Neural networks in the analysis of episodic growth hormone release

Pulsatile secretion of growth hormone (GH) has been observed in healthy controls as well as acromegalic patients. In healthy adults, highly regulated secretory pulses of GH occur 4-8 times within 24 h. This episodic pattern of secretion seems to be related to the optimal induction of physiological effects at the peripheral level. In contrast to normal subjects, acromegalic patients demonstrate an irregular pattern of excessive GH release. This pattern of secretion is responsible for many systemic effects, such as the stimulation of connective tissue growth, cardiovascular and cerebrovascular disease, diabetes mellitus and arthritis. Standard methods for the analysis of pulsatile patterns of hormone secretion did not consistently separate the temporal dynamics of GH release in healthy controls and acromegalic patients under various study conditions. Using the cutting edge technology of artificial neural networks for time series prediction, we were able to achieve significant separation of both groups under various conditions by means of the predictability of their GH secretory dynamics. Improving the predictive results by using a more refined system of multiple neural networks acting in parallel (adaptive mixtures of local experts), we found that this system performed a self-organized segmentation of hormone pulsatility. It separated phases of secretory bursts and quiescence without any prior knowledge of the form of a GH pulse or a model of secretion. Comparing the predictive results for the GH dynamics with those for computer-stimulated stochastic processes, we were able to define the irregular pattern of GH secretion in acromegaly as a random autonomous process. The introduction of neural networks to the analysis of dynamic endocrine systems might help to expand the existing analytical approaches beyond counting frequency and amplitude of hormone pulses.     

Disturbed release of growth hormone in mature dogs: a comparison with congenital growth hormone deficiency

An acquired defect in growth hormone secretion in mature dogs has been associated with some forms of generalised alopecia. In an attempt to elucidate the pathogenesis of the disturbance in growth hormone release, the plasma concentrations of growth hormone and insulin-like growth factor I (IGF-I) were measured in two seven-year-old poodles with alopecia and, for comparison, in two young German sheperd dogs with congenital hyposomatotropism (pituitary dwarfism). In the poodles the basal concentrations of growth hormone were low, although often above the detection limit of the assay. The concentrations of IGF-I were in the reference range for healthy poodles. No growth hormone could be detected in the plasma of the German sheperd dogs and the concentrations of IGF-I were very low. Stimulation with clonidine and growth hormone releasing hormone (GHRH) before and after repeated injections of GHRH did not result in significant increases in growth hormone concentrations in plasma. The concentrations of growth hormone in the poodles fluctuated at low levels during the test period. In the German sheperd dogs the levels of growth hormone remained unmeasurable during the stimulation tests. It was concluded that in the two poodles the basal concentrations of growth hormone were sufficient to maintain normal IGF-I concentrations, and thus the release of growth hormone was considered appropriate. Based upon measurements of urinary corticoids and a review of the literature it is suggested that the lack of a growth hormone response to stimulation was due to the enhanced release of somatostatin as a result of mild and fluctuating hyperadrenocorticism.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cytokine-mediated growth hormone release from cultured ovine pituitary cells

