The effect of synthetic ω-conotoxin (ω-CgTX) on the contractile responses of segments of rat ileum, stomach fundus and uterus and guinea pig taenia coli were investigated. ω-CgTX (10-9-5 × 10-6 M) did not inhibit the contractile responses of all smooth muscle segments to high KCl and/or ACh. However, unexpectedly, ω-CgTX (3 × 10-7-10-5 M) alone caused dose-dependent contraction of segments of the stomach fundus and uterus. These contractile responses to ω-CgTX alone depended upon the presence and/or the influx of extracellular Ca2+ and they were inhibited by calcium antagonists such as diltiazem, nitrendipine and verapamil, with the exception that the segments of stomach fundus was not inhibited by verapamil. With the segments of uterus, but not those of other tissues, ω-CgTX (10-7-5 × 10-6 M) significantly enhanced the contractile responses to various concentrations of ACh and high KCl. With rat ileum and guinea pig taenia coli segments, ω-CgTX (10-9-5 × 10-6 M) did not induce a contractile response or have an enhancing effect. These findings suggest that ω-CgTX may have a calcium agonist-like effect on smooth muscles such as the stomach fundus and uterus of rats.
Time course change in platelet function on liver damaged mice was studied by a whole blood aggregometer. The liver damaged animals were produced by single and multiple injections (p.o.) of 20% CCl4 in olive oil to ddY mice (6 weeks). Platelet aggregation and ATP-release were induced with collagen (final conc. of 2 μg/ml), ADP (final conc. of 20 μM) and arachidonic acid (AA: final conc. of 100 μM). After a single injection of CCl4, platelet counts increased at 5 and 12 hr, and then they decreased from 24 to 120 hr. Multiple injections of CCl4 resulted in a significant increase in platelet counts. A single injection of CCl4 suppressed aggregation by collagen at 24 and 48 hr and diminished the rate of ATP-release from 12 to 48 hr. AA-induced platelet aggregation was depressed at 48 hr, and ATP-release was also diminished from 24 to 72 hr after a single injection. ADP-induced platelet aggregation was decreased 24 and 48 hr after a single injection and at 48 hr after multiple injections, while, the rate of ATP-release by ADP was significantly increased after single and multiple injections. These changes in platelet functions might be consistent with our original report on the alterations in coagulative and fibrinolytic activities with CCl4-induced liver injury.
Heptaminol AMP amidate (HAA), a newly developed nucleotide derivative, was found to restore the immunosuppression in mice due to the induction of suppressor T (Ts) cells by concanavalin A (Con A) (50 μg/body). HAA also inhibited Con A-mediated in vitro induction of Ts cells. On the contrary, the administration of HAA in mice primed with keyhole lympet hemocyanin (KLH) (30 μg/body) caused an enhanced induction of antigen specific helper T (Th) cells. Effects of HAA on Ts and Th cells were found to be dependent on their level of induction. The administration of HAA also increased the spleen cell number and augmented the plaque forming cell response to some extent in cyclophosphamide treated mice. The present results suggested that HAA-mediated immunopotentiation was possible by a combined suppressive effect on Ts cells and enhancing effect on Th cells.
The frequency-dependency and voltage-dependency of the suppressing effect of pirmenol, a novel antiarrhythmic agent, on the maximum upstroke velocity (Vmax) of action potentials were examined and compared with those of disopyramide in guinea pig papillary muscles. Pirmenol in concentrations higher than 3 μM decreased Vmax with a slight increase in action potential duration. The reduction of Vmax by pirmenol was enhanced in a frequency-dependent manner over the range of 0.1-2.0 Hz. Pirmenol (30 μM) produced a small resting block (5.5%), whereas disopyramide (100 μM) produced a greater one (25.8%). The onset of frequency-dependent Vmax reduction at 2.0 Hz followed a monoexponential function with a slow rate constant (0.308±0.055 AP-1). The time constant for the recovery from the frequency-dependent block by pirmenol was also slow (33.5±5.4 sec), but faster than that of disopyramide (82.5±12.3 sec). At 1.0 Hz, pirmenol caused a shift (9.5 mV) of the curve relating the resting membrane potential and Vmax along the voltage axis in the hyperpolarizing direction. Thus, pirmenol is a Class la drug that has frequency and voltage-dependent inhibitory actions on Vmax, and its onset and offset kinetics are relatively slow.
Electrophysiological studies using reserpine-treated cats were carried out to elucidate the effects of L-threo-3, 4-dihydroxyphenylserine (L-threo-DOPS) on the noradrenergic pathway from the locus coeruleus (LC) to the caudate nucleus (CN) neurons, which were activated by iontophoretically applied bromocriptine, a dopamine D-2 receptor agonist. In the CN neurons, glutamate-induced firing was inhibited by iontophoretic application of noradrenaline, but not by repetitive stimulation of the LC or iontophoretically applied L-threo-DOPS. After intraventricular administration of L-threo-DOPS, however, LC stimulation inhibited the glutamate-induced firing. These results suggest that L-noradrenaline that was produced from the conversion of L-threo-DOPS inhibited the CN neurons which possess dopamine D-2 receptors.
