Calcitonin—C.N.S. action to control the pattern of intestinal motility in rats

Synthetic calcitonin injected into the lateral ventricles (ICV) of rats at picomolar concentration restores the “fasted” motility pattern of the small intestine in fed rats at doses as low as 0.083 picomoles. This effect which appeared in less than 5 min and persisted at least 2 hours for 0.83 picomole, was blocked by a previous intraventricular administration of 10 μg of calcium gluconate. At 0.83 picomole ICV, calcitonin also suppressed the disruption of the “fasted” pattern induced by intravenous infusion of Pentagastrin (6 μg·kg^?1·h^?1) but not that induced by insulin (0.5 U·kg^?1). These findings support the hypothesis that calcitonin acts centrally to control the pattern of intestinal motility by inhibiting the digestive influences responsible for the “fed” pattern. All of these peripheral influences are mediated by a Ca⁺⁺ sensitive central structure.     

TMB-8 inhibits secretion evoked by phorbol ester at basal cytoplasmic free calcium in quin2-loaded platelets much more effectively than it inhibits thrombin-induced calcium mobilisation

TMB-8 is widely regarded as an 'intracellular calcium antagonist', supposedly inhibiting the mobilisation of intracellular calcium. Rarely, however, have the effects of this compound on Ca2+ movements been measured. We report here that TMB-8 is not very effective in inhibiting thrombin-induced Ca2+ influx or internal release in human platelets judged from the fluorescent signal of cytoplasmic quin2. Only approx. 40% inhibition was seen at 500 microns TMB-8. Somewhat lower concentrations blocked the secretory response to thrombin and also the secretion evoked at basal [Ca2+]i by phorbol ester and collagen. It is suggested that one target for TMB-8 may be the C-kinase pathway.     

Cortical granule exocytosis in sea urchin eggs is inhibited by drugs that alter intracellular calcium stores

In sea urchin eggs fertilization is accompanied by cortical granule exocytosis, a secretory event thought to be initiated by release of intracellularly sequestered calcium. We have examined the effect of two drugs on this process: chlortetracycline (CTC), a known chelator of intracellular calcium, and 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8), an antagonist of intracellular calcium release in both skeletal and smooth muscle. Preincubation of eggs for 10 min with either CTC or TMB-8 blocked sperm entry, inhibited the burst of 45Ca2+ efflux normally seen postinsemination, and prevented fertilization envelope elevation. Half-maximal inhibition occurred with 200 microM CTC and 60 microM TMB-8. Electron microscopy confirmed that cortical granule exocytosis had been blocked, although inhibition was not due to a direct effect on exocytosis. CTC and TMB-8 had no effect on Ca2+-stimulated granule fusion in isolated egg cortices. Rather, these drugs block the early events in egg activation: sperm incorporation and triggering of exocytosis. These two effects appear to be independent since addition of either drug just before insemination permits sperm entry but inhibits calcium release and cortical granule exocytosis.     

A calcitonin-like action of prostaglandin E1

The pharmacological effects of PGE1 (6 and 9 days, 2-1,250 micrograms/kg per day subcutaneously) upon the growth and the bone resorption of mammals were studied using the proximal tibia and upper incisor of immature rats along with lead acetate as a time marker, and upon the serum calcium and inorganic phosphorus levels. The following results were obtained. 1. PGE1 hardly affected the body weight or the weight of organs of the rats but apparently inhibited the longitudinal growth of proximal tibia in a dose related manner. 2. PGE1 clearly inhibited not only the longitudinal growth (incisor growth) but also the appositional growth (dentin formation) of incisal dentin. 3. The grade of the inhibitory effect on the growth was in the order of bone growth greater than dentin formation greater than incisor growth. 4. The occurrence of osteoporosis due to a low calcium diet was inhibited by the simultaneous administration of PGE1, the mechanism being considered to be mainly due to the inhibitory effect on the bone resorption. 5. PGE1 lowered the level of serum calcium and the lowering effect was not observed in the thyro-parathyroidectomized rat. From the facts that the above effects were exactly the same as those of calcitonin (1), the possibility that the subcutaneous injection of PGE1 may induce a calcitonin-like action, a part of which may dependent on the calcitonin secretion is suggested.     

