[Improved Indophenol Titration Method for Ascorbic Acid Using a Dropper and Electronic Balance: Enhanced Convenience and Efficiency]

The analysis of ascorbic acid using the 2,6-dichloroindophenol (DCIP) titration method is a well-established technique, but requires the skilled handling of a burette for accurate measurements. In the present study, we propose a modified DCIP titrimetric method that replaces the burette with a dropper and employs an electronic balance to measure the titrated amount by weight. The dropper used can be flexibly selected, allowing for a wide range of drop sizes, from large to very small. This modification offers several advantages, including lower skill requirements, a 43% reduction in the analysis time, a 50% decrease in sample/reagent consumption, and the ability to prepare DCIP standard solutions tailored to the concentration of ascorbic acid in the sample being analyzed. Our analysis of several food samples using this improved method showed that inherent issues of the DCIP method, such as determining the titration end point, could not be resolved. Nevertheless, the improved titration method remains more convenient and adaptable than the original approach using a burette, enabling quick and accurate analysis, especially for unskilled analysts.

Comparison of CYP Induction by Coleus forskohlii Extract and Recovery in the Small Intestine and Liver of Mice

We examined CYP induction and recovery at various doses of Coleus forskohlii extract (CFE) to assess potential drug interactions by a mechanism involving intestinal CYP. Mice were administered diets with various doses of CFE up to 0.5% (equivalent to 700-800 mg/kg body weight) for 2 weeks, then CFE was withdrawn for 3 d. Changes in CYP activities and mRNA expression in the small intestine and liver were then evaluated. CFE induced CYP in the small intestine at a higher dose compared to the liver; CYP3A was induced at 0.5% and 0.005% CFE in the small intestine and liver, respectively. There was no sex difference in CFE dose for CYP induction. CYP induction quickly reverted after withdrawal of CFE, especially for CYP3A, in the small intestine; whereas, a gradual recovery was observed in the liver. In conclusion, CFE induced CYP in the small intestine and liver; however, a higher dose of CFE was needed for the small intestine. Moreover, the induction was soon recovered, suggesting actual interactions of CFE with prescription drugs are unlikely to occur through CYP in the small intestine.

Identification of Compounds in Coleus forskohlii Extract Involved in the Induction of Hepatic CYP and Fatty Liver in Mice

Coleus forskohlii extract (CFE), a popular weight-loss herbal product, induces hepatic cytochrome P450 (CYP) and fatty liver in mice; however, its main bioactive ingredient, forskolin, does not show such effects. To ensure the safety of CFE as a dietary supplement, identification of the compounds implicated in the induction of hepatic CYP and fatty liver is required. In this study, we separated a crude CFE extract into 5 fractions (Fr.) by column chromatography and administered the fractions to mice for one week to assess their ability to induce CYP and fatty liver. CYP induction was detected for all fractions, indicating that many compounds may be involved in CYP induction, while fatty liver was only detected for Fr. 2. Further isolation and purification of Fr. 2 by column chromatography identified 14-deoxycoleon U as a major compound and crocetin dialdehyde as a pigment compound. An in vivo mouse study revealed that crocetin dialdehyde had no effect on the liver and, as 14-deoxycoleon U was the major compound in Fr. 2, it is likely that the active compound inducing fatty liver in CFE is 14-deoxycoleon U. These findings will facilitate the preparation of standardized safe CFE ingredients for dietary supplements.

Induction of fatty liver by Coleus forskohlii extract through enhancement of de novo triglyceride synthesis in mice

Coleus forskohlii extract (CFE), an herbal ingredient, is used for weight-loss products. CFE's alleged efficacy is attributed to forskolin. However, CFE has been shown to induce fatty liver in mice, with components other than forskolin playing a part in this effect. The present study addressed the underlying mechanism of CFE-induced fatty liver by analyzing changes in CFE-treated mice of lipid concentrations and of the levels of mRNAs encoding enzymes and transcription factors known to be related to fatty liver. Mice were fed a diet containing 0, 0.3 and 1% CFE for 2 weeks. CFE at 1% clearly induced fatty liver, as demonstrated by histological examination and confirmed by increases in triglyceride concentrations in liver. However, treated mice did not exhibit elevation in plasma levels of non-esterified fatty acids. Comprehensive analysis of liver mRNA levels revealed accumulation of multiple transcripts, including mRNAs encoding enzymes acetyl-CoA carboxylase and long-chain elongase; transcription factor peroxisome proliferator-activated receptor gamma (PPARγ); and lipid-droplet-associated fat-specific protein 27 (Fsp27). These findings suggest that the de novo synthesis and accumulation of triglyceride in the liver, through the enhanced expression of specific lipogenic mRNAs, is a major underlying mechanism of fatty liver induction by CFE.

Coleus forskohlii extract attenuates the hypoglycemic effect of tolbutamide in vivo via a hepatic cytochrome P450-mediated mechanism

This in vivo study in rats evaluated whether Coleus forskohlii extract (CFE) taken orally interacted with tolbutamide, a hypoglycemic drug metabolized by CYP2C enzymes. Rats were fed 0%, 0.3%, 1% (w/w) CFE diet for 2 weeks, followed by 0% CFE diet for 1 day. They were then given 40 mg/kg tolbutamide by intragastric gavage. Blood glucose level was determined up to 6 h after tolbutamide administration. CFE treatment increased total CYP content and various CYP subtypes in the liver. In particular, increases in activity and protein expression were noted for the CYP2B, CYP2C, and CYP3A subtypes. CFE treatment dose-dependently attenuated both the hypoglycemic action of tolbutamide at 6 h and the plasma concentration of tolbutamide. The activity of (S)-warfarin 7-hydroxylase, a CYP2C enzyme was negatively correlated with plasma tolbutamide level, which also showed a negative correlation with the reduction of blood glucose level. These results indicate that CFE induced hepatic CYPs in rats and attenuated the hypoglycemic action of tolbutamide via a hepatic CYP2C-mediated mechanism.

[Effect of three herbal extracts on cytochrome P450 and possibility of interaction with drugs]

Herb-drug interactions are mainly mediated by hepatic cytochrome P450 (CYP) enzymes. Here, we examined the effect of three herbs (valerian, salacia and black cohosh) on CYP activity in vivo in mice and in liver microsomes in vitro. Extracts which showed activity in the preliminary tests were then fed to mice at various doses (0, 0.5, 1.5 and 4.5%). Valerian did not show any effect on hepatic CYPs. Black cohosh increased the liver weight, total CYP content and CYP activities (2B and 3A) in a dose-dependent manner (up to 4.5%). Salacia inhibited CYP1A2 activity in liver microsomes in vitro. Also, salacia at the dietary dose of 4.5% suppressed body weight gain, decreased hepatic total CYP content and increased CYP activities (1A1, 2B and 2C). These findings suggest that black cohosh and salacia at high dose affect the activity of hepatic CYPs, and therefore may interact with drugs that are metabolized by CYP.