Previous studies have demonstrated that intravenous lipopolysaccharide (LPS) will increase concentrations of growth hormone (GH). One possible explanation for this may reside in the response of the pituitary to specific cytokines. This study sought to determine the effects of recombinant bovine tumor necrosis factor alpha (TNF), recombinant ovine (ro) interleukin-1alpha (IL-1alpha), roIL-1beta, ro interleukin-2 (IL-2), and ro gamma-interferon (INT) on GH release from cultured sheep pituitary cells. Sheep were sacrificed and pituitary cells cultured in DMEM with 10% fetal bovine serum for 3 days. On day 4, cells were washed and serum-free DMEM added to cells. IL-1alpha and IL-1beta were used at 0.2, 2 and 20 ng/ml and the remaining cytokines at 2, 20 and 200 ng/ml. Neither IL-2 nor INT had effects on basal or on GH-releasing hormone (GRH)-stimulated GH release. TNF inhibited GRH-stimulated GH release (p < 0.05). Both IL-1alpha and IL-1beta stimulated GH release from cultured pituitary cells at all doses tested (p < 0.01). Neither IL-1alpha nor IL-1beta had an effect on GRH-stimulated GH release. IL-1 effects were inhibited by H-89 (p < 0.05; a protein kinase A inhibitor) and by nifedipine (p < 0.05; a calcium channel blocker). Both of these mechanisms are central signal transduction mechanisms mediating GRH-stimulated GH release. IL-1-stimulated GH release is partially inhibited (p < 0.05) by lipoxygenase pathway blockers. Phorbol myristate acetate downregulation of protein kinase C did not alter IL-1-stimulated GH release. IL-1beta increased the content of both GH and GH mRNA in cultured sheep pituitary cells. We conclude that IL-1 produces a strong stimulus to GH release, which is mediated by calcium entry and protein kinase A activation. IL-1 also activates lipoxygenase pathways. This latter pathway as well as calcium entry were shown to mediate LPS stimulation of GH release from cultured pituitary cells. The similarity between IL-1 and LPS signal transduction suggests that LPS may activate pituitary production of IL-1 to produce the stimulus to GH. The lack of inhibitory effects of INT, TNF and IL-2 as opposed to what is seen in the rat may suggest a partial mechanism to explain the different effects of LPS on GH release between sheep and that seen in cattle and rats.     

Pituitary growth hormone release and gene expression in cafeteria-diet-induced obese rats

PURPOSE: To determine prospectively the feasibility and accuracy of combined gadolinium-enhanced magnetic resonance (MR) angiography, MR urography, and MR nephrography in the presurgical evaluation of potential renal transplant donors. MATERIALS AND METHODS: Twenty-two potential donors for renal transplantation were evaluated with 1.5-T MR imaging. MR angiograms were evaluated for the number of renal arteries, presence of early arterial branches, and renal artery stenoses. The renal collecting system and ureters were evaluated on the MR urograms. Renal parenchyma was assessed on the MR nephrogram. Prospective interpretation of MR images was compared with that of conventional angiograms and excretory urograms and with surgical findings. RESULTS: Gadolinium-enhanced MR angiography enabled correct identification of the arterial supply to all 44 native kidneys (44 single or dominant renal arteries and nine accessory renal arteries), four of five early arterial branches arising in the proximal 2 cm of the renal artery, a mild truncal stenosis in one renal artery, and two anomalies of the draining renal veins. The MR urogram accurately depicted a duplicated collecting system and mild unilateral pelvicalicectasis. The MR nephrogram showed renal size and a solitary cyst in one kidney, confirmed with sonography. CONCLUSION: Combined gadolinium-enhanced MR angiography, MR urography, and MR nephrography can accurately depict the arterial supply, collecting system, and renal parenchyma of donor kidneys.     

Effects of hyperthyroidism and hypothyroidism on rat growth hormone release induced by thyrotropin-releasing hormone

The official final action method for sodium chloride in cereal foods, 14.129, was found to give erroneously low results because of loss of chloride during ashing. Comparison of the data with values obtained by the official first action potentiometric method, 32.A01-32.A06, which does not require ashing, showed that large and variable losses of chloride occurred. Official ashing methods for other foods specify addition of sodium carbonate to prevent conversion of chloride to volatile forms, but this was not specified in 14.129. In the present study it was found that sodium carbonate did not completely prevent loss of chloride. The official first action potentiometric method, 32.A01-32.A06, has been adopted as official first action for the determination of chloride in cereal foods to replace 14.129, which was repealed, official first action. A cross-reference to 32.A01-32.A06 has been added to 14.096.     

