Interfascicular matrix-mediated transverse deformation and sliding of discontinuous tendon subcomponents control the viscoelasticity and failure of tendons.

In the present article, we investigated the sliding of discontinuous tendon subcomponents and the variation of nonhomogeneous deformation in the human Achilles tendon (AT) over time using uniaxial tensile and relaxation tests. The deformation and the resulting strain distribution under uniaxial tension are examined using a vision-based 3-D digital image correlation (DIC) system, which allows estimation of the strain field in the axial and lateral directions. Relaxation test under B-mode ultrasound imaging with the use of DIC method provides information about the local strain variation over time in the axial and anteroposterior directions. The observed nonhomogeneous deformation, a result from the twisted structure of the tendon, shows both compressive and tensile transverse strains that can generate interfascicular matrix (IFM) failure and initiate water accumulation in the course of tendinopathy. Moreover, using B-mode elastography with the DIC method, we have observed areas of low stiffness when the strain values exceed the strength limits, and this could correspond to IFM carrying the load between discontinuous tendon subcomponents. Thus, IFM carrying complex multiscale stresses may be responsible for the strength and viscoelastic properties of the AT. The results presented here reveal a new pathomechanism of AT failure. This could be useful in further studies on tendinopathy as well as effective planning of the AT therapy.

Ultrasonographic Differentiation of Lateral Elbow Pain.

Lateral elbow pain is often attributed to degenerative or posttraumatic impairment of the common extensor tendon. Ultrasonography assesses the soft tissue structures of the lateral elbow, allowing the differentiation between various underlying processes, including angiofibroblastic degeneration, hyaline degeneration, and inflammation, and exclusion of other possible causes of pain such as posterior interosseous and lateral antebrachial nerve compression. Furthermore, the real-time imaging nature of ultrasonography enables the detection of impingement of the lateral synovial fold, degenerative changes in the elbow recess, and elbow posterolateral instability during dynamic maneuvers. Ultrasonography is widely accessible and well tolerated by patients, making it a perfect method for establishing an initial diagnosis and monitoring the healing process. This review describes the possible causes of lateral elbow pain and their ultrasonographic differentiation.

Effects of peripherally and centrally applied ghrelin in the pathogenesis of ischemia-reperfusion induced injury of the small intestine.

Ghrelin is an important hormone involved in the control of the human appetite center. Recently, protective properties of this hormone have been recognized in various models of impairment of the gastric mucosa, including stress, ischemia and reperfusion (I/R). Ghrelin is predominantly secreted by the gastric mucosa of stomach, but there are other sources of ghrelin, for example in the hypothalamus and various parts of the central nervous system (CNS) that should be taken into consideration. This hormone exerts biological effects via the activation of growth hormone secretagogue receptor (GHSR), the presence of which was confirmed in different parts of the gastrointestinal (GI) tract and midbrain structures. Although substantial evidence of the divergent biological effects of ghrelin and the mechanism of its action has been emphasized, the precise mechanisms of ghrelin which affords GI protection is still unclear. Particularly, there is a sparse amount of evidence concerning its action on the GI system. The major aim of the present study was to evaluate the importance of peripherally and centrally administered ghrelin at different times of the ischemia and reperfusion (I/R period in the modulation of resistance of the intestinal mucosa to the injury induced by ischemia and subsequent reperfusion. Secondly, we wanted to evaluate the possible mechanism of the action of ghrelin with a particular focus on its influence on the intestinal blood flow. Male Wistar rats were divided into 4 series (A-D) of the experimental groups (n=7). In series A the importance of peripherally administered ghrelin at different time of I/R period was studied. In series B the importance of centrally administered ghrelin at different time of I/R period was evaluated. In series C and D, the mechanisms of peripherally and centrally administered hormone were examined, respectively. Two models of the I/R period were selected: short lasting (30/60 min) and long lasting (60/120 min). The following drugs were used: ghrelin (50 µg/kg i.p. or 1 nmol in 10 µl i.c.v.), 6 hydroxy dopamine (50 mg/kg i.p.), nadolol (0.5 mg/kg i.p.), calcitonin gene related peptide fragment (CGRP(8-37), 100 µg /kg i.p.), capsaicin (5-10 mg/100 ml solution s.c.). The mesenteric blood flow (MBF-ml/min), the intestinal microcirculatory blood flow (LDBF-PU), the arterio-venous oxygen difference (AVO(2)-ml/O(2)/100 ml blood), and the intestinal oxygen uptake (VO(2)) in ml O(2)/min were measured. Mucosal impairment was assessed planimetrically with the use of a digital photo analyzer (LA) and histologically with the use of the six-point Park/Chiu scale. Peripheral administration of ghrelin evoked marked increase of MBF and LDBF by 42% and 48%, respectively, with significant reduction of LA by 38%. When ghrelin was administered at the beginning of the reperfusion period during the short I/R period or prior to the long lasting I/R period, the vascular reactions and protective effects were reduced, but not completely abolished. The central administration of ghrelin before the short I/R period significantly increased the MBF and LDBF by about 32% and 35%, respectively, as well as LA reduction by about 20% in comparison to the control group. However, when ghrelin was administered prior to the long I/R period or after the onset of completed ischemia, neither vascular nor protective effects were noticed. Sensory denervation and the blockade of the CGRP1 receptors totally blocked the protective and hyperemic effects of the peripherally administered ghrelin. Selective blockade of the adrenergic system or blunting of the vagal nerves (vagotomy) significantly but not totally eliminated the effects of centrally applied ghrelin, which were abolished when both adrenergic and parasympathetic pathways were ablated. These results indicate that ghrelin applied centrally or peripherally markedly increases resistance of the intestinal tissue during the I/R period induced mucosal and hyperemic impairment evoked by I/R. Ghrelin is an important mediator of the increase in the intestinal microcirculation and elevation of the intestinal metabolism, which seems to be, at least in part, responsible for the observed protection of the intestine subjected to I/R. Impairment of this microvasculature response due to I/R seems to be responsible for a markedly observed weaker effect of ghrelin when this hormone was administered after the ischemic period. The lack of a protective effect observed after central administration of this peptide against a long lasting I/R period is probably due to damage of neural pathways caused by I/R. Finally, the peripheral activity of ghrelin in the intestine is mediated by the sensory neurons with a prominent role of CGRP released from their endings. However, this peripheral action of ghrelin depends upon the proper functioning of both the sympathetic and parasympathetic system.

