Modulation of pentagastrin-induced histamine release by histamine H3 receptors in the dog

BACKGROUND: The histamine H3 receptor has been shown to inhibit pentagastrin-induced gastric acid secretion in dogs. Since pentagastrin releases histamine in dogs, we have now assessed whether the effects of H3-receptor ligands may be indirectly mediated by changes in gastric histamine release. METHODS: Pentagastrin infusions (1 or 6 micrograms/kg/h), alone or together with the H3-receptor agonist (R) alpha-methylhistamine (1.2 mumol/kg/h) or the antagonist thioperamide (0.1 mumol/kg/h), were performed in dogs. One group (anaesthetized) was used for enzyme immunoassays of plasma histamine and, when required. (R) alpha-methylhistamine in the gastrosplenic vein, and another group (non-anaesthetized) for measurement of gastric acid secretion. RESULTS: Histamine levels were increased five- and eight-fold after 1 and 6 micrograms/kg/h pentagastrin, respectively, whereas acid output was nearly maximal at the lower dosage. (R) alpha-methylhistamine, at a plasma concentration of 0.15 microM, inhibited histamine release by 78% (P < 0.007) and 37% (not significant) and the total acid output by 44% (P < 0.05) and 19% (not significant) after infusion of 1 and 6 micrograms/kg/h pentagastrin, respectively. Thioperamide, together with pentagastrin in low dose, significantly increased histamine release by 212% (P < 0.05), whereas acid output increased by 34% (not significant). CONCLUSIONS: The histamine H3 receptor mediates a negative feedback control of pentagastrin-induced release of gastric histamine. It is tonically activated by endogenous histamine after pentagastrin in low dosage. The control of acid secretion by the H3 receptor seems to involve modulation of endogenous histamine release, possibly by means of enterochromaffin-like cells.     

Exposing guinea pigs to ozone for 1 wk enhances responsiveness of rapidly adapting receptors

Acute exposure to ozone causes changes in breathing pattern and lung function which may be caused in part by stimulation of rapidly adapting receptors (RARs). The consequences of repeated daily ozone exposure on RAR responsiveness are unknown, although ozone-induced changes in pulmonary function diminish with repeated exposure. Accordingly, we investigated whether repeated daily ozone exposure diminishes the general responsiveness of RARs. Guinea pigs (n = 30) were exposed to 0.5 parts/million ozone or filtered air (8 h/day for 7 days). The animals were then anesthetized, and RAR impulse activity, dynamic compliance (Cdyn), and lung resistance were recorded at baseline and in response to four stimuli: substance P, methacholine, hyperinflation, and removal of positive end-expiratory pressure. Repeated daily ozone exposure exaggerated RAR responses to substance P, methacholine, and hyperinflation without causing physiologically relevant effects on baseline or substance P- and methacholine-induced changes in Cdyn and lung resistance. Because agonist-evoked changes in RAR activity preceded Cdyn changes, the data suggest that repeated daily ozone exposure enhances RAR responsiveness via a mechanism other than changes in Cdyn.     

Correlative physiological and morphological studies of rapidly adapting mechanoreceptors in cat's glabrous skin

1. A total of fifty-four mechanoreceptor afferent units with fast conducting axons in the tibial nerve innervating the glabrous skin of the hind leg were isolated in anaesthetized cats. 2. Twenty-six rapidly adapting units (RA), eighteen slowly adapting units (SA) and ten Pacinian corpuscle units (PC) were differentiated from each other mainly on the presence of the off response in RA and PC units to a ramp stimulation, the persistence of discharges of the SA units during steady pressure on the receptive field and the classical tuning curve seen in the PC units. A few PC units in the hairy skin were also studied for comparison. 3. Lamellated corpuscles were found histologically in the skin of the receptive field of RA units and identified as Krause's corpuscle of cylindrical type by their superficial location in the cutaneous tissue and their structure revealed by electron microscopy. 4. Physiological characteristics of RA units to various forms of mechanical stimulation were studied and compared with those of the other two kinds of units. SA units had the lowest critical slope among three groups and PC units the highest. 5. The discharge pattern of RA and PC units to a ramp stimulation was found to be time-locked, whereas with SA unites only the first spike appeared at a fixed latency from the start of stimulation. 6. Some RA units showed a tuning curve which was flat from 10 to 200 Hz. Those with narrowly tuned curves had a best turning frequency at around 20 Hz. They were easily differentiated from the SA and PC units. SA units were tuned best at 5 HZ or less, and PC units at around 200 HZ. 7. The relation between the indentation velocity and amplitude of the ramp and the spike discharges was analysed in eleven RA units. In most cases the relation between identation velocity and maximum instataneous frequency was found to be best fit with a power function although other kinds of functions (linear, logarithmic, and logarithmic hyperbolic tangent) could also fit the relation at the 1% significance level. The instantaneous impuse frequency in RA units in response to various indentation amplitudes showed a step function. 8. The "off" responses to a ramp stimulation in RA units were also analysed in detail.     

