalamic somatostatin tone using pyridostigmine and thyrotropin releasing hormone in patients with acromegaly

To indirectly evaluate the hypothalamic somatostatin (SS) tone in patients with acromegaly, the effects of pyridostigmine (PD), a cholinesterase inhibitor which can inhibit hypothalamic SS secretion, on TRH-induced TSH secretion and the effects of SMS 201-995 on TSH or GH secretion were studied in acromegalic patients (31-69 yr, n = 10), normal young (21-24 yr, n = 7) and normal old male subjects (62-71 yr, n = 7). After pretreatment with PD (60 mg po, -30 min), normal young subjects showed significantly enhanced TSH responses to TRH (500 micrograms i.v., 0 min) compared to single administration of TRH, whereas normal old and acromegalic patients did not show such enhancement. Plasma TSH response to a single administration of TRH in acromegalic patients was significantly lower than that of normal young and old subjects. Although normal young and old subjects showed significantly enhanced GH responses to GHRH (100 micrograms i.v. at 0 min) after the pretreatment with PD (60 mg, -30 min), no such enhancement was observed in acromegalic patients. In contrast, the decrement in plasma TSH after SMS 201-995 administration was similar between normal subjects (5 young 5 old) and 7 acromegalic patients. Further, the maximal plasma GH decrement after administration was significantly greater in acromegalic patients than in the 5 normal young and 5 old subjects p < 0.01). In conclusion, hypothalamic SS tone does not appear to be elevated in acromegalic patients compared to normal young and probably old subjects.

Effects of metoclopramide on the paradoxical growth hormone response to galanin in acromegaly

Galanin is able to enhance growth hormone (GH)-releasing hormone stimulated GH secretion in normal man. In acromegaly circulating GH levels are elevated and the GH response to GHRH may be exaggerated. Galanin has been recently shown to decrease circulating GH levels in acromegaly. Dopaminergic drugs were the only previously known agents able to cause a paradoxical GH fall in acromegaly. Aim of our study was to investigate the effects of a potent central dopaminergic receptor blocker, metoclopramide (MCP), on the galanin-induced paradoxical GH secretion in acromegalic subjects. Two male and three female patients with active acromegaly (age range 44-66 years, body mass index range 24.6-28 Kg/m2) were studied after 45 min i.v. infusion of porcine galanin (0.5 mg in 100 ml of saline) from 0 to 45 min combined with a 60 min i.v. infusion of a) saline (100 ml) or b) MCP (10 mg in 100 ml of saline) from -15 to 45 min. After galanin, GH values fell from baseline (27.5 +/- 10 micrograms/L) to a mean nadir of 16.4 +/- 6.1 micrograms/L; after galanin + MCP, circulating GH levels were also decreased (mean nadir 17.3 +/- 8.1 micrograms/L) in all the patients with respect to baseline (23.6 +/- 9.7 micrograms/L). No significant differences were found in absolute or percent of baseline GH levels after galanin+saline vs galanin + MCP. Our results suggest that the paradoxical GH fall after galanin in acromegalic patients is not mediated through dopaminergic receptor. It can be hypothesized that galanin may interact at the pituitary level with its own receptors expressed by GH-secreting adenomatous cells.

Hormonal and radiological effects of megavoltage radiotherapy in patients with growth hormone-secreting pituitary adenoma

Nineteen acromegalic patients (12 females and 7 males, aged 24-71 yr) were studied for 1-6 yr after radiotherapy (RT), administered by X-rays (18 MeV) by linear accelerator, with parallel opposite beams (doses 45-50.4 Gy, 1.8 Gy daily). Basal GH levels gradually decreased from 6.3-76.2 micrograms/L (mean +/- SE, 27.8 +/- 4.9) to 0.3-43.4 micrograms/L (11.7 +/- 3.6 micrograms/L; p < 0.005) at the last assessment. The earliest significant decrease was observed after one yr (14.9 +/- 3.8 micrograms/L; p < 0.005). Significant changes were observed also in IGF-I values (basal values 1.93-6.85 mU/ml, 3.22 +/- 0.30; last assessment 0.55-4.57 mU/mL, 1.58 +/- 0.31; p < 0.01). The earliest significant decrease of IGF-I values was observed after 2 yr (1.61 +/- 0.16 mU/ml; p < 0.005). GH levels < 5 micrograms/L together with normal IGF-I values were observed in 9 patients, 2-4 yr after RT. No changes were observed in PRL values, either in patients with pretreatment normal or elevated PRL levels. The CT and/or MRI picture of macroadenoma disappeared after 6-12 months in 3/12 patients. Moreover, a reduction (20-55%) in the diameter of the adenoma was shown after 6-36 months in other 4 patients. After RT 5/16 (31%) patients required cortisol and 4/19 (21%) thyroid replacement therapy. In 2/3 men a gonadal impairment was shown, that did not occur in the three female patients with normal gonadal function before RT.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Arginine abolishes the inhibitory effect of glucose on the growth hormone response to growth hormone-releasing hormone in man