Influence of dietary macronutrients on induction of hepatic drug metabolizing enzymes by Coleus forskohlii extract in mice

From studies in mice, we have reported that Coleus forskohlii extract (CFE), a popular herbal weight-loss ingredient, markedly induced hepatic drug metabolizing enzymes, especially cytochrome P450 (CYP), and interacted with co-administered drugs. This study was designed to examine how the induction of drug metabolizing enzymes by CFE was influenced by different levels of macronutrients in the diet. Mice were fed a non-purified diet or semi-purified diet with and without CFE (0.3-0.5%) for 14-18 d, and changes in the ratio of liver weight to body weight, an indicator of hepatic CYP induction, and hepatic drug metabolizing enzymes were analyzed. The ratio of liver weight to body weight, content and activities of CYPs, and activity of glutathione S-transferase were higher in a semi-purified standard diet (AIN93G formula) group than in high sucrose (62.9%) and high fat (29.9%) diet groups. Different levels of protein (7%, 20%, and 33%) in the diets did not influence CFE-induced CYP induction or increase the ratio of liver weight to body weight. The effect of CFE on the ratio of liver weight to body weight was higher with a semi-purified diet than with a non-purified diet, and was similar between dietary administration and intragastric gavage when the CFE dose and the diet were the same. There was a positive correlation between CFE-induced CYP induction and the content of starch in the diets, suggesting that dietary starch potentiates CFE-induced CYP induction in mice. The mechanism of enhanced CYP induction remains unclear.

Prevalence of inappropriate dietary supplement use among pregnant women in Japan

We investigated the characteristics of dietary supplements and their use by 1,076 Japanese pregnant women, the majority of whom were in mid- to late pregnancy. The subjects completed a self-reported survey on their sociodemographic characteristics, supplement use, and attitudes towards diet. The overall prevalence of supplement use did not change before and after pregnancy (75%); however, daily use increased by approximately twofold with pregnancy (20.2% versus 37.2%). After the onset of pregnancy, supplements containing folic acid were taken for fetal health. Daily users were more likely to be older, have a greater awareness of the risk of neural tube defects (NTD), view supplement use as acceptable, have less diet anxiety, and have more advisers regarding diet. Respondents used supplements containing folic acid alone or with other ingredients. Folic acid intake is recommended to reduce the risk of NTD. However, supplement use began after pregnancy recognition, suggesting a lack of knowledge on the appropriate timing of folic acid use. Information about supplements was obtained mostly from newspapers, magazines, flyers, and stores. These results indicate that more accurate information regarding the optimal timing of folic acid intake and the safety of dietary supplements must be disseminated.

Hepatic cytochrome P450 mediates interaction between warfarin and Coleus forskohlii extract in vivo and in vitro

Objectives

This study aimed to determine whether Coleus forskohlii extract (CFE) influences the anticoagulant action of warfarin in mice in vivo and its relationship with hepatic cytochrome P450 (CYP).

Methods

Mice were fed various doses of CFE standardised with 10% forskolin in a normal diet for one week, or in protein diets containing 7% and 20% casein (low and normal) for four weeks. They were then administered with warfarin by gavage on the last two days of the treatment regimen, and blood coagulation parameters, as well as hepatic CYP, were analysed at 18 h after the last dose. Direct interaction between CFE and forskolin with CYP2C was evaluated in vitro.

Key findings

CFE dose dependently increased hepatic total CYP content and S-warfarin 7-hydroxylase activity at a dietary level of ≥0.05%. Warfarin-induced anticoagulation was attenuated by CFE in parallel with CYP induction. The findings were similar in mice fed diets containing CFE and different ratios of protein. CFE directly inhibited CYP2C activity in mouse and human liver microsomes in vitro, whereas forskolin was only slightly inhibitory.

Conclusions

CFE attenuates the anticoagulant action of warfarin by inducing hepatic CYP2C; thus, caution is required with the combination of warfarin and dietary supplements containing CFE.

Ginkgo biloba extract attenuates warfarin-mediated anticoagulation through induction of hepatic cytochrome P450 enzymes by bilobalide in mice

Ginkgo biloba extract (GBE) is a popular herbal ingredient used worldwide, but it is reported to induce bleeding as a serious adverse event. In this study we examined whether GBE induced spontaneous bleeding or accelerated warfarin anticoagulation via herb-drug interaction. Mice were given GBE or various active components of GBE orally for 5 days and blood coagulation parameters and hepatic cytochrome P450 enzymes (CYPs) were measured. Mice also received warfarin (racemate, (S)- or (R)-enantiomer) for the last 3 days of the 5-day regimen to examine GBE-warfarin interactions. Neither GBE (up to 1000 mg/kg) nor ginkgolide B (up to 140 mg/kg), a platelet-activating factor antagonist, influenced blood coagulation parameters. In contrast, GBE attenuated the anticoagulant action of warfarin. Bilobalide, a component of GBE that markedly induced hepatic CYPs including (S)-warfarin hydroxylase, showed similar effects. For (S)-warfarin, the anticoagulation action and the interaction with GBE was clear, while the influence on metabolism was greater for (R)-warfarin than for (S)-warfarin, which corresponded to the CYP types induced by GBE. These results suggest that GBE and ginkgolide B have no influence on blood coagulation in vivo, and that GBE attenuates the anticoagulation action of warfarin via induction of hepatic CYPs by bilobalide.

Nicotinic receptors involved in gastric noradrenaline release evoked by electrical stimulation of the splanchnic nerve in rats

In the present experiment, we tried to compare the functional nicotinic receptors activated by electrical stimulation of the greater splanchnic nerve (containing preganglionic sympathetic nerves) to those activated by (-)-nicotine, using the isolated rat stomach. The stomach was perfused with Krebs-Ringer solution and endogenous noradrenaline released into the perfusate was electrochemically measured using high-performance liquid chromatography. The release of noradrenaline evoked by repeated application of 30 mM (-)-nicotine rapidly declined. However, the release of noradrenaline evoked by electrical stimulation of the splanchnic nerve at 2.5 Hz was not disturbed by the appearance of tachyphylaxis for (-)-nicotine. The (-)-nicotine-induced release of noradrenaline was abolished by diltiazem, but this reagent had no effect on the electrically evoked release of noradrenaline. The electrically evoked release of noradrenaline was not influenced by atropine, but was reduced to approximately 50% by hexamethonium. This electrically evoked release of noradrenaline was not influenced by alpha-bungarotoxin, alpha-conotoxin ImI (blockers of alpha 7 nicotinic receptors) or dihydro-beta-erythroidine (a blocker of alpha 4 beta 2 nicotinic receptors), but was reduced to about 50% by mecamylamine (a blocker of alpha 3 beta 4 nicotinic receptors). The (-)-nicotine-induced release of noradrenaline has already been shown to be partially blocked by dihydro-beta-erythroidine and to be abolished by mecamylamine as shown by Yokotani et al. [Eur. J. Pharmacol. 402 (2000) 223.]. These results suggest that the gastric release of noradrenaline in response to electrical stimulation of the greater splanchnic nerve is mediated by cholinergic (probably ganglionic alpha 3 beta 4 nicotinic receptor-mediated) and non-cholinergic mechanisms in rats. However, the functional nicotinic receptor activated by electrical stimulation of the splanchnic nerve seems to be different in character from that activated by (-)-nicotine.

