Naloxone inhibits arginine vasotocin- (AVT) induced prolactin release in urethane-anesthetized male rats in vivo

Arginine vasotocin (AVT) (1 microgram) elicited a two-fold increase in serum prolactin (Prl) levels 10 min following its i.v. injection into urethane-anesthetized adult male rats. At 20 min after AVT administration serum Prl concentrations had essentially returned to preinjection levels. Prior treatment of the animals with 0.2 mg/kg body weight of naloxone (Nal), an opiate antagonist, completely blocked the Prl response to a single injection of AVT. Nal itself did not alter the titers of Prl at any time point. The results suggest that the in vivo Prl-releasing effect of AVT is mediated via an interaction with opiate receptors.     

Indomethacin enhances in vitro histamine release induced by anti-IgE and Ca-ionophore but inhibits C5a-induced release reactions from basophils of atopics and normals

Preincubation of peripheral leukocytes from atopics and normals significantly enhanced histamine release induced by anti-IgE and calcium ionophore. On the other hand, there was a significant inhibition (ca. 40%) of C5a-induced histamine release by indomethacin both in atopics and controls. In the group of patients with atopic eczema, anti-IgE-induced histamine release was significantly higher than in controls both without and with indomethacin.     

Dimethyl sulfoxide inhibits histamine release induced by various chemicals

Dimethyl sulfoxide was found to inhibit histamine release induced by compound 48/80 at concentrations ranging from 0.6 to 10%. At higher concentrations (20 and 40%) the substance caused histamine release by itself. Heat inactivation at 50°C of the mast cells did not prevent this release, suggesting a lytic mechanism for this action and this was further proved by the trypan blue dye exclusion test. Dimethyl sulfoxide was also active in inhibiting histamine release induced by other polyamines such as bradykinin, polymyxin B and protamine, by concanavalin A and dextran, by ionophore A23187 and by three anthracyclines, doxorubicin, daunomycin and epirubicin. In contrast, the substance did not inhibit histamine release induced by a monoamine, chlorpromazine and by the detergent Triton X-100.     

Granulocyte-macrophage colony-stimulating factor enhances basophil histamine release induced by non-IgE-dependent stimulators

Some cytokines are known to affect IgE-mediated basophil histamine release. The effect of the cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF) on human basophil and masct cell histamine release was studies further. Blood leukocytes with approximately 2% basophils from 9 healthy individuals were incubated with recombinant human GM-CSF (0.3–30 U/ml) in combination with A23187 (10^–7–10^–6 M) or washedStaphylococcus aureus whole bacteria (0.3–2.5 mg/ml). Histamine release was measured spectrofluorometrically. GM-CSF in itself did not induce histamine release. The addition of GM-CSF to cells stimulated with A 23187 caused a dose-dependent enhancement amounting to mean 70% at 3 U/ml and mean 170% at 30 U/ml (P<0.05). GM-CSF enhanced the bacteria-induced histamine release by 30% at U/ml and by 65% at 3 U/ml (P<0.05). The enhancement did not depend on cell-bound IgE or LPS contamination. In preliminary mast cell experiments with lung tissue we did not find an enancing effect of GM-CSF on IgE-mediated histamine release.     

Virus enhances IgE- and non-IgE-dependent histamine release induced by bacteria and other stimulators

Histamine release from human basophil leukocytes was triggered byStaph. aureus, Salmonella enteriditis, non-haemolytic streptococci, orE. coli. Influenza A virus was found to enhance the mediator release and the effect was caused by synergism, since the virus did not induce release of histamineper se. This potentiating effect of the virus was seen both when the bacteria-induced histamine release was IgE-dependent (i.e. patient sensitized to the bacterium) and when the bacterium caused mediator release by a non-immunological mechanism independent of IgE (putative sugar-lectin mediated). Histamine release induced by anti-IgE and calcium ionophore or agarose-beads was also enhanced in the presence of the virus. These findings indicate that influenza A virus potentiates both IgE-and non-IgE-mediated histamine release induced by bacteria and other stimulators.     

The somatostatin receptor (sst1) modulates the release of somatostatin in rat retina

The aim of this study was to examine the ability of somatostatin receptor (sst(1)) to regulate the release of somatostatin in rat retina. Immunohistochemistry studies were performed to locate the somatostatin neurons, and radioligand binding to ascertain the presence of sst(1). The neuronal release of somatostatin was examined ex vivo in rat retinal explants in the presence of KCl (50 and 100 mM), and absence of Ca(++) (EGTA; 10 mM). Somatostatin levels, quantified by radioimmunoassay, were increased in the presence of KCl (100 mM, 151%) and attenuated in the absence of Ca(++) (31%). CH275 (sst(1) agonist) reduced the somatostatin levels in a concentration-dependent manner (10(-5)-10(-7) M), and this effect was reversed by NVP-SRA 880 (sst(1) antagonist;10(-5) M). MK678 (sst(2) agonist; 10(-5) M) had no effect. These data suggest an autoreceptor role for sst(1) in retina.     

