Basal Growth Hormone Research Articles

Inhibitory effect of leptin on growth hormone secretion of GH3 cells: Involvement of cell proliferation, apoptosis and intracellular free Ca 2+

Recent studies have identified leptin and leptin receptors in the pituitary of different species, which suggest that there may be endocrine and paracrine regulatory roles between leptin-producing cells and cells with leptin receptor in pituitary, including growth and secretion of GH cells. The aim of this study was to investigate the effects of leptin on growth hormone (GH) secretion of GH3 cell. GH3 cells were cultured and treated with leptin. Cell proliferation was evaluated by MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide) assay, distribution of cell cycle and rate of apoptosis determined by flow cytometry and fluorescence microscopy, and intracellular free Ca 2+ levels ([Ca 2+] i) of single GH3 cells measured by a laser scanning confocal microscope. Leptin (10 −9–10 −7 mol/L) at 1 day or longer of treatment inhibited the basal growth hormone secretion of GH3 cells ( P < 0.05), but had no significant effect on short-term treatment. Leptin inhibited cell proliferation, reduced the proportion of cells in DNA synthesis period (S phase) to inhibit DNA synthesis of GH3 cells, and accelerated cell apoptosis of GH3 cells. Furthermore, the level of [Ca 2+] i of single GH3 cell was found to decrease immediately upon the addition of leptin (10 −8 mol/L). Leptin inhibits the basal GH secretion of GH3 cells, which may be due to the inhibition of proliferation, DNA synthesis and advanced apoptosis of GH3 cell. The inhibition of leptin on GH synthesis and secretion may be related to intracellular free Ca 2+ level.

Determinants of GH-releasing hormone and GH-releasing peptide synergy in men

Age, sex steroids, and abdominal-visceral fat (AVF) jointly affect pulsatile growth hormone (GH) secretion. Pulsatile GH secretion in turn is controlled by GH-releasing hormone (GHRH), GH-releasing peptide (GHRP), and somatostatin. Marked stimulation of pulsatile GH secretion is achieved via GHRH-GHRP synergy. Nonetheless, how key modulators of GH secretion, such as age, sex steroids, and body mass index, modify GHRH-GHRP synergy is not known. The present strategy was to 1) infuse GHRH and GHRP-2 simultaneously to evoke synergy and 2) downregulate the gonadal axis with leuprolide and then restore placebo (Pl) or testosterone (T) to clamp the sex steroid milieu. Forty-seven men [18-74 yr of age, T = 7-1,950 ng/dl, estradiol (E(2)) = 5-79 pg/ml, insulin-like growth factor (IGF)-I = 115-817 microg/l, AVF = 11-349 cm(2)] were studied. GHRH-GHRP synergy correlated negatively with age and AVF (both P < 0.001) and positively with IGF-I (P < 0.001) and IGF-binding protein (IGFBP)-3 (P = 0.031). Unstimulated basal (nonpulsatile) GH secretion correlated positively with T (P = 0.015) and E(2) (P = 0.004) concentrations. Fasting pulsatile GH secretion varied negatively with age (P = 0.017) and positively with IGF-I (P = 0.002) and IGFBP-3 (P = 0.001). By stepwise forward-selection multivariate analyses, AVF, IGF-I, and IGFBP-3 together explained 60% of the variability in GHRH-GHRP synergy (P < 0.001), E(2) accounted for 17% of the variability in basal GH secretion (P = 0.007), and IGF-I explained 20% of the variability in fasting pulsatile GH secretion (P = 0.002). In conclusion, a paradigm examining GHRH-GHRP synergy under a sex steroid clamp reveals highly selective control of basal, pulsatile, and synergistic peptide-driven GH secretion by AVF, E(2), and IGF-I in healthy men.

Insulin-like growth factor-I feedback regulation of growth hormone and luteinizing hormone secretion in the pig: evidence for a pituitary site of action

