Role of interleukin-10 in the synovial fluid of the anterior cruciate ligament injured knee

OBJECTIVE

This review assesses the roles of IL-10 in post ACL reconstruction OA, and highlights the potential therapeutic effects of this cytokine.

MATERIALS AND METHODS

We conducted a systematic review of the literature in order to consolidate evidence of IL10 profiles in synovial fluid (SF) of patients with ACL tears. The review was conducted in accordance with the PRISMA statement. In total, 10 studies were found to be pertinent and were considered in depth. Seven studies reported on trends in IL-10 concentrations after an ACL tear; in addition, three studies described IL-10 concentrations after ACL reconstruction. In all studies, IL-10 levels were assessed using enzyme-linked immunosorbent assay.

RESULTS

IL-10 levels in SF were higher after ACL injury and ACL reconstruction compared to control knees. IL-10 levels were most elevated shortly after injury, but, decreased to more normal levels in chronic lesions. In contrast, the inflammatory cytokine TNF-α remained higher than controls immediately subsequent to, and, even 5 years post-injury.

CONCLUSIONS

IL-10 is a modulatory cytokine with an active role in antagonizing TNF-α in the knee joint environment. Consideration of the role of IL-10 in the knee has now shifted from simply a key biomarker to having active therapeutic potential in the prevention of OA after ACL injury.

Testosterone a key factor in gender related metabolic syndrome

Metabolic syndrome (MetS) is highly correlated with cardiovascular diseases. Although an excess of body fat is a determinant factor for MetS development, a reduced level of testosterone plays a fundamental role in its regulation. Low testosterone level is highly related to insulin resistance, visceral obesity and MetS. We have searched in Pubmed clinical trial with the password: testosterone and insulin resistance, and testosterone and MetS. We found 19 studies on the correlation between testosterone level with insulin resistance and 18 on the effect of testosterone therapy on MetS. A high correlation between low testosterone and insulin resistance has been found in men, but not in women. Testosterone administration in hypogonadal men improved MetS and reduced the mortality risk. Androgen and oestrogen receptors are expressed in adipocytes, muscle and liver tissue, and their activation is necessary to improve metabolic control. Normalization of testosterone level should be the primary treatment in men, along with caloric restriction and physical exercise. These findings come mainly from correlative data, and there remains a need for randomized trials to strengthen this evidence. This review will consider the effects of testosterone on the regulation and development of MetS in men and women.

Perineal Choristoma and Atresia Ani in 2 Female Holstein Friesian Calves

Atresia ani, a congenital anomaly of the anus, can be associated with other types of malformation. Two female Holstein Friesian calves had imperforate anus, rectovaginal fistula, and perineal choristomas. In one case, the choristoma was composed of mature adipose and fibrous tissue with nephrogenic rests. In the other calf, the choristoma consisted of fragments of trabecular bone coated by cartilage and containing marrow, mixed with mature adipose and fibrous tissue, striated muscle fibers, nerves, and vessels. This combination of malformations resembles the association of anorectal malformations and perineal masses in children.

Ghrelin control of GH secretion and feeding behaviour: the role of the GHS-R1a receptor studied in vivo and in vitro using novel non-peptide ligands

Energy homeostasis is controlled by a complex regulatory system of molecules that affect food intake and that are critical for maintaining a stable body weight during life. Ghrelin is a peptide of 28 amino acid synthesized predominantly by the stomach and the gut, which activate the type 1a growth hormone (GH) secretagogue receptor (GHS-R1a), a G-protein coupled receptor. The acylated form of ghrelin potently stimulates GH secretion both in vitro and in vivo in several animal species, including humans. Beside the endocrine effect, ghrelin shows also extraendocrine activities, including stimulation of feeding behaviour. Several classes of small synthetic peptide and non-peptide ligands of the GHS-R1a have been described and are able to release GH and stimulate food intake. However, in time, it appeared that the stimulating effects on GH secretion could be divorced from those on food intake, suggesting that more than a single receptor might be involved. Several experimental data have even questioned the physiological role of ghrelin in the control of GH secretion and energy metabolism. By using novel agonists, partial agonists, and antagonists for the GHS-R1a receptor, we have studied whether the stimulation of this receptor could account for the purported physiological role of ghrelin. Our results demonstrate that the ability to bind in vitro the GHS-R1a is not predictive of the in vivo biological activity of the compounds and that the endocrine and extraendocrine effects could be mediated also by receptors different from the GHS-R1a.

Feeding behavior during long-term hexarelin administration in young and old rats

Ghrelin, a 28-amino-acid peptide isolated from the stomach, is the natural ligand of the GH-secretagogues receptor-1a (GHS-R1a) and, so far, the only discovered circulating appetite-stimulating hormone. Similarly to ghrelin, many synthetic compounds belonging to the GHS family stimulate both GH secretion and feeding, whereas some stimulate GH secretion only. In the past years, studies have focused on the potential of the GHS to stimulate GH release during long-term treatment in humans and experimental animals. Few data are available about the extraendocrine effects of the GHS during several weeks of treatment, particularly in old rats. The aim of the present study was first to identify the lowest dose of hexarelin giving maximal stimulation of food intake both in young (3-month-old) and old rats (24-month-old). A dose-response study (80-320 microg/kg, s.c.) revealed that hexarelin at the dose of 80 microg/kg gave reproducibly maximal stimulation of food consumption in young as well as in old rats. Second, we evaluated the effect of 8-week daily sc treatment with hexarelin in young and old male rats. The outcome of the chronic study was that hexarelin (80 microg/kg, s.c., once daily) maintained a persistent significant orexigenic action throughout the treatment period, both in young and old rats. Interestingly, hexarelin treatment did not affect body weight gain either in young or old rats. We conclude that hexarelin is endowed with long-lasting orexigenic activity and might represent a potential therapeutic approach for pathological conditions characterized by a decline in food intake.

Central ghrelin gastroprotection involves nitric oxide/prostaglandin cross-talk

BACKGROUND AND PURPOSE

Ghrelin, a gut-brain peptide, is considered a gastroprotective factor in gastric mucosa. We investigated the role of prostaglandins (PG) and the possible interplay between PGs and nitric oxide (NO) in ghrelin gastroprotection against ethanol (EtOH)-induced gastric lesions.

EXPERIMENTAL APPROACH

We examined the effects of (1) central ghrelin (4 mug per rat) injection on PGE(2) accumulation in normal or EtOH-lesioned gastric mucosa, (2) pretreatment with indomethacin (10 mg kg(-1), p.o.), a non-selective cyclooxygenase (COX) inhibitor, and with a selective COX-1, SC560 (5 mg kg(-1), p.o.) or COX-2 inhibitor, celecoxib (3.5 mg kg(-1), p.o.) on ghrelin gastroprotection against 50% EtOH (1 mL per rat)-induced gastric lesions, (3) the NO synthase inhibitor, L-NAME (70 mg kg(-1), s.c), on gastric PGE(2) content in ghrelin-treated rats and (4) central ghrelin on the expression of constitutive and inducible NOS and COX mRNA and on the localization of the immunoreactivity for COX-2 in the gastric mucosa exposed to EtOH.

KEY RESULTS

Ghrelin increased PGE(2) in normal mucosa, whereas, it reversed the EtOH-induced PGE(2) surge. Ghrelin had no effect on mucosal COX-1 expression but reduced the EtOH-induced increase in COX-2 expression and immunoreactivity. Indomethacin and SC560, but not celecoxib, removed ghrelin gastroprotection. L-NAME prevented the PGE(2) surge induced by ghrelin and, like indomethacin, reduced EtOH-induced PGE(2) increase. Ghrelin enhanced eNOS expression and reduced iNOS mRNA.

CONCLUSIONS AND IMPLICATIONS

This study shows that COX-1-derived PGs are mainly involved in ghrelin gastroprotection and that the constitutive-derived NO together with PGE(2) are involved in ghrelin gastroprotective activity.

Central dysregulations in the control of energy homeostasis and endocrine alterations in anorexia and bulimia nervosa

In the last decades we have come to understand that the hypothalamus is a key region in controlling energy homeostasis. A number of control models have been proposed to explain the regulation of feeding behavior in physiological and pathological conditions, but all those based on imbalances of single factors fail to explain the disrupted regulation of energy supply in eating disorders such as anorexia nervosa and bulimia nervosa, as well as other psychiatric disorders. A growing amount of evidence demonstrates that many signaling molecules originated within the brain or coming from the adipose tissue or the gastro-enteric tract are involved in the highly complex process controlling food intake and energy expenditure. The recent discovery of leptin, ghrelin, and other factors have made it possible to penetrate in the still undefined pathophysiology of eating disorders with the hope of finding effective treatments for such diseases.

