Ferenc László

Evidence that the effects of arginine-8-vasopressin (AVP) on pituitary corticotropin (ACTH) release are mediated by a novel type of receptor

Ovine corticotropin releasing factor (oCRF-41) and AVP act synergistically to stimulate pituitary ACTH secretion. In the present study we have investigated whether the effect of AVP, either in the presence or in the absence of oCRF-41 (0.5 nmol/l), could be blocked by V1 (pressor)-antagonists. Furthermore, oxytocin, and [1-deamino,8-D-arginine] vasopressin (dDAVP) were tested for their ability to release ACTH. All experiments were carried out in vitro, using segments of rat anterior pituitary glands. The V1-antagonist [1-deamino,penicillamine(o-methyl-tyrosine)]AVP inhibited ACTH release induced by AVP or AVP + oCRF-41. However, it also had some agonistic activity which was more pronounced in the presence of oCRF-41. An equally potent V1-antagonist, [1-beta-mercapto-beta, beta-cyclopentamethyleneproprionic acid (o-methyl-tyrosine)]AVP, failed to inhibit AVP-stimulated ACTH secretion, and also had weak agonist potency. The relatively selective V2 (antidiuretic)-agonist dDAVP was 20-30 fold less potent than AVP. Oxytocin, a weak V1- and V2-agonist was only 4-8 fold less potent than AVP. These data are compatible with the suggestion that AVP receptors on pituitary corticotrope cells are neither classical V1- nor V2-receptors.

Medium-term Results of Endoscopic Treatment of Common Bile Duct Strictures in Chronic Calcifying Pancreatitis with Increasing Numbers of Stents

Objectives The goal of this study was to evaluate our medium-term results on common bile duct stenting with increasing numbers of stents on strictures due to chronic calcifying pancreatitis. Background Common bile duct strictures frequently complicate the course of chronic calcifying pancreatitis. The effectiveness of endoscopic stenting to resolve definitely these strictures is still debated. Study Twenty-nine patients with common bile duct stricture due to chronic calcifying pancreatitis were stented and followed up. Biliary sphincterotomy, dilation of the stricture, and insertion of plastic biliary stents (7.5–10 F) were performed. Patients were scheduled for elective stent changing/restenting at 3-month intervals or any time when it was urgently indicated. Our basic intention was to insert the maximum possible number of stents to reach as large diameter as the stricture allowed. All stents were removed after the disappearance of common bile duct dilatation or left in place in cases of persisting strictures. Results Eighteen patients (60%) had complete radiologic and serologic recovery after a mean of 21.1 months overall stenting time and had a stent free follow-up period for a mean of 12.1 months without recurrence of stricture. Five patients (16%) still have stents in place after 26 months. Three patients (13%) required surgery. There were 3 deaths (10%): 1 for unrelated cause and 2 with septic shock of biliary origin. Conclusions Most chronic calcifying pancreatitis patients with common bile duct strictures respond to the increasing numbers of endoscopic stents, and remain stent free for medium term periods. Less patients (30%) does not benefit of biliary stenting, who are candidates for surgery.

Importance of cytokines, nitric oxide, and apoptosis in the pathological process of necrotizing pancreatitis in rats

