Shigeki Hashimoto

Nitric oxide-dependent and -independent neurogenic relaxation of isolated dog urethra

In the presence of adrenergic and cholinergic blocking agents, transmural electrical stimulation evoked a relaxation in isolated dog urethra precontracted with histamine. The response was abolished by tetrodotoxin, indicating its neurogenic origin. The non-adrenergic and non-cholinergic relaxation developed rapidly and was transient at low stimulation frequencies (< or = 1 Hz). However, at higher frequencies (> or = 5 Hz) the recovery phase of the relaxation became slow and often showed a notch, suggesting the presence of transient and slow components. NG-Monomethyl-L-arginine, a nitric oxide synthase inhibitor, inhibited the transient relaxation but did not affect the relaxation evoked at high stimulation frequencies. NG-Nitro-L-arginine, a more potent nitric oxide synthase inhibitor, abolished the transient relaxation produced at low stimulation frequencies and markedly attenuated the transient component at high frequencies. However, NG-nitro-L-arginine did not affect the slow component. The inhibition by NG-monomethyl-L-arginine and NG-nitro-L-arginine was reversed by the addition of L- but not D-arginine. Exogenously applied vasoactive intestinal polypeptide (VIP) produced a slowly developing relaxation. The slow relaxation induced by transmural electrical stimulation and VIP was not affected by [4-Cl-D-Phe6,Leu17]VIP, a reportedly competitive VIP antagonist. NG-Nitro-L-arginine did not affect the relaxation induced by VIP and sodium nitroprusside. These results suggest that the non-adrenergic and non-cholinergic relaxation induced by transmural electrical stimulation is composed of nitric oxide-dependent and -independent components in the isolated dog urethra.

HIGHLY REGIO- AND STEREOSELECTIVE PHOTOCYCLOADDITION BETWEEN COUMARIN AND THYMINE BY MOLECULAR RECOGNITION

The photoreaction of Kemps imide-linked coumarin 1 and thymine 3 gave two crossadducts, cis-syn 4 cis-anti 5. The yield and ratio of 45 in benzene solution remarkably increased by factors of 4.2 and 10 than those in acetonitrile solution, respectively. On the other hand, the reaction of acetoxycoumarin 2 and 3 gave only the cis-anti crossadduct in each solution.

Inhibitory effect of inaperisone hydrochloride (inaperisone), a new centrally acting muscle relaxant, on the micturition reflex

We examined the effects of inaperisone hydrochloride (inaperisone), a new centrally acting muscle relaxant, on bladder function in anesthetized rats and isolated rat tissues. We also investigated its mechanism of action. When a balloon inserted into the bladder was expanded, rhythmic bladder contractions were observed; inaperisone (4 mg/kg i.v.) abolished these contractions, in both normal and decerebrated rats. The bladder tonus or bladder contraction induced by peripheral stimulation of the pelvic nerve was barely inhibited by inaperisone (4 mg/kg i.v.), but this dose of inaperisone abolished the efferent discharge from the pelvic nerve that accompanied the rhythmic bladder contractions. The doses of intracerebroventricularly (i.c.v.) and intrathecally injected inaperisone which abolished the rhythmic bladder contractions were 10 and 100 micrograms, respectively. The inhibitory effects of inaperisone (4 mg/kg i.v.) were not diminished by naloxone (1 mg/kg i.v.) or by bicuculline (0.5 mg/kg i.v.), but were diminished by phaclofen (30 mg/kg i.v. or 300 micrograms i.c.v.). The specific binding of [3H]baclofen to rat brain synaptosomal membranes was barely inhibited by inaperisone (up to 1 mM). From these results, it is speculated that, among other possible mechanisms, inaperisone inhibits the micturition reflex by acting indirectly on GABAB receptors in the brainstem.

Potent inhibition of spontaneous rhythmic contraction by a novel β2-adrenoceptor agonist, HSR-81, in pregnant rat uterus

We examined the effect of HSR-81 ((-)-(R)-alpha-[(tert-butylamino)methyl]-2-chloro-4-hydroxybenzyl alcohol L-tartrate), a newly developed, potent and selective beta 2-adrenoceptor agonist, as well as ritodrine and isoproterenol, on the spontaneous rhythmic contraction in uteri isolated from late pregnant, middle pregnant and non-pregnant (dioestrous and oestrous) rats. The three agonists inhibited the spontaneous rhythmic contraction at all the stages in a concentration-dependent manner. The pD2 value for HSR-81 was greater in late pregnancy than in dioestrus and oestrus. In the uterine preparations of late pregnancy and dioestrus, ICI-118,551 (1-(7-methylindan-4-yloxy)-3-isopropyl-aminobutan-2-ol , a selective beta 2-adrenoceptor antagonist) and atenolol (a selective beta 1-adrenoceptor antagonist) produced a parallel rightward shift of the concentration-response curves for HSR-81. The pKB values for ICI-118,551 and atenolol suggest that the inhibitory effect of HSR-81 was mediated through beta 2-adrenoceptors in the two stages. In the membranes prepared from rat uteri in late pregnancy and dioestrus, the equilibrium dissociation constant for [125I]iodocyanopindolol binding was not significantly different between the two stages. The three beta-adrenoceptor agonists and the two antagonists competed for the specific [125I]iodocyanopindolol binding and the pKi values were not significantly different between the two stages. However, the maximum number of binding sites was significantly greater in late pregnancy than in dioestrus. The configuration of the competition curves and the pKi values for the two antagonists confirmed the fact that these membranes contain predominantly beta 2-adrenoceptor subtype. These results indicate that the potent inhibition of the spontaneous rhythmic contraction by HSR-81 in the pregnant uterus may be due to the increased number of beta 2-adrenoceptors.

Nuclease activity of a hydroxamic acid derivative in the presence of various metal ions

Phenanthridine-linked hydroxamic acid 1 effectively cleaves ColE1 DNA in the presence of transition (ferrous, ferric and vanadyl) or lanthanide(III)(lutetium, thulium and europium) metal ions; in the presence of the former, the cleavage is inhibited by free radical scavengers, but in the latter case it is not.

Characterization of lanthanide-mediated DNA cleavage by intercalator-linked hydroxamic acids: comparison with transition systems

Phenanthridine-linked hydroxamic acids with alkyl chain of variable length (n= 3, 4, 5, 6 and 7) have been newly synthesized. Their DNA cleavage activities have been investigated by Col E1 plasmid relaxation assay in the presence of transition(II)(ferrous and vanadyl) or lanthanide(III)(lutetium) metal ions. Linker length is extremely determinant for lutetium-mediated DNA cleavage. The increase in cleavage activity of the lutetium system with increasing pH suggests the involvement of metal-bound hydroxide as catalytically active species. Middle (samarium and europium) and late (thulium, ytterbium and lutetium) trivalent lanthanide systems are effective for DNA cleavage. For maximal DNA cleavage activity, the lutetium/hydroxamic acid ratio has been found to be 2 whereas that of the transition system has been found to be 1. We propose a hydrolytic mechanism in which two lanthanide ions are acting in concert for effective DNA cleavage.

SYNTHESIS OF BISNETROPSIN-LINKED HYDROXAMIC ACIDS AND THEIR DNA CLEAVAGE STUDY IN THE PRESENCE OF TRANSITION OR LANTHANIDE METAL IONS

Nobel hydroxamic acids containing bis-netropsin units coupled by polymethylenetether (BNHA) have been synthesized. BNHA-ferrous complexes sequence-specifically cleaved pBR322 DNA fragment whereas corresponding cerium complexes showed low-sequence specific cleavage pattern.