The characterization of growth hormone release inhibiting hormone-like immunoreactivity in normal urine

Using a previously described radioimmunoassay for growth hormone release inhibiting hormone (GH-RIH), the presence of GH-RIH-like immunoreactivity in urine has been characterized by demonstrating mobility identical to synthetic GH-RIH standard on two sephadex gel chromatographic systems, and parallelism of dilutions of the sephadex fractions with synthetic GH-RIH. Furthermore, 74% of the sephadex fraction cross-reacting in the immunoassay bound to antibody conjugated to sepharose and could be eluted by 1 M acetic acid. This immunospecific eluate showed identity with synthetic GH-RIH on both ion exchange and thin layer chromatography. Thus GH-RIH-like immunoreactivity is present in normal urine; this may have potential relevance in the search for a physiological role for this peptide.     

Activin-like peptides in somatotrophs and activin stimulation of growth hormone release in goldfish

Activin and inhibin, dimeric protein hormones originally isolated from mammalian gonads, are involved in the regulation of pituitary gonadotropin secretion. Using domain-specific antibodies against activin and inhibin alpha, beta A, and beta B subunits, the present study demonstrates that immunoreactive activin and inhibin subunits, especially beta A, exist in goldfish pituitary. Immunocytochemical staining with anti-gonadotropin-II and anti-growth hormone showed that the pituitary cells containing immunoreactive activin beta subunits are somatotrophs. This is different from the situation in mammals where it is the gonadotrophs that produce activin molecules within the pituitary. The staining with anti-beta B was overall weak compared to that with anti-beta A, but both appear to localize in the same cells. Strong immunostaining with the anti-inhibin alpha subunit was also observed in the goldfish pituitary; however, the immunoreactivity is dissociated from those of beta A and beta B, and mainly associated with nerve fibers in the neurointermediate lobe. Based on this evidence, it is suggested that the goldfish pituitary predominantly produced activin-like molecules. Both porcine activin and inhibin stimulate growth hormone release from perifused goldfish pituitary fragments. Taken together with our previous findings that porcine activin stimulates gonadotropin-II release in goldfish, and the fact that the somatotrophs and gonadotrophs are in close contact with each other in the goldfish pituitary, it is hypothesized that somatotroph-derived activin may exert paracrine actions on the adjacent gonadotrophs to stimulate gonadotropin release and autocrine actions on somatotrophs to stimulate growth hormone secretion. This also provides a mechanism for communication between these two pituitary cell types.     

The galanin antagonist, M-15, inhibits growth hormone release in rats

The neuropeptide, galanin, has been implicated in the regulation of rat growth hormone (rGH) release. In the present study, adult male rats were implanted dually with cannulae to the lateral cerebral ventricle and the right atrium. After surgical recovery, rats were infused with M-15, a specific galanin antagonist, into the lateral ventricle. During the course of this brain infusion, rats were subjected to serial blood sampling with red cell and artificial plasma replacement under stress-free conditions. Plasma was saved for rGH assay. Treatment with M-15 reduced rGH pulse amplitude and pulse frequency when compared to vehicle-infused controls. These data suggest that brain galanin participates in the ongoing stimulation of pulsatile rGH release in the adult male rat.     

Effects of large doses of estrogen on prolactin and growth hormone release

The effects of large doses of estrogen on prolactin (PRL) release were assessed. Circulating PRL levels in response to intravenous infusion of 17 beta-estradiol (E2), at a rate of 50 mug per hour for 4 hours, were studied in 10 subjects, and a chronic administration of ethinyl estradiol (EE) at a dose of 400 mug per day, for 1 week, was evaluated in five hypogonadal subjects. There was a significant depression of serum level of PRL during the E2 infusion and a significant increase in PRL release after discontinuation of the infusion. The chronic treatment of large doses of EE induced a more rapid (within 36 hours) and a significantly greater elevation of PRL levels at the end of 1 week treatment than those found during smaller doses of EE administration, as reported previously. These data suggest that acute treatment of estrogen may have a biphasic action on the pituitary PRL section and that the augmentatory effect of estrogen on PRL secretion is dose-dependent in human beings.     