Objectives: Ischemia-reperfusion injury can be involved in the pathophysiology of acute necrotizing pancreatitis. The aim of our study was to determine the production of cytokines, tumor necrosis factor (TNF) and interleukin-6 (IL-6), the activation of the inducible nitric oxide synthase (iNOS), and the development of apoptosis during this pathologic process. Methods: Acute pancreatitis was produced in male Wistar rats by injection of 200 μL of 6% taurocholic acid into the main pancreatic duct in combination with the temporary (15 minutes) occlusion of the inferior splenic artery. Six and 24 hours later, the histologic damage was evaluated, and serum amylase, TNF, IL-6 levels, and iNOS and apoptotic activity from pancreatic and pulmonary tissues were determined. Results: Twenty-four hours after the induction of pancreatitis, the mortality rate was 63%. During this period, the serum TNF and IL-6 levels were permanently high (50 ± 12 and 58 ± 10 U/mL and 7083 ± 1610 and 6790 ± 850 U/mL after 6 and 24 hours, respectively). The iNOS activity showed an increasing tendency in the pancreas, and a decrease following an initial increase in the lung (from 4.2 ± 0.6 to 5 ± 0.4 and from 6.8 ± 0.6 to 3.8 ± 0.5 pmol/min/mg protein after 6 and 24 hours, respectively). Histologic examination confirmed severe necrotizing pancreatitis. In the pancreas, the apoptotic activity increased significantly (from 4 ± 4 to 27 ± 5/mm2 at 6 and 24 hours), while in the lungs, following an initial increase it declined during the course of necrotizing pancreatitis (from 49 ± 4 to 11 ± 6/mm2 at 6 and 24 hours). Conclusion: Our results indicate that intraductal taurocholic acid and ischemia-reperfusion provokes severe acute necrotizing pancreatitis with a high mortality rate and leads to systemic inflammatory reaction, which appears to be the consequence of the activation of the cytokine cascade and iNOS. The degree of NO overproduction by iNOS corresponds with the apoptotic process in the pancreas and the lung.

The role of nitric oxide in edema formation in L-arginine-induced acute pancreatitis.

Introduction Nitric oxide (NO) has been implicated in the regulation of the pancreatic circulation, the promotion of the capillary integrity, and the inhibition of leukocyte adhesion. Aims To investigate the rates of changes in the pancreatic constitutive NO synthase (cNOS) and inducible NOS (iNOS) activities and the role of NO in the vascular permeability changes during the development of L-arginine (Arg)–induced acute pancreatitis. Methodology Acute pancreatitis was induced in male Wistar rats by injecting 250 mg/100 g body weight of Arg i.p. twice at an interval of 1 hour, as a 20% solution in 0.15 M NaCl (group I). The control rats received the same quantity of glycine (group II). In group III, 30 mg/kg NG-nitro-L-arginine methyl ester (L-NAME) was injected i.p. 19 hours after the first Arg injection. The rats were killed at 6, 12, 24, or 48 hours following Arg administration, and the plasma amylase concentration and the pancreatic weight/body weight (pw/bw) ratios were evaluated. NOS activity was determined via the conversion of L-14C-Arg monohydrochloride to 14C-citrulline. The vascular permeability was examined by means of the extravasation of Evans blue dye (20 mg/kg bw) into the pancreatic tissue. Results The serum amylase level was already increased at 6 hours in group I animals, peaked at 12 hours after the Arg injection (11.800 ± 590 versus 6.618 ± 252 U/L in group II), and returned to the control level at 48 hours. The pw/bw ratio peaked at 24 hours in group I (6.63 ± 0.52 versus 4.02 ± 0.22 mg/g in group II) and returned to the control level at 48 hours. The cNOS activity was depleted at 6 hours in group I (0.02 ± 0.003 versus 0.23 ± 0.02 pmol/min/mg protein in group II); it then gradually increased to a level significantly higher than that in group II and decreased thereafter (0.45 ± 0.03 and 0.13 ± 0.01 pmol/min/mg protein at 24 and 48 hours). The iNOS activity was significantly increased at 24 and 48 hours versus that in group II (0.15 ± 0.05 and 0.07 ± 0.01 versus 0.04 ± 0.01 pmol/min/mg protein). The pancreatic concentration of Evans blue dye was significantly higher in group I than in group II (138.59 ± 11.04 versus 43.57 ± 2.67 (g/dry weight). Treatment with L-NAME significantly reduced the amylase activity, pw/bw, Evans blue concentration, and cNOS activity of the pancreas but did not exert any beneficial effect on the histologic score at 24 hours after the onset of pancreatitis, as compared with those values in group I (6.528 ± 673 U/L, 4.56 ± 0.65 mg/g, 86.84 ± 3.9 (g/dry weight, 0.14 ± 0.04 pmol/min/mg protein). Conclusion Endogenous NO is involved in the formation of pancreatic edema in Arg-induced acute pancreatitis by increasing the vascular permeability and protein extravasation. L-NAME treatment decreased the cNOS activity and edema formation but did not prevent the histologic damage in Arg-induced acute pancreatitis.