Chronic intracerebroventricular TLQP-21 delivery does not modulate the GH/IGF-1-axis and muscle strength in mice

OBJECTIVE

Biallelic ablation of VGF determines a dwarf phenotype. VGF precursor protein encodes for different biologically active peptides none of which has been related to growth or muscular abnormalities. Here we present the first attempt to fill this gap. We tested the hypothesis that a recently identified VGF-derived peptide, TLQP-21, shown to centrally modulate metabolic functions, could also modulate growth hormone (GH)-axis and muscle strength.

DESIGN

Adult male mice were chronically icv injected with TLQP-21 (15 microg/day for 14 days). Physiological, molecular and behavioral parameters related to the GH/IGF-1-axis were investigated.

RESULTS

Except for a reduction in the soleus weight, TLQP-21 did not affect GH/IGF-1-axis mediators, muscle strength and muscle weight.

CONCLUSIONS

Results collected exclude a role for TLQP-21 in modulating the GH/IGF1-axis and muscle functions. VGF-derived peptides involved in the dwarf phenotype of VGF-/- mice have to be identified yet.

Intracerebroventricular acute and chronic administration of obestatin minimally affect food intake but not weight gain in the rat

We studied the effect of the acute central administration of obestatin on food intake and body weight in short-term starved male rats, and those of 28-day continuous intracerebroventricular (icv) infusion of obestatin in free feeding rats. In 16-h starved rats, obestatin induced a trend toward a reduction of food intake that did not reach statistical significance. In fed rats, the icv infusion of obestatin significantly decreased food consumption in the first day of treatment; but the anorexigenic effect of obestatin vanished thereafter. Interestingly, the body weight of rats infused for 28 days with obestatin was superimposable to that of the respective control at all time intervals. In all, our results indicate that the anorexigenic effect of obestatin is of little account and that the peptide does not modify energy metabolism in the long-term administration.

TLQP-21, a VGF-derived peptide, increases energy expenditure and prevents the early phase of diet-induced obesity

The vgf gene has been identified as an energy homeostasis regulator. Vgf encodes a 617-aa precursor protein that is processed to yield an incompletely characterized panel of neuropeptides. Until now, it was an unproved assumption that VGF-derived peptides could regulate metabolism. Here, a VGF peptide designated TLQP-21 was identified in rat brain extracts by means of immunoprecipitation, microcapillary liquid chromatography-tandem MS, and database searching algorithms. Chronic intracerebroventricular (i.c.v.) injection of TLQP-21 (15 mug/day for 14 days) increased resting energy expenditure (EE) and rectal temperature in mice. These effects were paralleled by increased epinephrine and up-regulation of brown adipose tissue beta2-AR (beta2 adrenergic receptor) and white adipose tissue (WAT) PPAR-delta (peroxisome proliferator-activated receptor delta), beta3-AR, and UCP1 (uncoupling protein 1) mRNAs and were independent of locomotor activity and thyroid hormones. Hypothalamic gene expression of orexigenic and anorexigenic neuropeptides was unchanged. Furthermore, in mice that were fed a high-fat diet for 14 days, TLQP-21 prevented the increase in body and WAT weight as well as hormonal changes that are associated with a high-fat regimen. Biochemical and molecular analyses suggest that TLQP-21 exerts its effects by stimulating autonomic activation of adrenal medulla and adipose tissues. In conclusion, we present here the identification in the CNS of a previously uncharacterized VGF-derived peptide and prove that its chronic i.c.v. infusion effected an increase in EE and limited the early phase of diet-induced obesity.

Obestatin inhibits feeding but does not modulate GH and corticosterone secretion in the rat

Obestatin is a recently discovered 23 amino acids peptide derived from the ghrelin gene. As opposed to ghrelin, obestatin was shown to inhibit food intake in mice. The aims of this research were to study the effects of acute obestatin treatment on feeding behavior in the rat and its effects on GH and corticosterone secretion. Our results demonstrate that in young-adult male rats, obestatin effectively blunts the hunger caused by short-term starvation. Obestatin did not modify GH secretion in 10-day-old rats and did not antagonize the GH-releasing effects of hexarelin. Moreover, obestatin administration had no effects on spontaneous corticosterone secretion. In conclusion, these data demonstrate that in young-adult male rats the newly discovered obestatin can inhibit feeding but does not modify GH and corticosterone release in infant rats.

Evidence for a role of the GHS-R1a receptors in ghrelin inhibition of gastric acid secretion in the rat

Ghrelin, the endogenous ligand of the GH secretagogue receptor (GHS-R) has been previously shown to inhibit gastric acid secretion in pylorus-ligated rats. Two isoforms of GHS-R have been identified: GHS-R(1a) and GHS-R(1b). The present study aimed: (i) to characterise the type of GHS-R involved in the central gastric inhibitory activity of ghrelin by using des-octanoyl ghrelin, and synthetic GHS-R(1a) agonist (EP1572) and antagonist (D-Lys(3)-GHRP-6) and (ii) to investigate the relationship between ghrelin and cortistatin (CST) in the control of gastric acid secretion by using the natural neuropeptide CST-14 and the synthetic octapeptide CST-8. The specific interactions of all the compounds with GHS-R(1a) were determined by comparing their ability to displace labelled ghrelin or somatostatin from its receptors on rat hypothalamic membranes or on rat cardiomyocyte, respectively. Intracerebroventricular administration of 0.01 and 1 nmol/rat des-octanoyl ghrelin did not affect gastric acid secretion in pylorus-ligated rats, whereas EP1572 either i.c.v. (0.01-1 nmol/rat) or i.p. (10 and 20 nmol/kg) inhibited acid gastric secretion. Preteatment with D-Lys(3)GHRP-6 (3 nmol/rat, i.c.v.) was able to remove the inhibitory action of ghrelin (0.01 nmol/rat, i.c.v.) on gastric acid volume and acid output, thus indicating that the type 1a GHS-R likely mediates the gastric inhibitory action of ghrelin. This is supported by binding data showing that D-Lys(3)GHRP-6, but not des-octanoyl ghrelin, binds to hypothalamic GHS-R. CST-14 (1 nmol/rat, i.c.v.) did not affect either basal or ghrelin inhibition of gastric acid secretion. CST-8 (1 nmol/rat, i.c.v.) was able to counteract the gastric ghrelin response. The observation that CST-14 binds both GHR-S and somatostatin receptors, whereas CST-8 specifically displaces only ghrelin binding, indicates that CST-8 behaves as a GHS-R(1a) antagonist.

Ghrelin in gastroenteric pathophysiology

Ghrelin, an acylated peptide produced predominantly by the stomach, has been discovered to be a natural ligand of the growth hormone secretagogue receptor 1a (GHS-R1a). It is localized in distinct cells of the gastric mucosa, mainly distributed in the mid portion of the oxyntic gland characterized by P/D1 granules in man and X/A-like granules in rodents. The ghrelin cell represents the second most frequent endocrine cell type after the enterochromaffin-like cells in gastric oxyntic mucosa, pointing to a potentially relevant role in the physiology of the stomach. Ghrelin has no relevant homology with any known gastrointestinal peptide and displays strong GH-releasing activity both in animals and in humans. However, in addition to stimulating GH secretion, ghrelin possesses several other endocrine and extraendocrine biological activities that are explained by the widespread distribution of ghrelin and GHS-R1a expression. In the rat, ghrelin exerts a control in gastric acid secretion and motility: the gastric acid secretion is stimulated by peripheral administration of high doses of ghrelin, but inhibited by very low doses of ghrelin delivered into the central nervous system. Moreover, ghrelin provides a potent and dose-related gastroprotective action against ethanol- and stress-induced gastric ulcers. The integrity of both nitric oxide (NO) system and capsaicin afferent nerves are required for the gastroprotective effect of ghrelin, whereas the vagus nerve might be involved in conveying ghrelinergic signal from periphery to the brain. In addition, prostaglandins derived by the constitutive cyclooxygenase (COX) activity are essential for the protective activity of ghrelin in ethanol and stress-induced gastric lesions. Given its prevailing role in physiological and pathophysiological gastric function, the discovery of ghrelin will open new perspectives and potential clinical implications in the gastroenteric field.

Effects of hexarelin against acid-independent and acid-dependent ulcerogens in the rat

The effects of intracerebroventricular (icv) or subcutaneous (sc) hexarelin (Hexa) administration, against gastric ulcers induced by ethanol (50%, 1 ml/rat/os) or Indomethacin (20 mg/kg/os) were examined in conscious rats. Hexa at 1 nmol/rat, icv or 10 nmol/kg, sc reduced ethanol-induced ulcers by 47% and 32% respectively. Hexa, but not ghrelin significantly worsened (+40%) Indomethacin-induced ulcers when injected sc. Hexa-gastroprotection against ethanol-induced ulcers was removed by the GHS-R antagonist (D-Lys3)-GRPR-6 and by the inhibitor of NO-synthase (NOS) Nomega-nitro-L-arginine methyl ester. Semiquantitative RT-PCR assay of gastric NOS mRNA isoforms revealed that the reduction in iNOS-derived NO and the increase of constitutive-derived NO are relevant for the gastroprotection of Hexa against ethanol-induced gastric damage.