Treatment of Japanese monkeys for 8 months with a high fat, high cholesterol diet produced atherosclerotic lesions in the aorta and mesenteric arteries, such as fatty dots, streaks and plaques, intimal thickening with accumulation of spindle-shaped cells and macrophages and endothelial cell flattening. Contractile responses of mesenteric arteries from control and atherosclerotic monkeys to electrical stimulation of adrenergic nerves, norepinephrine and angiotensin II did not differ, whereas contractions caused by serotonin in the atherosclerotic monkey arteries were significantly greater. Ketanserin and cinanserin suppressed the serotonin-induced contraction. Relaxations caused by adenosine and K+ (5 mM) were moderately attenuated in atherosclerotic monkey mesenteric arteries, and those by acetylcholine were reduced only slightly or not affected in the arteries or aortas. Relaxations of control and atherosclerotic arteries in response to nitroglycerin, isoproterenol and prostaglandin 12 did not differ. The relaxant response to K+ was reversed to a contraction by ouabain. Acetylcholine-induced relaxations were dependent on the endothelium and suppressed by atropine. Diet-induced atherosclerosis appears to potentiate contractions mediated via serotonergic 5-HT2 receptors and to attenuate relaxations possibly caused by activation of the electrogenic Na+ pump in the smooth muscle cell membrane. Endothelium-dependent relaxations via muscarinic receptors would not evidently be affected in mesenteric arteries and aortas from atherosclerotic Japanese monkeys.
The binding to a Ca-channel of a novel 1, 4-dihydropyridine (DHP) Ca-antagonist, 2-nitratopropyl 3-nitratopropyl 2, 6-dimethyl-4-(3-nitrophenyl)-1, 4-dihydropyridine-3, 5-dicarboxylate (CD-349), was studied in rat myocardium and brain and hog coronary artery, and the binding was compared with that of other DHPs. In rat myocardium, the binding reaction of [3H]CD-349 was faster than that of nitrendipine (NTD). The association rate constant of [3H]CD-349 was about 10 times higher than that of [3H] NTD. The dissociation rate was also higher than that of [3H]NTD. Scatchard plot analysis of [3H]CD-349 binding showed one high affinity site for CD-349. The dissociation constant (Kd) and maximum number of binding sites (Bmax) were 333 pM and 286 fmoles/mg protein. They were almost the same as those for [3H]NTD. [3H]CD-349 and [3H]NTD bindings were dose dependently inhibited by 1, 4-DHPs: nifedipine, nimodipine, nicardipine and CD-349. The order of the inhibitory potency of these drugs was CD-349>nicardipine>nimodipine>nifedipine, when [3H]CD-349 and [3H]NTD were used as the ligands. Similar results were obtained for rat brain and hog coronary artery. [3H]-CD-349 binding was not changed by α- or β-adrenergic, cholinergic, histaminergic or serotonergic agents in rat myocardium. From these results, it is suggested that CD-349 binds to the Ca-channel reversibly with high affinity due to its high association rate for the site.
The calcium-channel blocking action of franidipine (CV-4093·2HCl) was investigated in vitro and in vivo. CV-4093·2HCl inhibited the 60 mM K+-induced contraction of rabbit aorta and those of coronary, renal, mesenteric and femoral arteries of dog less potently than nifedipine and nicardipine. In dog portal and femoral veins, CV-4093·2HCl inhibited K+-induced contraction as potently as nifedipine and nicardipine did. The inhibitory effect of this drug was fully developed by pretreatment for 60 min, and it lasted long after washout. The drug inhibited both K+-induced 45Ca-influx and K+-induced contraction at a similar concentration range in rabbit aorta and dog portal vein, but had no effect on 45Ca-efflux from either vessel. On the other hand, in the isolated, perfused kidneys and mesenteric vascular beds of SHR, CV-4093·2HCl inhibited K+-induced vasoconstriction more effectively than did nifedipine. Moreover, in pithed rats (i.v.) and ganglion-blocked conscious SHR (p.o.), CV-4093·2HCl inhibited more potently α2-adrenergic pressor responses than did nicardipine. These pharmacological properties of CV-4093·2HCl, especially those seen in the isolated, perfused kidney and mesenteric vascular beds, may be responsible for its potent and long-lasting action as an antihypertensive agent.