Role of brain arachidonic acid cascade on central CRF1 receptor-mediated activation of sympatho-adrenomedullary outflow in rats

The present experiments were designed to characterize the mechanisms involved in the corticotropin releasing factor (CRF)-induced activation of central sympatho-adrenomedullary outflow in rats. Intracerebroventricularly (i.c.v.) administered CRF and urocortin (0.5, 1.5 and 3.0 nmol/animal) effectively and dose-dependently elevated plasma levels of adrenaline and noradrenaline, and the effect of urocortin was almost the same as that of CRF. The elevation of catecholamines induced by CRF and urocortin (1.5 nmol/animal) was reduced by CP-154,526(butyl-ethyl-(2,5-dimethyl-7-(2,4,6trimethylphenyl)-7H-pyrrolo [2,3-d] pyrimidin-4-yl]amine), a selective CRF1 receptor antagonist, in a dose dependent manner (1.2 and/or 2.4 micromol/animal, i.c.v.), and abolished by indomethacin (1.2 micromol/animal, i.c.v.), an inhibitor of cyclooxygenase. Furegrelate (1.8 micromol/animal, i.c.v.), an inhibitor of thromboxane A2 synthase, abolished the CRF-induced elevation of adrenaline, but had no effect on the evoked release of noradrenaline. These results suggest that activation of brain CRF1 receptor facilitates the central sympathetic and adrenomedullary outflow in distinct central pathways in rats; brain thromboxane A2 is involved in the central adrenomedullary outflow; an active metabolite of arachidonic acid other than thromboxane A2 (probably prostaglandin E2) may be involved in the central sympathetic outflow.

Neurotransmitter contents in the retina of RCS rat

BACKGROUND

Retinitis pigmentosa is a hereditary disease characterized by gradually developing degeneration of photoreceptors. The Royal College of Surgeons (RCS) rat is an experimental model of retinitis pigmentosa. However, there is a paucity of information concerning neurotransmitter contents in the retina of RCS rats. Thus, we determined the retinal contents of neurotransmitters in RCS rats at 4 and 23 weeks postnatally and in age-matched congenic control rats.

METHODS

Dopamine (DA) and acetylcholine (ACh) were electrochemically measured by high-performance liquid chromatography (HPLC). Neuroactive amino acids, including gamma-aminobutyric acid (GABA) and taurine, were determined by means of an HPLC-precolumn derivatization method.

RESULTS

Contents of DA, ACh, glutamate, aspartate and GABA in the retina of RCS rats 4 weeks postnatally were within normal ranges. At 23 weeks, the retinal contents of DA, glutamate and aspartate in the RCS rats were significantly lower than in the age-matched control rats, while the contents of ACh and GABA were unaffected even at this later stage. On the other hand, the retinal content of glycine in the RCS rats at 23 weeks was significantly higher than that in the age-matched control rats. It is interesting to note that the content of taurine in the RCS rats had already decreased at 4 weeks postnatally and the decrease was more marked at 23 weeks.

CONCLUSION

The decrease in taurine content is probably the first sign of degeneration revealed by the retinal neurotransmitters of RCS rats.

Characterization of nicotinic acetylcholine receptor-mediated noradrenaline release from the isolated rat stomach

We characterized nicotinic acetylcholine receptor-mediated noradrenaline release from the isolated, vascularly perfused rat stomach. The stomach was perfused via the coeliac artery with Krebs-Ringer solution at a constant flow rate of 4 ml per minute. Endogenous noradrenaline released into the perfusate was electrochemically measured using high-performance liquid chromatography. Nicotinic receptor agonists were applied once into the perfusion medium for 2 min and nicotinic receptor antagonists were administered throughout the experiments. The (-)-nicotine (3x10(-5) M)-induced noradrenaline release was abolished by tetrodotoxin and hexamethonium and partially blocked by dihydro-beta-erythroidine (up to 10(-5) M) (a relatively selective antagonist of alpha4beta2 nicotinic receptors) and abolished by mecamylamine (10(-5) M) (a relatively selective antagonist of alpha3beta4 nicotinic receptors), but not influenced by alpha-bungarotoxin (3x10(-7) M) or alpha-conotoxin ImI (10(-6) M) (antagonists of alpha7 nicotinic receptors). (+/-)-Epibatidine (3x10(-7) M) (a very potent, but non-selective agonist) and (-)-cytisine (3x10(-4) M) (an agonist of beta4 nicotinic receptors) effectively evoked the release of noradrenaline, while (E)-N-methyl-4-(3-pyridinyl)-3-butene-1-amine (RJR-2403) (up to 10(-4) M) (an agonist of alpha4beta2 nicotinic receptors) had no effect. The potency of these agonists was as followed; (+/-)-epibatidine>>(-)-nicotine>(-)-cytisine>>>RJR -2403. These results are compatible with the published view that alpha3beta4 nicotinic receptors are predominant in other parts of the autonomic nervous system. These receptors (probably located on the gastric sympathetic ganglia) are involved in the release of noradrenaline from the rat stomach.

Brain phospholipase A(2)-arachidonic acid cascade is involved in the activation of central sympatho-adrenomedullary outflow in rats

The present experiments were designed to explore the role of the brain phospholipase A(2)-arachidonic acid cascade in the activation of central sympatho-adrenomedullary outflow in rats, using melittin (an activator of phospholipase A(2)) and arachidonic acid. Intracerebro-ventricularly administered melittin (2.5, 10, and 25 microg/animal) or arachidonic acid (75, 150, 300 microg/animal) effectively and dose dependently elevated plasma levels of adrenaline and noradrenaline. The elevation of both catecholamines induced by melittin (10 microg/animal) was abolished by centrally administered mepacrine (an inhibitor of phospholipase A(2)), but not by neomycin (an inhibitor of phospholipase C). However, mepacrine had no effect on the increase induced by arachidonic acid (150 microg/animal). Indomethacin (an inhibitor of cyclooxygenase) abolished all responses induced by melittin and arachidonic acid. Furegrelate (an inhibitor of thromboxane A(2) synthase) abolished the elevation of adrenaline induced by melittin and arachidonic acid, but had no effect on the elevation of noradrenaline induced by these compounds. These results suggest that activation of the brain phospholipase A(2)-arachidonic acid cascade facilitates the central sympatho-adrenomedullary outflow in rats. Brain thromboxane A(2) is involved in the activation of central adrenomedullary outflow and an active metabolite of arachidonic acid other than thromboxane A(2) may be involved in activation of the central sympathetic outflow.

Nicotine-induced noradrenaline release from the isolated rat stomach by activation of L- and N-type calcium channels

We examined the effect of nicotine on the release of endogenous noradrenaline (NA) from the isolated, vascularly perfused rat stomach. The stomach was perfused via the coeliac artery with Krebs-Ringer solution containing 10 microM pargyline at a constant flow rate of 4 ml per minute. Nicotine was once applied in the perfusion medium for 2 min. Nicotine (10(-6) - 10(-4) M) evoked NA release in a concentration-dependent manner. The nicotine (3 x 10(-5) M)-evoked NA release was abolished by hexamethonium and tetrodotoxin. Diltiazem and isradipine [blockers of L-type voltage-activated calcium channel (VACC)] and omega-conotoxin GVIA (a blocker of N-type VACC) also abolished this nicotine-evoked NA release. Previously we reported that N-type, but not L-type, VACCs are located on the gastric postganglionic sympathetic nerve terminals, since the NA release evoked by electrical stimulation of periarterial nerves around the left gastric artery (postganglionic sympathetic nerves) was abolished by omega-conotoxin GVIA, but not by diltiazem (Yokotani et al., Jpn. J. Pharmacol. 78, 75- 77, 1998). From these results, it was suggested that nicotine activates nicotinic acetylcholine receptors located on the sympathetic ganglia, thereby evoking NA release by activation of L-type VACC located on the gastric sympathetic ganglia and N-type VACC probably located on the sympathetic nerve terminals in the rat stomach.

