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Increasing evidence suggests a role for ghrelin in the control of articular inflammatory diseases like osteoarthritis (OA). In the present study we examined the ability of ghrelin to counteract LPS-induced necrosis and apoptosis of chondrocytes and the involvement of GH secretagogue receptor (GHS-R)1a in the protective action of ghrelin. The effects of ghrelin (10−7–10−11 mol/L) on equine primary cultured chondrocytes viability and necrosis in basal conditions and under LPS treatment (100 ng/ml) were detected by using both acridine orange/propidium iodide staining and annexin-5/propidium iodide staining. The presence of GHS-R1a on chondrocytes was detected by Western Blot. The involvement of the GHS-R1a in the ghrelin effect against LPS-induced cytotoxicity was examined by pretreating chondrocytes with D-Lys3-GHRP-6, a specific GHS-R1a antagonist, and by using des-acyl ghrelin (DAG, 10−7 and 10−9 mol/L) which did not recognize the GHS-R 1a. Low ghrelin concentrations reduced chondrocyte viability whereas 10−7 mol/L ghrelin protects against LPS-induced cellular damage. The protective effect of ghrelin depends on the interaction with the GHS-R1a since it is significantly reduced by D-Lys3-GHRP-6. The negative action of ghrelin involves caspase activation and could be due to an interaction with a GHS-R type different from the GHS-R1a recognized by both low ghrelin concentrations and DAG. DAG, in fact, induces a dose-dependent decrease in chondrocyte viability and exacerbates LPS-induced damage. These data indicate that ghrelin protects chondrocytes against LPS-induced damage via interaction with GHS-R1a and suggest the potential utility of local GHS-R1a agonist administration to treat articular inflammatory diseases such as OA.

In the present study we investigated the mechanisms involved in the endocrine effect of nociceptin/orphanin FQ (OFQ) in the rat and the possible interaction between OFQ and morphine in the control of growth hormone (GH) secretion. The intracerebroventricular administration of OFQ (2.3 or 23 microg/rat, i.c.v.) in freely moving male rats caused an increase in the secretion of both GH and prolactin (PRL). The possible involvement of the catecholaminergic (CA) system was studied by administering OFQ to CA-depleted rats (rats given 200 mg/kg of alpha-methyl-p-tyrosine subcutaneously 2 h before the i.c.v. dose of OFQ). In these CA-depleted rats, administration of OFQ (23 microg/rat, i.c.v.) did not stimulate GH secretion, whereas it significantly enhanced PRL secretion. In rats anesthetized with ketamine, which induces a significant increase of GH, PRL and corticosterone secretion by activating the sympathetic tone, OFQ (23 microg/rat, i.c.v.) did not modify GH and corticosterone levels, whereas again it significantly potentiated PRL secretion. Overall these results indicate that CA system is involved in the stimulatory action of OFQ on GH but not on PRL secretion. In fact the stimulation of PRL, but not that of GH, was still evident after impairment of the CA system. Pretreatment with OFQ (23 microg/rat, i.c.v.) attenuated the GH secretion induced by morphine (1 mg/kg, given by intra-arterial injection), thus showing a negative interaction between OFQ and morphine in the control of GH secretion.

Central administration of amylin (2.2 microg/rat, i.c.v.) reduces (from a minimum of 67% to 83%) indomethacin (Indo, 20 mg Kg(-1), orally) induced ulcers in rats. The anti-ulcer effect of the peptide is not removed by the administration of prokinetic drugs like domperidone or neostigmine but it is reduced by 35% in rats treated with capsaicin or with the CGRP antagonist, CGRP(8-37). These data indicate that amylin gastroprotection involves capsaicin-sensitive nerve fiber leading to CGRP-dependent gastric vasodilatory effect. Additional mechanisms could involve noradrenergic alpha(2) receptors as the peptide gastroprotective activity is reduced from 67% to 20% by the alpha(2) antagonist yohimbine.