Calcium rather than calcitonin is dominant to mediate gastric emptying in thyroidectomized rats

Both calcium and calcitonin are important in mediating gastrointestinal motility. Present study tried to study what was the dominant role of calcitonin or calcium replacement on the gastric emptying in thyroidectomized animals. Adult Sprague-Dawley male rats received thyroidectomy or sham operation and then housed for two weeks until motility study, which was conducted using radiochromium to measure gastric emptying. Before motility study these rats were i.p. injected with saline or human calcitonin in the doses of 0.1, 1 and 10 microgM/kg, respectively. Another group of thyroidectomized rats received i.v. infusion of saline or CaCl2 for 30 min before motility study. Among thyroidectomized rats, neither saline nor various doses of calcitonin treatment disturbed gastric emptying compared to this of sham operated rats. Thyroidectomy diminished plasma calcium level, however, additional calcitonin treatment did not restore the suppressed calcium level (P<0.01). Of rats following saline or CaCl2 infusion, thyroidectomy did not change gastric emptying, whereas CaCl2 infusion enhanced gastric emptying (P<0.05). In conclusion, exogenous calcium treatment further enhances gastric emptying in thyroidectomized rats, whereas calcitonin replacement has no effect on gastric emptying. We suggest that calcium rather than calcitonin is dominant to mediate gastric emptying.     

Interferon γ stimulates prostaglandin E2 production by mouse Kupffer cells

When mononuclear phagocytes, including Kupffer cells, are activated by various agents, they synthesize and release arachidonic acid metabolites, prostaglandins (PGs) and leukotrienes (LTs). In this study, we examined the effect of in vitro Kupffer cell activation with recombinant murine IFN gamma on PGE2 and LTB4 secretion. IFN gamma enhanced PGE2 secretion, and this effect of IFN gamma was stronger than that of IL-1 or TNF. Moreover, IFN gamma promoted LTB4 release especially in the absence of PGs. On the other hand, dexamethasone and indomethacin inhibited and, EGTA and TMB-8, which reduce intracellular Ca++ Levels, blocked IFN gamma induced PGE2 production, which suggested that the activation of phospholipase A2 and cyclooxygenase in Kupffer cells requires the elevation of intracellular Ca++ levels.     

Prophylactic and therapeutic benefits of COX-2 inhibitor on motility dysfunction in bowel obstruction: roles of PGE₂ and EP receptors

We reported previously that mechanical stretch in rat colonic obstruction induces cyclooxygenase (COX)-2 expression in smooth muscle cells. The aims of the present study were to investigate whether in vivo treatment with COX-2 inhibitor has prophylactic and therapeutic effects on motility dysfunction in colon obstruction, and if so what are the underlying mechanisms. Partial colon obstruction was induced with a silicon band in the distal colon of 6-8-wk-old Sprague-Dawley rats; obstruction was maintained for 3 days or 7 days. Daily administration of COX-2 inhibitor NS-398 (5 mg/kg) or vehicle was started before or after the induction of obstruction to study its prophylactic and therapeutic effects, respectively. The smooth muscle contractility was significantly suppressed, and colonic transit rate was slower in colonic obstruction. Prophylactic treatment with NS-398 significantly prevented the impairments of colonic transit and smooth muscle contractility and attenuated fecal collection in the occluded colons. When NS-398 was administered therapeutically 3 days after the initiation of obstruction, the muscle contractility and colonic transit still improved on day 7. Obstruction led to marked increase of COX-2 expression and prostaglandin E(2) (PGE(2)) synthesis. Exogenous PGE(2) decreased colonic smooth muscle contractility. All four PGE(2) E-prostanoid receptor types (EP1 to EP4) were detected in rat colonic muscularis externa. Treatments with EP1 and EP3 antagonists suppressed muscle contractility in control tissue but did not improve contractility in obstruction tissue. On the contrary, the EP2 and EP4 antagonists did not affect control tissue but significantly restored muscle contractility in obstruction. We concluded that our study shows that COX-2 inhibitor has prophylactic and therapeutic benefits for motility dysfunction in bowel obstruction. PGE(2) and its receptors EP2 and EP4 are involved in the motility dysfunction in obstruction, whereas EP1 and EP3 mediate PGE(2) regulation of colonic smooth muscle contractile function in normal state.     