Three experiments (EXP) were conducted to determine the role of insulin-like growth factor-I (IGF-I) in the control of growth hormone (GH) and LH secretion. In EXP I, prepuberal gilts, 65 ± 6 kg body weight and 140 days of age received intracerebroventricular (ICV) injections of saline (n = 4), 25 μg (n = 4) or 75 μg (n = 4) IGF-I and jugular blood samples were collected. In EXP II, anterior pituitary cells in culture collected from 150-day-old prepuberal gilts (n = 6) were challenged with 0.1, 10 or 1000 nM [Ala15]-h growth hormone-releasing hormone-(1-29)NH2 (GHRH), or 0.01, 0.1, 1, 10, 30 nM IGF-I individually or in combinations with 1000 nM GHRH. Secreted GH was measured at 4 and 24 h after treatment. In EXP III, anterior pituitary cells in culture collected from 150-day-old barrows (n = 5) were challenged with 10, 100 or 1000 nM gonadotropin-releasing hormone (GnRH) or 0.01, 0.1, 1, 10, 30 nM IGF-I individually or in combinations with 100 nM GnRH. Secreted LH was measured at 4 h after treatment. In EXP I, serum GH and LH concentrations were unaffected by ICV IGF-I treatment. In EXP II, relative to control all doses of GHRH increased (P < 0.01) GH secretion. Only 1, 10, 30 nM IGF-I enhanced (P < 0.02) basal GH secretion at 4 h, whereas by 24 h all doses except for 30 nM IGF-I suppressed (P < 0.02) basal GH secretion compared to control wells. All doses of IGF-I in combination with 1000 nM GHRH increased (P < 0.04) the GH response to GHRH compared to GHRH alone at 4 h, whereas by 24 h all doses of IGF-I suppressed (P < 0.04) the GH response to GHRH. In EXP III, all doses of IGF-I increased (P < 0.01) basal LH levels while the LH response to GnRH was unaffected by IGF-I (P > 0.1). In conclusion, under these experimental conditions the results suggest that the pituitary is the putative site for IGF-I modulation of GH and LH secretion. Further examination of the role of IGF-I on GH and LH secretion is needed to understand the inhibitory and stimulatory action of IGF-I on GH and LH secretion.

Acromégalie

Acromegaly is a rare disease usually caused by growth hormone (GH) hypersecretion, due to a pituitary adenoma; in very rare cases, acromegaly is due to ectopic secretion of GHRH, responsible for pituitary hyperplasia. Owing to its insidious onset, acromegaly is often diagnosed late (4 to > 10 years after onset), at an average age of about 40 years, in front of an acquired, slowly progressing disfigurement mainly involving the face and extremities. Acromegaly has also rheumatologic, cardiovascular, respiratory and metabolic consequences which determine its prognosis. The diagnosis is based on an increased serum GH concentration unsuppressed following an oral glucose load (oral glucose tolerance test -OGTT-) and an increased insulin-like growth factor-I (IGF-I); according to a 2000 Consensus statement, if the basal serum GH is above 0,4microg/L (1.2mIU/L) and/or if the IGF-I is elevated, an OGTT must be performed. If the lowest GH value (nadir) during OGTT remains above 1microg/L (3mIU/L), acromegaly is confirmed. With the generalized use of very sensitive assays nowadays, it has recently been considered that this cutoff should be decreased to 0,3microg/L (0.9mIU/L). Treatment is aimed at correcting (or preventing) tumor compression by excising the culprit lesion, and at reducing GH and IGF-I levels to normal values (or at least to a "safe" GH level of < 2microg/L or < 6mIU/L). A stepwise therapeutic strategy is used: transsphenoidal surgery is often the first-line treatment; when surgery fails to correct GH/IGF-I hypersecretion, medical treatment with somatostatin analogs and/or radiotherapy can be used, somatostatin analogs being generally preferred; the GH antagonist (pegvisomant) is used in patients that are resistant or intolerant to somatostatin analogs. Prognosis of acromegaly has improved in the recent years: adequate hormonal disease control is achieved in most cases, allowing life expectancy similar to that of the general population.

Growth hormone overproduction in a patient with multiple endocrine neoplasia type I

Abstract. Hermans MMH, Lips CJM, Bravenboer B (Catharina Hospital Eindhoven, Eindhoven, and University Hospital Utrecht, Utrecht, the Netherlands). Growth hormone overproduction in a patient with multiple endocrine neoplasia type I (Case Report). J Intern Med 2000; 248: 527–532. In a 69-year-old woman with a complicated history of multiple endocrine neoplasia type I (MEN 1), growth hormone overproduction was found without clinical features of acromegaly. Zollinger-Ellison syndrome was diagnosed at the age of 36 years. Total gastrectomy and partial pancreatectomy were performed. Two years later hypercalcaemia occurred, hyperparathyroidism was suspected and three hyperplastic parathyroid glands were removed. In 1994 the plasma gastrin level was elevated and a computertomography of the abdomen revealed a 1.5-cm large pancreatic tumour. Screening of the pituitary functions was unremarkable and a magnetic resonance scan of the pituitary gland showed no abnormalities. In 1995 type II diabetes mellitus was diagnosed. In 1997 basal plasma growth hormone levels were raised and plasma IGF-I levels were alternately high and normal. The patient had no clinical signs of acromegaly, but glucose tolerance testing resulted in a paradoxical rise in growth hormone concentration compatible with the diagnosis of growth hormone overproduction. Magnetic resonance imaging of the pituitary gland revealed a microadenoma.