Raloxifene, an oestrogen–receptor modulator, prevents decreased constitutive nitric oxide and vasoconstriction in ovariectomized rats

Administration of graded doses of [Arg(8)]vasopressin (0.06-0.18 microg kg(-1), i.v.) induced a dose-dependent increase in arterial blood pressure in the catecholamine-depleted (phentolamine; 10 mg kg(-1), i.p.) intact and ovariectomized female rat, with the elevation of blood pressure more marked following ovariectomy. In addition, ovariectomy caused the down-regulation of aortic Ca(2+)-dependent constitutive nitric oxide synthase (assessed by the citrulline assay). The down-regulation of the Ca(2+)-dependent constitutive nitric oxide synthase and augmentation of vasopressin-induced blood pressure responses were prevented by the therapy (1 month, p.o.) with the selective oestrogen receptor modulator, raloxifene (0.3-1.0 mg kg(-1) day(-1)), or with 17beta-oestradiol (0.3 mg kg(-1) day(-1)) in ovariectomized rats. Thus, oestrogen deficiency down-regulates vascular constitutive nitric oxide synthase, which appears to be involved in the increased sensitivity of the vasculature to vasopressin, since both effects can be reversed by the exogenous administration of the natural oestrogen 17beta-oestradiol or the selective oestrogen-receptor modulator raloxifene.

Site-specific lesion formation, inflammation and inducible nitric oxide synthase expression by indomethacin in the rat intestine

The involvement of nitric oxide (NO) formed by the inducible isoform of NO synthase (iNOS) has been investigated in the development of rat intestinal lesions following indomethacin administration. Over a 72-h period, indomethacin (10 mg kg(-1), s.c.) provoked a time-dependent increase in expression of iNOS (assessed by the conversion of radiolabelled L-arginine to citrulline) and enhancement of vascular leakage of radiolabelled human serum albumin in the jejunum which commenced 18 h after indomethacin. Similar effects were not observed in the ileum, colon or caecum. In addition, macroscopic lesions were detectable and myeloperoxidase activity (an index of neutrophil recruitment) were increased in the rat jejunum 18-24 h after indomethacin, but remained at basal levels in the ileum and colon. These findings suggest that indomethacin provokes a site-selective expression of iNOS in the rat jejunum which correlates with lesion formation and vascular leakage, whereas both the ileum and colon are spared.

Autoimmune pancreatitis associated with immune-mediated inflammation of the papilla of Vater: report on two cases.

Autoimmune pancreatitis (AIP) is defined histologically by periductal and interacinar lymphocytic infiltration. Immunohistochemically, the majority of these lymphocytes are identified as T cells. Epithelial HLA-DR antigen expression was also described as a marker of autoimmunity in this type of chronic pancreatitis. We report 2 cases, a 56-year-old man and a 29-year-old woman, with AIP associated with immune-mediated inflammation of the main duodenal papilla (MDP). Serologically, antinuclear antibody positivity was detected in the male patient. The female patient, treated medically for ulcerative proctitis, had no serological evidence of autoimmune disease. Macroscopic papillitis was present only in the male patient, and endoscopic biopsy samples were taken from this swollen MDP. Since we could not exclude malignancy, a pancreatic head resection was performed in both patients. The histologic and immunohistochemical studies of the resected specimens showed periductal T-lymphocytic infiltration in the pancreatic and papillary tissues. Furthermore, HLA-DR-antigen expression was also demonstrated in epithelial cells of the pancreas and MDP. The immunohistological features of endoscopic biopsy samples from the swollen MDP were identical as in the surgically resected specimens. Immune-mediated inflammation of the MDP may be associated with AIP.

Estrogen-mediated up-regulation of the Ca-dependent constitutive nitric oxide synthase in the rat aorta and heart.