Mechanisms by which vegetable consumption reduces genetic damage in humans

A previous intervention study had shown that consumption of carotenoid-containing vegetable juices reduces oxidative DNA damage in lymphocytes of 23 male subjects. It was the aim of this study to elucidate the potential mechanisms involved. Specifically, we studied the modulation of protein expression and determined susceptibility factors. Cryopreserved lymphocytes from the study were analyzed for genetic polymorphisms of glutathione S-transferase (GSTM1, GSTP1, and GSTT1) using multiplex PCR, GSTP1-protein with an ELISA, total protein by a colorimetric enzyme reaction, and DNA-repair enzymes with the Comet Assay. Analyses of the genotoxicity data revealed a more steady state of protection for GSTM1*+ than for GSTM1*0 (15 and 8 of 23, respectively) genotypes. Increased expression of cytosolic protein was observed in 11 of 23 subjects, increased expression of GSTP1 in 6 of 23 subjects, and capacity of repair of oxidized DNA bases in 9 of 21 subjects. GSTP1 induction was independent of the GSTP1 genotype (GSTP1a or GSTP1b/c alleles). Kinetics of induction of cytosolic protein and of GSTP1 were compared in one GSTM1*+ and one GSTM1*0 subject and showed an efficacy of tomato and carrots, but not of spinach. Reduced genetic DNA damage in lymphocytes may be due to the enhancement of cytosolic GSTP1, and DNA-repair proteins by tomato and carrot juices. Enhancement of cytosolic proteins may be indicative of increased gene expression by vegetable juices, some of which may be associated with protective activities.     

Mechanisms by which Hange-shashin-to reduces prostaglandin E2 levels

To determine the mechanisms by which Hange-shashin-to (TJ-14) reduces prostaglandin E2 (PGE2) levels, the effects on blood corticosterone levels were examined in vivo and the effects on cyclooxygenase (COX) activity in vitro assessed. TJ-14, orally administered to rats at dose levels between 125 and 1000 mg/kg, caused a dose-dependent increase in blood corticosterone levels. We also showed that Glycyrrhizae Radix and Ginseng Radix, constituents of TJ-14, are involved in the increase in blood corticosterone. The activity of COX-1 was not inhibited by TJ-14 even at a dose of 1000 microg/ml, while COX-2 was inhibited at dose levels between 10 and 1000 microg/ml. The constituents Scutellariae Radix, Glycyrrhizae Radix and Coptidis Rhizoma were believed to be involved in COX-2 inhibition. These results suggest that the effect of TJ-14 in decreasing PGE2 is partially mediated by corticosterone and inhibition of COX-2.     

Relationship between weight gain and lymph flow in dog lungs

Lung weight is a useful indicator of increases in lung extravascular volume. In addition, the lung lymph flow rate (QL) is an important factor in lung fluid balance. We have studied the weight and QL responses to elevations in capillary pressure (Pc) in intact dog lung lower left lobes. We measured lobe weight continuously. We also measured QL from small lymph vessels from the same lobes. The base-line QL was 1.7 +/- 1.5 microliter/min, and the weight was constant. After we increased Pc by 8-20 cmH2O, both weight and QL increased transiently. In most lungs the weight reached a new steady state. When we increased Pc further, weight increased continuously; however, QL reached a plateau. The continuous weight gain was due to edema. These results show that weight and QL respond similarly in nonedematous lungs; however, the weight and QL responses in edematous lungs may be different.     