Pituitary hypoplasia and growth hormone deficiency in a woman with glycogen storage disease type Ia: a case report

IntroductionGrowth retardation is one of the cardinal manifestations of glycogen storage disease type Ia. It is unclear which component of the growth hormone and/or insulin-like growth factor axis is primarily disrupted, and management of growth impairment in these patients remains controversial. Here we report the first case in the literature where glycogen storage disease type Ia is associated with pituitary hypoplasia and growth hormone deficiency.Case presentationA 20-year-old woman with glycogen storage disease type Ia was admitted to our endocrinology department because of growth retardation. Basal and overnight growth hormone sampling at 2-hour intervals demonstrated low levels; however, provocative testing revealed a relatively normal growth hormone response. A hypoplastic anterior pituitary with preserved growth hormone response to provocative testing suggested the possibility of growth hormone neurosecretory dysfunction and/or primary pituitary involvement.ConclusionPituitary hypoplasia may result from growth hormone-releasing hormone deficiency, a condition generally known as growth hormone neurosecretory dysfunction. It is an abnormality with a spontaneous and pulsatile secretion pattern, characterized by short stature, growth retardation and normal serum growth hormone response to provocative testing. However, in the case described in this report, a normal although relatively low growth hormone response during insulin tolerance testing and pituitary hypoplasia suggested that primary pituitary involvement or growth hormone neurosecretory dysfunction may occur in glycogen storage disease type Ia. This is a potential cause of growth failure associated with a lower somatotroph mass, and may explain the variable responsiveness to growth hormone replacement therapy in people with glycogen storage disease.

Endogenous estradiol may influence IGF-I levels in acromegalic women treated with pegvisomant

We present the case of a 46-year-old woman with acromegaly currently being treated with the growth hormone (GH) receptor antagonist pegvisomant showing strongly fluctuating IGF-I levels. We prospectively measured estradiol, IGF-I, IGF-I binding protein, acid labile subunit, basal endogenous GH, binding protein and pegvisomant levels for 6 months every week. Estradiol levels showed a strongly negative correlation with IGF-I (r = -0.733, P < 0.001), and less so with ALS (r = -0.433, P < 0.05) and IGFBP3 (r = -0.590, P < 0.01). Estradiol was not significantly correlated with endogenous GH or pegvisomant levels. Likewise, IGF-I did not correlate with endogenous GH or pegvisomant levels. In our patient, endogenous estradiol levels have a significant influence on IGF-I levels. When female acromegalic patients on permanent pegvisomant treatment show fluctuating IGF-I levels, estradiol levels should be taken into consideration.

Evaluación de dos inmunoensayos altamente sensibles para la determinación de IGF-1 y GH séricas tras sobrecarga oral de glucosa en controles sanos

To evaluate 2 highly sensitive assays for serum insulin-like growth factor-1 (IGF-1) and growth hormone (GH) determination following an oral glucose tolerance test (OGTT) in healthy controls.Nineteen healthy adults underwent a standard 75g OGTT and GH and IGF-1 were measured. Serum GH and IGF-1 levels were assayed by a sensitive immunoradiometric assay (IRMA) and a highly sensitive chemiluminescent immunometric assay (CLIA).The mean IGF-1 concentration was 153±65ng/ml measured by IRMA and 144±56ng/ml measured by CLIA. The median (interquartile range) basal GH concentrations by IRMAvs CLIA were 0.8 (0.5-3) μg/l vs 0.5 (0.1-2.4) μg/l. The median nadir GH measured by IRMA in these subjects was 0.4 (0.3-0.5) μg/l, and the mean nadir GH by CLIA was 0.08 (0.01-0.22) μg/I. When a ratio of basal IRMA/CLIA GH was calculated in each subject, the median ratio of basal IRMA/CLIA GH concentrations in subjects overall was 1.68. Similarly, the median ratio of nadir IRMA/CLIA GH values was 4.44. One of the subjects did not achieve GH suppression into the established normal range, with a GH nadir of 1.2 μg/l by IRMA and 1 μg/l by CLIA, overlapping with the traditional cut-off defining acromegaly when GH suppression was measured by IRMA.Highly sensitive chemiluminescent immunometric assays should be used to assess the GH/IGF-1 axis. In our opinion, there is no need for a lower GH suppression cut-off for diagnosing acromegaly. We found no significant gender-, BMI- or age-related differences in nadir GH levels and thus our results do not support different OGTT criteria for screening of acromegaly in men and women, or in younger and older subjects.