Inhibition of dibutyryl cyclic AMP induced steroidogenesis in rat adrenocortical cells by the putative calcium antagonist TMB-8

A significant proportion of the steroidogenic response of isolated rat adrenocortical cells to dibutyryl cyclic AMP does not require extracellular calcium, and this component is profoundly depressed by low concentrations of the putative calcium antagonist, TMB-8. The inhibition is reversed by either the readdition of calcium or the calcium ionophore A23187. The steroidogenic response to pregnenolone, whose mode of action does not require calcium, was not depressed by TMB-8. Corticotropin (ACTH)-induced steroidogenesis, which requires extracellular calcium, was markedly depressed by TMB-8, although enhanced cyclic AMP formation is only slightly depressed by this drug. Adrenal cortical microsomes possess an ATP-dependent 45calcium (45Ca2+) uptake system which responded to EGTA with a rapid efflux of 45Ca2+; EGTA-induced calcium efflux from this microsomal fraction was markedly reduced by a concentration of TMB-8 that blocked dibutyryl cyclic AMP-evoked steroidogenesis. TMB-8 produced a smaller but significant reduction of EGTA-facilitated 45Ca2+ efflux from a mitochondrial-enriched fraction. We interpret these results to mean that TMB-8 blocks the steroidogenic effect of dibutyryl cyclic AMP by interfering with the mobilization of a cellular pool of calcium that is probably localized to the endoplasmic reticulum. The physiological implications of these findings in relation to the complex interactions between calcium and cyclic AMP in adrenal steroidogenesis are discussed.     

Action of TMB-8 (8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate) on cytoplasmic free calcium in adrenal glomerulosa cell

To clarify the action of 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8) on cellular calcium handling, changes in cytoplasmic free calcium concentration ([Ca2+]c) were studied in adrenal glomerulosa cell with a calcium-sensitive photoprotein, aequorin. Results of our previous study demonstrate that 100 microM TMB-8 almost completely blocks aldosterone response to angiotensin II (Biochem. J. 232 (1985) 87-92). At 50 or 100 microM, TMB-8 decreased basal [Ca2+]c significantly; however, these doses of TMB-8 had little effect on an angiotensin-induced increase in [Ca2+]c. When angiotensin-induced calcium release from an intracellular pool(s) was assessed by measuring changes in [Ca2+]c in the presence of 1 microM extracellular Ca2+, 100 microM TMB-8 had little inhibitory effect on angiotensin-induced calcium release. A higher dose of TMB-8 (250 microM) slightly inhibited calcium release. Additionally, TMB-8 did not affect exogenous arachidonic acid-induced calcium release. In contrast, 50 microM TMB-8 markedly inhibited 8 mM potassium-induced increase in [Ca2+]c. These results indicate that a major action of TMB-8 on cellular calcium is an inhibition of calcium influx but not of calcium release. We suggest that TMB-8 should not be used as an 'inhibitor of calcium release'.     

Calcitonin gene-related peptide: Brain and spinal action on intestinal motility

The effects of intracerebroventricular (ICV) and intrathecal (IT) administration of calcitonin gene-related peptide (CGRP) on intestinal motility were examined in conscious rats chronically fitted with intraparietal electrodes in the duodeno-jejunum and a cannula in a cerebral lateral ventricle or catheter in the subarachnoid space. ICV administration of CGRP (0.5–10 μg) restores the fasted pattern of intestinal motility in fed rats in a dose-related manner. Intrathecal administration of CGRP or calcitonin also induces fasted pattern but after a 30 min delay. These effects persisted after transection of the spinal cord and no change in intestinal motility appeared after intravenous administration of CGRP at a dose effective when given IT. This study suggests that CGRP, as calcitonin, has a neuromodulatory role in the control of intestinal motility at both brain and spinal cord levels.     