Acute hyperglycemia inhibits the growth hormone (GH) response to several stimuli including growth hormone-releasing hormone (GHRH), likely acting by stimulation of endogenous somatostatin release. The aim of our study was to verify whether arginine ([Arg] 30 g intravenously [IV] in 30 minutes), a well-known GH secretagogue likely acting via inhibition of hypothalamic somatostatin release, counteracts the inhibitory effect of oral glucose (OG) administration (100 mg orally) on the GH response to GHRH (1 micrograms/kg IV bolus) in seven normal subjects (aged 20 to 30 years). The GH response to GHRH (peak, 11.6 +/- 1.8 micrograms/L) was inhibited by previous OG load (peak, 7.4 +/- 0.8 micrograms/L; P less than .02 v GHRH alone) and potentiated by Arg coadministration (peak, 36.2 +/- 8.8 micrograms/L; P less than .03 v GHRH alone). The potentiating effect of Arg on the GHRH-induced GH increase was unaffected by previous OG load (peak, 30.4 +/- 6.9 micrograms/L). In conclusion, our results show that Arg abolishes the inhibitory effect of OG administration on the GHRH-induced GH response in man. These data, although indirect, suggest that both acute hyperglycemia and Arg act at the hypothalamic level, stimulating and inhibiting, respectively, the release of somatostatin.

Atrial natriuretic factor in patients with acromegaly

In acromegaly the plasma volume is chronically elevated and it returns to normal when the disease is successfully treated. To define the role of ANF in such a chronic disorder of extracellular fluid volume homeostasis the plasma level was assayed in 37 acromegalic patients with active or inactive (successfully treated) disease. Five patients were studied before and after therapy. The effects of acute change in sodium-fluid status on plasma ANF levels was examined in 7 active and 4 inactive acromegalic patients and in 7 healthy subjects. As compared to 14 patients with inactive acromegaly, 23 patients with active acromegaly had an expanded plasma volume (n = 12; 50.1 vs 37.6 ml.kg-1 BW) and an increased blood concentration of growth hormone (n = 23; 22.5 vs 2.1 ng.ml-1). Plasma ANF concentrations in active and inactive acromegalic patients (33.2 and 26.6 pg.ml-1, respectively) did not differ significantly from one another or from the level in the controls (26.9 pg.ml-1). In those patients there was no correlation between plasma volume and ANF level. Infusion of 21 isotonic saline in 2 h led to a similar, significant increase in ANF levels in active (from 26.2 to 72.4 pg.ml-1) and in inactive acromegalic patients (from 33.6 to 96.7 pg.ml-1) as well as in healthy subjects (from 21 to 70.6 pg.ml-1). Successful treatment reduced the plasma volume (from 49.2 to 35.8 ml.kg-1 BW) and growth hormone level (from 10.1 to 2.6 pg.ml-1), while the ANF level remained unchanged (from 33.8 to 35.5 pg.ml-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Pituitary adenocarcinoma in an acromegalic patient: response to bromocriptine and pituitary testing: a review of the literature on 36 cases of pituitary carcinoma

There are 36 reported cases of metastatic pituitary carcinoma and almost half (44%) of these were associated with syndromes of hormonal hypersecretion. The case of a 56-year-old acromegalic man with cervical lymphatic and spinal metastases from a primary pituitary carcinoma is described. Elevated basal levels of plasma growth hormone (GH) and insulin growth factor-1/Somatomedin C (IGF-1/SmC) were found. GH levels did not increase after TRH or LHRH administration but decreased after L-Dopa and glucose. Immunostaining of the metastatic tumor for GH and electron microscopy findings confirmed the diagnosis of pituitary GH-secreting carcinoma. Striking clinical improvement and a 46% decrease in plasma GH levels were observed with bromocriptine treatment, although IGF-1/SmC levels increased during therapy. The clinical course of most reported cases of pituitary adenocarcinoma has been one of progressive intracranial expansion of a pituitary neoplasm. In only 25% were metastatic lesions discovered antemortem, and disabling symptomatology caused by metastases was rare. Only four previously reported patients of 36 with pituitary carcinoma had acromegaly.

