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H Moritoki

Publications and source records attributed to H Moritoki.

At least 19 recordsLinked to original sources
PubMed1992

Possible mechanisms of age-associated reduction of vascular relaxation caused by atrial natriuretic peptide.

We investigated the effect of aging on atrial natriuretic peptide (ANP)-induced relaxation and cyclic GMP (cGMP) formation in the rat thoracic aorta. In the aorta from young rats (4 weeks old), removal of the endothelium, and treatment with the nitric oxide synthesis inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), the radical scavenger, hemoglobin (Hb), and the soluble guanylate cyclase inhibitor, methylene blue (MB), attenuated ANP-induced relaxation and considerably reduced ANP-stimulated cGMP formation. With increasing age of the rats, the ANP-induced relaxation and cGMP formation in endothelium-intact aorta decreased, and Hb, L-NAME and MB no longer inhibited the ANP-induced effects, irrespective of whether the endothelium was present or absent. In the arteries without endothelium, the age-associated reduction in ANP-induced relaxation was less than in arteries with endothelium. Aging also decreased the relaxation induced by the soluble guanylate cyclase activator, nitroprusside. Potentiation due to the cGMP-phosphodiesterase (cGMP-PDE) inhibitor, M&B 22948, of the ANP-induced relaxation was greater in aortas from old rats than in those from young rats, suggesting that the degradation of cGMP may be accelerated in old rats. These results suggest that the relaxant action of ANP on the thoracic aorta from young rats is in part modulated by endothelium-derived relaxing factor (EDRF/nitric oxide), which in turn activates soluble guanylate cyclase, thus elevating the cGMP level. Aging may decrease the ANP-induced relaxation and ANP-stimulated increase in cGMP level by decreasing the ability of endothelial cells to produce EDRF, by decreasing guanylate cyclase activity, and by enhancing cGMP-PDE activity.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed1992

Nitric oxide synthase responsible for L-arginine-induced relaxation of rat aortic rings in vitro may be an inducible type.

1. Characteristics of L-arginine-induced non-endothelial nitric oxide (NO) formation in rat isolated thoracic aorta were investigated. 2. Relaxation to L-arginine in arterial rings devoid of endothelium developed about 2 h after the first challenge with L-arginine and reached a maximum after a further 4 h of incubation. 3. After the arteries had relaxed in response to L-arginine, guanosine 3':5'-cyclic monophosphate (cyclic GMP) production was stimulated. In fresh arteries that had not yet relaxed in response to L-arginine, L-arginine failed to elevate cyclic GMP levels. 4. Glucocorticoids, actinomycin D and polymyxin B prevented the development of L-arginine-induced relaxation and L-arginine-stimulated increase in cyclic GMP formation. 5. Once L-arginine-induced relaxation developed, these agents no longer suppressed the relaxation and increase in cyclic GMP formation to L-arginine. 6. From these results, it is suggested that in the isolated thoracic aorta of the rat, endotoxin in the medium triggers induction of a non-endothelial NO synthase during prolonged incubation, which accelerates production of NO from added L-arginine to cause relaxation of the arteries via cyclic GMP. Glucocorticoids and protein synthesis inhibitors may prevent induction of NO synthase. It is suggested that the NO synthase mediating the production of muscle-derived NO from L-arginine is an inducible type.

Amino Acid Oxidoreductases↗
PubMed1992

Involvement of nitric oxide pathway in the PAF-induced relaxation of rat thoracic aorta.

1. The mechanism of the vasorelaxant effect of platelet activating factor (PAF) on rat thoracic aorta and the effect of aging on the PAF-induced relaxation were investigated. 2. PAF at concentrations causing relaxation induced marked increases in guanosine 3':5'-cyclic monophosphate (cyclic GMP) production, but did not induce an increase in adenosine 3':5'-cyclic monophosphate (cyclic AMP). 3. Removal of the endothelium by mechanical rubbing, and treatment with the PAF antagonists CV-3988, CV-6209 and FR-900452, the nitric oxide biosynthesis inhibitor, NG-nitro L-arginine, the radical scavenger, haemoglobin, and the soluble guanylate cyclase inhibitor, methylene blue, inhibited PAF-induced relaxation and abolished or attenuated PAF-stimulated cyclic GMP production. 4. The relaxation was greatest in arteries from rats aged 4 weeks. With an increase in age, the response of the arteries to PAF was attenuated. 5. Endothelium-dependent cyclic GMP production also decreased with increase in age of the rats. 6. These results suggest that PAF stimulates production of nitric oxide from L-arginine by acting on the PAF receptors in the endothelium, which in turn stimulates soluble guanylate cyclase in the smooth muscle cells, and so increases production of cyclic GMP, thus relaxing the arteries. Age-associated decrease in PAF-induced relaxation may result from a reduction of cyclic GMP formation.