Bradykinin and prostaglandin E₁ regulate calcitonin gene-related peptide expression in cultured rat sensory neurons

Primary cultures of adult rat dorsal root ganglia (DRG) sensory neurons were used to determine whether bradykinin and prostaglandins E? (PGE?), E? (PGE?) or I? (PGI?) stimulate long-term calcitonin gene-related peptide (CGRP) mRNA accumulation and peptide release. Treatment (24 h) of neurons with either bradykinin or PGE?, significantly increased CGRP mRNA content and iCGRP release. However, PGE? or PGI? was without effect. Exposure of the cultured neurons to increasing concentrations of bradykinin or PGE? demonstrated that the stimulation of CGRP expression was concentration-dependent, while time-course studies showed that maximal levels of CGRP mRNA accumulation and peptide release were maintained for at least 48 h. Treatment of the neuronal cultures with a bradykinin B? receptor antagonist significantly inhibited the bradykinin-induced increase in CGRP expression and release. In addition, preincubation of neuronal cultures with the cyclooxygenase inhibitor indomethacin did not alter the PGE?-mediated stimulation of CGRP but blocked completely the bradykinin-induced increase in CGRP production. Therefore, these data indicate that bradykinin and PGE? can regulate the synthesis and release of CGRP in DRG neurons and that the stimulatory effects of bradykinin on CGRP are mediated by a cyclooxygenase product(s). Thus, these findings suggest a direct relationship between chronic alterations in bradykinin/prostaglandin production that may arise from pathophysiological causes and long-term changes in CGRP expression.     

Mechanisms involved in the stimulation by cycloheximide of prostaglandin production in the guinea-pig uterus

Cycloheximide produced a large increase in prostaglandin (PG) E2 output and smaller increases in PGF2 alpha and 6-keto-PGF1 alpha when superfused over the guinea-pig uterus for 20 min. This stimulation of the outputs of these 3 PGs by cycloheximide did not require extracellular calcium. TMB-8 (an intracellular calcium antagonist) had no effect on the stimulation of PGE2 output by cycloheximide, but it completely prevented the stimulation of PGF2 alpha and 6-keto-PGF1 alpha outputs. W-7 (a calmodulin antagonist) had no effect on the stimulation of PGE2 and PGF2 alpha outputs by cycloheximide, but it partially reduced and delayed the stimulation of 6-keto-PGF1 alpha output. Neomycin (a phospholipase C inhibitor) did not prevent the increases in PGE2 and 6-keto-PGF1 alpha outputs produced by cycloheximide. However, neomycin (5 and 10 mM, but not 1 mM) inhibited the small increases in PGF2 alpha caused by cycloheximide. On its own, neomycin produced a dose-dependent, transient increase in 6-keto-PGF1 alpha output without affecting the outputs of PGF2 alpha and PGE2. It is concluded that different mechanisms are involved in the processes by which cycloheximide stimulates the syntheses of PGE2, PGF2 alpha and 6-keto-PGF1 alpha in the guinea-pig uterus.     

Anti-alopecia mechanisms of soymetide-4, an immunostimulating peptide derived from soy beta-conglycinin

Previously, we found that orally administered soymetide-4 (MITL), an immunostimulating peptide derived from soybean beta-conglycinin alpha' subunit, suppressed alopecia induced by the anti-cancer drug etoposide in neonatal rats. Soymetide-4 has weak affinity for N-formyl-methionyl-leucyl-phenylalanine (fMLP) receptor. fMLP showed an anti-alopecia effect after intraperitoneal administration, though it was inactive after oral administration. Anti-alopecia effect of fMLP was blocked by pyrilamine or cimetidine, antagonists for histamine H1 or H2 receptor, respectively. However, the anti-alopecia effect of soymetide-4 was not inhibited by the histamine antagonists but by indomethacin, an inhibitor of cyclooxygenase (COX), or AH-23848B, an antagonist of the EP4 receptor for PGE2. Anti-alopecia effect of soymetide-4 was also blocked by pyrrolidine dithiocarbamate, an inhibitor of nuclear factor-kappaB (NF-kappaB). These results suggest that PGE2, which is produced after activation of COX by soymetide-4, might suppress apoptosis of hair matrix cells and etoposide-induced alopecia by activating NF-kappaB.     