Ghrelin Induces Growth Hormone Secretion Via a Nitric Oxide /cGMP Signalling Pathway

The presence of ghrelin and its receptor, growth hormone (GH) secretagogue receptor, in the hypothalamus and pituitary, and its ability to stimulate GH release in vivo and in vitro, strongly support a significant role for this peptide in the control of somatotroph function. We previously demonstrated that ghrelin elicits GH secretion directly in somatotrophs by activating two major signalling cascades, which involve inositol phosphate and cAMP. In as much as nitric oxide (NO) and its mediator cGMP have been recently shown to contribute substantially to the response of somatotrophs to key regulatory hormones, including GH-releasing hormone, somatostatin and leptin, we investigated the possible role of this signalling pathway in ghrelin-induced GH release in vitro. Accordingly, cultures of pituitary cells from prepuberal female pigs were challenged with ghrelin (10(-8) m, 30 min) in the absence or presence of activators or blockers of key steps of the NO synthase (NOS)/NO/guanylate cyclase (GC)/cGMP route and GH secretion was measured. Two distinct activators of the NO route, S-nitroso-N-acetylpenicillamine (SNAP) (5 x 10(-4) m) and L-arginine methyl ester hydrochloride (L-AME) (10(-3) m), comparably stimulated GH secretion when applied alone. The presence of L-AME enhanced ghrelin-stimulated GH secretion, whereas SNAP did not alter its effect. Conversely, two different NOS/NO pathway inhibitors, N(w)-nitro-L-arginine methyl ester hydrochloride (10(-5) m) or haemoglobin (20 microg/ml), similarly blocked ghrelin-induced (but not basal) GH release, thus indicating that NO contributes critically to ghrelin action in somatotrophs. Moreover, incubation with a permeable cGMP analogue, 8-Br-cGMP (10(-8) m) stimulated GH secretion, but did not modify the stimulatory action of ghrelin, suggesting that cGMP could mediate the action of NO. Indeed, inhibition of GC by 10 microm LY-53,583 did not alter basal GH secretion but abolished the GH-releasing action of ghrelin. Taken together, our results provide novel evidence indicating that ghrelin requires activation of the NOS/NO route, and its subsequent GC/cGMP signal transduction pathway, as necessary steps to induce GH secretion from somatotrophs.

Discrepancy between the Growth Hormone and Insulin-like Growth Factor-I Concentrations in Patients with Acromegaly

Background: This study was performed to evaluate the frequency and clinical characteristics of patients with active acromegaly and who show discordance of the growth hormone (GH) level and the insulin-like growth factor-I (IGF-I) level. Methods: We reviewed the medical records of the patients who were diagnosed with acromegaly between 01/01/1995 and 6/30/2007 at Seoul National University Hospital. We selected only the patients whose basal GH and IGF-I levels were available. We investigated the pre- and post-operative clinical characteristics, as well as the blood concentrations of GH and IGF-I. The concordance rate between the two hormones was examined. The patients were considered to have active disease on the basis of their IGF-I levels above the normal range, after adjustment for age and gender, and their mean basal GH value was ≥ 2.5 μg/L. The hormone levels and the clinical parameters were compared between the hormone concordant and discordant groups. Results: We reviewed the preoperative records of 103 acromegalic patients, and these patients met the above-mentioned criteria. 53 postoperative patients who were not cured by operation were monitored without them receiving radiation or medical therapy. Both the basal GH and IGF-I levels were above normal in 103 patients preoperatively, and the discordant rate was 0% (0/103 cases). Postoperatively, the discordant rate between the two hormones was increased to 30.2% (16/53 cases). Age, gender, body mass index and tumor size were insignificantly different between the concordant and discordant groups. However, postoperative residual tumors were less frequently observed in the discordant group (P = 0.006). Conclusion: For the patients with acromegaly, unlike the 0% discordance preoperatively, 30.2% of patients showed a discrepancy between their GH and IGF-I levels postoperatively. The patients who had hormonal discrepancy were less likely to have residual tumors after operation. Considering the frequency of this hormonal discrepancy, both hormone levels should be measured to evaluate the disease activity after treatment. Further, oral glucose tolerance testing should be performed and especially for the patients with an increased GH level, but who have a normal IGF-I concentration. (J Korean Endocr Soc 23:395~403, 2008)