Aging↗
PubMed1991

L-arginine induces relaxation of rat aorta possibly through non-endothelial nitric oxide formation.

1. The relaxation of rings of rat thoracic aorta induced by L-arginine and its derivatives was investigated. 2. L-Arginine (0.3-100 microM), but not D-arginine, induced relaxation of the arteries, which was detectable after 2 h and maximal after 4-6 h on its repeated application; it was endothelium-independent. 3. L-Arginine methyl ester, N alpha-benzoyl L-arginine and L-homo-arginine had essentially similar effects to those of L-arginine. 4. NG-nitro L-arginine methyl ester (L-NAME, 3 microM), NG-nitro L-arginine (L-NNA, 1 microM) and NG-monomethyl L-arginine (L-NMMA, 10 microM), inhibitors of nitric oxide (NO) formation from L-arginine, inhibited or reversed the L-arginine-induced relaxation, irrespective of the presence or absence of the endothelium. In contrast, NG-nitro D-arginine was without effect. 5. Haemoglobin (Hb, 10 nM) and methylene blue (MB, 0.3 microM) inhibited or reversed the L-arginine-induced relaxation. 6. L-Arginine (1-100 microM), but not D-arginine, increased guanosine 3':5'-cyclic monophosphate (cyclic GMP) levels in the tissues that relaxed in response to L-arginine. This effect of L-arginine was suppressed by Hb (3 microM), MB (1 microM) and L-NAME (100 microM). Removal of the endothelium did not significantly alter the L-arginine-induced cyclic GMP production. 7. These results suggest that L-arginine itself caused a slowly developing relaxation of rat aorta, possibly via formation of NO by an endothelium-independent mechanism.

Animals↗
PubMed1991

[Physiologically active compounds in the extracts from tochukaso and cultured mycelia of Cordyceps and Isaria].

Tochukaso is a Chinese traditional medicine composed of a fruit body of Cordyceps sinensis and its parasitic host larva. Tochukaso (C. sinensis) and the cultured mycelia of five species of Cordyceps and four species of Isaria were each extracted with hot water and examined for the inotropic effect on guinea-pig right atrium in vitro system. The extracts from C. militaris and I. felina showed a negative inotropic effect to approximately the same extent as that from Tochukaso. These three extracts also showed inhibitory action on twitch response of guinea-pig ileum and aggregation of human blood platelet. It is suggested that these activities are ascribed to the combination of adenosine, 5'-adenosine monophosphate and several other nucleic acid-related compounds, all of which have been shown to be present in the extracts.

Animals↗
PubMed1990

Resolution, absolute stereochemistry, and enantioselectivity of 2-methyl-4-phenyl-1,2,3,4-tetrahydroisoquinolin-4-ol.

Racemic 2-methyl-4-phenyl-1,2,3,4-tetrahydroisoquinolin-4-ol (PI-OH) (1) was found to be an effective potentiator of the contractile response of norepinephrine (NE) on rat anococcygeus muscle. This paper describes the resolution of racemic PI-OH by an HPLC method to give the optically pure enantiomers (+)-1 and (-)-1. The absolute configuration of (+)-1 was R as determined by CD analysis and by single-crystal X-ray diffractometric analysis of the methiodide 6 derived from (+)-1. Examination of the effects of the enantiomers to potentiate the contraction of the rat anococcygeus muscle by NE showed a high degree of enantioselectivity. The NE potentiation was found to reside exclusively in (R)-(+)-1; the activity ratio being 21 at 3 x 10(-6) M, whereas (S)-(-)-1 did not show any potentiating and inhibiting activity.

Animals↗
PubMed1990

Dual effects of capsaicin on responses of the rabbit ear artery to field stimulation.