Pulmonary vascular responses to inhalation anaesthesia in isolated dog lungs

To study the mechanisms of action of four inhalation anaesthetics (diethyl ether, halothane, methoxyflurane, and nitrogen monoxide) upon the pulmonary circulation, the authors carried out 45 experiments in isolated, perfused and ventilated canine lungs. The effects of the anaesthetics were studied at 1) normotonic perfusion, 2) enhanced pulmonary blood flow, 3) microembolism-induced pulmonary hypertension. In the first two-experimental series, no effects of the test anaesthetics on the pulmonary vascular responses became manifest; at microembolism-induced pulmonary hypertension, halothane lowered the pulmonary vascular resistance, whereas diethyl ether stabilized the elevated vascular tone. Methoxyflurane and nitrogen monoxide had no marked effects on the pulmonary vascular responses. On the basis of their experiences and of data published in the literature the authors conclude that there exist regional mechanisms of action of anaesthetics on the lung vessels, activated by the release or action of mediators.     

Prostaglandin E2 stimulates ion transport in prairie dog gallbladder

The effects of progesterone and RU486, a synthetic anti-progesterone, on ovarian 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) activity, a key enzyme of progesterone production, were studied during ovulation in immature 22-day-old rats primed with pregnant mares' serum gonadotrophin (PMSG) and human chorionic gonadotrophin (hCG). Ovarian 3 beta-HSD activities had increased significantly 4 h after hCG injection. These increases were inhibited at 4 and 6 h after hCG when 20 mg RU486 kg-1 was administered 2 h before hCG. However, RU486 had no influence on the activity of 3 beta-HSD when administered at the same time as hCG injection. A histochemical study revealed that 3 beta-HSD activities in the granulosa cell layer, but not in the theca cell layer, were inhibited when RU486 was given 2 h before hCG. Serum progesterone concentrations, but not oestradiol concentrations, were significantly suppressed by RU486 treatment 4 and 6 h after hCG. The effect of progesterone on ovarian 3 beta-HSD activity was tested by administering graded doses of progesterone exogenously to rats 2 h before hCG injection. Ovarian 3 beta-HSD activity was increased in a dose-dependent manner, and more than 20 mg progesterone kg-1 significantly stimulated the activity. Although 10 mg progesterone kg-1 did not stimulate ovarian 3 beta-HSD activities, the RU486-inhibited activities were recovered by the concomitant administration of 10 mg progesterone kg-1 with RU486. These results indicate that ovarian 3 beta-HSD activity depends on progesterone concentrations, and suggest an autocrine regulation of progesterone production during ovulation in immature rat ovaries stimulated with PMSG and hCG.     

Mechanisms of histamine stimulated secretion in rabbit ileal mucosa

Histamine is present in high concentrations in the intestine and we investigated the possibility that it might have a role here in intestinal transport. When added to the basal side of rabbit ileal mucosa in vitro histamine (10(-4)M) induced a short-lived increase in electrical potential difference and short circuit current. It inhibited net chloride absorption but did not influence sodium transport. Alkali secretion, measured by a pH stat technique, was inhibited, suggesting that bicarbonate secretion was reduced. Both the electrical and ion flux responses to histamine were blocked by the H1 receptor blocker diphenhydramine, but not by the H2 receptor blocker cimetidine. The presence of specific H1 histamine receptors was further supported by shifts in the dose-response curve to histamine by four different concentrations of diphenhydramine. Calculation of a pA2 value from these "Schild' plots provided a figure of 7.85, which is similar to that for H1 receptors in other tissues. Aminoguanidine, a histaminase blocker, had no electrical effects alone but shifted the histamine dose response curve to the left. These studies indicate that histamine inhibits chloride absorption and alkali secretion, possibly by influencing a chloride/bicarbonate exchange process, through specific mucosal H1 receptors. Enhancement of histamine effects by a histaminase inhibitor suggests that histaminases are present in the intestinal mucosa and supports the possibility of a role for endogenous histamine in influencing ion transport. The observations indicate a mechanism by which absorption might be impaired in diseases in which histamine is liberated locally in the intestine.     