Prevalence of Thyroid Nodules Detected by Ultrasonography in Adults for Health Check-up and Analysis of Fine Needle Aspiration Cytology

Background: This study was performed to evaluate the frequency and clinical characteristics of patients with active acromegaly and who show discordance of the growth hormone (GH) level and the insulin-like growth factor-I (IGF-I) level. Methods: We reviewed the medical records of the patients who were diagnosed with acromegaly between 01/01/1995 and 6/30/2007 at Seoul National University Hospital. We selected only the patients whose basal GH and IGF-I levels were available. We investigated the pre- and post-operative clinical characteristics, as well as the blood concentrations of GH and IGF-I. The concordance rate between the two hormones was examined. The patients were considered to have active disease on the basis of their IGF-I levels above the normal range, after adjustment for age and gender, and their mean basal GH value was ≥ 2.5 μg/L. The hormone levels and the clinical parameters were compared between the hormone concordant and discordant groups. Results: We reviewed the preoperative records of 103 acromegalic patients, and these patients met the above-mentioned criteria. 53 postoperative patients who were not cured by operation were monitored without them receiving radiation or medical therapy. Both the basal GH and IGF-I levels were above normal in 103 patients preoperatively, and the discordant rate was 0% (0/103 cases). Postoperatively, the discordant rate between the two hormones was increased to 30.2% (16/53 cases). Age, gender, body mass index and tumor size were insignificantly different between the concordant and discordant groups. However, postoperative residual tumors were less frequently observed in the discordant group (P=0.006). Conclusion: For the patients with acromegaly, unlike the 0% discordance preoperatively, 30.2% of patients showed a discrepancy between their GH and IGF-I levels postoperatively. The patients who had hormonal discrepancy were less likely to have residual tumors after operation. Considering the frequency of this hormonal discrepancy, both hormone levels should be measured to evaluate the disease activity after treatment. Further, oral glucose tolerance testing should be performed and especially for the patients with an increased GH level, but who have a normal IGF-I concentration.

Acromegaly with Normal IGF-1 Levels Probably due to Poorly Controlled Diabetes Mellitus

Acromegaly is characterized by the somatic disfigurement and excessive production of growth hormone (GH) and insulin-like growth factor-1 (IGF-1). Here we report a patient with aromegaly and diabetes mellitus, who showed normal IGF-1 levels in spite of elevated GH levels. The patient was a 52-year-old woman with acromegalic manifestations. Serum GH level was elevated (32.4 ng/mL) with hyperglycemia (fasting plasma glucose, 277 mg/dL) and an extremely high level of glycosylated hemoglobin (HbA1c 17.7%), whereas serum IGF-1 level was within normal range (110 ng/mL, normal range 37-266). Brain magnetic resonance imaging detected a pituitary tumor, with involvement of the right cavernous sinus. Oral glucose tolerance test (OGTT) showed no suppression of serum GH. Thyrotropin-releasing hormone test showed paradoxical increases in serum GH. We therefore diagnosed acromegaly accompanied with diabetes mellitus. A large amount of insulin (34 units/day) was required to control the blood glucose level. The patient was treated with octreotide, a somatostatin analogue, followed by transsphenoidal surgery. After the surgery, serum GH levels were suppressed by OGTT, although basal serum GH levels remained to be high. Basal serum GH levels, however, were normalized 5 months later. Blood glucose became well controlled by the diet alone. In contrast, serum IGF-1 increased to the range of 219-233 ng/mL. Pre-operative serum IGF-1 levels were low probably due to poorly controlled diabetes mellitus. In conclusion, the presence of normal serum IGF-1 levels cannot exclude the diagnosis of acromegaly especially when the patient is accompanied by diabetes mellitus.