Angiotensinergic neurons physiologically inhibit prolactin, growth hormone, and thyroid-stimulating hormone, but not adrenocorticoptropic hormone, release in ovariectomized rats

Angiotensin II (AII)-containing neurons with cell bodies in the rostral medial hypothalamus and axons project to the external layer of the median eminence, so that AII maybe released into the hypophyseal portal vessels for actions on the pituitary gland. Indeed, intrahypothalamic actions of the peptide on the release of hypothalamic hormones and direct actions on the pituitary have been reported. To determine the role of endogenously released AII in hypothalamic-pituitary hormone release, we have determined the effects of central immunoneutralization of AII upon the plasma concentrations of prolactin (PRL), growth hormone (GH), thyroid-stimulating hormone (TSH), and adrenocorticotropic hormone (ACTH). Specific antiserum directed against AII (AB-AII) or normal rabbit serum (NRS), as a control, was microinjected into third ventricular (3 V) cannulae of conscious, ovariectomized (OVX) rats. Immediately before and at various intervals after this procedure, blood samples were withdrawn through previously implanted external jugular catheters. Three hours after injection of the AB-AII, plasma PRL levels diverged from those of the NRS-injected animals and progressively increased from 4 to 24 h after administration of the antiserum. Results were similar with respect to plasma GH, except that the increase in the AB-AII animals above that in the NRS-injected controls from 4 to 6 h was not significant, but was highly significant on measurement 24 h after injection, at which time plasma GH was three times higher than in control rats. Similarly, following injection of AB-AII, plasma TSH values did not diverge significantly from those of the NRS-injected controls until 3 h after injection. From 3 to 5 h they remained constant and significantly elevated above values in the NRS-injected controls with a further nonsignificant increase at 6 h. At 24 h, there was no longer a difference between the values in both groups. In contrast to the significant elevations in plasma hormone levels observed with respect to PRL, GH, and TSH following injection of the antiserum, there was no change in plasma ACTH between the AB-AII-injected and NRS-injected animals throughout the same period of observation. Previous results by others have shown that intraventricular injection of AII has a suppressive action on the release of PRL, GH, and TSH. Consequently, we believe that the antiserum is acting intrahypothalamically to block the action of AII within the hypothalamus, resulting in the elevation of the three hormones mentioned. Therefore, the AII neurons appear to have a physiologically significant suppressive action on the release of hypothalamic neurohormones controlling the release of PRL, GH, and TSH. In contrast, there apparently is no effect of intrahypothalamically released AII on the secretion of corticotropin-releasing factors under these nonstress conditions. We cannot rule out an action of the antiserum at the pituitary level; however, in view of the fact that the actions of AII directly on the gland are to stimulate PRL, GH, TSH, and ACTH release, it appears that the antiserum was acting at the hypothalamic level.     

Growth hormone receptor activity is stimulated by insulin-like growth factor binding protein 5 in rat osteosarcoma cells

Osteoblast-like UMR-106.01 rat osteosarcoma cells express high affinity growth hormone (GH) receptors (GHRs). Because osteoblasts secrete insulin-like growth factor binding protein-5 (IGFBP-5), we evaluated whether it also modulates GH binding and GHR expression in UMR cells. Human recombinant intact IGFBP-5 stimulated 125I-hGH binding in a dose-dependent manner (dose range 300-3000 ng/ml), inducing an increase to 193.6 +/- 2.1% of control binding at 3000 ng/ml (P < 0.001). Carboxy-truncated IGFBP-5 also stimulated GH binding but with less potency (125 +/- 2.7% of control at 3000 ng/ml, P < 0.01). GHRs identified by chemical crosslinking of 125I-hGH to cell monolayers increased after treatment with IGFBP-5 and decreased in response to insulin-like growth factor-I (IGF-I). GHR mRNA levels, as quantitated by a solution hybridization RNAse protection assay, increased up to 3 to 7-fold in a time-dependent manner by intact IGFBP-5 but not by carboxy-truncated IGFBP-5. An antiserum to IGFBP-5 reduced basal GH binding to 56.7 +/- 4.3% of control value at a concentration of 0.5% (P < 0.001), showing that IGFBP-5 produced by the cells is a strong regulator of GH binding. IGFBP-5 antiserum also decreased GH binding to 85.9 +/- 0.9% of IGFBP-5 stimulated value (P < 0.001), showing the specificity of IGFBP-5 stimulation. To determine whether the GHR upregulation was physiologically significant, cell proliferation was evaluated after coincubation of IGFBP-5 with low, non-stimulatory concentrations of GH. IGFBP-5 (1000 ng/ml) induced cell proliferation to 116.2 +/- 3.2% of control levels, and coincubation with hGH at 10 ng/ml induced an increase to 133.3 +/- 0.1% of control levels. We conclude that exogenous and endogenous IGFBP-5 upregulate GHR mRNA levels and GH binding and this interaction potentiates GH-stimulated mitogenesis in osteoblastic cells.     