Effects of ingestion of glucose on GH and TSH secretion: evidence for stimulation of somatostatin release from the hypothalamus by acute hyperglycemia in normal man and its impairment in acromegalic patients

Ingestion of glucose is known to induce suppression of GH secretion in normal subjects and this phenomenon is often absent in acromegalic patients. To clarify the mechanism of GH suppression in acute hyperglycemia in normal subjects and disturbed GH response in acromegalic patients, the effects of acute hyperglycemia on plasma GH and TSH levels were examined in normal subjects and acromegalic patients. Plasma GH levels were significantly lowered 45-60 min after ingestion of 75 g glucose and elevated at 210 and 240 min in nine normal subjects. Plasma TSH levels were also significantly lowered between 45 and 120 min after ingestion; levels then gradually rose. Subcutaneous administration of 50 micrograms SMS 201-995, a long acting somatostatin analog, lowered plasma TSH levels in both normal subjects and acromegalic patients, and there was no significant difference in the degree of decrease in plasma TSH levels between the normal subjects and patients. These results, taken together with several reports that somatostatin suppresses TSH secretion as well as GH secretion, suggest that acute hyperglycemia stimulates somatostatin release from the hypothalamus, thus causing inhibition of GH and TSH secretion. However, in ten acromegalic patients, only two showed suppression of plasma GH levels to below 50% of basal level and the degree of suppression of TSH secretion was significantly less than in normal subjects in the glucose tolerance test. It is, therefore, suggested that somatostatin release in response to acute hyperglycemia is impaired in most acromegalic patients and that this abnormality may be one of causes for the absence of the normal GH response to acute hyperglycemia in this disorder.

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)

Evidence of an endogenous digitalis-like factor in the plasma of patients with acromegaly

Evidence suggests that plasma-volume expansion leads to the release of a digitalis-like factor, which is thought to act on the renal tubular cells and cause natriuresis. We postulated that this factor might be present in patients with acromegaly (in whom plasma volume is elevated) and might return to normal levels when the disease was treated successfully. We measured the ability of plasma extracts from patients with acromegaly to inhibit the binding of ouabain to the sodium pump in normal red cells and to inhibit the enzymatic activity (sodium-potassium-ATPase) of the sodium pump in membrane preparations from normal kidneys. In 21 patients with active acromegaly, the mean (+/- SE) level of ouabain-binding inhibition (1.56 +/- 0.38) was higher (P less than 0.01) than that in either 11 successfully treated patients (0.18 +/- 0.05) or in 27 normal controls (0.19 +/- 0.03). The inhibition of sodium-potassium-ATPase activity by plasma was also greater in patients with active acromegaly (38.1 +/- 6.8 percent) than in successfully treated patients (18.4 +/- 5.6 percent, P less than 0.05) or controls (21.1 +/- 2.7 percent, P less than 0.05). Significant correlations were found between plasma volume and ouabain-binding inhibition in 23 patients (r = 0.72, P less than 0.01) and sodium-potassium-ATPase inhibition in 19 patients (r = 0.62, P less than 0.01). Pituitary adenomectomy decreased plasma volume and the inhibition by plasma of ouabain binding. We conclude that an endogenous digitalis-like factor is present in the plasma of patients with chronic volume expansion due to acromegaly. These results are consistent with the hypothesis that this natriuretic factor may have a physiologic role in water and sodium homeostasis.