Perfusion of the hypothalamic paraventricular nucleus with N-methyl-D-aspartate produces thromboxane A2 and centrally activates adrenomedullary outflow in rats

We applied a microdialysis technique for the measurement of hypothalamic thromboxane B2, a stable metabolite of thromboxane A2, in urethane-anesthetized rats. Perfusion with N-methyl-D-aspartate (1.5 and 2.5mM) of the paraventricular nucleus by microdialysis probe concentration-dependently elevated the levels of thromboxane B2 in this region and plasma levels of catecholamines. The elevation of adrenaline was much more marked than that of noradrenaline. Pretreatment with dizocilpine maleate (0.1 mM), a non-competitive antagonist of N-methyl-D-aspartate receptors, of the paraventricular nucleus by microdialysis probe attenuated the N-methyl-D-aspartate (1.5 mM)-induced elevations of both thromboxane B2 and plasma catecholamines. Intracerebroventricular administration of furegrelate (250 microg/animal), a thromboxane A2 synthase inhibitor, also abolished the responses evoked by N-methyl-D-aspartate. These results indicate that N-methyl-D-aspartate applied into the paraventricular nucleus produces thromboxane A2 in this region and elevates plasma levels of catecholamines, especially adrenaline. Thromboxane A2 produced in this hypothalamic nucleus is probably involved in the N-methyl-D-aspartate-induced central adrenomedullary outflow.

Histamine H(3) receptor-mediated inhibition of endogenous acetylcholine release from the isolated, vascularly perfused rat stomach

We studied the effects of histamine H(3) receptor ligands on the release of endogenous acetylcholine from the isolated, vascularly perfused rat stomach. The stomach was perfused via the celiac artery with modified Krebs-Ringer solution containing physostigmine. Released acetylcholine from the portal vein was electrochemically measured using high-performance liquid chromatography and an enzyme system. Vagus nerves were electrically stimulated twice for 2 min (0.5 or 2.5 Hz). Acetylcholine release evoked at 2.5 Hz was slightly inhibited by histamine and effectively potentiated by thioperamide, a histamine H(3) receptor antagonist. Acetylcholine release evoked at 0.5 Hz in the presence of atropine was not influenced by thioperamide, but effectively inhibited by histamine, R-alpha-methylhistamine or imetit, histamine H(3) receptor agonists. These inhibitory effects were abolished by thioperamide or pertussis toxin. These results suggest that histamine attenuates acetylcholine release from vagus nerves through histamine H(3) receptor-mediated and pertussis toxin-sensitive mechanisms in the rat stomach.

U-46619, a selective thromboxane A2 mimetic, inhibits the release of endogenous noradrenaline from the rat hippocampus in vitro

Possible roles of thromboxane A2 (TXA2) in the release mechanism of hippocampal noradrenaline (NA) were examined in vitro. Slices or crude synaptosomes prepared from the rat hippocampus were superfused with modified Krebs-Ringer solution. Application of 20 mM KCl for 5 min increased the release of NA from the slices, and this release was consistently reproduced. Application of U-46619 (9,11-dideoxy-9alpha,11alpha-methanoepoxy prostaglandin F2alpha), a specific TXA2 mimetic, just before the second KCl (20 mM) stimulation decreased the KCl-evoked NA release in a concentration-dependent manner (10-100 microM). This U-46619 (50 microM)-induced inhibition of NA release was abolished by 10 microM SQ29548, a specific TXA2 receptor antagonist. In experiments with hippocampal crude synaptosomes, however, KCl (20 and 40 mM)-evoked release of NA was not attenuated by U-46619 (100 microM). Furthermore, the inhibitory effect of U-46619 (50 microM) in the sliced preparations was not modified by 100 microM (-)-bicuculline, a GABA(A)-receptor antagonist. The present results indicate that U-46619 inhibits the release of NA from the rat hippocampus by activation of TXA2 receptors. Activation of TXA2 receptors probably excites an unidentified but not GABAergic neuron system, thereby inhibiting the NA release from the rat hippocampus.

Melatonin inhibits the central sympatho-adrenomedullary outflow in rats

Central effects of melatonin on the sympatho-adrenomedullary outflow were investigated in urethane-anesthetized rats. In the intact animals, intracerebroventricularly (i.c.v.) administered interleukin-1beta (IL-1beta) (100 ng/animal) slightly, but significantly, elevated the plasma level of noradrenaline (NA), but not the level of adrenaline (Ad). Melatonin (100 microg/animal, i.c.v.) did not modulate the effects of IL-1beta on plasma levels of catecholamines. In the pinealectomized animals, however, the same dose of IL-1beta markedly elevated plasma levels of both Ad and NA, and the elevation of Ad was more potent than that of NA. In these pinealectomized animals, the serum level of melatonin was significantly lower than that in the sham-operated control animals. Furthermore, the IL-1beta-induced elevations of plasma catecholamines in these pinealectomized animals were attenuated by i.c.v. administered melatonin. These results suggest that melatonin plays an inhibitory role in the central regulation of sympatho-adrenomedullary outflow in rats.

Thromboxane A2 is involved in the nitric oxide-induced central activation of adrenomedullary outflow in rats

The central effect of 3-morpholinosydnonimine, a nitric oxide donor, on the sympatho-adrenomedullary system was investigated in urethane-anesthetized rats. Intracerebroventricular administration of 3-morpholinosydnonimine (100, 250 and 500 microg/animal) induced a marked elevation of adrenaline levels and a slight elevation of noradrenaline levels in the plasma. These 3-morpholinosydnonimine (250 microg/animal)-induced elevations of catecholamines were abolished by intracerebroventricular treatments with 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-l-oxyl 3-oxide (750 microg/animal), a nitric oxide scavenger, and indomethacin (500 microg/animal), a cyclo-oxygenase inhibitor, but not with superoxide dismutase (250 units/animal), a superoxide anion scavenger. Furthermore, the 3-morpholinosydnonimine (250 microg/animal)-induced elevation of plasma adrenaline levels was abolished by intracerebroventricular treatments with thromboxane A2 synthase inhibitors [furegrelate (100, 250 and 1000 microg/animal) and carboxyheptyl imidazole (500 microg/animal)], and also with thromboxane A2 receptor blockers [(+)-S-145 (100, 250 and 1000microg/animal) and SQ29548 (8microg/animal)]. The elevation of noradrenaline levels was, however, not attenuated by these thromboxane A2-related test agents. The present results indicate that nitric oxide but not peroxynitrite markedly activates central adrenomedullary outflow. Thromboxane A2 in the brain is probably involved in this central activation of adrenomedullary outflow.

Involvement of mu-receptor in endogenous opioid peptide-mediated inhibition of acetylcholine release from the rat stomach

We examined the effect of endogenous opioid peptides on vagally evoked release of acetylcholine (ACh) from the isolated, vascularly perfused rat stomach. The vagus nerves were electrically stimulated twice at 2.5 Hz for 2 min, and test substances were administered during the second stimulation. beta-Endorphin (10(-7) and 3 x 10(-7) M), an endogenous nonselective agonist of mu-receptors, inhibited the release of ACh. However, [Leu5]-enkephalin, an endogenous nonselective agonist of delta-receptors, and U-50488, a kappa-receptor agonist, had no effect at a higher dose of 10(-6) M. Beta-endorphin-induced inhibition was abolished by naloxone. Endomorphins 1 and 2 (3 x 10(-7) and 10(-6) M), endogenous selective agonists of mu-receptors, also inhibited the release of ACh. These results suggest that the mu-receptor is involved in the endogenous opioid peptide-induced inhibition of the release of ACh from the rat stomach.