Effect of histamine on intestinal fluid secretion in the dog

Intra-arterial infusion of histamine into the small intestine caused about a onefold increase of blood flow, edema of the intestinal tissues and mesentery, and produced a copious secretion of fluid. The jejunal secretions had an ionic composition similar to that of plasma, whereas ileal secretions contained high concentrations of HCO3 with relative low concentrations of Cl. The secretions contained protein (1.5 +/- .2 g/100 ml, range 0.5-2.4) with a similar electrophoretic pattern of plasma protein. When lissamine green was present in the blood, it also appeared in the secretion to a considerable concentration. It is inferred from these findings that a major mechanism of fluid secretion by the action of histamine involves a filtration process across the mucosal epithelium by the incrreased tissue fluid pressure due to extensive capillary leak.     

Relationship of AaDO2 TO AIRWAY PCO2 in dog lungs

We measured the arterial Po2 and AaDo2 in open-chest dogs respired with air and with 5% CO2 in air at various lung volumes using a constant hyperventilatory pattern. The AaDo2 was an inverse function of lung volume with both air and 5% CO2 and was also an inverse function of both alveolar and arterial Pco2 values except at quite high lung volumes. There were two series of closed-chest experiments. In the first series, ventilation was varied to produce alveolar Pco2 and Po2 changes. In the second series, the dogs were hyperventilated at a constant rate and Pco2 was varied by adding CO2 with alveolar Po2 levels kept relatively constant. In both series the AaDo2 was inversely related to Pco2. We conclude that, in dogs, the AaDo2 is independent upon the Pco2 and speculate that this may be related to the effect of CO2 on collateral ventilation, although the Bohr effect may account for some of the dependence.     

Encoding of shape and orientation of objects indented into the monkey fingerpad by populations of slowly and rapidly adapting mechanoreceptors

The peripheral neural representation of object shape and orientation was studied by recording the responses of a spatially distributed population of rapidly and slowly adapting type I mechanoreceptors (RAs and SAs, respectively) to objects of different shapes and orientations indented at a fixed location on the fingerpad of the anesthetized monkey. The toroidal objects had a radius of 5 mm on the major axis, and 1, 3, or 5 mm on the minor axis. Each object was indented into the fingerpad for 4 s at orientations of 0, 45, 90, and 135 degrees using a contact force of 15 gwt. Estimations of the population responses (PRs) were constructed by combining the responses of 91 SA and 97 RA single afferents at discrete times during the indentation. The PR was composed of the neural discharge rates (z coordinate) plotted at x and y coordinates of the most sensitive spot of the receptive field. The shapes of the PRs were related to the shapes of the objects by fitting the PRs with Gaussian surfaces. The orientations of the PRs were determined from weighted principal component analyses. The SA PR encoded both the orientation and shape of the objects, whereas the RA PR did neither. The SA PR orientation was biased toward the long axis of the finger. The RA PR encoded orientation only for the object with the highest curvature but did so ambiguously. Only the SA PR was well fit by a Gaussian surface. The shape of the object was discriminated by the SA PR within the first 500 ms of contact, and the form of the SA PR remained constant during the subsequent 3.5 s. This was manifested by constant widths of the PR along the major and minor axes despite a peak response that decreased from its maximum at 200 ms to an asymptotic value starting at 1 s. Thus the shape and orientation of each object were coded by the shape and orientation of the SA PR.     