The role of endogenous estrogens has been studied in the regulation of the Ca-dependent constitutive nitric oxide synthase (cNOS) enzyme activity in aortic and cardiac tissues of the rat. The activity of cNOS enzyme was measured by the citrulline assay in the abdominal aorta and in the left ventricle of the heart obtained from male, sham-operated female and ovariectomized female Wistar rats. Estrogen replacement therapy (17-beta-estradiol, 20-100 microg/kg/day, s.c.) has been performed in ovariectomized rats over two weeks. We found that cNOS activity was higher in the aorta and heart of female rats compared to males. Ovariectomy decreased cNOS activity in both tissues to that level what could be observed in males. Estrogen supplementation caused a dose-dependent elevation of cNOS enzyme activity in cardiac and aortic tissues, where the higher dose (100 microg) completely restored cNOS enzyme activity to the levels found in females. We concluded that endogenous estrogens up-regulate the activity of the cNOS isoenzymes in the rat aorta and heart.

Effects of testosterone on the rat renal medullary vasopressin receptor concentration and the antidiuretic response

The renal concentrating ability declines with age in humans and animals. Studies suggest that the concentrating defect is due to a decrease in renal vasopressin sensitivity. With ageing, expression of the renal vasopressin V2 receptor in rat is impaired; the normal receptor expression is restored by testosterone treatment. The effect of testosterone on the renal sensitivity to vasopressin was investigated in young rats. Male rats after orchidectomy and chronic antiandrogen cyproterone acetate treatment, and female rats after chronic testosterone phenylpropionate treatment, were used. The plasma arginine-vasopressin (AVP) and testosterone concentrations, and the antidiuretic responses to AVP and the V2 agonist deamino-[8-D-arginine]-vasopressin (dDAVP) after volume loading were measured, and the renal [3H]AVP binding density was determined. The plasma AVP level decreased slightly, but not significantly, in male rats after orchidectomy and cyproterone acetate treatment, but did not alter in female rats after testosterone treatment. The AVP and dDAVP sensitivities decreased in male rats after orchidectomy and cyproterone acetate administration, and increased in female rats treated with testosterone, as compared with the animals with a normal gonadal function. [3H]AVP binding to the renal inner medullary membranes was decreased following orchidectomy or antiandrogen treatment in male rats, and increased in testosterone-treated female rats. The results suggest that testosterone may play a physiological role in maintenance of the V2 vasopressin receptor expression and hence in the normal urinary concentrating ability in rat.

Protective effect of ischaemic preconditioning on ischaemia/reperfusion-induced microvascular obstruction determined by on-line measurements of coronary pressure and blood flow in pigs

We investigated the protective effect of ischaemic preconditioning (IP) on the maintenance of coronary patency using on-line measurements of coronary pressures and blood flow in a closed-chest reperfused acute myocardial infarction (MI) model in pigs. Catheter-based 90-min occlusion followed by 60-min reperfusion of the left anterior descending coronary artery (LAD) was performed in anesthetised pigs (MI group). IP was applied (IP group) through two cycles of 5-min occlusion and 5-min reperfusion of the LAD before MI induction. Coronary patency was determined by measurements of coronary wedge pressure, collateral fractional flow reserve (FFRcoll), collateral pressure index (CPI) and absolute coronary blood flow (CBF). Inducible and constitutive nitric oxide synthase (iNOS/cNOS) activities and expressions were determined in the myocardium. Plasma levels of myeloperoxidase (MPO, index of activated leukocytes) and mean platelet volume (MPV, index of activated platelets) were measured. IP resulted in significantly lower levels of MPO (0.52 ± 0.19 vs. 1.05 ± 0.24 U/l, p<0.001) and MPV (9.1 ± 0.6 vs. 9.6 ± 1.0 fl, p=0.04), higher FFRcoll (0.17 ± 0.05 vs. 0.04 ± 0.05, p<0.001), CPI (0.13 ± 0.05 vs. 0.02 ± 0.05, p<0.001) and CBF (70.7 ± 4.2 vs. 50.8 ± 4.8 m/min, p<0.001) post-reperfusion as compared with the MI group. IP resulted in significantly higher cNOS activity and eNOS expression. Significant negative correlation was found between MPO and measures of coronary patency (FFRcoll, CPI and CBF) and cNOS activity. Moreover, cNOS activity correlated significantly with FFRcoll, CPI and CBF. In conclusion, IP attenuates the release of MPO and platelet activation, thereby contributing to the maintenance of vessel patency at microvascular level after reperfusion of the infarct-related artery.