Involvement of N-type voltage-activated Ca2+ channels in the release of endogenous noradrenaline from the isolated vascularly perfused rat stomach

We characterized the voltage-activated Ca2+ channels involved in noradrenaline (NA) release from gastric sympathetic neurons using isolated, vascularly perfused rat stomach. The evoked NA release by electrical stimulation of periarterial nerves was abolished by calcium removal from the perfusion medium and by cadmium. Omega-conotoxin GVIA (N-type Ca2+-channel blocker) effectively and omega-conotoxin MVIIC (N/P/Q-type blocker) slightly inhibited the evoked NA, while omega-agatoxin IVA (P-type blocker) had no effect. These results suggest that omega-conotoxin GVIA and omega-conotoxin MVIIC-sensitive N-type Ca2+ channels are involved in NA release from the rat gastric sympathetic nerve terminals.

Properties of calcium channels coupled to endogenous glutamate release from the vascularly perfused rat stomach in vitro

We have demonstrated that both high-K+ and electrical stimulation of the vagus nerves release endogenous glutamate from the vascularly-perfused rat stomach in a calcium-dependent manner. In the present study, we examined properties of calcium channel subtypes mediating endogenous glutamate release from the stomach. Application of 50 mM KCl elicited a release of glutamate, and this release was abolished in calcium-free medium. The release of glutamate was significantly inhibited by both omega-agatoxin IVA, a P/Q-type calcium channel antagonist, and isradipine, an L type calcium channel antagonist. Omega-conotoxin GVIA, an N type calcium channel antagonist and flunarizine, a nonselective T-type calcium channel antagonist were without effect. In contrast to this case of glutamate, omega-conotoxin GVIA induced a marked inhibition in the release of gastric noradrenaline. The combined treatment with omega-agatoxin IVA plus isradipine produced a marked synergistic inhibition of the glutamate release. This inhibition was, however, much less than that by cadmium. The present results suggest that P/Q and L type calcium channels coexist to regulate the release of gastric glutamate. Furthermore, it is possible that unidentified calcium channels other than P/Q and L type channels are also involved in the release of glutamate in the stomach.

Brain histamine mediates the bombesin-induced central activation of sympatho-adrenomedullary outflow

Intracerebroventricular (i.c.v.) administration of bombesin (0.3 nmol) increased plasma levels of both adrenaline and noradrenaline in urethane anesthetized rats. These bombesin-induced increases were inhibited by i.c.v. pretreatment with pyrilamine, an H1-receptor antagonist. Ranitidine, an H2-receptor antagonist also inhibited the increase of adrenaline, however, its effective dose was much larger than that of pyrilamine. Furthermore, the bombesin-induced increase of noradrenaline was not effectively inhibited by ranitidine. In the next series, turnover of histamine was assessed by measuring accumulation of tele-methylhistamine (t-MH), a major metabolite of brain histamine. I.c.v. administration of bombesin (0.3-3 nmol) increased turnover of hypothalamic histamine, while its intravenous administration was without effect. The present results suggest that the bombesin-induced central activation of sympatho-adrenomedullary outflow is probably, at least in part, mediated through brain histaminergic neurons.

Centrally applied nitric oxide donors inhibit vagally evoked rat gastric acid secretion: involvement of sympathetic outflow

ntracerebroventricularly (i.c.v.) administered nitric oxide (NO) donors, 3-morpholinosydnonimine (SIN-1) (100-500 microg/animal) and sodium nitroprusside (SNP) (100-250 microg/animal) dose-dependently inhibited the rat gastric acid secretion evoked by vagal stimulation at 3 Hz. Furthermore, the inhibitory effect of SIN-1 (250 microg/animal) was more marked and its onset was more rapid than that of SNP (250 microg/animal). The SIN-1 (250 microg/animal)-induced antisecretory effect was abolished by both splanchnicotomy and phentolamine (5 mg/kg, i.m.), and also by indomethacin (500 microg/animal, i.c.v.). These results suggest that i.c.v. administered NO donors inhibit vagally evoked gastric acid secretion by activation of central sympathetic outflow. Central prostaglandin is probably implicated in this NO-mediated antisecretory effect.

Nitric oxide mediates central activation of sympathetic outflow induced by interleukin-1 beta in rats

The excitatory mechanism of central sympathetic outflow induced by interleukin-1 beta was investigated in urethane-anesthetized rats. Intracerebroventricular administration of interleukin-1 beta induced a gradually developing elevation of plasma noradrenaline levels in a dose-dependent manner (50, 100 and 200 ng/animal), while the levels of adrenaline were not affected. The elevation of noradrenaline levels induced by interleukin-1 beta (100 ng/animal i.c.v.) was abolished by the following treatments with: (1) a chemical sympathectomizer, 6-hydroxydopamine (15 mg/kg i.v., 3 days before); (2) a prostaglandin synthesis inhibitor, indomethacin (500 micrograms/animal i.c.v.); (3) a nitric oxide synthase inhibitor, L-NG-nitroarginine methyl ester (100 micrograms plus 10 micrograms/min i.c.v.); and (4) a nitric oxide scavenger, oxyhemoglobin (32.3 micrograms plus 3.23 micrograms/min i.c.v.). In contrast to these results, D-NG-nitroarginine methyl ester, an inactive isomer of L-NG-nitroarginine methyl ester, and methemoglobin, a metabolite of oxyhemoglobin, were without effect. Furthermore, prostaglandin E2 (100 ng/animal i.c.v.) rapidly and markedly elevated the plasma level of noradrenaline but not adrenaline. This prostaglandin E2-induced elevation of plasma noradrenaline levels was not attenuated by L-NG-nitroarginine methyl ester (100 micrograms plus 10 micrograms/min i.c.v.). The present results suggest that nitric oxide is involved in the interleukin-1 beta-induced central activation of sympathetic outflow. Furthermore, there probably exists nitric oxide-linked prostaglandin-generating system in the brain.

Brain prostaglandins mediate the bombesin-induced increase in plasma levels of catecholamines

Intracerebroventricular (i.c.v.) administration of bombesin (0.1, 1.0, 10.0 nmol/animal) in urethane-anesthetized rats induced long-lasting and dose dependent increases in plasma levels of adrenaline and noradrenaline. These effects of bombesin were inhibited by i.c.v. pretreatment with indomethacin (50-500 micrograms/animal), while the same dose of indomethacin by the intravenous route was without effect. The bombesin-induced increases in plasma levels of catecholamines were also inhibited by i.c.v. pretreatment with diclofenac (100-500 micrograms/animal), a cyclooxygenase inhibitor other than indomethacin. I.c.v. administration of thyrotropin releasing hormone (TRH) (10 nmol/animal) also induced increases in plasma levels of adrenaline and noradrenaline, however, these increases were not modified by i.c.v. pretreatment with indomethacin. The present results suggest that the bombesin-induced increases in plasma levels of catecholamines are probably due to prostaglandins synthetized in the brain with this neuropeptide. Furthermore, it is likely that prostaglandins are not always involved in central activation of sympatho-adrenomedullary system by other brain neuropeptides.

Calcium-dependent release of endogenous glutamate from vascularly perfused rat stomach in vitro

To investigate a possible physiological role for glutamate in the stomach, release of endogenous glutamate from an isolated vascularly-perfused rat stomach preparation was studied. Glutamate was measured by the bioluminescence assay method. High concentrations of KCI (30-75 mM) induced a dose-dependent release of glutamate. This KCI-induced release of glutamate was abolished in calcium-free medium containing ethylene glycol bis (beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA). Electrical stimulation of the vagus nerves also induced a release of glutamate. This vagal stimulation-induced release of glutamate was abolished by both calcium removal and tetrodotoxin (TTX). Amounts of 13 other amino acids in the medium, detectable by the automatic amino-acid analyzer, were not significantly affected by both high-K+ and the vagal stimulation. These results provide additional evidence that glutamate probably serves as a neurotransmitter in the stomach.