Enhancement of insulin and glucagon secretion by arginine after hepatic vagotomy

The hepatic vagus nerve consists of mostly afferent fibers in the rat, and is a major afferent pathway between the liver and the medulla. The present study was carried out to examine the role of the hepatic branch of the vagus nerve in secretion of insulin and glucagon after intraperitoneal injection of arginine (1 g/kg body wt.) in rats. Measurements were made one week after section of this branch. Intraperitoneal arginine enhanced both plasma insulin and glucagon concentrations; more in hepatic-vagotomized than in sham-vagotomized rats. The results suggest that inhibition of the secretion of insulin and glucagon after arginine stimulation is mediated by the hepatic branch of the vagus nerve. The existence of 'sensors' in the liver for arginine, or its derivatives, is proposed as an explanation for the inhibition of the secretion of insulin and glucagon by the hepatic vagus nerve.     

Anti-pokeweed mitogen antiserum inhibits and enhances blastogenesis of mononuclear cells induced by pokeweed mitogen

The interaction between pokeweed mitogen (PWM) and peripheral blood mononuclear cells (PBMC) was investigated using rabbit anti-PWM antiserum (anti-PWM) and¹²⁵ I-PWM. Incubation of PBMC with PWM in the presence of anti-PWM resulted in an inhibition of the mitogenic effect of PWM. Anti-PWM predominantly blocked the interaction of PWM with monocytes, which is essential for optimal stimulation of lymphoid cells with PWM.Addition of anti-PWM to PBMC at several time-points after incubation with PWM showed inhibition of mitogenic activity when anti-PWM was added within 8 hours. However, enhancement of PWM-induced blast cell formation was found when anti-PWM was added after 48 hours. Further analysis revealed that the inhibition of PWM stimulation was mediated by the F(ab)₂ part of anti-PWM IgG. On the other hand F(ab)₂-anti-PWM was not able to enhance the effect of PWM.Incubation of PBMC with¹²⁵I-PWM and anti-PWM simultaneously, decreased the binding of PWM to both lymphocytes and monocytes. In contrast, addition of anti-PWM 48 hours after the incubation of PBMC with PWM resulted in an increased binding of PWM to monocytes.These results show that anti-PWM can moculate the lymphocyte reaction to PWM and suggest two possible mechanisms by which PWM can stimulate PBMC, both of which are dependent on the interaction of PWM with monocytes.     

Oestradiol enhances in vitro the histamine release induced by embryonic histamine-releasing factor (EHRF) from uterine mast cells.

The relationship between maternal hormones and factors secreted by the implanting embryo is still controversial. We have analysed the in-vitro effect of oestradiol and human embryo-derived histamine-releasing factor (EHRF) on histamine release from rat uterine mast cells. Rat uterine mast cells which were preincubated with oestradiol and then challenged with human EHRF gave histamine release values two- to threefold higher than those without preincubation. The enhancement observed was time- and temperature-dependent. A similar enhancement was obtained with human sensitized basophils but not with rat peritoneal mast cells. Oestradiol, used as a direct challenge, did not induce any histamine release from either rat uterine or peritoneal mast cells, or from human sensitized basophils. Oestradiol preincubation also enhanced the histamine release induced by anti-IgE but did not enhance the histamine release induced by substance P or compound 48/80, two secretagogues that are not mediated by IgE. Moreover, uterine fragments derived from rats at various oestrus phases, with different amounts of endogenous oestrogen, were challenged in vitro with EHRF. The release of histamine by mast cells was higher at the proestrus and preimplantation phases than at dioestrus. All these findings suggest that the interaction of oestradiol with rat uterine mast cells was capable of enhancing in vitro the histamine releasing effect of EHRF.     

Centrally administered galanin inhibits osmotically stimulated arginine vasopressin release in conscious rats.

The effect of centrally administered galanin on arginine vasopressin (AVP) release was investigated in conscious rats. Intracerebroventricular injection of porcine galanin suppressed hypertonic saline-induced increase in plasma AVP in a dose-dependent manner (12.5-100 pmol/rat) at 10 min after the injection. Pretreatment with subcutaneous injection of naloxone (1 mg/100 g b.wt.) partially blocked the galanin-induced effect on plasma AVP. These results suggest that central galanin inhibits osmotically stimulated AVP release and endogenous opioids are, at least in part, involved in the mechanism.     

NG-L monomethyl arginine (L-NMMA) enhances bile canalicular contractions in cultured rat hepatocytes

Time lapse cinematographic analysis revealed that the frequency of canalicular contractions in primary monolayer-cultured hepatocytes (couplets or triplets) isolated from rat livers increased in the presence of monolayer-sinusoidal endothelial cells by the N^G-L monomethyl arginine (L-NMMA)-treatment as compared to that in a control. Transmission electron microscopy revealed an enhanced vesicular transport to the canalicular lumens at the contracted bile canaliculi in the L-NMMA-treated couplets or triplets.     