Late onset isotretinoin resistant acne conglobata in a patient with acromegaly

A 55 year-old male presented with multiple pus-discharging abscesses and sinuses and mutilating scarring on the gluteal region and back prevalent for the last ten years with exacerbations and remissions. Physical examination revealed acromegaly with frontal bossing, prognathism, a barrel chest and acral hypertrophy. Dermatological examination revealed cutis verticis gyrata, thick eyelids, a large triangular nose, a thickened lower lip, macroglossia, widely spaced teeth and widened skin pores with wet and oily skin. Hair was fine and nails were flat and wide. There were multiple inflammatory papules, tender nodules, draining sinuses, and grouped, polyporous comedones as well as multiple and extensive depressed and keloidal scars localized predominantly over the gluteal region with a few scattered lesions over the back. A computed tomography (CT) scan showed widened sella turcica. His basal fasting growth hormone (GH) levels were markedly raised (230 ng/mL; normal 1-5 ng/mL) while the prolactin levels were moderately raised (87 ng/mL; normal 2-5 ng/mL). These findings were consistent with a diagnosis of acromegaly. The patient was put on antibiotics, nonsteroidal antiinflammatory drugs and isotretinoin at a dose of 1 mg/kg/day, which was increased to 1.5 mg/kg/day. Except for an initial mildly beneficial response, the skin lesions were largely resistant to high doses of isotretinoin at the end of four months.

Management of autoimmune urticaria

A 55 year-old male presented with multiple pus-discharging abscesses and sinuses and mutilating scarring on the gluteal region and back prevalent for the last ten years with exacerbations and remissions. Physical examination revealed acromegaly with frontal bossing, prognathism, a barrel chest and acral hypertrophy. Dermatological examination revealed cutis verticis gyrata, thick eyelids, a large triangular nose, a thickened lower lip, macroglossia, widely spaced teeth and widened skin pores with wet and oily skin. Hair was fi ne and nails were fl at and wide. There were multiple infl ammatory papules, tender nodules, draining sinuses, and grouped, polyporous comedones as well as multiple and extensive depressed and keloidal scars localized predominantly over the gluteal region with a few scattered lesions over the back. A computed tomography (CT) scan showed widened sella turcica. His basal fasting growth hormone (GH) levels were markedly raised (230 ng/mL; normal 1-5 ng/mL) while the prolactin levels were moderately raised (87 ng/mL; normal 2-5 ng/mL). These fi ndings were consistent with a diagnosis of acromegaly. The patient was put on antibiotics, nonsteroidal antiinfl ammatory drugs and isotretinoin at a dose of 1 mg/kg/day, which was increased to 1.5 mg/kg/day. Except for an initial mildly benefi cial response, the skin lesions were largely resistant to high doses of isotretinoin at the end of four months.

Pituitary Function and the Somatotrophic System in Patients with Idiopathic Parkinson’s Disease Under Chronic Dopaminergic Therapy

Idiopathic Parkinson's disease and dopaminergic medication may influence pituitary hormone secretion. The present study aimed to reveal any abnormalities of the somatotrophic system induced by the disease itself and/or the dopaminergic therapy. Investigations of other pituitary hormones under basal and stimulated conditions, as well as an analysis of body composition, were also performed. This was a controlled diagnostic study in which luteinising hormone-releasing hormone, thyroid-releasing hormone, corticotrophin-releasing hormone and arginine hydrochloride were administered to ten patients with idiopathic Parkinson's disease under dopaminergic medication. Basal and stimulated hormone concentrations and bioelectrical impedance analyses were compared with those of healthy, age-matched controls. Basal growth hormone (GH) at -30 and 0 min was higher in Parkinsonian patients (2.74 +/- 3.79 ng/ml versus 0.53 +/- 0.10 ng/ml and 2.12 +/- 2.44 ng/ml versus 0.51 +/- 0.03 ng/ml; P < 0.05). The area under the GH curve after stimulation was greater in Parkinsonian patients (502.4 +/- 202.6 ng x min/ml versus 312.0 +/- 98.5 ng x min/ml; P < 0.05), depending on higher basal GH levels, rather than a greater arginine response. No differences in insulin growth factor (IGF)-1 or IGF-BP3 concentrations were detected. There were no differences between the groups in basal and stimulated gonadotrophic, corticotrophic and thyrotrophic function, or body composition. Prolactin was below the detection limit in the patients during the course of the study. Parkinsonian patients experience marked hypoprolactinaemia and repeated stimulation of GH secretion during chronic dopaminergic therapy. Our findings suggest a peripheral GH resistance in these chronically-treated patients.