PGE2 secretion from organ cultured gastric mucosa: correlation with cyclooxygenase activity and endogenous substrate release.

In gastrointestinal research the in vitro release of prostaglandins from incubated or cultured biopsies is a widely used method to estimate prostaglandin synthesis. We therefore investigated the rate limiting mechanisms of PGE2 release in organ cultured gastric mucosa of the rabbit, determining PGE2 secretion from organ cultured mucosal biopsies by radioimmunoassay and prostaglandin synthesizing capacity by in vitro incubation of mucosal homogenate or microsomes with [14C]-arachidonic acid. Freshly taken biopsies secreted PGE2 at an initial high rate, that decreased during the following 4 hrs of culture. This PGE2 release was dose dependently reduced by inhibitors of the prostaglandin cyclooxygenase. 5mM acetylsalicylic acid (ASA) maximally suppressed PGE2 secretion to 7% of controls, and the inhibition by ASA was quantitatively similar at every given culture period. PGE2 release was markedly increased by carbenoxolone but was only slightly activated by extracellular calcium and the Ca(++)-ionophore A23187. However, Ca++/A23187 were unable to maintain PGE2 secretion at the initial rate. PGE2 secretion was undisturbed in calcium-free medium but was reduced to 50-60% of controls by excess EDTA. The intracellular calcium chelator 1,2-bis-(2-aminophenoxy)-ethane-N,N,N',N',-tetraacetic acid-acetoxymethyl ester (BAPTA-AM) similarly inhibited PGE2 release to 72% of controls. In contrast, PGE2 release was unaffected by the intracellular calcium antagonist 3,4,5-trimethylene-bis(4-formylpyridinium bromide) dioxime (TMB-8), the calmodulin antagonists N-(6-aminohexyl)-1-5-chloro-1-naphthalenesulfonamide (W-7) and calmidazolium (compound R24571) or various direct inhibitors of endogenous arachidonic acid release like tetracaine, bromophenacyl bromide, neomycin or low dose quinacrine, indicating that the reduction of PGE2 release by EDTA or BAPTA may be mediated by mechanisms different from substrate release. In contrast, an inhibition of PGE2 secretion by quinacrine at high concentrations (greater than or equal to 0.8 mM) was attributed to a direct inhibition of the prostaglandin cyclooxygenase, similar to ASA. Finally, the reduction of the prostaglandin synthesizing capacity by ASA was strongly correlated with the inhibition of PGE2 secretion, also at low concentrations and minor degrees of inhibition. From these data we conclude, that the activity of the prostaglandin cyclooxygenase is rate limiting for PGE2 secretion from organ cultured mucosal biopsies rather than arachidonic acid release by a phospholipase A2. This should be considered for interpretation of studies based on prostaglandin release from cultured mucosa.     

Effects of thromboxane synthase and cyclooxygenase inhibition on PAF-induced changes in lung function and arachidonic acid metabolism.

PAF was administered as an intravenous bolus (0.1 micrograms/kg) to eight chronically instrumented awake sheep. The effects of pretreatment with an inhibitor of cyclooxygenase (meclofenamate) on PAF-induced changes in lung function were compared to those observed with a specific inhibitor of thromboxane synthase (DP1904). Each animal was studied four times in varied order: PAF alone, PAF + DP1904, PAF + meclofenamate, and DP1904 alone. Saline alone (control), DP1904 alone, and meclofenamate alone did not cause changes in any of the measured variables. DP1904 and meclofenamate significantly attenuated the PAF-induced fall in lung compliance, elevation in peak pulmonary artery pressure, and increased lung lymph flow. Both drugs abolished the PAF-induced increases in lung lymph thromboxane B2 concentrations. Meclofenamate, but not DP1904, blocked the rise in lymph 6-keto-PGF1 alpha. Although meclofenamate blocked the rise in lymph PGE2, DP1904 resulted in levels 2.7 times higher than PAF alone. We conclude that: (1) inhibition of thromboxane synthase is as effective as inhibition of cyclooxygenase in attenuating PAF-induced changes in lung function, and (2) thromboxane synthase inhibition results in augmented production of PGE2 following PAF administration in vivo.     