The age-related decline in growth hormone (GH) secretion has been implicated in the pathogenesis of involutional bone loss. Whether restoration of GH secretion might be helpful in maintaining and/or improving bone mass during aging is still unsettled. The aim of the present study was to examine the effects of 30-day treatment with hexarelin (HEXA, 50 microg/kg subcutaneously b.i.d.), a highly effective GH-releasing compound, on bone metabolism and bone mineral density (BMD) in intact and osteopenic gonadectomized (GDX) mature male rats. Serum total alkaline phosphatase (ALP, bone formation marker) and bone resorption markers (lysylpyridinoline, LP and hydroxylysylpyridinoline, HP) were measured before and 7, 14 and 30 days after treatment. BMD was measured by dual-energy X-ray absorptiometry at lumbar vertebrae, femoral metaphysis and diaphysis before and at the end of the experiment. In intact rats, HEXA significantly (P0.05) decreased LP (-36.3%) and HP (-22.8%) excretion at day 7, whereas it did not change serum ALP activity and BMDs. In GDX rats, HEXA completely prevented the significant (P0. 01) increase in urinary excretion of both LP (+143.8%) and HP (+119. 4%), the early decrease in ALP activity (-26.5%) and the significant (P0.05) decrease in BMDs in the femoral metaphysis (-7.9%) and lumbar vertebrae (-6.8%) caused by androgen deficiency. The bone-protective effects of HEXA could be attributed, at least in part, to its GH-releasing activity since chronic-treated rats maintained the GH response to an acute challenge with HEXA. The evidence that HEXA, unlike GH, inhibits bone resorption indicates that other mechanisms contribute to the bone sparing effect of HEXA.

Data have been collected indicating possible functions for histamine in brain but there are only a very few data, collected exclusively with behavioural tests, about the effects of histamine on the perception of the pain, an important aspect in the homeostasis of the human body. The purpose of the present study was to investigate the effects of histamine, injected directly into the lateral cerebral ventriculi on the firing of nociceptive thalamic neurones, detected by electrophysiological techniques in rats rendered arthritic by injection of Freund's adjuvant into the left hindfoot. The noxious test stimuli used were either extension or flexion of the ankle or mild lateral pressure on the heel. With increasing doses of histamine (5, 10, 20, 40 micrograms) it was possible to observe an increasing inhibitory and long-lasting effects of the evoked activity, with a significant dose-effect linear regression. The inhibitory responses, induced by histamine, probably by a hyperpolarization phenomenon that decreased excitatory postsynaptic potentials, were clues for the presence of a histaminergic pathway in parallel with and/or in connection with other adrenergic, gabaergic, serotoninergic and opioidoergic pathways that regulate the transmission and the modulation of algogenic electrophysiological messages.

The distribution of binding site for [125I]-eel-calcitonin (ECT) to rat central nervous system, studied by an autoradiographic technique, showed concentrations of binding in the diencephalon, the brain stem and the spinal cord. Large accumulations of grains were seen in the hypothalamus, the amygdala, in the fasciculus medialis prosencephali, in the fasciculus longitudinalis medialis, in the ventrolateral part of the periventricular gray matter, in the lemniscus medialis and in the raphe nuclei. The density of grains in the reticular formation and in the nucleus tractus spinalis nervi trigemini was more moderate. In the spinal cord, grains were scattered throughout the dorsal horns. Binding of the ligand was displaced equally by cold ECT and by salmon CT(sCT), indicating that both peptides bind to the same receptors. Human CT was much weaker than sCT in displacing [125I]-ECT binding. The administration of ECT into the brain ventricles of rats dose-dependently induced a significant and long-lasting enhancement of hot-plate latencies comparable with that obtained with sCT. The antinociceptive activity induced by ECT is compatible with the topographical distribution of binding sites for the peptide and is a further indication that fish CTs are active in the mammalian brain.

The effects of synthetic human calcitonin gene-related peptide (CGRP) on nociceptive response were evaluated in rats by two behavioral tests (tail-flick and hot-plate) and by electrophysiological recording of the firing of thalamic neurons evoked by peripheral noxious mechanical stimuli. CGRP was administered intracerebroventricularly (i.c.v.) and its effects were compared with that of salmon calcitonin (sCT). In the tail-flick test, CGRP (0.25, 2.5 and 5 micrograms/rat) dose-dependently increased response latencies, whereas sCT (0.125, 2.5, 5 and 10 micrograms/rat) did not. Conversely, in the hot-plate test CGRP was effective in enhancing response latencies only at the highest dose of 10 micrograms/rat, while sCT (0.125, 0.25 and 2.5 micrograms/rat) inhibited the hot-plate response dose-dependently. In electrophysiological studies, CGRP (2.5 micrograms/rat, i.c.v.) completely inhibited the evoked neuronal thalamic firing and the same dose of sCT induced only a partial reduction. Furthermore, the antinociceptive effects of CGRP in the tail-flick test and in the electrophysiological studies were not prevented by naloxone. These results demonstrate that central administration of CGRP is effective in inhibiting nociceptive responses and its action like that of sCT does not involve an opioid mechanism. The differences in the antinociceptive profiles of CGRP and sCT suggest that the inhibitory effects of these peptides may involve different neuronal pathways.