Basal insulin, glucagon, and growth hormone replacement

Conclusions drawn from the pancreatic (or islet) clamp technique (suppression of endogenous insulin, glucagon, and growth hormone secretion with somatostatin and replacement of basal hormone levels by intravenous infusion) are critically dependent on the biological appropriateness of the selected doses of the replaced hormones. To assess the appropriateness of representative doses we infused saline alone, insulin (initially 0.20 mU.kg(-1).min(-1)) alone, glucagon (1.0 ng.kg(-1).min(-1)) alone, and growth hormone (3.0 ng.kg(-1).min(-1)) alone intravenously for 4 h in 13 healthy individuals. That dose of insulin raised plasma insulin concentrations approximately threefold, suppressed glucose production, and drove plasma glucose concentrations down to subphysiological levels (65 +/- 3 mg/dl, P < 0.0001 vs. saline), resulting in nearly complete suppression of insulin secretion (P < 0.0001) and stimulation of glucagon (P = 0.0059) and epinephrine (P = 0.0009) secretion. An insulin dose of 0.15 mU.kg(-1).min(-1) caused similar effects, but a dose of 0.10 mU.kg(-1).min(-1) did not. The glucagon and growth hormone infusions did not alter plasma glucose levels or those of glucoregulatory factors. Thus, insulin "replacement" doses of 0.20 and even 0.15 mU.kg(-1).min(-1) are excessive, and conclusions drawn from the pancreatic clamp technique using such doses may need to be reassessed.

Beneficial effects of GLP-1 on endothelial function in humans: dampening by glyburide but not by glimepiride

Sulfonylureas (SU) with glucagon-like peptide-1 (GLP-1)-based therapy are an emerging therapeutic combination for type 2 diabetes. Prior human studies have hinted at endothelial effects of GLP-1 and SU. To study the endothelial effects of GLP-1 per se and to evaluate the modulatory effects, if any, of SU agents on GLP-1-induced changes in endothelial function, healthy, nondiabetic, normotensive, nonsmokers, age 18-50 yr with no family history of diabetes, were studied. Subjects were randomized to either placebo (n = 10), 10 mg of glyburide (n = 11), or 4 mg of glimepiride (n = 8) orally. Euglycemic somatostatin pancreatic clamp with replacement basal insulin, glucagon, and growth hormone was performed for 240 min. Forearm blood flow (FBF) was measured by venous occlusion plethysmography with graded brachial artery infusions of acetylcholine (Ach) and nitroprusside (NTP) before and after intravenous infusion of GLP-1. GLP-1 (preinfusion 3.4 +/- 0.2, postinfusion 25.5 +/- 2.8 pM) enhanced (P < 0.03) Ach-mediated vasodilatation (Delta+6.5 +/- 1.1 vs. Delta+9.1 +/- 1.2 ml.100 ml(-1).min(-1), change from baseline FBF) in those on placebo. However, in contrast, glyburide abolished GLP-1-induced Ach-mediated vasodilatation (Delta+11.7 +/- 2.0 vs. Delta+11.7 +/- 2.5 ml.100 ml(-1).min(-1)). On the other hand, glimepiride did not alter the ability of GLP-1 to enhance Ach-mediated vasodilatation (Delta+7.9 +/- 0.5 vs. Delta+10.2 +/- 1.3 ml.100 ml(-1).min(-1), P < 0.04). Neither GLP-1 nor SU altered NTP-induced vasodilatation. These data demonstrate that GLP-1 per se has direct beneficial effects on endothelium-dependent vasodilatation in humans that are differentially modulated by SU.

The PPAR-Gamma Activator Rosiglitazone Fails to Lower Plasma Growth Hormone and Insulin-Like Growth Factor-1 Levels in Patients with Acromegaly