Arachidonic acid- and prostaglandin E2-induced cerebral vasodilation is mediated by carbon monoxide, independent of reactive oxygen species in piglets

Arachidonic acid (AA) and prostaglandin (PG) E(2) stimulate carbon monoxide (CO) production, and AA metabolism is known to be associated with the generation of reactive oxygen species (ROS). This study was conducted to address the hypothesis that CO and/or ROS mediate cerebrovascular dilation in newborn pigs. Experiments were performed on anesthetized newborn pigs with closed cranial windows. Different concentrations of AA (10(-8)-10(-6) M), PGE(2) (10(-8)-10(-6) M), iloprost (10(-8)-10(-6) M), and their vehicle (artificial cerebrospinal fluid) were given. Piglets with PGE(2) and iloprost received indomethacin (5 mg/kg iv) to inhibit cyclooxygenase. AA, PGE(2), and iloprost caused concentration-dependent increases in pial arteriolar diameter. The effects of both AA and PGE(2) in producing cerebral vascular dilation and associated CO production were blocked by the heme oxygenase inhibitor chromium mesoporphyrin (2 × 10(-5) M), but not by the prostacyclin analog, iloprost. ROS inhibitor tempol (SOD mimetic) (1 × 10(-5) M) and the H(2)O(2) scavenger catalase (1,000 U/ml) also do not block these vasodilator effects of AA and PGE(2). Heme-L-lysinate-induced cerebrovascular dilation and CO production was blocked by chromium mesoporphyrin. Hypoxanthine plus xanthine oxidase, a combination that is known to generate ROS, caused pial arteriolar dilation and CO production that was inhibited by tempol and catalase. These data suggest that AA- and PGE(2)-induced cerebral vascular dilation is mediated by CO, independent of ROS.     

NS-398: cyclooxygenase-2 independent inhibition of leukocyte priming for lipid body formation and enhanced leukotriene generation

Because the induction of new lipid body formation in leukocytes correlates with and likely contributes to their enhanced 'primed' prostaglandin and leukotriene formation, we evaluated two selective cyclooxygenase (COX)-2 inhibitors. Three types of stimuli, cis -unsaturated fatty acids, platelet activating factor and protein kinase C activators, stimulate lipid body formation. NS-398 (0.1-10 microM), but not another COX-2 inhibitor, SC58125 (0.1- 10 microM), blocked leukocyte lipid body formation elicited by all three types of stimuli and also blocked priming for enhanced LTB(4) production and PGE(2) production. The effect of NS-398 on lipid body formation was independent of its inhibitory effects on COX-2 since arachidonate-induced lipid body formation in COX-2-deficient mouse leukocytes was also inhibited by NS-398. By means of its ability to inhibit leukocyte lipid body formation, NS-398 may exert actions independent of its COX-2 inhibition and more broadly contribute to the suppression of formation of COX-1 and lipoxygenase-derived eicosanoids.     

Glycine blocks the increase in intracellular free Ca2+ due to vasoactive mediators in hepatic parenchymal cells