Retinoic acid stimulates early cellular proliferation in the adapting remnant rat small intestine after partial resection

Following loss of small bowel surface area, the remnant intestine undergoes a remarkable adaptive response. To define more fully the underlying molecular mechanisms, we have identified genes that are specifically induced in the adapting remnant after partial small bowel resection. Several of these, including cellular retinol binding protein II (CRBP II) and apolipoprotein (apo) AI, participate in vitamin A and lipid trafficking. The CRBP II and apo A-I promoters contain response elements for the nuclear retinoid X receptor RXR-alpha. It is well established that vitamin A is essential for normal cell growth, differentiation and maintenance of epithelial tissues and that CRBP II functions to facilitate intestinal vitamin A absorption and metabolism. On the basis of these considerations, changes in CRBP II and apo A-I mRNA levels could reflect a role for retinoids in modulating the intestinal adaptive response. To explore this hypothesis, we used a rat resection model of intestinal adaptation to examine the temporal patterns of CRBP II, apo A-I and RXR-alpha expression postresection. CRBP II and apo A-I mRNA levels were increased in the remnant intestine in distinct temporal patterns, whereas RXR-alpha expression was unchanged. To address directly the effects of vitamin A in adaptation, retinoic acid or vehicle was administered intravenously to rats immediately after 70% small bowel resection. Compared with vehicle, all-trans-retinoic acid significantly stimulated crypt cell proliferation in the adapting remnant intestine by 6 h after surgery. These data suggest that retinoic acid acts to modulate intestinal proliferation in the adapting small intestine after loss of functional small bowel surface area.     

Excitatory mechanism of veratridine on slowly adapting pulmonary stretch receptors in anesthetized rabbits

The excitatory effects of veratridine on slowly adapting pulmonary stretch receptors (SARs) were studied before and after administration of ouabain (a Na+-K+ ATPase inhibitor) in anesthetized, artificially ventilated rabbits after vagus nerve section. Administration of veratridine (40 microg/kg) stimulated SAR activity but did not significantly alter tracheal pressure. Administration of ouabain (50 microg/kg) initially stimulated SAR activity during both inflation and deflation, but after 20 min, two different types of SAR responses were observed; one became silent at the peak, of inflation only, and the other maintained excitatory activity during both inflation and deflation phases. Veratridine usually inhibited SAR activity in ouabain-treated animals, irrespective of the difference of ouabain effects. These results suggest that veratridine-induced stimulation of SARs is closely related to the change in the Na+ ion gradient, which is regulated by Na+ pump activity.     

Insulin stimulates pp120 endocytosis in cells co-expressing insulin receptors

pp120, a substrate of the insulin receptor tyrosine kinase, is a plasma membrane glycoprotein that is expressed in the hepatocyte as two spliced isoforms differing by the presence (full-length) or absence (truncated) of most of the intracellular domain including all phosphorylation sites. Co-expression of full-length pp120, but not its phosphorylation-defective isoforms, increased receptor-mediated insulin endocytosis and degradation in NIH 3T3 fibroblasts. We, herein, examined whether internalization of pp120 is required to mediate its effect on insulin endocytosis. The amount of full-length pp120 expressed at the cell surface membrane, as measured by biotin labeling, markedly decreased in response to insulin only when insulin receptors were co-expressed. In contrast, when phosphorylation-defective pp120 mutants were co-expressed, the amount of pp120 expressed at the cell surface did not decrease in response to insulin. Indirect immunofluorescence analysis revealed that upon insulin treatment of cells co-expressing insulin receptors, full-length, but not truncated, pp120 co-localized with alpha-adaptin in the adaptor protein complex that anchors endocytosed proteins to clathrin-coated pits. This suggests that full-length pp120 is part of a complex of proteins required for receptor-mediated insulin endocytosis and that formation of this complex is regulated by insulin-induced pp120 phosphorylation by the receptor tyrosine kinase. In vitro GST binding assays and co-immunoprecipitation experiments in intact cells further revealed that pp120 did not bind directly to the insulin receptor and that its association with the receptor may be mediated by other cellular proteins.     