Inhibition of vagally mediated gastric acid secretion by activation of central prostanoid EP3 receptors in urethane-anaesthetized rats

1. We studied the effects of intracerebroventricular (i.c.v.) administration of prostanoid EP receptor ligands on vagally stimulated gastric acid secretion in rats anaesthetized with urethane. 2. Administration of misoprostol (EP3/EP2 receptor agonist) and sulprostone (EP3/EP1 receptor agonist) reduced vagally mediated gastric acid secretion in a dose-dependent manner (0.1, 0.3 and 1.0 nmol per animal). Butaprost (EP2 receptor agonist) (0.3 and 3.0 nmol per animal) was without effect. 17-Phenyl-omega- trinor PGE2 (EP1/EP3 receptor agonist) attenuated vagally mediated gastric acid secretion only at its highest dose (1.0 nmol per animal); this antisecretory effect was not prevented by pretreatment with SC-19220 (selective EP1 receptor antagonist) (20 nmol per animal, i.c.v.). 3. The potency of these test agents in attenuation of vagally mediated gastric acid secretion was as follows: misoprostol > or = sulprostone > > 17-phenyl-omega-trinor PGE2 > > > butaprost. These results suggest that activation of central prostanoid EP3 receptors induces inhibition of vagally mediated gastric acid secretion in rats.

Recombinant interleukin-1 beta inhibits gastric acid secretion by activation of central sympatho-adrenomedullary outflow in rats

The inhibitory mechanism of gastric acid secretion induced by human recombinant interleukin-1 beta was investigated in bilaterally vagotomized, urethane-anesthetized rats. Intracerebroventricular administration of interleukin-1 beta (10, 50 and 100 ng/animal) dose dependently inhibited the gastric acid secretion induced by electrical stimulation of the vagus nerve at 3 Hz. Inhibition of gastric acid secretion induced by interleukin-1 beta (50 ng/animal) was abolished both by splanchnectomy and by phentolamine (5 mg/kg i.m.). Greater splanchnic nerves ramify into the adrenal branch and gastric sympathetic preganglionic branch. The interleukin-1 beta (50 ng/animal)-induced inhibition was also abolished by intracerebroventricular pretreatment with indomethacin (500 micrograms/animal), while pretreatment with the same dose of this reagent by the intraperitoneal route was without effect. These results suggest that centrally administered interleukin-1 beta induces a prostaglandin-mediated central excitation of the sympatho-adrenomedullary system, and the resultant activation of gastric alpha-adrenoceptors inhibits the vagally stimulated gastric acid secretion in rats.

Elevation of plasma noradrenaline levels in urethane-anaesthetized rats by activation of central prostanoid EP3 receptors

1. We studied the effects of intracerebroventricular (i.c.v.) administration of prostaglandin E2 (PGE2) and its receptor subtype ligands on plasma levels of catecholamines in urethane-anaesthetized rats. 2. Administration of PGE2 (0.15, 0.3 and 1.5 nmol per animal, i.c.v.) dose-dependently elevated plasma levels of noradrenaline (NA), while the levels of adrenaline were not affected. 3. Administration of sulprostone (EP3/EP1 agonist) and misoprostol (EP3/EP2 agonist) effectively elevated plasma NA levels in a dose-dependent manner (0.1, 0.3, and 1.0 nmol per animal). Butaprost (EP2 agonist) (0.3, 1.0 and 3.0 nmol per animal) was without effect. 17-Phenyl-omega-trinor PGE2 (EP1/EP3 agonist) effectively elevated plasma NA levels only at its highest dose (1.0 nmol per animal), but this elevation was not attenuated by pretreatment with SC-19220 (selective EP1 antagonist) (20 nmol per animal, i.c.v.). 4. The potency of these test agents in elevating plasma levels of NA was as follows; misoprostol > sulprostone > PGE2 > > 17-phenyl-omega-trinor PGE2 > > > butaprost. These results suggest that activation of central prostanoid EP3-receptors induces central sympathetic outflow in rats.

Centrally applied bombesin increases nerve activity of both sympathetic and adrenal branch of the splanchnic nerves

We reported that centrally applied bombesin probably excites both the gastric sympathetic and adrenomedullary systems and thus induces inhibition of gastric acid secretion. In the present study, therefore, we examined whether or not centrally applied bombesin directly affects sympathetic nerve activities in rats anesthetized with urethane. Intracerebroventricular administration of bombesin (0.3 and 3.0 nmol) increased discharge rates of the sympathetic branch as well as those of the adrenal branch of preganglionic greater splanchnic nerves. These effects were not secondary to changes in arterial blood pressure by bombesin. In conclusion, centrally applied bombesin directly activates both the sympathetic and adrenomedullary systems.

Properties of the voltage-gated calcium channels mediating dopamine and acetylcholine release from the isolated rat retina

We examined the properties of voltage-gated calcium channels mediating endogenous dopamine (DA) and acetylcholine (ACh) release in the isolated rat retina. Application of 30 mM KCl elicited the release of DA and ACh, and these releases were abolished in Ca(2+)-free medium. The high K(+)-evoked DA release was largely blocked by both of omega-agatoxin IVA and omega-conotoxin MVIIC, P- and Q-type calcium channel antagonists, and partly blocked by isradipine, and L-type calcium channel antagonist, and omega-conotoxin GVIA, an N-type calcium channel antagonist. omega-Agatoxin IVA at a small dose, sufficient to block P-type channels alone, was however without effect. On the other hand, the high K(+)-evoked ACh release was partly blocked by omega-agatoxin IVA and omega-conotoxin MVIIC, but was resistant to isradipine and omega-conotoxin GVIA. Flunarizine, a non-selective T-type calcium channel antagonist, did not inhibit the release of DA and ACh. Cd2+ markedly blocked the release of both DA and ACh, Co2+ and Ni2+ slightly blocked the release of DA, and the release of ACh was not blocked by these two divalent cations. These results suggest that the high K(+)-evoked release of retinal DA is largely mediated by omega-agatoxin IVA and omega-conotoxin MVIIC sensitive calcium channels (probably Q-type channels), while the release of retinal ACh is largely mediated by as yet uncharacterized Cd2+ sensitive calcium channels. The properties of voltage-gated calcium channels involved in the release of ACh in the rat retina differ from those of DA.

Muscarinic M3 receptor-mediated release of gastrin from canine antral G cells in primary culture

The functional role of the cholinergic nervous system in regulating gastrin release was investigated using enriched canine antral G cells. Gastrin content was 30.1 +/- 2.9 pmol per well and basal gastrin release was 900 +/- 27 fmol per well (n = 45). Carbachol (10(-8) to 10(-5) M) dose-dependently stimulated gastrin release with a maximal stimulatory response achieved at a concentration of 10(-5) M (330% over basal). To characterize the muscarinic receptor which mediates gastrin release from antral G cells, we examined the effect of three muscarinic receptor antagonists on carbachol-stimulated gastrin release; atropine (nonselective muscarinic receptor antagonist), pirenzepine (M1 muscarinic receptor antagonist) and 4-DAMP (M3 muscarinic receptor antagonist). Atropine (10(-9) to 10(-6) M), pirenzepine (10(-8) to 10(-5) M) and 4-DAMP (10(-9) to 10(-6) M) had no effect on the basal gastrin release. However, carbachol (10(-5) M)-stimulated gastrin release was effectively inhibited by atropine and 4-DAMP with Ki values of 0.48 and 0.66 nM, respectively. Pirenzepine at a high concentration (10(-5) M) also inhibited carbachol-stimulated gastrin release with a Ki value of 46.3 nM. These results suggest that the cholinergic nervous system directly stimulates gastrin release via M3 muscarinic receptors located on antral G cells.