Oral glucose inhibits growth hormone secretion induced by human pancreatic growth hormone releasing factor 1-44 in normal man

The interaction between the inhibitory effect on growth hormone secretion of a 75 g oral glucose load and the stimulatory effect of human pancreatic growth hormone releasing factor 1-44 (hpGRF 1-44, 10 micrograms i.v.) has been studied in six normal subjects. hpGRF 1-44 alone induced a rise in growth hormone concentrations (maximum mean +/- SEM, 16.5 +/- 1.7 mU/l 15 min after injection) while growth hormone levels were suppressed by oral glucose alone (less than 1.5 mU/l from 45 to 135 min after glucose ingestion). When hpGRF 1-44 was injected 60 min after oral glucose, the growth hormone response was attenuated (maximum, 6.7 +/- 1.4 mU/l at 15 min, P less than 0.05). Increments of blood glucose within the physiological range diminish the growth hormone response to hpGRF 1-44 in normal man.

The effects of oral clonidine on the growth hormone level in acromegalic patients

The effects of the noradrenergic agent clonidine on GH secretion of the adenohypophysis were studied in 10 healthy volunteers and 11 acromegalic patients. Orally administered clonidine led to a considerable serum human growth hormone (GH) level increase in the healthy individuals. In the acromegalic patients the clonidine resulted in a slight, but not significant GH increase. These results support the findings that the mechanism of noradrenergic regulation of serum GH secretion is impaired in acromegaly.

Clinical use of pre- and postsurgical evaluation of abnormal GH responses in acromegaly

The criteria by which acromegalic patients are considered "cured" after surgical therapy are still controversial. Since the abnormal growth hormone (GH) increase after the administration of some agents has been demonstrated to be characteristic of the tumoral somatotrophs, its disappearance after surgery may be taken as an index of the complete removal of the tumor. Serum GH increases after thyrotropin-releasing hormone (TRH, 200 micrograms intravenously), gonadotropin-releasing hormone (Gn-RH, 100 micrograms intravenously), and sulpiride (100 mg intramuscularly) injected during dopamine infusion (DA-Slp test), were evaluated in 68 acromegalic patients before and after transnasosphenoidal adenomectomy, and every 12 to 18 months during a follow-up period of 6 months to 11 years (average 42 months). Forty-two patients had abnormal responses to at least one test before surgery: 32 out of 68 (47%) to TRH, six out of 40 (15%) to Gn-RH, and 20 out of 28 (71%) to the DA-Slp test. Of 18 patients who underwent all three tests, 78% had abnormal responses to at least one of them. Twenty-three patients became unresponsive after surgery, and none of them had a recurrence or became abnormally responsive again during the follow-up period. Three out of six patients with postoperative serum GH levels between 5.1 and 10 ng/ml and three out of six patients with postoperative serum GH levels between 2.1 and 5 ng/ml remained abnormally responsive: one of them relapsed 1 year after the operation. The abnormal responses were lost in all 11 patients whose postoperative serum GH levels were below 2 ng/ml, and abnormal responses were maintained in all the patients in whom surgery was considered unsuccessful because postoperative serum GH levels were higher than 10 ng/ml. The TRH, Gn-RH, and DA-Slp tests should thus be considered useful tools in verifying the total removal of an adenoma. The reappearance of active acromegaly in the patient with low postoperative GH levels, who was still responsive to TRH, should be regarded as a reactivation and not a true recurrence of the disease.

Childhood acromegaly successfully treated with interstitial irradiation using yttrium-90

A child with a growth hormone producing tumour presented at the age of 4 1/2 years. The onset of the disease was at 18 months of age. Treatment was given with three doses of interstitial irradiation using yttrium-90 implants. There were no local complications from the procedures. Now, 11 years after diagnosis, she is asymptomatic, of normal appearance, and her height and the size of the pituitary fossa are normal. Growth hormone levels are almost normal, thyroid function is intact, and she is maintained on prednisone and sex hormones.