IGF-I stimulates proliferation of spontaneously immortalized human keratinocytes (HACAT) by autocrine/paracrine mechanisms

HaCaT keratinocytes are derived from adult human skin and although spontaneously immortalized, remain highly related to their normal counterparts. We observed that HaCaT cells can proliferate in serum-free medium (SFM), in contrast to normal human keratinocytes whose growth in vitro requires a feeder layer and/or the supplementation with hormones and growth factors. Since autocrine production of growth factors has been proposed as the pathway that cells may exploit to escape growth regulation, we have investigated whether this is occurring in HaCaT cultured in SFM. Either epidermal growth factor (EGF) or insulin-like growth factor-1 (IGF-I) was effective and dose-dependently stimulated HaCaT replication. The ability of these keratinocytes to express EGF and IGF-I and their receptors was investigated by northern blot and reverse transcriptase-polymerase chain reaction (RT-PCR). We report that HaCaT cells synthesize mRNAs for IGF-I, IGF-II, IGF-IR and EGF-R but not EGF mRNA. Immunoneutralization of IGF-I with specific monoclonal antibodies blocked spontaneous HaCaT proliferation in SFM, as did incubation with antibodies against IGF-IR. These data demonstrate that an autocrine/paracrine loop based on IGF-I may allow HaCaT keratinocytes to proliferate autonomously in culture in contrast to keratinocytes in primary culture. A similar mechanism may be involved in the development of hyperproliferative diseases of human skin and its functional disruption may represent the target for therapeutic approaches.

Ghrelin protects against ethanol-induced gastric ulcers in rats: studies on the mechanisms of action

Ghrelin, the endogenous ligand for GH secretagogue receptors, has been reported to influence acid gastric secretion and motility, but its potential gastroprotective effect is unknown. The aims of this study were 1) to examine the effects of central and peripheral administration of ghrelin on ethanol-induced gastric ulcers in conscious rats, and 2) to investigate the possible roles of nitric oxide (NO), vagal nerve, and sensory fibers in the gastric effects of ghrelin. Ghrelin was administered either intracerebroventricularly or sc 30 min before ethanol, and mucosal lesions were examined macroscopically. Additionally, rats were either treated with the inhibitor of NO synthesis N(omega)-nitro-L-arginine methyl ester (L-NAME) or underwent bilateral cervical vagotomy or capsaicin-induced sensory denervation. Conventional histology and immunohistochemistry for ghrelin, gastrin, and somatostatin were performed on gastric specimens from representative rats. Central ghrelin (4-4,000 ng/rat) dose-dependently reduced ethanol-induced gastric ulcers by 39-77%. Subcutaneous ghrelin administration (80 micro g/kg) reduced ulcer depth only. L-NAME and capsaicin, but not vagotomy, prevented the gastroprotective effect of central ghrelin (4000 ng/rat). This is the first evidence that ghrelin exerts a potent central gastroprotective activity against ethanol-induced lesions. The gastroprotective effect of ghrelin is mediated by endogenous NO release and requires the integrity of sensory nerve fibers.

Moexipril and quinapril inhibition of tissue angiotensin-converting enzyme activity in the rat: evidence for direct effects in heart, lung and kidney and stimulation of prostacyclin generation

The activation of angiotensin converting enzyme (ACE) may contribute to the development of vascular and myocardial structural changes. The level of ACE is stable in human plasma, and only limited data are available on its regulation at the tissue level. The aim of this study was to characterize the effects of two ACE inhibitors, moexipril and quinapril on tissue ACE activity. Adult male rats were treated intragastrically once daily for 6 days either with 2 mg/kg moexipril or quinapril. After single treatment, moexipril and quinapril effectively inhibited ACE activity in plasma and slightly in heart and aorta, whereas after 6 days of treatment they inhibited ACE activity in plasma (87% and 94%, respectively), lung (92% and 93%), myocardium (26% and 23%), kidney (21% and 20%), and aorta (39% and 40%), but not in skeletal muscle. Interestingly, the two ACE-inhibitors also induced a significant increase in cardiac homogenates of 6-keto-PGF1alpha levels, an important index of PGI2 generation. To test whether the reduced effects of ACE inhibitors in heart and kidney were caused by a limited availability of the drugs, 100 microl of lung, heart and kidney homogenates from control rats were incubated in vitro with moexipril and quinapril immediately before assay. Both drugs were more effective in lung than heart and kidney homogenates, with inhibition values superimposable to those obtained in vivo. These results clearly indicate that inhibition of tissue ACE activity does not depend primarily on the availability of ACE inhibitors in each organ.

[Ghrelin and GH secretion]

Ghrelin is an acylated peptide recently isolated from rat and human stomach that potently stimulates GH release in vivo and in vitro in rats and humans. Ghrelin specifically activates the receptor for the growth hormone secretagogues (GHS) and it has been proposed that it may be the endogenous ligand mimicked by these synthetic compounds. Ghrelin is primarily produced in endocrine cells of the stomach, and to a lesser extent, in other peripheral tissues, including the pituitary. Although ghrelin is the most potent GH-secretagogue so far identified, its circulating levels do not correlate with those of GH either in physiological and pathological conditions. Because of these and many other observations, it may be postulated that ghrelin is not physiologically involved in the regulation of growth hormone secretion. Nonetheless, ghrelin may serve as a very useful model for the development of more potent synthetic GHS, which may be therapeutically useful for the treatment of human GH deficiency.

EP1572: a novel peptido-mimetic GH secretagogue with potent and selective GH-releasing activity in man

EP1572 UMV1843 [Aib-DTrp-DgTrp-CHO]) is a new peptido-mimetic GH secretagogue (GHS) showing binding potency to the GHS-receptor in animal and human tissues similar to that of ghrelin and peptidyl GHS. EP1572 induces marked GH increase after s.c. administration in neonatal rats. Preliminary data in 2 normal young men show that: 1) acute i.v. EP1572 administration (1.0 microg/kg) induces strong and selective increase of GH levels; 2) single oral EP1572 administration strongly and reproducibly increases GH levels even after a dose as low as 0.06 mg/kg. Thus, EP1572 is a new peptido-mimetic GHS with potent and selective GH-releasing activity.

Evidence for a central inhibitory role of growth hormone secretagogues and ghrelin on gastric acid secretion in conscious rats

We examined the possible central and peripheral effects of synthetic growth hormone secretagogues (GHS), hexarelin (Hexa) and EP 40737 (D-Thr-D-Trp (2-Me)-Ala- Trp-D-Phe-Lys-NH2), and of their endogenous counterpart, ghrelin, on gastric acid secretion. The compounds were administered intracerebroventricularly (i.c.v.) or subcutaneously (s.c.) in conscious male rats and the volume of gastric secretion and gastric acid output were examined 3 h after pylorus ligation (Shay-test). Central Hexa, EP 40737 and ghrelin administration (from 0.1 pmol to 1 nmol/rat, i.c.v.) significantly inhibited gastric acid secretion. The maximum inhibitory effect on gastric acid output was detected at the dose of 10 pmol/rat, i.c.v. for Hexa (-51.3%), of 100 pmol/rat, i.c.v. for EP 40737 (-70%) and of 1 pmol/rat, i.c.v. for ghrelin (-60%). All peptides were less effective at the highest dose used (1 nmol/rat, i.c.v.). Hexa, EP 40737 and ghrelin injected s.c. did not modify gastric acid secretion. The inhibitory action of Hexa on gastric acid secretion seems to involve brain somatostatinergic system since Hexa (10 pmol/rat, i.c.v.) did not inhibit gastric acid secretion in rats pretreated (4 h before) with cysteamine (300 mg/kg, s.c.), a depletor of endogenous somatostatin. These results show that synthetic GHS and ghrelin exert a central long-lasting inhibitory effect on gastric acid secretion in conscious pylorus-ligated rats. The fact that very low doses of ghrelin and GHS inhibit gastric secretion, provide evidence for a tonic inhibitory role of the peptides in the central control of gastric secretory function.