Roles of adrenoceptors in isolated canine parietal cells

Functional roles of adrenoceptors in parietal cells were pharmacologically investigated using isolated canine parietal cells. In the crude membranes obtained from preparations highly purified in parietal cells (> 95% of purity), the specific binding of [3H]dihydroalprenolol (DHA) was observed with a Kd value of 2.9 nM and Bmax of 234 fmol/mg protein, while the specific binding of [3H]prazosin and [3H]rauwolscine were not attained. Propranolol concentration-dependently reduced the specific binding of [3H]dihydroalprenolol with a Ki value of 2.6 nM. Isoproterenol concentration-dependently stimulated [14C]aminopyrine accumulation in preparations enriched in parietal cells (about 70% purity) with the maximum at 10 nM. Isoproterenol increased the content of cyclic AMP in preparations enriched in parietal cells (70%) with the maximum at 100 nM. The isoproterenol-induced stimulatory effect of [14C]aminopyrine accumulation in preparations enriched in parietal cells (70%) was completely abolished by 1 microM propranolol but not by 1 microM phentolamine. In the presence of 1 microM propranolol, 100 microM noradrenaline did not affect carbachol- and histamine-induced [14C]aminopyrine accumulation in preparations enriched in parietal cells (70%). The present study suggests that stimulation of beta-adrenoceptors located on canine parietal cells evokes acid production in a cyclic-AMP-dependent manner. Furthermore, a possibility arises that canine parietal cells are not the site of action of alpha-adrenoceptors in mediating inhibition of gastric acid secretion.

Release of endogenous acetylcholine from a vascularly perfused rat stomach in vitro; inhibition by M3 muscarinic autoreceptors and alpha-2 adrenoceptors

We measured endogenous overflow of acetylcholine (ACh) from a vascularly perfused rat stomach in vitro with modified Krebs-Ringer solution containing 100 microM physostigmine. Evoked ACh overflow by vagal stimulation at 2.5 Hz for 2 min was abolished by tetrodotoxin (3 x 10(-7) M) or Ca++ removal and reduced by hexamethonium (10(-4) M). The evoked overflow was inhibited by oxotremorine (10(-7) to 10(-5) M), but not attenuated by 4-(N-[3-chlorophenyl]carbamoyloxy)-2-butynyltrimethylammonium chloride (10(-6) and 10(-5) M). The evoked ACh overflow was enhanced by atropine (10(-9) to 10(-6) M), 4-diphenylacetoxy-N-methylpiperidine (10(-8) to 10(-6) M), methoctramine (10(-8) to 10(-6) M) and pirenzepine (10(-8) to 10(-6) M) in a concentration-dependent manner with the following potency; atropine > 4-diphenylacetoxy-N-methylpiperidine > methoctramine > pirenzepine. In the presence of 10(-6) M atropine, clonidine (10(-8) and 10(-7) M), but not phenylephrine (10(-7) and 10(-6) M), concentration-dependently decreased the evoked overflow of ACh at 1 Hz. Electrical stimulation of periarterial gastric sympathetic nerves (5 and 10 Hz for 2 min) frequency-dependently inhibited the evoked ACh overflow at 1 Hz in the presence of atropine and sympathetic inhibition mediated at 5 Hz was abolished by 10(-6) M rauwolscine, but not by 10(-6) M prazosin. These results indicate that the ACh release from gastric parasympathetic neurons is inhibited by M3 muscarinic autoreceptors and alpha-2 adrenoceptors.

Roles of central nicotinic receptors in regulation of gastric functions

In the first part of this paper, the effects of single administration of nicotine on gastric motility of urethane-anesthetized rats are briefly summarized from our recently reported papers. Then, the effects of repeated administration of nicotine on the nicotine-induced changes in gastric motility and release of hypothalamic noradrenaline, in vitro, are described, with special references to up-regulation of nicotinic receptors. Nicotine 0.1 nmol administered into the dorsal motor nucleus of the vagus (DMV) elicited a dual change, a decrease followed by an increase in gastric motility. Intravenous administration of nicotine 300 nmol/kg decreased gastric motility. This decrease in gastric motility was inhibited by microinjection of hexamethonium into the DMV and was terminated by bilateral vagotomy. In animals pretreated with nicotine 200 nmol intracerebroventricularly (icv) administered once a day for 5 days, nicotine 100 nmol administered icv induced the decrease but not the increase in gastric motility. In conclusion, nicotine activates nicotinic receptors in the DMV and a resultant vagally-mediated dual change in gastric motility occurs. Furthermore, gastric inhibitory mechanisms in the DMV are susceptible to nicotine more than the excitatory mechanisms, and desensitization to nicotine occurs easily in the excitatory mechanisms.

Microinjection of alpha-calcitonin gene-related peptide into the hypothalamus activates sympathetic outflow in rats

Effect of rat alpha-calcitonin gene-related peptide (alpha-CGRP) microinjected into various hypothalamic nuclei on plasma levels of catecholamines and arterial blood pressure were investigated in urethane-anesthetized rats. alpha-CGRP (0.05 and 0.25 nmol) microinjected into the hypothalamic paraventricular nucleus (PVN) increased the plasma level of noradrenaline (NA), but not that of adrenaline (AD), in a dose-dependent manner. A similar increase in plasma level of NA was also observed by alpha-CGRP (0.05 nmol) microinjected into the preoptic area (POA), anterior hypothalamus (AH), dorsomedial hypothalamus (DMH) and ventromedial hypothalamus (VMH). A significant increase in arterial blood pressure was observed by microinjection of alpha-CGRP (0.05 nmol) into the PVN, POA, AH and DMH, and the most prominent increase was caused by its microinjection into the PVN. Microinjection of the same dose of this peptide into the VMH, lateral hypothalamic area and posterior hypothalamus was without effect. The increase in plasma level of NA induced by alpha-CGRP (0.05 nmol) into the PVN was not affected by bilateral adrenalectomy. Electrical stimulation of the PVN elicited increases in plasma levels of both NA and AD. This increase in NA was abolished by chemical sympathectomy with 6-hydroxydopamine (50 mg/kg, i.v., 3 days before experiments). These results suggest that activation of the PVN by electrical stimulation elicits both sympathetic and adrenomedullary outflow. alpha-CGRP microinjected into the PVN selectively activates the sympathetic outflow.