Bromocriptine therapy in acromegaly. A long-term review of 35 cases

Bromocriptine (CB-154, Parlodel, Sandoz) was given to 35 acromegalic patients for a period of 6-36 months. Basal and post-therapy endocrine functions including estimation of serum growth hormone (GH) profile; and GH kinetics during oral glucose tolerance test, augmented insulin tolerance test and thyrotrophin releasing hormone test were determined. The pituitary tumour size was delineated by a pneumoencephalogram. The mean GH levels ranged from 14 micrograms/l to 316 micrograms/l. Bromocriptine suppressed GH values to 5 micrograms/l or less in 16 patients and less than 10 micrograms/l in a further 6 patients. In 33 patients GH values fell to 50% of the basal value or less. There was no significant GH reduction in 2 'nonresponders'. Bromocriptine did not block the stress-induced GH secretion. It did not disturb pituitary functions other than prolactin which was suppressed much earlier and was maintained with smaller doses. GH suppression on the other hand was shortlived and rebounded when the drug was omitted. It had no adverse effect on tumour size in 2 patients having suprasellar extension of the tumour. Bromocriptine improved carbohydrate tolerance and sexual function although it did not affect insulin and gonadotrophin values. It seems reasonable to offer a trial of bromocriptine in all patients with acromegaly where therapy is deemed necessary as it is well tolerated, has insignificant side effects and no adverse drug interactions. Its high cost and prolonged course are obvious disadvantages. Caution should be exercised in cases with suprasellar extension and visual field involvement.

Clinical evaluation of pituitary adenomas

Improvements in both diagnostic methods and surgical and medical treatment modalities for pituitary disease have been a major advance in endocrinology. Future refinements in visualization techniques and dynamic testing of pituitary function are to be expected and will further add to understanding of this complex spectrum of diseases.

Diminished prolactin reserve in acromegaly

Prolactin (PRL) secretion has been evaluated in twenty acromegalic patients. All had intact LH, FSH, and cortisol levels and normal thyroid function. Five patients had persistent hyperprolactinemia. The remainder had decreased basal PRL levels with impaired PRL responses to TRH and the dopaminergic antagonist metoclopramide (MET). Despite adequate hypoglycemia and an intact cortisol response, there was no PRL rise following insulin hypoglycemia. The imparied PRL response to TRH was evident in treated and untreated patients and was independent of GH levels. Basal hyperprolactinemia may be related to PRL secretion by the tumor cells or interference with the transport of PIF by the tumor. The decreased PRL reserve noted in the majority of the patients may be related to a decrease in lactotrope cell mass or, alternatively, to enhanced dopaminergic activity.

Evaluation and treatment of patients with prolactin-secreting pituitary tumors

Six women with secondary amenorrhea and hyperprolactinemia, four of whom had associated galactorrhea, were studied. Four were found to have prolactin-secreting pituitary microadenomas and two had macroadenomas. Suppression of prolactin secretion and stimulation of prolactin, serum growth hormone and thyroid-stimulating hormone secretion were studied, and gonadotropin and adrenocorticotropic hormone reserves were evaluated. The most sensitive techniques available for the diagnosis of pituitary adenomas in patients with amenorrhea and hyperprolactinemia appear to be the measurement of the magnitude of plasma prolactin elevation and hypocycloidal tomography of the sella turcica. The dynamic function tests proved to be of little diagnostic, but of great prognostic, value for patients with small pituitary tumors.

Evaluation of acromegaly by radioimmunoassay of somatomedin-C

We measured serum concentrations of somatomedin-C by radioimmunoassay in 57 acromegalic patients and compared them with various indicators of disease activity. The mean fasting somatomedin-C concentration was 6.8 U per milliliter (range, 2.6 to 21.7) for the acromegalics and 0.67 U per milliliter (range, 0.31 to 1.4) for 48 normal, fasting adults. The somatomedin-C concentration correlated significantly with: heel-pad thickness (r = 0.73), fasting glucose (r = 0.74), and one-hour postprandial glucose (r = 0.77). In contrast, "glucose-suppressed" growth hormone correlated weakly (r = 0.34, 0.36, 0.34) with these clinical indexes of severity. Fasting growth hormone levels showed no correlation (r = 0.14). Five active acromegalics had "normal" growth hormone levels after glucose suppression, but they had elevated somatomedin-C. In 15 patients studied one year after treatment, changes in somatomedin-C concentrations paralleled the degree of clinical improvement. Measurement of somatomedin-C appears to provide a reliable means for confirming the diagnosis of acromegaly and of clinical disease activity than measurement of growth hormone concentrations.