Growth hormone-inhibiting activity of cortistatin in the rat

Cortistatin-14 (CST-14) is an endogenous neuropeptide with notable structural similarities to native somatostatin-14 (SS-14), but different physiological functions. Differences in the physiology of the two peptides do not provide conclusive evidence for a specific receptor for CST. To date, the effects of CST-14 on anterior pituitary hormones have never been reported. Aim of this study was to investigate the in vivo effects of CST-14 on GH secretion in comparison to SS-14. Our results demonstrate that CST-14 was very effective in reducing GH secretion in normal male anaesthetized rats. Its activity was similar to that of SS-14 and had a rapid onset and a slightly longer duration of action. In conclusion, we have reported for the first time that CST is a potent and effective inhibitor of GH release in rats and that its action may be mediated by the interaction with one or different SS receptor subtypes.

Growth hormone (GH) rebound rise following somatostatin infusion withdrawal: studies in dogs with the use of GH-releasing hormone and a GH-releasing peptide

OBJECTIVE

Evidence has been presented that in both animals and humans the rebound secretion of growth hormone (GH) following withdrawal of an infusion of somatostatin (SS) is due to the functional activation of the hypothalamic GH-releasing hormone (GHRH) neurons of the recipient organism. Based on this premise, this study has sought to assess the existence of functional interactions between endogenous GHRH released by a SS infusion withdrawal (SSIW) and growth hormone-releasing peptides (GHRPs), a class of compounds allegedly acting via GHRH.

METHODS

Five young dogs (3 to 4 years old, 2 male and 3 female) were administered, on different occasions, three consecutive intravenous boli of physiological saline (0.1 ml/kg), or GHRH (2 microg/kg), or EP92632 (125 microg/kg), a GHRP compound, or GHRH plus EP92632 at the end of three cycles of 1-h SS infusions (8 microg/(kg x h)) or during a 6-h infusion of saline.

RESULTS

Under saline infusion (SALI), plasma GH levels were unaltered, whereas each SSIW cycle was followed by similar GH secretory episodes. Administration of the first GHRH bolus under SALI induced a rise in plasma GH concentrations slightly higher than that induced by the first cycle of SSIW, but the GH response to the second and third GHRH boli was similar to that after SSIW. Following SSIW, the response to the first bolus of GHRH was higher than that during SALI, but the second and third cycles of SSIW induced GH responses similar to those evoked by the GHRH bolus. During SALI, administration of the first bolus of EP92632 induced a rise in plasma GH which was higher than that induced by the first GHRH bolus, the second bolus elicited a GH peak of lesser amplitude and there was a partial restoration of the GH response to the third peptide bolus. SSIW strikingly enhanced the GH release to the first EP92632 bolus, a pattern also present, although to a lesser extent, with the second and third cycles of SSIW. Under SALI, combined administration of GHRH and EP92632 had a synergistic effect on GH release, but a progressive reduction was present in the GH response to the second and third GHRH plus EP92632 boli. SSIW increased only weakly the GH response to the first co-administration of the peptides over that present after administration of EP92632 alone, and did not induce a GH response higher than that present during SALI when the second bolus of the peptides was administered; after the third SSIW a GH rise higher than that present during SALI was elicited by the combined administration of the peptides.

CONCLUSIONS

(i) the uniformity of the GH rebound responses to multiple cycles of SSIW may indicate that the latter activate a physiological mechanism which mimics that normally controlling GH pulse generation; (ii) EP92632 elicits, under our experimental conditions, a plasma GH rise higher than that induced by GHRH; (iii) SSIW enhances the GH response to EP92639 alone, to an extent reminiscent of that following combined administration of GHRH and EP92632. This pattern reinforces the view that SSIW elicits release of endogenous GHRH, and infers that the GHRP challenge after SSIW may be exploited in humans to distinguish between healthy and GH-deficient adults.

Effects of molsidomine on scopolamine-induced amnesia and hypermotility in the rat

Nitric oxide (NO) is hypothesized to be a novel intracellular messenger in the central nervous system. Recently, NO involvement in learning and memory processes has been proposed. Compounds that inhibit nitric oxide synthase, the key synthesizing enzyme, may block cognition, while NO donors may facilitate it. The aim of this study was to assess in the rat the effects of the NO donor molsidomine (2 and 4 mg/kg, i.p.) on memory deficits caused by scopolamine. For this purpose, the object recognition task and the step-through passive avoidance procedure were chosen. In addition, the effects of molsidomine in antagonizing the scopolamine-induced hypermotility were also examined. Scopolamine at 0.2 mg/kg (object recognition) and 0.75 mg/kg (passive avoidance) disrupted acquisition in both the tasks and induced locomotor hyperactivity at the dose of 0.2 mg/kg. Molsidomine at either dose reversed the scopolamine-induced deficits in the object recognition paradigm but did not counteract the hypermotility and the deficits occurred in the passive avoidance test. These results suggest that to some extent, the NO donor molsidomine is involved in memory processing.

Permeability of the peptidic GH secretagogues hexarelin and EP 51389, across rat jejunum

The intestinal permeability of hexarelin and EP 51389, two growth hormone releasing hexa- and tri- peptide analogues, was assessed in vitro with side-by-side diffusion chambers in the apical-to-basolateral (AP-to-BL) and in the basolateral-to-apical (BL-to-AP) direction using excised rat jejunal segments. The effect of EP 51389 on P-glycoprotein (P-gp) was evaluated by rhodamine 123 accumulation on monolayers of CH(R)C5 cells with increasing concentrations of EP 51389. Hexarelin and EP 51389 permeability were found to be < 1%. Permeability coefficients (P(app)) were 18.87 +/- 2.86 (x10(-7) cm/s) and 5.87 +/- 0.45 (x10(-7) cm/s) for hexarelin and EP 51389, respectively. Bidirectional studies revealed that hexarelin transport was similar in both directions. EDTA did not influence hexarelin permeability. Permeability was predominantly secretory for EP 51389 as P(app) in the BL-to-AP direction [32.56 +/- 6.11 (x10(-7) cm/s)] was greater than AP-to-BL. Confirming involvement of a secretory transport system, chlorpromazine inhibited EP 51389 transport across the jejunum. EP 51389 inhibited P-gp in a dose dependent manner resulting in the intracellular accumulation of rhodamine in CH(R)C5 cells. These results suggest that: 1) the intestinal permeability of hexarelin and EP 51389 is poor; 2) the passage of hexarelin is mainly via a transcellular passive pathway since the contribution of paracellular permeability to the overall permeability is rather low; 3) P-gp may act as a potential barrier for the intestinal absorption of EP 51389.

Binding of 125I-labeled ghrelin to membranes from human hypothalamus and pituitary gland

Ghrelin has been proposed as a natural ligand of the GH secretagogue receptor(s) (GHS-R), which was an orphan receptor activated by synthetic peptidyl (hexarelin) and non-peptidyl (MK-0677) GHS to strongly release GH in animals and humans. Herein we studied: 1) the binding of 125I-labeled human ghrelin to membranes from human hypothalamus and pituitary gland; 2) the ability of human ghrelin (either octanoylated or desoctanoylated), as well as of some GHS and neuropeptides to compete with the radioligand. The saturation binding analysis showed, in both tissues, the existence of a single class of high-affinity binding sites with limited binding capacity. The Bmax (maximal number of binding sites) values of ghrelin receptors in the hypothalamus were significantly greater (p<0.001) than those detected in the pituitary, whereas the Kd (dissociation constant) values in the two tissues were similar. 125I-ghrelin bound to hypothalamic membranes was displaced by ghrelin, hexarelin, MK-0677, various GHS antagonists (EP-80317, [D-Arg1-D-Phe5-D-Trp7,9-Leu11]-substance P) and some natural (cortistatin-14) and synthetic (vapreotide) SRIH-14 agonists. In contrast, no competition was seen in the presence of GHRH-44, SRIH-14 or desoctanoylated ghrelin, a ghrelin precursor that is devoid of GH-releasing properties. In conclusion, this preliminary study firstly demonstrates that ghrelin needs octanoylation to bind its hypothalamo-pituitary receptors. These receptors are the specific binding sites for GHS and their antagonists, as well as for SRIH analogs (vapreotide and cortistatin- 14), but not for native SRIH.