Cholinergic M2 muscarinic receptor-mediated inhibition of endogenous noradrenaline release from the isolated vascularly perfused rat stomach

We measured endogenous noradrenaline (NA) overflow from a vascularly perfused rat stomach in vitro. The stomach was perfused with Krebs-Ringer solution containing 10 microM pargyline. Periarterial nerves, which contain postganglionic sympathetic nerves, around the left gastric artery were stimulated for 1 min with square-wave pulses of 2 msec duration, 2.5 to 5.0 Hz, supramaximal intensity (10 mA). Oxotremorine (10(-8) to 10(-6) M) concentration-dependently inhibited the periarterial nerve stimulation-evoked NA overflow under the presence of 10(-6) M phentolamine. Bilateral vagus nerve stimulation (5 Hz, 2 msec duration, 10 mA, for 1 min) reduced the evoked NA overflow. Oxotremorine (10(-7) M)-induced inhibition of NA overflow was attenuated by atropine, methoctramine (muscarinic M2 receptor antagonist), 4-diphenylacetoxy-N-methylpiperidine (M3 receptor antagonist) and pirenzepine (M1 receptor antagonist) with the following potency; atropine > methoctramine > 4-diphenylacetoxy-N-methylpiperidine >> pirenzepine. The oxotremorine-induced inhibition was attenuated by N-ethylmaleimide (3 x 10(-5) M for 50 min), but was not affected by pertussis toxin pretreatment (10 micrograms/rat, for 4 days). However, this pretreatment with pertussis toxin abolished completely negative chronotropic and inotropic effects of oxotremorine in rat atria. These results suggest that NA release from gastric sympathetic nerve terminals is inhibited by activation of muscarinic M2 receptor, and this receptor-mediated inhibitory mechanisms are insensitive to pertussis toxin.

Release of endogenous noradrenaline from the vascularly perfused rat stomach in vitro: modulation by pre- and postsynaptic adrenoceptors

We developed an experimental in vitro model to detect a very small amount of endogenous noradrenaline (NA) released from the rat gastric sympathetic nerve terminals. The stomach was perfused via celiac artery with modified Krebs-Ringer solution containing 10 mM pargyline and 0.1% bovine serum albumin at a constant flow of 4 ml/min. The right greater splanchnic (SPL) nerve (preganglionic nerve of the gastric sympathetic nerve) was stimulated electrically with square-wave pulses of 2 msec duration and supramaximal intensity (5 mA) for 1 min. The rat stomach contained about 750 ng of NA and spontaneous overflow was about 0.05% of tissue content per 2 min. The NA overflow induced by SPL nerve stimulation at 5 Hz was abolished by tetrodotoxin (3 x 10(-7) M) and by Ca(++)-free medium containing 2 mM ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetic acid. Hexamethonium (5 x 10(-4) M) significantly decreased the NA overflow induced by SPL nerve stimulation at 5 Hz. Yohimbine (10(-7) and 10(-6) M) and prazosin (10(-7) and 10(-6) M) dose-dependently enhanced the NA overflow induced by SPL nerve stimulation at 5 Hz. Clonidine (10(-7) and 10(-6) M) and methoxamine (10(-5) M) significantly decreased the NA overflow induced by SPL nerve stimulation at 1 Hz and this methoxamine-induced inhibition was abolished by 8-(p-sulfophenyl)-theophylline (5 x 10(-5) M).(ABSTRACT TRUNCATED AT 250 WORDS)

Chemical sympathectomy with 6-hydroxydopamine potentiates intracerebroventricularly applied bombesin-induced increase in plasma adrenaline

Intracerebroventricular administration of bombesin induced a marked increase in plasma level of adrenaline and a slight increase in that of noradrenaline in rats anesthetized with urethane. The bombesin-induced increase in adrenaline was potentiated by chemical sympathectomy with 6-hydroxydopamine (6-OHDA). On the other hand, adrenalectomy did not affect plasma level of noradrenaline in the bombesin-treated animals. In the splanchnicotomized rats, direct stimulation of the adrenal glands by intravenously administered nicotine increased plasma level of both adrenaline and noradrenaline. These increases were, however, not potentiated by chemical sympathectomy with 6-OHDA. Pretreatment with capsaicin, a potent toxin selective to sensory neurons, potentiated the bombesin-induced increase in plasma level of adrenaline. In these capsaicin pretreated rats, chemical sympathectomy did not potentiate the bombesin-induced increase in plasma level of adrenaline to any great extent. These results suggest that chemical sympathectomy with 6-OHDA potentiated the bombesin-induced increase in plasma adrenaline probably due to a disinhibitory activation of the splanchnic nerve by as yet unidentified but capsaicin sensitive neuron mechanisms.

Somatostatin receptors on canine fundic D-cells: evidence for autocrine regulation of gastric somatostatin

Somatostatin is known to have inhibitory effects on the release and action of a wide variety of gut peptides. Previous studies in vivo have suggested a potential inhibitory role for somatostatin even on its own secretion. To determine whether this autoregulatory effect is the result of a direct action of the peptide on the cell that is responsible for its secretion, we examined the effect of a non-immunoreactive but biologically active analogue of somatostatin ([Leu8-D-Trp22-Tyr25]S28) on release of somatostatin-like immunoreactivity (SLI) from isolated canine fundic D-cells. We identified somatostatin binding sites with dissociation constants of 1.2 X 10(-9) and 3.8 X 10(-8) M that coenriched with D-cells. Somatostatin 14, somatostatin 28, and [Leu8-D-Trp22-Tyr25]S28 were equivalent in displacing 125I-[Leu8-D-Trp22-Tyr25]S28 from the binding sites. [Leu8-D-Trp22-Tyr25]S28 inhibited SLI release from D-cells stimulated with (DBcAMP), and pentagastrin. Pertussis toxin pretreatment prevented the inhibitory effects of [Leu8-D-Trp22-Tyr25]S28 on both SLI secretion and cAMP accumulation by on both SLI secretion and cAMP accumulation by D-cells stimulated with epinephrine and forskolin. In contrast, [Leu8-D-Trp22-Tyr25]S28 inhibition of SLI release induced by DBcAMP and pentagastrin was not altered by pertussis toxin. Our data suggest that somatostatin autoregulates its own secretion via specific receptors on D-cells. This inhibitory effect is mediated by mechanisms that are both dependent on and independent of pertussis toxin-sensitive inhibitory guanine nucleotide binding proteins.

Central depletion of dopamine in rats by 1-methyl-4-phenylpyridine

Effects of 1-methyl-4-phenylpyridine(MPP+), a putative neurotoxic metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine(MPTP), on the contents of dopamine were examined in the various regions of the rat brain. Under anesthesia with pentobarbital sodium and flunitrazepam, MPP+ 150 micrograms/rat was intracerebroventricularly infused for 5 hours, at 30 micrograms/100 microliters/hr. Seven days later, the contents of dopamine, but not those of noradrenaline and activities of choline acetyl transferase in the brain were found to be significantly decreased, as compared to findings in the respective controls. The MPP+-induced depletion of dopamine was most evident in the striatum (38% of control). Contents of dopamine in the substantia nigra and ventral tegmental area were not significantly affected by MPP+. These results are interpreted to mean that intracerebroventricular continuous infusion of MPP+, in a relatively low concentration, induces a moderate but relatively specific disruption of central dopaminergic nerve terminals in rats, presumably by the selective accumulation of this neurotoxic agent into these nerve terminals.

Alpha-2-adrenoceptor-mediated inhibition of vagally induced gastric acid secretion with the anti-ulcer agent DQ-2511

Effects of DQ-2511, a new peripherally acting anti-ulcer agent, on vagally induced gastric acid output and mucosal blood flow (MBF) were investigated in urethane-anesthetized rats with gastric fistula. Intravenous infusion of DQ-2511 (2 or 20 mg/kg/hr, for 30 min) reduced the vagally induced gastric acid output and MBF, and these inhibitory effects were abolished by pretreatment with phentolamine. The DQ-2511-induced inhibition of acid output was abolished with yohimbine, but not with prazosin. These observations suggest that DQ-2511 possesses the properties of an adrenergic alpha-2-adrenoceptor agonist. DQ-2511 presumably acts on adrenergic alpha-2-adrenoceptors located on the parasympathetic neurons in the gastric wall, thereby reducing the vagally-induced gastric acid output.