A perifusion method for examining arginine vasopressin (AVP) release from hypothalamo-neurohypophyseal system

A perifusion method has been developed using rat hypothalamo-neurohypophyseal system (HNS) or neural lobe to investigate the control mechanism of arginine vasopressin (AVP) release. A specific radioimmunoassay (RIA) for AVP was developed to measure AVP in perifusion medium employing anti-AVP serum which was obtained by immunizing rabbits. At a final dilution of 1/12,000, the antiserum showed less than 0.66 and 0.01% cross reactivity with lysine-vasopressin and oxytocin, respectively. But it did not cross reacted with other peptide hormones. The lowest detectable level of vasopressin was 0.5 pg/tube. The intra-assay coefficient of variation averaged 10.4%. The dilution curve of perifused medium was well paralled to the standard curve of AVP assay. AVP release from HNS or neural lobe gradually declined to the stable level in 90-120 min after the initiation of perifusion. Good repeatability of the AVP release from neural lobe was recognized by repeated stimulation with 10 min perifusion of 60 mM KCl at every 60 min. HNS released AVP in dose related manner to the osmotic challenge of sodium or glucose, and AVP release was stimulated from HNS by prostaglandin E2, but not by dopamine. These results show that the perifusion methods using AVP-RIA is a useful method to examine the AVP release from HNS or neural lobe.     

Endogenous hyperglycemia restores insulin release impaired by somatostatin analogue

These studies assessed the ability of des-Asn5-[D-Trp8-D-Ser13]-somatostatin (d-ATS-SS) to selectively inhibit insulin release and produce a hyperglycemia sufficient to compensate for the original impairment. d-ATS-SS at 0.017 micrograms/min inhibited basal insulin output (delta = -38 +/- 6%, P less than 0.005) and increased basal pancreatic glucagon output (delta - +21 +/- 6%, P less than 0.05, n = 5). d-ATS-SS at 0.17 micrograms/min markedly inhibited insulin output (delta = -84 +/- 4%, P less than 0.0005) and slightly inhibited glucagon output (delta = -14 +/- 6%, P less than 0.05, n = 5). d-ATS-SS at 0.055 micrograms/min decreased basal and stimulated insulin release but not basal nor stimulated glucagon release. By 3.5 of analogue infusion, plasma glucose had risen by 116 +/- 13 mg/dl, and base-line insulin levels and the insulin responses to both isoproterenol and arginine, but not glucose, increased toward control values. We conclude that d-ATS-SS produces selective insulinopenia resulting in hyperglycemia which in turn compensates for the original impairment. Thus, the hyperglycemia observed in other states of selective insulin deficiency (e.g., noninsulin-dependent diabetes mellitus) may compensate for defects in beta-cell function.     

Bcl-x(L) inhibits Bax-induced alterations in mitochondrial respiration and calcium release

Apoptosis is a natural cell elimination process involved in a number of physiological and pathological events. This process can be regulated by members of the Bcl-2 family. Bax, a pro-apoptotic member of this family, accelerates cell death, while the pro-survival member, Bcl-x(L), can antagonize the pro-apoptotic function of Bax to promote cell survival. In the present study, we have evaluated the effect of Bcl-x(L) on Bax-induced alterations in mitochondrial respiration and calcium release. We found that in primary cultured astrocytes, recombinant Bcl-x(L) is able to antagonize Bax-induced decrease in mitochondrial respiration and increase in mitochondrial calcium release. In addition, we found that Bcl-x(L) can lower the calcium store in the endoplasmic reticulum, thus limiting potential calcium flux induced by apoptosis. This regulation of calcium flux by Bcl-x(L) may represent an important mechanism by which this protein promotes cell survival.     

Effect of islet-activating protein (IAP) on glucagon release from isolated perifused rat islets

The present study was undertaken to evaluate the effect of islet-activating protein (IAP) on glucagon release using perifused isolated rat pancreatic islets. Glucagon release stimulated by 20 mM arginine was significantly enhanced in the IAP-treated rat pancreatic islets as compared with the IAP-untreated controls. Additionally, the effect of 1 ng/ml somatostatin on glucagon release was examined during ongoing stimulation by arginine. In the IAP-treated islets somatostatin inhibits glucagon secretion to the same extent as in the IAP-untreated islets. These results demonstrate that IAP potentiates arginine-induced glucagon release from perifused rat pancreatic islets, and IAP fails to antagonize the inhibitory effect of somatostatin in the pancreatic A cell.     

Cephalic-phase insulin release induced by taste stimulus of monosodium glutamate (umami taste)

In order to confirm the effect of umami taste stimulation on visceral functions, blood insulin and glucose assays and an electrophysiological study were performed on the rat. Blood insulin and glucose assays were carried out in conscious and free-moving rats. When the oral cavity was infused by MSG solution, a transient increase in blood insulin level was recognized at 3 min after this oral stimulation. The electrophysiological study revealed that applications of monosodium glutamate (MSG) glucose to the tongue in the anesthetized rat caused an increase in efferent activity of the pancreatic branch of the vagus nerve. These observations support the conclusion that taste stimulation of MSG induces cephalic-phase insulin secretion.