1. The effects of capsaicin (Cap) on contractions of ring segments of rabbit ear artery induced by field stimulation were studied. 2. At low concentrations (0.3-3 microM) Cap caused transient enhancement and at higher concentrations (above 3 microM) inhibition of stimulation-induced contractions, without affecting noradrenaline (NA)-induced contractions. 3. In the continuous presence of high concentrations of Cap, rebound facilitation was observed after inhibition, and at this stage, Cap elicited less inhibition of the response. 4. Repeated application of Cap at 60 min intervals irreversibly desensitized the artery to the inhibitory effect of Cap. 5. Functional removal of the endothelium enhanced the facilitatory effect of low concentrations of Cap and attenuated its inhibitory effect. 6. Pretreatment with indomethacin abolished the facilitatory effect of Cap and enhanced its inhibitory effect, indicating that prostaglandins are involved in the action of Cap. The effect of indomethacin was more marked in preparations from which the endothelium had been removed. 7. Desensitization to substance P (SP) or substance K (SK), did not affect either the inhibitory or the facilitatory effect of Cap. 8. These results suggest that the dual effects of Cap on stimulation-induced contractions of rabbit ear artery may arise from the release of multiple mediators that act prejunctionally to modulate NA release. The stimulant effect seems to be mediated by prostanoids, while the inhibitory effect seems to be caused by a substance(s) that is not SP or SK. The possibility that the mediator is calcitonin gene-related peptide requires further study.

Animals↗
PubMed1990

Evidence for the involvement of cyclic GMP in adenosine-induced, age-dependent vasodilatation.

1. Adenosine-induced dilatation of rat aorta was present in aorta taken from 4 week-old rats, attenuated with increase in age of rats to 8 weeks, and was virtually absent in the aorta from 12 week-old rats. 2. Removal of the endothelium by mechanical rubbing attenuated adenosine-induced dilatation. 3. Haemoglobin and methylene blue partly reversed the adenosine-induced endothelium-dependent dilatation. 4. The order of potency of adenosine derivatives was 5'-(N-ethylcarboxamido)adenosine (NECA) greater than 2-phenylaminoadenosine (CV-1808) greater than 2-chloroadenosine greater than N6-([R]-[-]-phenylisopropyl)adenosine (R-PIA) greater than adenosine greater than N6-cyclohexyladenosine (CHA) greater than N6-([S]-[+]-phenylisopropyl)adenosine (S-PIA), indicating that adenosine receptors mediating the dilatation are of the A2 subtype. 5. [3H]-NECA bound to preparations of membranes from rats of 4 weeks old; it was displaced more effectively by NECA and the A2 ligand CV-1808 than by the A1 ligands CHA and S-PIA. ligands CHA and S-PIA. 6. The number but not affinity of specific binding sites for NECA decreased considerably with increase in age of rats to 8 weeks, and binding sites for [3H]-NECA were hardly detected in membrane preparations from rats of 20 weeks old. 7. Adenosine caused a marked increase in cyclic GMP production, but did not induce an increase in the cyclic AMP level. 8. This increase in cyclic GMP production induced by adenosine was abolished by methylene blue or 8-phenyltheophylline, or by removal of the endothelium. 9. The age-associated decrease in adenosine-induced dilatation was found to be associated with a reduction in the formation of cyclic GMP, but not of cyclic AMP. 10. These results suggest that adenosine causes dilatation via A2 receptors by inducing production of an endothelium-derived relaxing factor (EDRF), which in turn stimulates soluble guanylate cyclase, and so increases production of cyclic GMP. It is also suggested that the main reason for the age-associated decrease in adenosine-induced dilatation is a decrease in the number of A2-receptors or the ability of the endothelium to produce EDRF, leading to decreased production of cyclic GMP.

Adenosine↗
PubMed1989

Solution syntheses of two enkephalin-containing peptides, peptide E and dynorphin(1-24), using Nin-(2,4,6-triisopropylphenylsulfonyl)tryptophan.

Two enkephalin-containing peptides, peptide E and dynorphin(1-24), were synthesized by conventional solution methods employing a new Trp derivative, Nin-(2,4,6-triisopropylphenylsulfonyl)tryptophan [Trp(Tps)]. All protecting groups employed including the Tps group were removed by treatment with 1 M trifluoromethanesulfonic acid (TFMSA)-thioanisole in trifluoroacetic acid (TFA) at the final steps of these syntheses. Subsequent purifications by Sephadex G-25 chromatography, CM-Biogel A ion exchange chromatography, and reversed-phase high-performance liquid chromatography afforded highly purified samples. Both synthetic peptide E and dynorphin(1-24) exhibited high in vitro opioid activity. The usefulness of this new tryptophan derivative for practical peptide synthesis was established through these syntheses of complex Trp-containing peptides.