Hexarelin, but not growth hormone, protects heart from damage induced in vitro by calcium deprivation replenishment

The effects of hexarelin, a growth hormone (GH) secretagogue, and human GH on the mechanical and metabolic changes measured in isolated rat hearts submitted to 5 min of Ca2+ deprivation followed by reperfusion with Ca2+-containing medium, the so-called calcium paradox phenomenon, were studied. Hexarelin (80 microg/kg bid, subcutaneously) administered for 7 d to male rats effectively antagonized the sudden increase in resting tension measured in vitro on Ca2+ repletion. Moreover, during Ca2+ repletion the release of creatine kinase activity (an index of cell damage) in the perfusate of these hearts was reduced up to 40% compared with controls. By contrast, administration of hexarelin for 3 d or GH (400 microg/kg bid, subcutaneously) for 7 d did not affect the mechanical and metabolic alterations induced by the calcium paradox. To assess its direct and acute cardiac effects, hexarelin (8 microg/mL) was perfused in vitro in recirculating conditions for 60 min through the hearts of normal rats. In this case, hexarelin did not stimulate heart contractility and failed to prevent ventricular contracture upon Ca2+ readmission, whereas diltiazem, a Ca2+channel blocker, effectively antagonized the calcium paradox phenomenon. We conclude that short-term in vivo exposure to hexarelin, but not GH, enables cardiac myocyites to prevent cytoplasmatic electrolytic unbalance and to control intracellular Ca2+ gain, two functions largely impaired during the calcium paradox phenomenon. Moreover, because the effect of hexarelin is not acute but dependent on the length of in vivo treatment, we suggest that it requires modifications of myocardiocyte physiology.

Somatostatin octapeptides (lanreotide, octreotide, vapreotide, and their analogs) share the growth hormone-releasing peptide receptor in the human pituitary gland

The binding affinity of somatostatin-14 (SRIF), various SRIF derivatives, and some peptides belonging to the growth hormone-releasing peptide (GHRP) family to specific receptors for SRIF and GHRP in the human pituitary gland has been measured. GHRP receptors have been identified using [125I]Tyr-Ala-hexarelin, a peptide that thas been demonstrated to be a potent growth hormone (GH) releaser in humans. Tyr-Ala-hexarelin binding was displaced in a dose-dependent manner by different GHRPs (hexarelin, GHRP-2, and EP-51216). Surprisingly, some SRIF octapeptide derivatives such as vapreotide, lanreotide, octreotide, and their analogs were also able to displace the GHRP ligand. By contrast, no inhibition of Tyr-Ala-hexarelin binding was observed in the presence of SRIF or SRIF derivatives (SRIF H-2186, H-2485, and H-3382) that are known to have a weak SRIF-like activity. When [125I]Tyr1-SRIF-14 was used as a ligand, we observed displacement with SRIF and the octapeptide SRIF analogs but not with GHRPs and other SRIF derivatives. The results point to a sharing of the GHRP receptor with the octapeptide SRIF analogs, but not SRIF. Our data are consistent with the hypothesis that the putative natural GH secretagogue ligand may be a growth hormone release inhibiting factor that is different from SRIF and that is antagonized by GHRP.

Contrasting effects of nitric oxide on food intake and GH secretion stimulated by a GH-releasing peptide

OBJECTIVE

Among the many actions of nitric oxide (NO) are those on endocrine and feeding behaviour. Based on NO involvement in the GH-releasing effect of the GH-releasing peptides (GHRPs) and the reported orexigenic activity of these compounds, we sought to evaluate the effect of the combined administration of a long-acting NO donor, molsidomine, and the newly synthesized GHRP EP92632 on food intake and GH secretion in rats. Moreover, to verify the specificity of a potential NO involvement, we evaluated whether or not the effects of GHRPs were abolished by a pre-treatment with an inhibitor of NO synthase, N-nitro-arginine-methyl-ester (NAME).

METHODS

In the food intake experiments, adult Sprague-Dawley male rats underwent acute administration of: (1) EP92632 (160 microg/kg, s.c.); (2) molsidomine (100 mg/kg, i.p.); (3) EP92632+molsidomine; (4) l-NAME (40 and 60 mg/kg, i.p.); (5) EP92632+l-NAME (60 mg/kg, i.p.); (6) EP92632+molsidomine+l-NAME (60 mg/kg, i.p.); and (7) 0.9% saline (0.1 ml/kg, i.p.). After treatments, the cumulative food intake in the 6 post-treatment hours was carefully evaluated. In the neuroendocrine experiments, rats were given the same compounds according to the above reported schedule, except for the use of one dose of NAME (60 mg/kg, i.p.) and a lower EP92632 dose (80 microg/kg, s.c.), and were sampled via atrial cannula.

RESULTS

EP92632 significantly stimulated food intake, an effect which was further enhanced by molsidomine, though the latter did not elicit per se any orexigenic effect. l-NAME given alone significantly decreased food intake and abolished the orexigenic effect of the GHRP and the enhancing effect of molsidomine. Plasma GH levels increased significantly following administration of EP92632 but, in contrast to the food intake experiments, molsidomine significantly inhibited both basal and EP92632-stimulated GH secretion; moreover, NAME had a biphasic effect on the EP92632-stimulated GH release: initially inhibitory and then, from 45 min on, stimulatory. NAME did not affect basal GH levels but, surprisingly, combined administration of molsidomine and NAME induced a striking inhibition of both basal and the peptide-stimulated GH release.

CONCLUSIONS

In summary, these data indicate that NO in the rat is physiologically involved in a stimulatory way in the GHRP-mediated effect on food intake, but exerts a dual action, probably stimulatory at hypothalamic and inhibitory at pituitary levels, on basal and GHRP-stimulated GH secretion.

Penile erection induced by EP 80661 and other hexarelin peptide analogues: involvement of paraventricular nitric oxide

The effect of GAB-D-Trp(2-Me)-D-Trp(2-Me)-LysNH(2) (EP 80661), GAB-D-Trp(2-Me)-D-Trp(2-Me)-D-Trp(2-Me)-LysNH(2) (EP 60761), GAB-D-Trp(2-Me)-LysNH(2) (EP 91071) and GAB-D-Trp(2-Me)-D-beta Nal-Phe-LysNH(2) (EP 50885), four hexarelin peptide analogues that induce penile erection when injected into the paraventricular nucleus of the hypothalamus of male rats, on the concentration of NO(2)(-) and NO(3)(-) in the paraventricular dialysate was studied in male rats. EP peptides (1 microg) induced penile erection and increased the concentration of NO(2)(-) and NO(3)(-) in the paraventricular dialysate. In contrast, hexarelin (1 microg) was ineffective on either penile erection or paraventricular NO(2)(-) and NO(3)(-). EP peptide-induced penile erection was prevented by the nitric oxide synthase inhibitor N(G)-nitro-l-arginine methylester given into the paraventricular nucleus (20 microg), which also reduced the concomitant increase of NO(2)(-) and NO(3)(-) concentration in the paraventricular dialysate. In contrast, the oxytocin receptor antagonist [d(CH(2))(5)Tyr(Me)(2)-Orn(8)]vasotocin (1 microg) given into the paraventricular nucleus, was ineffective on penile erection and on the NO(2)(-) and NO(3)(-) increase induced by EP peptides, despite its ability to prevent the sexual response induced by the above peptides when given into the lateral ventricles. The present results show that EP peptides induce penile erection by activating nitric oxide synthase in the paraventricular nucleus of the hypothalamus, possibly in the cell bodies of oxytocinergic neurons that control penile erection.

Differential orexigenic effects of hexarelin and its analogs in the rat hypothalamus: indication for multiple growth hormone secretagogue receptor subtypes

We have previously reported that hexarelin and some of its analogs, including EP 50885, stimulated GH secretion and feeding after systemic administration in the rat, whereas EP 40904 selectively stimulated food intake and EP 40737 only GH release. The precise mechanism of growth hormone-releasing peptides (GHRPs) actions is still unclear, but the integrity of the arcuate nucleus of the hypothalamus (ARC) appears crucial for their endocrine effects. To better characterize the site(s) and mechanisms(s) of the orexigenic action of GHRPs, we have investigated their effects after infusion into the arcuate, paraventricular, ventromedial and medial preoptic areas of the hypothalamus. Food intake was measured for 60 min following injection of the test compound (2 microg/rat). Hexarelin, EP 40904 and EP 50885 had significant orexigenic effects after injection into the ARC. A specific NPY antagonist significantly inhibited the effect of hexarelin, whereas a GHRH antagonist was ineffective. In the paraventricular nucleus, only EP 50885 stimulated feeding, whereas all peptides were ineffective in the ventromedial nucleus and medial preoptic area. Taken altogether, these results demonstrate that GHRPs are endowed with site-specific orexigenic actions and that endogenous NPY, but not GHRH, mediates these effects. The additional orexigenic action of EP 50885 in the paraventricular nucleus suggests the existence of a GHRP receptor subtype different from the already cloned one.