Selective total removal of a growth-hormone-secreting adenoma: evidence that acromegaly is a primary pituitary disease

Acromegaly is caused by hypersecretion of growth hormone by the pituitary. There is some debate as to whether the primary etiology of the disease is abnormal hypothalamic stimulation of the pituitary or a primary pituitary tumor. This paper presents a case of acromegaly in which growth hormone dynamics in response to stimulation and suppression tests were abnormal. After transsphenoidal adenomectomy of a small tumor, growth hormone levels returned to normal and suppression and stimulation test results reverted to normal within 1 wk postoperatively and remained normal for 2 yr. The findings suggest that the acromegaly in this case was due to a primary pituitary dysfunction. Microsurgical removal of growth-hormone-secreting tumors provides a unique opportunity to study the etiology of acromegaly.

Evaluation of the results of trans-sphenoidal surgery in acromegaly by assessment of the growth hormone response to thyrotrophin-releasing hormone

Eighteen acromegalic patients GH-responsive to TRH were reinvestigated following trans-sphenoidal surgery and radiotherapy. Basal serum GH decreased below 10 microgram/1 in thirteen cases; nine of them became GH-unresponsive to TRH 1 month after operation, and another one following conventional pituitary irradiation. Four of these ten patients also showed a normal GH response to L-Dopa after treatment, and five responded normally to insulin-induced hypoglycaemia; two patients had a normal GH secretory pattern after both these stimuli. No recurrences were observed over a follow-up period of 15-80 months among the ten patients who became GH-unresponsive to TRH following operation, while one of the three subjects still responsive to TRH in spite of normalized basal serum GH concentration relapsed 10 months after surgery. Three patients with normalized TRH test following operation were repeatedly reinvestigated over a 3-6 years period and always found unresponsive. The present study shows that the 'paradoxical' GH responses to TRH and L-Dopa frequently disappear after surgery, that complete normalization of GH secretory pattern may rarely be attained, and that the disappearance of GH response to TRH probably indicates satisfactory treatment of acromegaly. These data suggest that the 'paradoxical' GH responses frequently found in acromegaly are dependent on the adenoma per se and not on hypothalamic dysfunction.

Loss of central nervous system component of dopaminergic inhibition of prolactin secretion in patients with prolactin-secreting pituitary tumors

The administration of l-dopa suppresses prolactin (PRL) secretion in normal subjects and in patients with hyperprolactinemia, although it is not known whether this effect, which requires the conversion of dopa to dopamine, is mediated peripherally or through the central nervous system. To distinguish between these effects, 10 normal subjects (6 male, 4 female) and 8 patients with hyperprolactinemia associated with pituitary tumors were given l-dopa, 0.5 g alone, or 0.1 g after a 24-h pretreatment with carbidopa, 50 mg every 6 h, which produces peripheral dopa decarboxylase inhibition. Similar degrees of PRL suppression were observed in normal subjects (basal plasma PRL 13+/-2 ng/ml) after l-dopa alone (48+/-4%) and after l-dopa plus carbidopa (58+/-6%). In patients with pituitary tumors and elevated plasma PRL (73+/-14 ng/ml), l-dopa alone led to PRL suppression comparable with that in normal subjects (47+/-6%). However, l-dopa plus carbidopa resulted in only minimal suppression of plasma PRL (19+/-4%) which was significantly less than after l-dopa alone (P < 0.001). Urinary homovanillic acid excretion, which reflected peripheral dopa decarboxylation was similar in controls and tumor patients after l-dopa both alone and after carbidopa pretreatment. Comparable suppression of PRL levels in response to a dopamine infusion (4 mug/kg per min for 3 h) was observed in controls and tumor patients. The results indicate that although peripheral conversion of exogenous dopa to dopamine can suppress PRL secretion, in normals, the central nervous system conversion of dopa to dopamine in the presence of peripheral dopa decarboxylase inhibition is sufficient to account for its PRL-suppressive effects. In contrast, patients with tumors, while retaining peripheral dopaminergic inhibitory effects on PRL secretion, exhibit a marked reduction of central dopaminergic inhibition of PRL secretion.

Transsphenoidal microhypophysectomy in acromegaly

✓ From July, 1970, to March, 1975, 62 transsphenoidal operations were performed on 61 acromegalic patients (39 males, 22 females). Of these patients, 58 presented with symptoms of hypersecretion of human growth hormone (HGH), with relatively infrequent local effects. Each patient was evaluated neuroradiologically, and each tumor was classified as an enclosed or an invasive adenoma, with or without suprasellar extension. Anterior pituitary function was also evaluated for each patient, pre- and postoperatively. During the transsphenoidal procedure, selective gross total removal of the adenomatous tissue was attempted, and was successful in 53 patients; selective subtotal tumor removal was performed in eight patients.