The influence of µ-opioid receptor agonist and antagonist peptides on peripheral blood mononuclear cells (PBMCs).

Milk is one of the main source of biologically-active peptides that may function as regulatory substances called food hormones. After passing the gut-blood barrier, the µ-opioid receptor agonist and antagonist peptides may become the new factors influencing various functions of the human organism. The aim of the conducted research was to determine the influence of µ-opioid receptor agonist peptides: human and bovine ß-casomorphin-7 (h/bBCM-7) and antagonistic peptides: casoxin-6 and- D (CXN-6/D) on proliferation and cytokine secretion of human peripheral blood mononuclear cells (PBMCs). The PBMCs proliferation was measured by the use of the BrdU test, which assesses the DNA synthesis activity and the WST-1 test which assesses the activity of mitochondrial dehydrogenase enzymes. The influence of all the investigated peptides on secretion of IL-4, IL-8, IL-13 and IFN-γ was determined by the use of the ELISA tests. Incubating the cells with the peptides has not caused any changes to their enzymatic activity, which has been proved by a WST-1 test. When using a BrdU test, however, it has been observed that there appear changes to proliferation of PBMCs correlated to amounts of bromodeoxyuridine incorporated into the cellular DNA. Moreover, changes to secretion of IL-4 and IL-13 by the cells under the influence of agonists were detected, as well as changes to secretion of IFN-gamma under the influence of all the examined substances. The obtained results provide information on immunomodulatory effects of food-derived opioid peptides, which may be of clinical significance especially in the case of allergic diseases in newborns.

Histamine H3 receptors modulate reactive hyperemia in rat gut.

Reactive hyperemia (RH) is an abrupt blood flow increase following release from mechanical occlusion of an artery, with restoration of intra-arterial pressure. The mechanism of this postocclusion increase in blood flow in the gut is multifactorial. Relaxation of intestinal resistance vessels, observed during RH, may involve myogenic, metabolic, hormonal and neurogenic factors. Evidence exists that histamine is an important endogenous mediator of various functions of the gut, including blood flow. The vascular effects of histamine in the intestinal circulation are due its agonistic action on histamine H1, H2 and H3 receptors. In the present study the hypothesis was tested that peripheral histamine H3 receptors are involved in the mediation of RH in the intestinal circulation. In anesthetized rats, anterior mesenteric artery blood flow (MBF) was determined with ultrasonic Doppler flowmeter, and arterial pressure (AP) was determined with a transducer. The increase in the volume of blood accumulating during RH (RH-volume), the peak increase of arterial blood flow (RH-peak response) and the duration of the hyperemia (RH-duration) were used to quantify RH after occluding the anterior mesenteric artery for 30, 60 and 120 s. Hyperemia parameters were determined before and after administration of the selective histamine H3 receptor antagonist clobenpropit. Pretreatment with clobenpropit was without any effect on control MBF and AP but significantly reduced most of RH responses. These findings support the hypothesis that histamine H3 receptors do not play any role in the control of intestinal vasculature at basal conditions but these receptors participate in the intestinal hyperemic reaction in response to complete temporal intestinal ischemia.

Involvement of central and peripheral histamine H(3) receptors in the control of the vascular tone and oxygen uptake in the mesenteric circulation of the rat.