Amino Acid Sequence↗
PubMed1988

Age-associated decrease in histamine-induced vasodilation may be due to reduction of cyclic GMP formation.

1. The effects of aging on histamine-induced vasodilatation and cyclic GMP production in rat thoracic aorta were investigated. 2. This histamine-induced dilatation of the aorta was mediated by H1-receptors and was dependent on the endothelium. 3. Histamine induced the greatest dilatation of arteries of 3-4 week old rats, progressively less of those of rats of 8 to 56 weeks old, and scarcely detectable dilatation of those of 100 week old rats. 4. Histamine induced cyclic GMP production in aorta from rats of 4 weeks old, with no change in the cyclic AMP level. This increase in the cyclic GMP level induced by histamine also decreased with age, being about 70% as great at 8 weeks, 50% as great at 50-60 weeks, and 10% as great at 130 weeks of age. 5. Removal of the endothelium completely abolished the histamine-induced increase in cyclic GMP. 6. The dilator effect of nitroprusside, which enhances cyclic GMP production by stimulating guanylate cyclase directly (not indirectly via the endothelium derived relaxing factor, EDRF), also showed age-related attenuation. 7. The dilator effect of 8-bromo cyclic GMP, which stimulates cyclic GMP-dependent protein kinase, also decreased during aging. 8. These results suggest that aging reduces the ability of the endothelium to produce EDRF, which stimulates guanylate cyclase, and so decreases cyclic GMP production. Thus the decreased dilator response of the arteries to histamine during aging is probably due to both loss of endothelial function and reduction of guanylate cyclase activity. Alteration of cyclic GMP-dependent protein kinase activity may also participate in the age-related changes.

Aging↗
PubMed1987

Verapamil enhances the non-adrenergic twitch response of rat vas deferens.

Verapamil (3 X 10(-6)-3 X 10(-5) M) enhanced the twitch contractions of the epididymal and prostatic portions of vas deferens stimulated at 0.1 Hz. This verapamil effect was essentially similar to those of diltiazem, D-600 and Bay K 8644. However, when stimulation at 2 Hz was used verapamil (3 X 10(-5) M) attenuated the contractions of the epididymal portion by half but still augmented those of the prostatic portion. Verapamil enhanced the reserpine- and prazosin-resistant component of the stimulation-induced contractions of both portions of the vas deferens. Yohimbine augmented the twitch response but attenuated the verapamil-augmented response. Verapamil did not augment norepinephrine- or tyramine-induced contractions whereas it augmented ATP-induced contractions of the prostatic portion but not of the epididymal portion. Verapamil increased the stimulation-evoked 3H-efflux from the vas deferens labelled with [3H]norepinephrine. It is suggested that verapamil augments non-adrenergic responses of both portions of the vas deferens by acting as a Ca agonist on the prejunctional site to increase the release of co-transmitter, or by acting on the postjunctional site to enhance the action of the substance released. Its effect in augmenting norepinephrine release is concluded not to contribute to the potentiating action.

Animals↗
PubMed1987

Capsaicin enhances the non-adrenergic twitch response of rat vas deferens.

1 Capsaicin (Cap) enhanced the twitch response of the epididymal and prostatic portions of rat vas deferens induced by field stimulation at 0.1 Hz. The effect of Cap was reproducible and showed no desensitization. 2 Prazosin, and pretreatment with reserpine or Cap did not affect the potentiating effect of Cap, whereas pretreatment with 6-hydroxydopamine abolished the action of Cap. 3 Cap tended to attenuate the contractions induced by noradrenaline, tyramine and ATP. 4 Like Cap, substance K and substance P augmented the twitch response without causing desensitization, but their effects differed somewhat from that of Cap. Calcitonin gene-related peptide inhibited the twitch response. 5 These results suggest that Cap enhances a stimulation-induced, prazosin-resistant non-adrenergic twitch response of rat vas deferens through an as yet undefined prejunctional mechanism. This mechanism is possibly mediated by some peptide released in response to Cap from sensory neurones, which in turn acts on sympathetic nerves and increases stimulation-induced release of a mediator or cotransmitter responsible for the non-adrenergic twitch response. However, the possibility that Cap has a direct action on sympathetic nerves cannot be ruled out.

Animals↗
PubMed1986

Age-related change in serotonin-mediated prejunctional inhibition of rat vas deferens.