In 38 patients who had not undergone prior therapy, a selective total excision was achieved in 36; of these, 30 patients were considered cured, on the basis of relief of clinical symptoms and reduction of the serum HGH level to below 10 mg/ml. There was no significant difference in cure rates between the enclosed and the invasive adenomas, and no cures were achieved by any procedure short of selective total tumor removal. In these latter cases, postoperative irradiation was employed. Eighteen patients had received prior therapy in the forms of cryohypophysectomy (eight cases), cryohypophysectomy and irradiation (two cases), craniotomy (two cases), craniotomy and irradiation (two cases), and irradiation alone (four cases). The treatment results in this group were less favorable. In the entire series of 62 operations, complications occurred in eight patients in the form of cerebrospinal fluid leak, meningitis, sinusitis, nasal-oral fistula, transient diabetes insipidus (six cases), and carotid and cavernous injuries. In the group of 43 previously untreated patients, endocrine complications occurred in five, of which only three have permanent deficits. In the previously treated 18 patients, one developed compromised pituitary function from the transsphenoidal procedure. In the entire series, there was no surgical mortality, although two patients died of surgically unrelated causes.

Stimulation of growth hormone release by luteinizing hormone-releasing hormone and melanocyte-stimulating hormone-release inhibiting hormone in the hypophysectomized rat bearing an ectopic pituitary

Intrajugular administration of LHRH (0-6 and 1-2 mug) in hypophysectomized rats which received renal grafts of anterior pituitary induced a small but significant rise in plasma GH 5 and 10 min post-treatment. LHRH, at the same dose levels, was ineffective in weight-matched intact controls. MIF, at the dose of 1-2 mug, induced a slight GH rise 5 min after treatment in hypophysectomized trasnplanted rats, while it was ineffective in intact controls. Unlike the two hypothalamic peptides, alpha-MSH (0-6 and 1-2 mug) was ineffective as a GH-releaser in both transplanted and intact rats.

Suppression of plasma growth hormone levels with glucose infusion in patients with acromegaly

Intravenous glucose infusion which increased blood glucose levels over 27-8 mmo1/1 suppressed plasma GH levels by 41-74% in five acromegalic patients with basal concentrations of less than 20 mu/1, but not in six patients with basal levels over 80 mu/1. Oral 100 g glucose loading had little suppressing effect in both groups. These results appear to indicate that the suppressibility with hyperglycaemia is partially retained or restored in some, if not all, patients of acromegaly with lower GH secreting activity.

Growth hormone excess and sexual precocity in polyostotic fibrous dysplasia (McCune-Albright syndrome): evidence for abnormal hypothalamic function

A 5-5/12-year-old boy with gigantism and precocious puberty associated with the McCune-Albright syndrome is presented. Serum concentrations of growth hormone were extremely elevated (128-163 ng/ml) and were not suppressed by hyperglycemia or chlorpromazine. Serum LH (7.4 +/- 1.0 SD mIU/ml) and FSH (5.3 +/- 0.3 SD mIU/ml) concentrations were in the range observed in midpuberty. The secretion pattern of LH was episodic. The administration of estradiol suppressed the secretion of FSH and had an apparent positive feedback effect on release of LH. These findings are compatible with abnormal hypothalamic function as the mechanism for the endocrinopathies associated with the McCune-Albright syndrome.

A critical review of the clinical relevance of growth hormone and its measurement in the nuclear medicine laboratory

A wide variety of metabolic and stressful stimuli, both physical and psychologic, produce rapid elevation of plasma growth hormone (GH). In addition, spontaneous elevation of GH occurs during the day, and a rise in GH occurs in association with the initial slow-wave sleep episode at night. Although the identity of the long-sought GH releasing factor has not yet been established, a hypothalamic factor inhibiting GH release named somatostatin has been identified and synthesized. Most, if not all, of the GH rises are mediated by neural mechanisms, and therefore they may be disrupted by many disease processes affecting the pituitary or the hypothalamus...