Data concerning cardiovascular effects of peripherally and centrally located histamine H(3) receptor stimulation are contradictory, and despite excessive studies their role in the control of the cardiovascular function have not been cleared yet. Effect of histamine H(3) receptors activation have been attributed to modulation of sympathetic system activity but exact role of peripherally and centrally located histamine H(3) receptors stimulation in the modulation of vascular tone of the mesentery and intestinal metabolism remains unexplored. Aim of the present study was to evaluate the role of centrally and peripherally located histamine H(3) receptors in the modulation of vascular tone of the mesentery and metabolic activity of intestinal tissue. In anesthetized rats total mesenteric blood flow (MBF), mucosal intestinal blood flow (LDBF), intestinal oxygen uptake (VO(2)) and arterial pressure (AP) were determined. Intestinal arterial conductance (C) was also calculated. Administration of the selective histamine H(3) receptor agonist imetit (10 micromol/kg i.a) evoked marked changes in hemodynamic and metabolic parameters; MBF, LDBF, C and VO(2) were significantly increased, whereas AP was significantly decreased. Pretreatment with histamine H(3) receptor antagonist clobenpropit (4 micromol/kg i.a.) abolished imetit-induced circulatory and oxygen uptake responses. Clobenpropit (4 micromol/kg i.a.) alone failed to affect the MBF, LDBF, AP, C and VO(2) values. Central administration of imetit (0.1 micromol i.c.v.) markedly increased AP and decreased MBF, LDBF, C and VO(2). Pretreatment with histamine H(3) receptor antagonist clobenpropit (0,4 micromol i.c.v.) diminished circulatory and metabolic responses to centrally injected imetit. Central histamine H(3) receptors blockade by clobenpropit evoked no significant changes in the mesenteric arterial and mucosal microcirculatory blood flow, intestinal metabolism and mean arterial pressure. We conclude that, peripheral histamine H(3) receptors when stimulated decreases vasoconstrictory tone of the mesenteric artery and precapillary structures and evokes increase of intestinal oxygen uptake. This might be in part due to inhibition of sympathetic postganglionic fibers vasopressor activity. Central histamine H(3) receptor stimulation activates vasoconstrictory sympathetic adrenergic system with possible involvement of other, presumably non-histaminergic receptors system. At basal conditions neither central nor peripheral histamine H(3) receptors are involved in the control of mesenteric macro- and microcirculation and intestinal oxygen consumption.

Role of calcitonin gene related peptide in the modulation of intestinal circulatory, metabolic, and myoelectric activity during ischemia/reperfusion.

Calcitonin gene related peptide (CGRP) is widely distributed in the myenteric neurons along GI tract. Biological effects of CGRP on gastrointestinal tract include increase in the intestinal blood flow, relaxation of the smoth muscle and slight increase in the slow wave amplitude (SWA) with no effect on frequency (SWF) of intestinal myoelectric activity (IMA). The aim of this study was to evaluate the possible protective effects of endo- and exogenous CGRP against ischemia/reperfusion (I/R) induced bowel injury in rats. Experiments were performed on 30 fasted anesthetized Wistar rats. Systemic arterial blood pressure (AP), mesenteric blood flow (MBF) and microcirculatory intestinal blood flow (LDBF) were measured. Oxygen consumption (VO2) was estimated from MBF and mesenteric AVO2 difference. IMA was recorded by 4 monopolar electrodes in proximal jejunum and analyzed using computer program with Fourrier analysis of SWF. Control ischemia induced by 30 min total occlusion of anterior mesenteric artery (AMA) reduced SWA by 25+/-5% and SWF by 24+/-4%. At the end of 60 minute reperfusion period SWA and SWF values were restored to control values but SWF showed instability. At the 15th minute of reperfusion period MBF, LDBF and VO2 increased to 109+/-6, 119+/-11 and 120+/-7% of control values respectively. Infusion of exogenous CGRP (0,16 microg/kg/min i.a.) increased MBF, LDBF and VO2 by 26+/-6, 31+/-9 and 20+/-4% respectively in comparison to control values. In the same experimental group SWA increase of 14% was observed with not significant changes in SWF. In the group where CGRP was administrated before and during 30 min period of intestinal ischemia MBF, LDBF and VO2 values at 15th minute of reperfusion were significantly higher by 24+/-6, 32+/-7 and 17+/-5% respectively in comparison to the values observed in the control reperfusion. In that group SWA values were restored to preocclusion values at 15th minute of reperfusion yet and SWF showed much more stability. Infusion of CGRP receptor antagonist (CGRP 8-37) reduced MBF, LDBF and VO2 by 12+/-7, 14+/-8 and 11+/-6% respectively (differences not significant versus control). In I/R group when CGRP 8-37 was given hemodynamic parameters (during reperfusion) were significantly lower and IMA parameters were not restored to preocclusion values. We conclude, that endogenous and exogenous CGRP attenuate circulatory parameters of the small intestine during ischemia and reperfusion. A direct correlation exists between hemodynamic, metabolic and myoelectric effects of CGRP.