Anticonvulsant activities of 3-methylphenytoin (3-MP) and 1, 3-dimethylphenytoin (1, 3-DMP) were observed to peak 3 hr after i.p. administration of the drugs dissolved in dimethylsulphoxide (DMSO), while maximal activity was obtained within 15 min with phenytoin. HPLC was employed to monitor the plasma concentrations of all three compounds at various time intervals after injecting 3-MP or 1, 3-DMP. In both cases, phenytoin appeared in the plasma, gradually reaching 14-15 μg/ml in 3 hr. The time course of increase in plasma phenytoin levels correlated with that of anticonvulsant activities. It was also found that 1, 3-DMP gave rise to a major unidentified metabolite as well as 3-MP and phenytoin. This unidentified metabolite eluted only half a minute in front of 3-MP in the HPLC. Mice injected with high doses of 3-MP (100 mg/kg) in DMSO exhibited severe epileptiform activities. Phenobarbital, diazepam and clonazepam were found to protect against such seizures, but not phenytoin, carbamazepine and valproic acid. This shows that 3-MP is at least a pro-convulsant, taking into account that its effects might have been enhanced by DMSO. Unlike phenytoin, 3-MP lacked the ability to inhibit synaptosomal uptakes of both glutamate and GABA. This difference may be related to the fact that phenytoin, but not 3-MP, possesses potent anticonvulsant activity.
As part of an investigation on the behavioral characteristics of SART-stressed animals, an animal model of autonomic imbalance, the open-field behavior of SART-stressed (repeated cold-stressed) rats was studied and compared with that of rats exposed to other types of stress. In addition, the effects of several drugs on it were also studied. As compared with normal rats, SART-stressed rats exhibited increased locomotor activity, rearing and center-field penetration, together with decreased grooming and increased defecation, whereas they showed no significant changes in spontaneous movements in the daytime as measured by an Animex activity meter. These behavioral abnormalities were remarkably different from those due to 1-hr cold, 48-hr cold and repeated restraint stresses. These abnormal forms of open-field behavior due to SART stress were considerably inhibited by chlorpromazine, imipramine and neurotropin at doses having no corresponding influence on normal rats; and they were partially inhibited by alprazolam, diazepam and carpipramine at doses exerting considerable influence on normal rats. The above results show that SART-stressed rats exhibit open-field behavioral abnormalities that are different from those of rats exposed to other types of stress. Such abnormalities include excessive activity, which is considered to be caused by excessive emotionality.
In order to examine the effect of cimetidine on the production of prostanoids in the stomach mucosa, the amounts of prostaglandin (PG) E2, F1α and thromboxane (TX) B2 were determined after the specimens from the rat stomach corpus were incubated in the presence of cimetidine. Cimetidine significantly stimulated the production of PGE2 in the specimens at a concentration of 10 μM, but did not significantly affect the production of PGF1α and TXB2 at concentrations of 1 to 100 μM.
Effects of oxiracetam and piracetam on acquisition of the discrete two-way shuttle avoidance response were investigated in normal mice of the dd strain. When oxiracetam or piracetam was administered only once immediately before the training session, the mice showed a greater number of avoidance responses in comparison with the saline-treated control mice, with the maximum effect at 30 mg/kg of oxiracetam and 100 mg/kg of piracetam. These results suggest that oxiracetam and piracetam facilitate the avoidance acquisition in normal mice.
The effect of methotrexate (MTX) on local cerebral blood flow (I-CBF) was studied with autoradiographic [14C]-iodoantipyrine methods in normal conscious rats. I-CBF was reduced by 30-57% in the rats given MTX (100 mg or 200 mg/body) as compared to that in the saline injected control group, but no dose-dependent effect was observed. The mechanism of I-CBF reduction by MTX was discussed.
Effect of AF102B (cis-2-methylspiro-(1, 3-oxathiolane-5, 3')-quinuclidine) on experimental amnesia was examined using a passive avoidance task in rodents. The amnesia was produced by anti-cholinergic agents, AF64A (intracerebroventricularly) and scopolamine (subcutaneously). AF102B ameliorated the memory deficits in AF64A-treated rats at 0.1-1 mg/kg, i.p. and at 1-5 mg/kg p.o. and in scopolamine-treated mice at 1-10 mg/kg, i.p. These results suggest that AF102B may compensate for central cholinergic defects and could be developed as a possible therapeutic drug for senile dementia of the Alzheimer type.
In isolated canine epicardial coronary arteries perfused with Krebs-Henseleit solution at 37°C, DN-9693, a newly synthesized selective cyclic AMP phosphodiesterase inhibitor, induced vasodilation in a dose-related manner. The threshold dose for inducing vasodilation to DN-9693 was very small, but the maximum vasodilation was not great. The order of potency for ED20 (20% dilatation) was DN-9693>IBMX>aminophylline, but that for ED70 was IBMX>aminophylline >DN-9693, suggesting that these three PDE inhibitors have different properties.
Using the cannula inserting method, we investigated whether vascular responses to norepinephrine, phenylephrine, clonidine, tyramine and KCl were altered by cooling (37°C to 27°C) in isolated canine ear arteries. Vasoconstrictor responses to norepinephrine, phenylephrine and tyramine were slightly depressed or unchanged, whereas those to clonidine and KCl were significantly suppressed by cooling. It is suggested that activation of Ca channels via alpha-2 adrenoceptors may be depressed by cooling in dog ear arteries.