EP 60761- and EP 50885-induced penile erection: structure-activity studies and comparison with apomorphine, oxytocin and N-methyl-D-aspartic acid

The effect of 10 peptides structurally related to the growth hormone (GH) releasing peptide hexarelin, injected into the paraventricular nucleus of the hypothalamus (PVN), on penile erection was studied in male rats. Six out of the 10 peptides tested induced penile erection in a dose-dependent manner. Among them, the most potent were EP 80661, EP 60761 and EP 91072, which were active at doses of 20-200 ng. The potency of these peptides in inducing penile erection is comparable to that of apomorphine, oxytocin and N-methyl-D-aspartic acid similarly injected into the PVN. Other peptides found active were EP 50885, EP 90101 and EP 91071, which induced penile erection at doses of 200-2000 ng. In contrast, EP 51322, EP 70555, EP 51216 and EP 91073 were inactive, as were hexarelin, EP 40904 and EP 40737 in a previous study. The majority of EP peptides found active when injected into the PVN induced penile erection, although to a lesser extent, also when given systemically (endovenously). The proerectile effect of EP peptides was prevented by the oxytocin receptor antagonist [d(CH2)5 Tyr(Me)2-Orn8]-vasotocin given into the lateral ventricles but not into the PVN, by the nitric oxide (NO) synthase inhibitor N(G)-nitro-1-arginine methyl ester given either into the lateral ventricles or into the PVN, by the N-type Ca2+ channel blocker omega-conotoxin GVIA and by morphine, but not by the dopamine receptor antagonist cis-flupenthixol or by the N-methyl-D-aspartic acid receptor antagonist dizolcipine, given into the PVN. As the structure-activity relationship of EP peptides for proerectile activity is different from those of other biological actions of these compounds, ie for GH release and eating behaviour, the present results suggest that EP peptides induce penile erection by acting on specific hypothalamic receptor sites that activate paraventricular oxytocinergic neurons projecting to extrahypothalamic brain areas that mediate this sexual function by a mechanism similar to that of dopamine receptor agonists, oxytocin and N-methyl-D-aspartic acid.

EP 60761 and EP 50885, two hexarelin analogues, induce penile erection in rats

The effect of hexarelin and four related peptide analogues, EP 40904, EP 40737, EP 50885 and EP 60761, injected into the paraventricular nucleus of the hypothalamus of male rats in doses between 2 and 2000 ng on spontaneous penile erection was studied. Of these peptides, EP 60761 and EP 50885, but not hexarelin, EP 40904 or EP 40737, increased dose-dependently the number of spontaneous penile erections. EP 60761 was active already at the dose of 20 ng, which induced the sexual response in 70% of the treated rats. The maximal response was induced by 200 ng of the peptide. EP 50885 was less potent than EP 60761, with 1000 ng being the minimal effective dose and 2000 ng as the dose required to induce the maximal response. At the doses used, both peptides also increased slightly the number of spontaneous yawning episodes. EP 60761- and EP 50885-induced penile erection was prevented by the oxytocin receptor antagonist [d(CH(2))(5)Tyr(Me)(2)-Orn(8)]vasotocin (0.1-1 microg) given intracerebroventricularly (i.c.v.), but not into the paraventricular nucleus (0.1-1 microg), by the competitive nitric oxide (NO) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) given either into the paraventricular nucleus (10-20 microg) or i.c.v. (75-150 microg), by the N-type Ca(2+) channel blocker omega-conotoxin-GVIA (2-5 ng) or by the opiate morphine (1-10 microg), but not by the dopamine receptor antagonist (Z)-4-[3-[2-(trifluoromethyl)-9H-thioxanthen-9-ylidene]propyl]-1-p ipe razine-ethanol (cis-flupenthixol) (10 microg) or by the N-methyl-D-aspartic acid (NMDA) receptor antagonist (5R, 10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5, 10-imine ((+)-MK-801) (1 microg), all given into the paraventricular nucleus before either peptide. The present results show that EP 60761 and EP 50885 induced penile erection by increasing central oxytocin transmission, possibly by activating NO synthase in the cell bodies of oxytocinergic neurons located in the paraventricular nucleus that control penile erection.

Hexarelin, a growth hormone secretagogue, protects the isolated rat heart from ventricular dysfunction produced by exposure to calcium-free medium

The effect of hexarelin, a potent synthetic growth hormone (GH)-secretagogue, and of human GH were studied on the mechanical and metabolic changes elicited by the calcium-paradox phenomenon in isolated rat hearts submitted to 5 min Ca(2+)-depletion followed by reperfusion with reintegrated Ca(2+)medium. Hexarelin, (80 microg kg(-1)s.c.) administered to normal male young rats for 3 and 7-day, time-dependently antagonized the sudden increase in resting tension of the isolated perfused hearts upon Ca(2+)-repletion. The beneficial effect of hexarelin was particularly evident in the 7-day treatment. In this instance, ventricular contraction peaked at 30 +/- 2 mmHg (controls, 76 +/- 7 mmHg) and the recovery of left ventricular developed pressure (LVDP) was two times higher (P<0.001) than that recorded in controls (LVDP, 29 +/- 2 mmHg). Moreover, the release of creatine kinase into the heart effluent during Ca(2+)-repletion was reduced by 40% (P<0.001) as compared to controls. The protecting activity of hexarelin against the damage induced by calcium-paradox in the heart was apparently divorced from any stimulation of the GH/insulin-like growth factor (IGF) axis, since plasma and heart concentrations of IGF-1 were similar to those measured in control rats. In contrast to hexarelin, administration of GH (400 microg kg(-1) s.c.) for 7 days did not affect the mechanical and metabolic manifestations of calcium-paradox in the perfused rat hearts. Hexarelin (8 microg ml(-1)) perfused for 60 min through the hearts in recirculating conditions did not modify heart contractility and failed to prevent ventricular hypercontractility developed on Ca(2+)-readmission. In conclusion, the mode of action of hexarelin in protecting the rat heart from calcium-paradox events is presently unknown; it would seem, however, that only prolonged exposure to hexarelin makes myocardial cells competent to maintain cytoplasmatic electrolyte balance and to control of Ca(2+)gain, two functions that are impaired during the 'calcium-paradox' phenomenon.

Growth hormone and hexarelin prevent endothelial vasodilator dysfunction in aortic rings of the hypophysectomized rat

The endothelial vasodilation mechanism(s) has been investigated in aortic rings of hypophysectomized male rats as well as hypophysectomized rats treated for 7 days with growth hormone (GH, 400 microg/kg, s.c.) or hexarelin (80 microg/kg, s.c.). Tissue preparations from intact animals were taken as controls. The results obtained indicate that the release of 6-keto-prostaglandin F1alpha (6-keto-PGF1alpha) from aortic rings of hypophysectomized rats was markedly reduced (51%; p<0.01) as compared with that of control preparations; the peak response to cumulative concentration of endothelin-1 (ET-1, from 10(-11) to 10(-5) M) was increased 2.4-fold (p<0.01) versus controls; the relaxant activity of acetylcholine (ACh, from 10(-10) to 10(-4) M) in norepinephrine-precontracted aortic rings was reduced by 39.5+/-4.4%. Pretreatment of hypophysectomized rats with GH or hexarelin markedly antagonized the hyperresponsiveness of the aortic tissue to ET-1 and allowed a consistent recovery of both the relaxant activity of ACh and the generation of 6-keto-PGF1alpha. Collectively these findings support the concept that dysfunction of vascular endothelial cells may be induced by a defective GH function. Because a replacement regimen of GH restored the somatotropic function and increased plasma insulin-like growth factor-I (IGF-I) concentrations in the hypophysectomized rats, it is suggested that IGF-I may have protected the vascular endothelium acting as a biologic mediator of GH action. In contrast to GH, hexarelin replacement neither increased body weight nor affected the plasma concentrations of IGF-I, indicating that its beneficial action on vascular endothelium was divorced from that on somatotropic function and was likely due to activation of specific endothelial receptors.

Growth hormone-independent cardioprotective effects of hexarelin in the rat

We previously reported that induction of selective GH deficiency in the rat exacerbates cardiac dysfunction induced by experimental ischemia and reperfusion performed on the explanted heart. In the same model, short-term treatment with hexarelin, a GH-releasing peptide, reverted this effect, as did GH. To ascertain whether hexarelin had non-GH-mediated protective effects on the heart, we compared hexarelin and GH treatment in hypophysectomized rats. Hexarelin (80 microg/kg sc), given for 7 days, prevented exacerbation of the ischemia-reperfusion damage induced by hypophysectomy. We also demonstrate that hexarelin prevents increases in left ventricular end diastolic pressure, coronary perfusion pressure, reactivity of the coronary vasculature to angiotensin II, and release of creatine kinase in the heart perfusate. Moreover, hexarelin prevents the fall in prostacyclin release and enhances recovery of contractility. Treatment with GH (400 microg/kg sc) produced similar results, whereas administration of EP 51389 (80 microg/kg sc), another GH-releasing peptide that does not bind to the heart, was ineffective. In conclusion, we demonstrate that hexarelin prevents cardiac damage after ischemia-reperfusion, and that its action is not mediated by GH but likely occurs through activation of specific cardiac receptors.