Novel hexarelin analogs stimulate feeding in the rat through a mechanism not involving growth hormone release

Growth hormone-releasing peptides (GHRPs) are a class of small peptides that stimulate growth hormone (GH) release in several animal species, including the human. Moreover, GHRPs injected into the brain ventricles stimulate feeding in the rat. The aim of this study was to evaluate the GH-releasing properties of a series of novel GHRP analogs and the possible existence of functional correlations between the GH-releasing activity and the effects on feeding behavior. Two well-known hexapeptides, GHRP-6 and hexarelin, given s.c., dose dependently stimulated both GH release and feeding behavior in satiated rats. However, in a series of tri-, penta- and hexapeptide analogs of hexarelin, some compounds were active either on GH release or on eating behavior. Interestingly, even minor structural modifications resulted in major changes of the pharmacological profile. We conclude that GHRPs have orexigenic properties after systemic administration which are largely independent from the effects they exert on GH release.     

Oral administration of arginine enhances the growth hormone response to growth hormone releasing hormone in short children

We have evaluated the effect of oral administration of arginine chlorhydrate on the growth hormone response to growth hormone releasing hormone in a group of nine short prepubertal children (six boys and four girls). Arginine chlorhydrate 10 g, administered orally 60 min before an i.v. bolus injection of growth hormone releasing hormone 1-29, 1 microgram/kg, significantly enhanced the growth hormone response to the neuropeptide, confirming the results of previous studies which used the i.v. route. Furthermore, our data strengthen the view that the effects of arginine chlorhydrate on growth hormone secretion are mediated by inhibition of endogenous somatostatin release.     

Effect of endothelin-1 in man--impact on basal and stimulated concentrations of luteinizing hormone, follicle-stimulating hormone, thyrotropin, growth hormone, corticotropin, and prolactin

The effect of endothelin-1 on basal and stimulated serum (plasma) concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), thyrotropin (TSH), prolactin (PRL), growth hormone (GH), and corticotropin was investigated in healthy male volunteers (n = 5). Intravenous (IV) administration of endothelin-1 (5 ng/kg/min for 15 minutes, followed by 2.5 ng/kg/min for 105 minutes) induced an increase in basal plasma concentrations of corticotropin. Serum concentrations of PRL, TSH, LH, FSH, and GH remained unchanged. The increase in serum concentrations of these pituitary hormones induced by IV administration of LH-releasing hormone ([LH-RH] 100 micrograms), thyrotropin RH ([TRH] 400 micrograms), GH-RH (100 micrograms), and corticotropin-releasing factor ([CRF] 100 micrograms) was suppressed in regard to PRL (P < .01) and GH (P < .01) and enhanced in regard to corticotropin (P < .01). Stimulated serum concentrations of LH and FSH also tended to be higher following administration of endothelin-1 (P < .05), whereas the increase in serum concentrations of TSH remained unchanged. Thus, when administered in pharmacological doses, endothelin-1 influences pituitary hormone secretion in man.     