Background/Aim: Despite combined therapy consisting of surgery, external X-ray, and medical therapy, a significant number of acromegaly patients continue to have uncontrolled growth hormone (GH) secretion and active disease. These patients, particularly those with large or invasive tumors, require additional therapy to decrease their GH levels. Our aim was to investigate whether patients with documented GH-secreting pituitary adenomas leading to acromegaly would respond with attenuation of GH and insulin-like growth factor-1 (IGF-1) levels after treatment with a peroxisome proliferator-activated receptor gamma (PPAR-γ) agonist. Methods: We conducted prospective analyses in the Endocrinology Clinic of the Pamukkale University. Acromegaly patients who had active disease participated in two admissions: before and after 6 weeks of daily treatment with 8 mg of oral rosiglitazone. Four male and 3 female patients have completed the study. Basal and nadir GH levels during an oral glucose tolerance test were determined, and the IGF-1 and IGF-binding protein-3 levels were also measured both before and 6 weeks after the rosiglitazone treatment. Results: Treatment with rosigitazone did not reduce basal and nadir GH levels during the oral glucose tolerance test and the IGF-1 levels in the patient population as a whole (p > 0.05). Conclusions: The PPAR-γ activator rosiglitazone, used at maximum approved dosage, did not reduce plasma GH and IGF-1 levels in patients with acromegaly. Further studies with higher doses and longer duration of PPAR-γ agonist administration would be required to determine its usefulness in the treatment in this group of patients.

Metabolic Regulation in Danish Bull Calves and the Relationship to the Fertility of Their Female Offspring

The objective of this work was to estimate the genetic variation of free fatty acids (FFA), glucose, growth hormone (GH), and insulin in juvenile male dairy calves and to assess the relationships, if present, with the fertility of their female offspring. This study used data from 1,498 (269.5 d of age±11.1) male calves from a multiple ovulation and embryo transfer breeding scheme (data collected from 1997 to 2002). Calves were Danish Holstein (n=1,047), Danish Jersey (n=200), and Red Dane (n=251), and were sampled following an overnight fast at approximately 9 mo of age. Plasma samples were assayed for basal FFA, glucose, GH, and insulin. Estimated breeding values of female fertility (high values indicating better fertility), based on progeny-test results for approximately 100 daughters per sire, were available for a subset (n=810) of the male calves as adult sires. Data from Danish Holstein alone or Danish Holstein, Red Dane, and Danish Jersey combined (all breeds) were analyzed for each trait. In both data sets, the estimates of heritabilities of glucose (0.27±0.06), FFA (0.11±0.05), and insulin (0.21±0.06) were moderate, and that of GH (0.09±0.05) was low. Correlations of estimated breeding values for fertility traits with glucose and FFA breeding values were negative, indicating that male calves with high glucose or FFA had female offspring with reduced fertility. Selection for bull calves with lower concentrations of glucose and FFA following an overnight fast could result in female offspring with genetically better fertility. Glucose and FFA may therefore be of interest to enhance selection for improved female fertility, as a measurement in young bulls.

Growth Hormone (GH) Receptor Isoform in Acromegaly: Lower Concentrations of GH but Not Insulin-Like Growth Factor-1 in Patients with a Genomic Deletion of Exon 3 in the GH Receptor Gene

A genomic deletion of exon 3 (d3-GHR) of the growth hormone (GH) receptor (GHR) has been linked to the effectiveness of GH therapy in children with GH deficiency. Carriers of the d3-GHR genotype had higher GH-induced growth rates than children homozygous for the full-length (fl)-GHR. The aim of this study was to test whether the relationship between GH and insulin-like growth factor-1 (IGF-1) concentrations is influenced by the GHR genotype in patients with acromegaly. Study participants were 44 adult patients with established diagnosis of acromegaly. The genotype of the GHR was determined in leukocyte DNA from peripheral blood. Clinical and biochemical findings at the time of diagnosis of acromegaly were obtained from the medical records of the patients. fl-GHR homozygosity was found in 22 (50%) of patients, and 22 (50%) of patients had at least 1 d3 allele (d3-GHR). Demographic and clinical characteristics (age, height, weight, estimated duration of disease, and mean tumor size) of the 2 groups were comparable. Median (range) serum IGF-1 concentrations at the time of diagnosis were 670 (447-1443) microg/L in the fl-GHR group and 840 (342-1494) microg/L in the d3-GHR group (P = not significant). Basal GH concentrations were higher in the fl-GHR group [29.7 (3.8-159) microg/L] than in the d3-GHR group [8.4 (2.6-74 microg/L), P = 0.002], and so were mean (30.4 vs 6.1 microg/L, P = 0.005) and nadir (20.5 vs 5.1 microg/L, P = 0.003) GH concentrations during an oral glucose tolerance test. The GHR fl/d3 genotype modulates the relationship between GH and IGF-1 concentrations in patients presenting with acromegaly.