Recently, glycine has been shown to prevent liver injury after endotoxin treatment in vivo. We demonstrated that ethanol and endotoxin stimulated Kupffer cells to release PGE(2), which elevated oxygen consumption in parenchymal cells. Because glycine has been reported to protect renal tubular cells, isolated hepatocytes, and perfused livers against hypoxic injury, the purpose of this study was to determine whether glycine prevents increases in intracellular free Ca(2+) concentration ([Ca(2+)](i)) in hepatic parenchymal cells by agonists released during stress, such as with PGE(2) and adrenergic hormones. Liver parenchymal cells isolated from female Sprague-Dawley rats were cultured for 4 h in DMEM/F12 medium, and [Ca(2+)](i) in individual cells was assessed fluorometrically using the fluorescent calcium indicator fura 2. PGE(2) caused a dose-dependent increase in [Ca(2+)](i) from basal values of 130 +/- 10 to maximal levels of 434 +/- 55 nM. EGTA partially prevented this increase, indicating that either extracellular calcium or agonist binding is Ca(2+) dependent. 8-(Diethylamino)octyl 3,4,5-trimethoxybenzoate (TMB-8), an agent that prevents the release of Ca(2+) from intracellular stores, also partially blocked the increase in [Ca(2+)](i) caused by PGE(2), suggesting that intracellular Ca(2+) pools are involved. Together, these results are consistent with the hypothesis that both the intracellular and extracellular Ca(2+) pools are involved in the increase in [Ca(2+)](i) caused by PGE(2). Interestingly, glycine, which activates anion (i.e., chloride) channels, blocked the increase in [Ca(2+)](i) due to PGE(2) in a dose-dependent manner. Low-dose strychnine, an antagonist of glycine-gated chloride channel in the central nervous system, partially reversed the inhibition by glycine. When extracellular Cl(-) was omitted, glycine was much less effective in preventing the increase in [Ca(2+)](i) due to PGE(2). Phenylephrine, an alpha(1)-type adrenergic receptor agonist, also increased [Ca(2+)](i), as expected, from 159 +/- 20 to 432 +/- 43 nM. Glycine also blocked the increase in [Ca(2+)](i) due to phenylephrine, and the effect was also reversed by low-dose strychnine. Together, these data indicate that glycine rapidly blocks the increase in [Ca(2+)](i) in hepatic parenchymal cells due to agonists released during stress, most likely by actions on a glycine-sensitive anion channel and that this may be a major aspect of glycine-induced hepatoprotection.     

Biological actions of human and rat calcitonin and calcitonin gene-related peptide

We assessed the central and peripheral biological actions of human and rat calcitonin and calcitonin gene-related peptide (CGRP). After intravenous administration, human and rat calcitonin, but neither human nor rat CGRP significantly decreased plasma calcium and phosphorus concentrations in awake, freely moving rats. After intracerebroventricular as well as after intravenous administration, human and rat calcitonin and human and rat CGRP significantly inhibited gastric acid secretion in conscious rats. Intracerebroventricular administration of rat calcitonin did not alter plasma calcium and phosphorus concentrations. Linear, partially protected CGRP and calcitonin did not exhibit any biological effects. These studies indicate that calcitonin, but not CGRP, affects calcium and phosphorus homeostasis while both peptides decrease gastric acid secretion similarly. Furthermore, these studies support the hypothesis that the calcium and phosphorus lowering effects of calcitonin are peripheral while the gastric inhibiting actions of the calcitonin and CGRP are mediated by the central nervous system.     

Prostaglandin E2 increases growth and motility of colorectal carcinoma cells

Chronic use of nonsteroidal anti-inflammatory drugs results in a significant reduction of risk and mortality from colorectal cancer in humans. All of the mechanism(s) by which nonsteroidal anti-inflammatory drugs exert their protective effects are not completely understood, but they are known to inhibit cyclooxygenase activity. The cyclooxygenase enzymes catalyze a key reaction in the conversion of arachidonic acid to prostaglandins, such as prostaglandin E(2) (PGE(2)). Here we demonstrate that PGE(2) treatment of LS-174 human colorectal carcinoma cells leads to increased motility and changes in cell shape. The prostaglandin EP(4) receptor signaling pathway appears to play a role in transducing signals which regulate these effects. PGE(2) treatment results in an activation of phosphatidylinositol 3-kinase/protein kinase B pathway that is required for the PGE(2)-induced changes in carcinoma cell motility and colony morphology. Our results suggest that PGE(2) might enhance the invasive potential of colorectal carcinoma cells via activation of major intracellular signal transduction pathways not previously reported to be regulated by prostaglandins.