In vitro influence of apatite-granule-specific area on human growth hormone loading and release

PURPOSE: The study was conducted to evaluate risk factors, natural history, and clinical consequences of a periprosthetic leak after endovascular repair of an abdominal aortic aneurysm. METHODS: We reviewed the initial and follow-up data, including angiograms, contrast-enhanced computed tomography (CT) scans, abdominal duplex scans, and plain abdominal films for all patients undergoing tube graft repair using the endovascular graft system (early prototype) between February 10, 1993, and January 24, 1995. RESULTS: Sixty-eight patients underwent placement or attempted placement of a tube graft implant in 13 centers in the United States. Nine patients required conversion to open repair, leaving 59 patients with functioning grafts for evaluation. The mean follow-up time was 27 +/- 8 months (range, 2 to 48 months). Twenty-eight (47%) of 59 patients had initial periprosthetic leaks (6 proximal, 14 distal, 3 proximal and distal, 5 indeterminate) on their first postoperative CT scans. Fourteen (50%) of the initial 28 leaks sealed spontaneously. Two other patients had their leaks sealed by endovascular means, leaving 12 patients with persistent leaks for follow-up evaluation. Four patients developed late leaks between 18 and 24 months of follow-up: one who had a spontaneously sealed initial leak, one with a second leak, and two who developed late leaks. Of the 16 patients with sealed leaks, 10 had aneurysm size reduction during follow-up. Three aneurysm sacs enlarged before spontaneous sealing but have not had sufficient follow-up time to document the size change since the seal. One patient died of respiratory failure 5 months after graft implantation. One patient whose leak was sealed by intervention has not yet had a CT scan for evaluation. In one patient with a sealed leak and whose aneurysm had initially shrunk, the area reopened and progressed to a nonfatal rupture that was surgically corrected. There were two late deaths from unrelated causes. Twelve patients in the sealed group are alive and well. Of the 12 patients with persistent leaks, five underwent open surgical repair without complication, and one underwent successful endovascular repair with a second graft. Six patients continue to live with their initial grafts and have an average aneurysm sac enlargement of 0.1 cm per year. CONCLUSIONS: Although initial periprosthetic leaks were common with the use of this early prototype, 50% spontaneously sealed. The subsequent clinical course of patients with persistently sealed leaks was no different from that of patients who had no leaks. However, continued CT surveillance is warranted, because in one patient with an initially sealed leak, the area reopened and progressed to nonfatal rupture. Another two patients without initial leaks developed late leaks. In a small group of selected patients with continued leaks, their aneurysms appeared to enlarge at a rate considerably slower than would have been expected in patients with untreated aneurysm, suggesting that even a person after endovascular repair with a persistent leak may have had some beneficial hemodynamic modification.     

Expression of growth hormone secretagogue-receptors by growth hormone-releasing hormone neurons in the mediobasal hypothalamus

A novel class of synthetic compounds, termed GH-secretagogues (GHSs), have been shown to be potent stimulators of GH release, although their mechanism of action and functional significance remains obscure. The recent cloning of the rat GHS receptor (GHS-R) permitted the identification of numerous sites of expression of GHS-R in brain, but nothing is yet known about the cell types that express this receptor. We performed dual chromogenic and autoradiographic in situ hybridization to test the hypothesis that GHRH neurons in the hypothalamus coexpress GHS-R mRNA. GHS-R-hybridizing cells showed extensive overlap with GHRH-expressing neurons in both the arcuate (Arc) and ventromedial (VMN) hypothalamic nuclei. Quantification of the double-labeled cells revealed that approximately 27% of GHRH-hybridizing neurons in the Arc, and 22% of those in the VMN, expressed the GHS-R gene. These studies are the first to colocalize the GHS-R to any neurochemical cell type in rat brain. The results provide evidence that the GHSs may directly modulate GHRH release, and thereby stimulate GH secretion, through interaction with the GHS-R on hypothalamic GHRH mRNA-containing neurons.