Mechanisms of neuronal calcium homeostasis destabilization caused by hyperstimulation of glutamate receptors

The present paper summarizes the data obtained in studying the mechanisms of glutamate-induced deterioration of neuronal Ca2+ homeostasis. In the cultured mammalian central neurons, a short-term (< 1 min) glutamate (GLU, 100 mu) challenge is known to induce a readily reversible (transient) neuronal [Ca2+]i increase. In contrast, a long-term (15-30 min) GLU exposure leads to the appearance of high [Ca2+]i plateau or to the partial recovery of the increased [Ca2+]i. Experiments show that impaired [Ca2+]i recovery in the postglutamate period cannot be explained by the increased [Ca2+]i permeability of the neuronal membrane, as earlier considered. Moreover, a sustained elevation of [Ca2+]i during and after chronic GLU application is associated with a progressive decrease in Ca2+ permeability. The major cause of GLU-induced Ca2+ overload is the mitochondrial depolarization resulted from excessive Ca2+ influx into the mitochondria, the generation of free radicals and the opening of a "giant pore" in the inner mitochondrial membrane. This in turn suppresses both ATP synthesis and Ca2+ electrophoretic uptake into the mitochondrial matrix. In combination with [Ca2+]i-dependent acidification, this leads to the suppression of Ca2+ release from the cell via Na+/Ca2+ exchanger and Ca2+/H+ pump of the neuronal membrane. Therefore, [Ca2+]i recovery following a long-term GLU treatment becomes strongly or even irreversibly compromised.     

Mechanisms of kinin B1-receptor-induced hypotension in the anesthetized dog

Our study was performed to investigate the mechanism underlying the phypotensive effect of kinin B1-receptor activation with des-Arg9-bradykinin (des-Arg9-BK), in comparison with B2-receptor activation with bradykinin (BK), in anesthetized dogs. Bolus intravenous and intraarterial injections of both kinins were compared. BK (0.6 microgram/kg) produced a transient hypotension of the same magnitude, regardless of the route of administration (from 110 +/- 6 mm Hg to 66 +/- 6 mm Hg, or -41 +/- 5%). In contrast, intraarterial injection of des-Arg9-BK (0.6 microgram/kg) induced a weaker hypotension compared with its intravenous injection (-27 +/- 2% vs. -39 +/- 3%, p < 0.05). The hypotension induced by both kinins was accompanied by increases in heart rate, maximum left ventricular dP/dt, and aortic blood flow, suggesting a reduction in peripheral resistance. The positive inotropic and chronotropic effects of BK and des-Arg9-BK were found to be mediated by the sympathetic nervous system, because they were abolished by propranolol. The hypotension induced by intravenous and intraarterial injections of BK and intravenous injections of des-Arg9-BK was only slightly reduced after nitric oxide (NO) synthase inhibition with NG-nitro-L-arginine (L-NNA). In contrast, the hypotensive effect of intraarterial injection of des-Arg9-BK was reduced by half after treatment with L-NNA (p < 0.05). Neither bilateral vagotomy nor ganglionic blockade with pentolinium reduced the hypotension induced by both kinins. In conclusion, the hypotensive effect of des-Arg9-BK and BK results from a peripheral vasodilation. The contribution of NO in this vasodilation is substantial for des-Arg9-BK when administered intraarterial but limited for BK and intravenous des-Arg9-BK.     

Osmoltye and tryptophan receptors controlling gastric emptying in the dog

The effect of three monosaccharides, three disaccharides, two dipeptides, combinations of tryptophan with two hexoses, one hexitol, and two amino acids ongastric emptying was studied in dogs to further define the samll intestinal receptors responsive to osmolytes and tryptophan. On a molar basis the disacchardies and dipeptides were almost twice as potent as their respective constituent monosaccharides or amino acids implying that the osmoreceptor is deep to the brush border disaccharidases and cytosol dipeptidases. Tryptophan probably acts by a mechanism different from the osmoreceptor since slowing of gastric emptying by tryptophan was inhibited by methionine which has no effect on a stimulant of the osmoreceptor mechanism. Lysine unlike methionine does not share the neutral amino acid transport pathway with tryptophan. Lysine did not change the inhibitory effect of tryptophan on gastric emptying. This imples that transport of tryptophan into the intestinal cell is necessary for its slowing effect. Glucose and galactose also inhibited the tryptophan effect whereas a nonabsorbed hexitor, mannitol, was without effect. Interference by the hexoses was also probably by competition with tryptophan for transport into the cell. These studies further indicate that the tryptophan receptor is different from the osmoreceptor.