Neuroendocrine control of growth hormone secretion

The secretion of growth hormone (GH) is regulated through a complex neuroendocrine control system, especially by the functional interplay of two hypothalamic hypophysiotropic hormones, GH-releasing hormone (GHRH) and somatostatin (SS), exerting stimulatory and inhibitory influences, respectively, on the somatotrope. The two hypothalamic neurohormones are subject to modulation by a host of neurotransmitters, especially the noradrenergic and cholinergic ones and other hypothalamic neuropeptides, and are the final mediators of metabolic, endocrine, neural, and immune influences for the secretion of GH. Since the identification of the GHRH peptide, recombinant DNA procedures have been used to characterize the corresponding cDNA and to clone GHRH receptor isoforms in rodent and human pituitaries. Parallel to research into the effects of SS and its analogs on endocrine and exocrine secretions, investigations into their mechanism of action have led to the discovery of five separate SS receptor genes encoding a family of G protein-coupled SS receptors, which are widely expressed in the pituitary, brain, and the periphery, and to the synthesis of analogs with subtype specificity. Better understanding of the function of GHRH, SS, and their receptors and, hence, of neural regulation of GH secretion in health and disease has been achieved with the discovery of a new class of fairly specific, orally active, small peptides and their congeners, the GH-releasing peptides, acting on specific, ubiquitous seven-transmembrane domain receptors, whose natural ligands are not yet known.

TE671 cell-based ELISA for anti-acetylcholine receptor antibody determination in myasthenia gravis

BACKGROUND

Acetylcholine receptor (AChR) from human muscles is the antigen used currently in radioimmunoprecipitation assays (RIPAs) for the determination of anti-AChR antibodies in the diagnosis of myasthenia gravis (MG). Our aim was to develop and validate an ELISA using TE671 cells as the source of AChR.

METHODS

After TE671 cell homogenization, the crude AChR extract was used for plate coating. Anti-AChR antibodies were determined in 207 MG patients and in 77 controls.

RESULTS

The mean intra- and interassay CVs (for two samples with different anti-AChR antibody concentrations) were 9.7% and 15.7%, respectively. Test sensitivity and specificity, for generalized MG, were 79.5% (95% confidence interval, 72.8-85.0%) and 96.1% (89.0-99.1%). The detection limit was 2 nmol/L. Anti-AChR antibody concentrations from 53 MG patients, as tested with our ELISA, showed good agreement with an RIPA with a mean difference (SD) of 1.0 (5.6) nmol/L.

CONCLUSION

Our ELISA is a simple screening test for the diagnosis of MG and enables rapid and inexpensive patient follow-up.

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.

Identification of a pituitary growth hormone-releasing peptide (GHRP) receptor subtype by photoaffinity labeling

Hexarelin, an analogue of GHRP-6, in which D-Tryptophan has been replaced by its 2-methyl derivative, is known to release growth hormone (GH) in vivo and in vitro by direct action on receptors present in anterior pituitary cells. Measurement of second messengers (c-AMP, Ca++, IP3) upon somatotrophs stimulation, suggests the existence of more than one GHRP receptor subtype. In order to document such an hypothesis, we have used a new photoactivatable derivative of Hexarelin, Tyr-Bpa-Ala-Hexarelin. This derivative was shown to be fully active in the release of GH in vivo with neonate rats. Using this photoactivatable ligand, we have specifically labeled a protein with an apparent Mr of 57,000 in human, bovine and porcine anterior pituitary membranes. Hexarelin and the spiroindoline sulfonamide MK-0677 displaced the Mr-57,000 photolabeled band with an apparent ED50 of 6x10(-7) M and 2x10(-5) M respectively. Taking into account the high efficiency (>60%) of covalent incorporation of the Bpa residue, this photoactivatable Hexarelin derivative has allowed the identification of a pituitary GHRP receptor subtype, which is apparently distinct from the recently cloned GH secretagogue receptor.

Growth hormone secretagogues: focus on the growth hormone-releasing peptides

This review systematically analyses recent knowledge of the biology of the growth hormone-releasing peptides. Many years before native GHRH had been isolated and sequenced, the synthesis of an enkephalin analog, devoid of any opioid activity but capable of specifically releasing GH from in vitro pituitaries, prompted the design of a number of structurally interrelated GHRPs with improved GH-releasing activity. Nowadays, GHRPs are the most effective GH-secretagogues known and could be used profitably in humans with GH hyposecretory disturbances to promote a pattern of GH secretion that mimics physiology in a better way than the exogenously administered GH.

Effects of GH and IGF-I administration on GHRH and somatostatin mRNA levels: II. A study in the infant rat

It is generally accepted that growth hormone influences its own secretion by modulating the activity of GHRH and SRIF neurons. To investigate if GH feedback mechanisms are already operating in the early postnatal life of the rat, we have studied in 10-day-old pups the effects of rhGH and rhIGF-I administration on GHRH and somatostatin mRNA levels. The same experiment was also performed in pups passively immunized with an anti-GHRH antiserum from the day of birth. The latter animal model had been previously characterized for presenting reduced levels of circulating GH and IGF-I. In control pups, neither rhGH (250 micrograms/kg, b.i.d., sc) nor rhIGF-I (150 micrograms/kg, b.i.d., sc) administration induced significant changes of GHRH and SRIF gene expression. The passive immunization against GHRH induced per se a trend toward an increase and a reduction of GHRH and SRIF mRNA levels, respectively. Also in these rats the treatment for 3 days with rhGH and rhIGF-I did not further modify the GHRH and SRIF mRNA levels. Based on these results, we conclude that in the 10-day-old rat GH feedback mechanisms are poorly operative, though a direct ultra-short loop mechanism involving the GHRH and SRIF systems seems already operating.

Effects of GH and IGF-I administration on GHRH and somatostatin mRNA levels: I. A study on ad libitum fed and starved adult male rats

The individual role played by GH and IGF-I in the regulation of hypothalamic GHRH and SRIF gene expression is still object of debate. We have investigated the effect of exogenously administered recombinant hGH (rhGH) and recombinant hIGF-I (rhIGF-I) in ad libitum fed control and starved rats, the latter an animal model which is characterized by low circulating levels of endogenous GH and IGF-I. Adult male rats were fed ad libitum (C) or food-deprived (S) for 72 hours; rats in either C or S groups were treated with systemic administration of rhGH and rhIGF-I for 3 days. GHRH, SRIF and GH mRNA levels were evaluated by Northern and slot blot hybridization. Administration of rhGH (250 micrograms/kg/twice daily, sc) induced a significant inhibition of GHRH and a significant stimulation of SRIF mRNA levels in C rats; GH treatment was, however, ineffective on both neuropeptide mRNA levels in the S group. Continuous infusion of rhIGF-I (300 micrograms/kg/day, sc) induced a significant increase of SRIF levels in both C and S rats but did not modify GHRH mRNA levels in either group. In the pituitary, GH mRNA levels followed a pattern very similar to that of GHRH. These results provide evidence for a direct role of GH in the inhibition of GHRH mRNA levels; IGF-I appears more involved in the direct stimulation of SRIF mRNA levels.

Hexarelin stimulation of growth hormone release and mRNA levels in an infant and adult rat model of impaired GHRH function

Hexarelin, a GH-releasing peptide, is an effective GH secretagogue in man and a variety of experimental animals. In the present study, we sought to characterize the effects of short-term Hexarelin treatment on GH release and GH mRNA levels in infant and young-adult rats and in rats of either age passively immunized with an antiserum against GHRH (GHRH-Ab). Hexarelin (80 micrograms/kg, b.i.d. s.c.), administered for 3, 5 or 10 days to 8-, 6- and 1-day-old rats, respectively, induced a progressive enhancement of the plasma GH rise elicited by a subsequent acute Hexarelin (80 micrograms/kg s.c) challenge when pups were 10 days old. As expected, GHRH-Ab treatment decreased GH concentrations in 10-day-old pups. In GHRH-Ab-treated pups, Hexarelin administration for 3-10 days significantly enhanced the GH response to the acute Hexarelin injection, though the mean plasma GH values remained significantly lower than in the respective control group. Hexarelin treatment did not alter GH mRNA levels in control pups. In GHRH-Ab-treated pups Hexarelin treatment for 3 and 5 days, but not 10 days, restored GH mRNA levels to control values. In young-adult male rats, regardless of antiserum treatment, Hexarelin administration for 5 or 10 days significantly suppressed the GH response to a subsequent acute challenge with the peptide. Yet, 5-10 days of Hexarelin treatment did not alter GH mRNA in control young-adult rats. In adult rats GHRH-Ab also decreased GH mRNA levels, but 10 days of Hexarelin treatment were necessary to return GH mRNA back to normal levels. These results indicate that: (1) the effects of Hexarelin on GH release and GH mRNA levels may be unrelated events; (2) deprivation of GHRH function discloses the ability of Hexarelin to stimulate GH mRNA levels; (3) age plays a crucial role in setting the pituitary responsiveness to short-term Hexarelin treatment, and (4) the different ability of Hexarelin to stimulate GH release and GH synthesis in neonatal and young-adult rats may have clinical relevance in the chronic administration of the peptide.