The effect of age on the serotonin (5-HT)-induced prejunctional inhibition of twitch contractions induced in rat vas deferens by single-pulse field stimulation at 0.1 Hz was studied. The inhibitory effect of 5-HT gradually decreased with increasing age of the rats (4-15 weeks old) and was no longer detectable in preparations from rats over 15 weeks old. Moreover, on a further increase in age to 45 weeks, 5-HT conversely enhanced the twitch response of the vas deferens. The 5-HT2 antagonists ketanserin and mianserin potentiated the 5-HT-induced inhibition of contractions of the vas deferens of young rats (8-15 weeks old), and attenuated the amplifying effect of 5-HT on the responses of preparations from old rats (95 weeks old). Thus unmasking of the inhibition depended on the age of rats. This change occurred earlier in life in the prostatic portion of the vas deferens than in the epididymal portion. A functional decrease in 5-HT-mediated prejunctional inhibition and the resultant increase in amplification of the twitch response by 5-HT are probably responsible for the age-related decrease in prejunctional inhibition.

Adenosine Triphosphate↗
PubMed1986

Age-related decrease in endothelium-dependent dilator response to histamine in rat mesenteric artery.

The effect of aging on the vasodilator responses to histamine, 2-pyridylethylamine and 4-methylhistamine of ring segments of rat mesenteric arteries were investigated. The maximal extent of histamine-induced dilatation of the arteries previously contracted with norepinephrine was greatest for arteries from rats aged 2 and 8 weeks. The maximal response decreased progressively with an increase in age to 13 and 56 weeks. Arteries from 99 week old rats scarcely responded to histamine. Under these conditions, the dilatation induced by papaverine showed no change with age. The vasodilatation caused by 2-pyridylethylamine and 4-methylhistamine also decreased age dependently. The dilatation of the arteries induced by these agents was inhibited by the H1-antagonist chlorpheniramine, but not by the H2-antagonist cimetidine. Removal of the endothelium completely abolished the vasodilator effect of histamine, leaving the effect of papaverine unaffected. Hydroquinone and methylene blue reversed the dilatation induced by histamine, without affecting that caused by papaverine. These results suggest that the age-related decrease in dilatation of rat mesenteric artery in response to histamine is mainly due to a decrease in the ability of the endothelium to liberate a mediator(s).

Aging↗
PubMed1986

Ketanserin potentiates the prejunctional inhibitory effect of 5-hydroxytryptamine on rat vas deferens.

5-Hydroxytryptamine (5-HT) slightly inhibited the twitch contractions of rat vas deferens caused by single pulse field stimulation at 0.1 Hz. The inhibitory effect of 5-HT was much less in the epididymal portion than in the prostatic portion of the vas deferens. Ketanserin potentiated the prejunctional inhibitory effect of 5-HT and attenuated its stimulatory effect. This potentiation was observable only in the epididymal portion, of the vas deferens. Cyproheptadine and mianserin, but not methysergide, had essentially similar potentiating effects to those of ketanserin. These results suggest that the 5-HT receptor that mediates prejunctional inhibition is not of the 5-HT2 type, and that ketanserin acts by suppressing the 5-HT-induced stimulatory effect, which is possibly mediated by a postjunctional 5-HT2 receptor, thus unmasking the inhibitory effect of 5-HT.

Animals↗
PubMed1985

Possible mechanism of action of diazepam as an adenosine potentiator.

Diazepam (10(-5)-3 X 10(-4) M) selectively enhanced the negative inotropic responses of guinea-pig atria and the relaxation of guinea-pig taenia coli caused by adenosine and ATP. In the atria, the effect of 2-chloroadenosine, a stable analog of adenosine, was not affected by diazepam. Segments of guinea-pig atria or taenia coli took up 3H-activity during incubation with [3H]adenosine but did not take up 32P-activity from [32P]ATP. Diazepam at concentrations sufficient to enhance the in vitro responses reduced by half the uptake of 3H-activity into the preparations. Adenosine (10(-6) M) and ATP (10(-6) M) were degraded to inactive inosine during incubation with atrial segments and their degradation was inhibited by diazepam. In contrast, in rat atria, diazepam did not enhance the negative inotropic effects of adenosine and ATP, and did not prevent the uptake of adenosine. These results suggest that in guinea-pig atria and taenia coli, diazepam like dipyridamole, acts as an adenosine potentiator by preventing the uptake and degradation of adenosine.

2-Chloroadenosine↗