Mechanism of action of Hexarelin. I. Growth hormone-releasing activity in the rat

We have reported Hexarelin (HEXA), an analog of growth hormone-releasing peptide 6 (GHRP-6), potently stimulates growth hormone (GH) secretion in infant and adult rats. This study was undertaken to further investigate Hexarelin's mechanisms of action. In 10-day-old pups, treatments with HEXA (80 micrograms/kg, b.i.d.) for 3-10 days significantly enhanced, in a time-related fashion, the GH response to an acute HEXA challenge. Qualitatively similar effects were elicited in pups passively immunized against growth hormone-releasing hormone (GHRH) from birth. In adult male rats, a 5-day pretreatment with HEXA (150 micrograms/kg, b.i.d.) did not enhance the effect of the acute challenge, and the same pattern was present after a 5-day pretreatment in male rats with surgical ablation of the mediobasal hypothalamus (MBH-ablated rats). In addition, in adult sham-operated rats, Hexarelin (300 micrograms/kg, i.v.) induced a GH response greater (p < 0.05) than that induced by GHRH (2 micrograms/kg, i.v.). However, in MBH-ablated rats 7 days after surgery, GHRH was significantly (p < 0.05) more effective than HEXA, and 30 days after surgery HEXA and GHRH evoked similar rises of plasma GH. Finally, the in vitro Hexarelin (10(-6) mol/l) effect was transient while GHRH (10(-8) mol/l) induced a longer lasting and greater GH release. Three different mechanisms, not mutually exclusive, are postulated for Hexarelin stimulation of GH secretion in vivo: a direct action on the pituitary, though of minor relevance; an indirect action that involves release of GHRH, of relevance only in adult rats; and an action through the release of a still unknown hypothalamic "factor", which in infant and adult rats elicits GH release acting sinergistically with GHRH.

Involvement of brain catecholamines and acetylcholine in growth hormone hypersecretory states. Pathophysiological, diagnostic and therapeutic implications

Secretion of growth hormone (GH) is excessive in acromegaly, but also in a number of other pathological states such as anorexia nervosa, insulin-dependent diabetes mellitus (IDDM), liver cirrhosis, depression, renal failure and GH-insensitivity syndrome. Abnormalities in the neuroendocrine control of GH secretion and/or a state of insensitivity to GH contribute to hypersecretion of GH in these states, with the possible exception of acromegaly, which appears to be a primary pituitary disease. GH hypersecretion may also occur in neonates or adolescents with tall stature, thus reflecting particular physiological or paraphysiological conditions. In the cohort of brain neurotransmitters, catecholamines and acetylcholine reportedly play a major role in the control of neurosecretory GH-releasing hormone (GHRH) and somatostatin (SS)-producing neurons, and hence GH secretion. Activation of alpha 2-adrenoceptors or of muscarinic cholinergic receptors in the hypothalamus stimulates GH release, probably through stimulation of GHRH and inhibition of SS release, respectively. Activation of dopamine receptors likewise stimulates GH release, while activation of beta-receptors inhibits GH release through stimulation of hypothalamic SS function. This review discusses the involvement of brain catecholamines and acetylcholine in GH hypersecretory states, including anorexia nervosa, acromegaly, IDDM, liver cirrhosis, depression, renal failure and GH insensitivity syndrome, with a view to providing a fuller understanding of their pathophysiology and, whenever possible, diagnostic and therapeutic implications.

Small peptides as potent releasers of growth hormone

Newly synthesized peptides are described which release growth hormone in the infant rat and their biological activity is compared with known GHRPs. Some of these peptides are the most potent GHRPs reported to date.

The reduction of circulating growth hormone and prolactin in streptozocin-induced diabetic male rats is possibly caused by hypothalamic rather than pituitary changes

To gain further information on diabetes-related disorders in the somatotrophic and lactotrophic axes, we undertook a functional, morphometrical and densitometrical study of the arcuate nucleus (AN), median eminence (ME) and anterior pituitary gland of adult male rats one month after streptozocin-induced diabetes (STZ-D). The basal secretory activity of somatotrophs and lactotrophs was tested by the reverse haemolytic plaque assay (RHPA) and plasma GH and prolactin (PRL) levels were determined by RIA. The number of GH-releasing factor (GRF)-labelled axons and the amount of axonal tyrosine hydroxylase (TH)-immunoreactivity increased in STZ-D. There were no significant differences in any of the other densitometrical measurements performed on GRF-, somatostatin-, thyrotropin-releasing hormone- and TH-labelled ME axon cross-sections as well as those on tuberoinfundibular-dopaminergic neurones of the AN in STZ-D compared with control rats. Plasma GH and PRL levels and measurements on anterior pituitary GH- and PRL-labelled structures were decreased in STZ-D. However, the GH and PRL plaque areas were increased after RHPA implying that the secretory capacity of somatotrophs and lactotrophs was not impaired. Taken together, these results suggest that the accumulated GRF in the ME is due to reduced GRF release. This could account for the reduced amplitude and/or frequency of GH secretory pulses. The increased axonal TH-immunoreactivity may indicate an increased dopamine synthesis. If coupled to increased release this could, in turn, be partly responsible for the reduced plasma and anterior pituitary PRL concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanism of action of hexarelin and GHRP-6: analysis of the involvement of GHRH and somatostatin in the rat

We have recently reported oral and parenteral bioactivity for a new GH-releasing peptide, hexarelin. In the present study, we have examined the neuroendocrine mechanism by which hexarelin and GHRP-6, two GH-releasing peptides, mediate their actions. Although previous studies have looked at the role of growth hormone-releasing hormone (GHRH) and somatostatin in regulating the action of GHRP-6 in culture and in stressed animals, our study looked at the role of both somatostatin and GHRH in regulating the action of hexarelin as well as GHRP-6 in conscious and freely-moving, nonstressed rats. Adult male rats, prepared with indwelling jugular catheters, were pretreated i.v. with either control antiserum (CTLas), growth hormone-releasing hormone antiserum (GHRHas), somatostatin antiserum (SSas), or both GHRHas and SSas. Animals were then treated i.v. with 25 micrograms/kg of either hexarelin or GHRP-6 4 h after i.v. antisera pretreatment. Blood samples were collected every 20 min for the 3 h prior to peptide treatment and at 5, 10, 15, 20, 40 and 60 min following hexarelin or GHRP-6 injection. The peak plasma GH responses in rats pretreated with CTLas were 552 +/- 125 ng/ml following hexarelin administration and 386 +/- 132 ng/ml following GHRP-6 administration. Rats pretreated with SSas exhibited peak GH responses following hexarelin or GHRP-6 of 702 +/- 115 and 312 +/- 42 ng/ml, respectively. These plasma GH responses were similar to those observed in the CTLas-pretreated animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Somatotropic dysregulation in old mammals

In old mammals, including humans, the spontaneous growth hormone (GH) secretory pattern is markedly reduced resulting in lower amounts of GH released over 24 h, and the GH response to administration of GH-releasing hormone (GHRH) is reduced. In agreement with these in vivo findings, an impaired responsiveness to GHRH is evident in the pituitary of old male and female rats in vitro, and this is linked with a diminished stimulation of adenylate cyclase by GHRH. The poor GH responsiveness to GHRH in old mammals, which in the rat is coupled to a defective number of GHRH receptors in the somatotrophs, is likely due to a primary deficiency of GHRH availability, as implied by the diminished GHRH immunoreactivity and gene expression in and GHRH release from the hypothalamus of old rats. Attempts have been made to stimulate the sluggish somatotrophic function in elderly humans and dogs using GHRH; in either species positive results were obtained though, overall, it would seem that the GHRH hypofunction does not entirely account for the GH hyposecretory state during ageing. Concerning somatostatin, although the expression of this peptide decreases with age in the rat hypothalamus, secretion and activity of this hormone is increased, resulting in an altered relationship between GHRH and somatostatin gene expression and secretion. It is likely that defects, especially in catecholaminergic and cholinergic neurons, are instrumental in altering specific peptidergic neurons. Reportedly, catecholamines induce GH release by stimulating GHRH neurons and inhibiting somatostatin-releasing neurons; acetylcholine stimulates GH release via muscarinic receptors, in this way inhibiting the action of somatostatin neurons.(ABSTRACT TRUNCATED AT 250 WORDS)