The group of drugs described as “Ca2+-entry blockers” is chemically and pharmacologically heterogenous. It is believed now that these drugs are useful in the treatment of ischemic disease. In an effort to define which drugs could offer the best therapeutic alternative, a comparative pharmacological study was made. Nine drugs (D-600 diltiazem, flunarizine, nicardipine, nifedipine, nimodipine, nitrendipine, verapamil, tiapamil) were tested in experimental screening models of brain hypoxia, ischemia, cellular intoxication and against bicucullineinduced seizures. Three types of activity were found. Verapamil, D-600, tiapamil and diltiazem were almost inactive, possibly due to their poor brain penetration. The dihydropyridines had a broad spectrum of activity, but considerable differences between these compounds exist. They all were active against hypoxia and less active against ischemia. Out of this subgroup, only nicardipine protected against metabolic intoxication and nifedipine and nicardipine could block seizure components at very high doses. Flunarizine was the only compound with a doserelated effect in all the tests. These results suggested that this combination of screening tests could be used to find compounds with an interesting activity in the field of cerebral protection.
To evaluate the antitumor activity of Agrimonia pilosa LEDEB., the effects of the methanol extract from roots of the plant (AP-M) on several transplantable rodent tumors were investigated. AP-M significantly prolonged the life span of S180-, Meth-A fibrosarcoma and MM-2 mammary carcinoma-bearing mice by intraperitoneal (i.p.) pre- or postmedication. AP-M also inhibited the growth of 5-180 solid type tumor. On the other hand, the prolongation of life span induced by AP-M on S-180 ascites type tumor-bearing mice was markedly minimized or abolished by the pretreatment of cyclophosphamide. AP-M showed considerably strong cytotoxicity on MM-2 cells in vitro, but the effect was diminished to one-tenth by the addition of serum to the culture. Against the host animals, the peripheral white blood cells in mice were significantly increased from 2 to 5 days after the i.p. injection of AP-M. On 4th day after the injection of AP-M, the peritoneal exudate cells which possessed the cytotoxic activity on MM-2 cells in vitro were also increased to about 5-fold those in the non-treated control. The spleen of the mice was enlarged, and the spleen cells possessed the capacity to uptake 3H-thymidine. However, AP-M did not show direct migration activity like other mitogens against spleen cells from non-treated mice. These results indicate that the roots of Agrimonia pilosa contain some antitumor constituents, and possible mechanisms of the antitumor activity may be some host-mediated actions and direct cytotoxicity.
The significance of anionic and cationic charges of glycocalyx, phospholipid or protein, etc. on the cell surface of the rat brain was examined for β-adrenoceptors using the radioligand binding assay method. Thus, this experiment was designed to assess the effects of polymeric effectors, DNA, heparin, polymyxin B, histone, gelatin, colominic acid and bovine serum albumin (BSA), on the affinity of β-adrenoceptors. The rat brain was used and the β-adrenoceptor binding assay was carried out using 3H-dihydroalprenolol as a radioligand. Polymyxin B, DNA and heparin significantly caused a reduction in the maximum number of β-adrenoceptors (Bmax), but only small changes were observed with histone, gelatin, BSA and colominic acid. Only DNA induced a decrease in the value of the dissociation constant (Kd) of β-adrenoceptors. These results suggest that anionic or cationic charges in the environment of the receptor sites could have a crucial role in drugreceptor interaction.
In order to confirm whether dopamine inhibits the antidiuretic action of vasopressin in mammalian kidney, we examined interactions among arginine vasopressin (AVP), dopamine and haloperidol in water-loaded ethanol anesthetized rats. The submaximal dose of AVP causing antidiuresis was 80 μU in this preparation. Dopamine at the doses of 0.11, 1.1 and 11 μg/100 g body weight (i.v.) inhibited the antidiuretic effect of 80 μU AVP by 18±7, 27±6 and 36±14%, respectively. The effect of 1.1 μg/100g body weight dopamine in inhibiting the action of AVP was completely reversed by haloperidol at 2.3 μg/100g body weight. Single administration of dopamine or haloperidol was without effect on urine flow. These observations support the view that dopamine inhibits the antidiuretic action of vasopressin by dopaminergic receptors also in the mammalian kidney.
The autonomic and antihypertensive activities of amosulalol (YM-09538) were studied in conscious rats. Single oral administration of amosulalol antagonized the phenylephrine-induced pressor and isoproterenol-induced positive chronotropic responses with DR10 values of 11.5 and 13.6 mg/kg in pithed rats, respectively, indicating that the compound inhibits both α1- and β1-adrenoceptors to almost the same extent in agreement with previously reported results in vitro. Amosulalol was approximately 50 times less potent than prazosin and 12 times more potent than labetalol at α1-adrenoceptors, and it was approximately as effective as labetalol and 2 times more potent than propranolol at β1-adrenoceptors. In spontaneously hypertensive rats (SHR), renal hypertensive rats and DOCA/salt hypertensive rats, a single oral administration of amosulalol (3-30 mg/kg) lowered acutely systolic blood pressure with a duration of over 6 hr and was found to be approximately 50 times less potent than prazosin and 3 times more potent than labetalol in lowering blood pressure. Propranolol did not cause such an immediate hypotensive effect. Amosulalol and labetalol did not increase heart rate, whereas prazosin induced a tachycardia in the hypertensive rats. Repeated oral administrations of amosulalol and labetalol (50 mg/kg/day, b.i.d., for 12 weeks) produced not only an antihypertensive effect without evidence of tolerance, but also reductions in plasma renin activity (PRA) and heart rate in SHR with established hypertension. We conclude that α-adrenoceptor blockade by amosulalol might account for its antihypertensive activity and that its β-adrenoceptor blockade might inhibit reflexogenic increases in heart rate and PRA due to the reduction in blood pressure.
Alcohol-sensitive Japanese subjects with facial flushing and an increase in heart rate during ethanol intoxication exhibited marked individual variation in accumulation of acetaldehyde. This variation correlated well with the intensity of the above mentioned physiological responses. Oral pretreatment with 10 mg/kg 4-methylpyrazole, which inhibited the ethanol elimination rate by 15-25%, strongly suppressed both acetaldehyde accumulation and the associated responses. Under this condition, the sensitivity to acetaldehyde appeared to be reduced, and the correlation between the acetaldehyde level and the physiological responses disappeared. The effectiveness of even a low dose of 4-methylpyrazole suggests its clinical usefulness for alleviation of acute acetaldehyde toxicity in alcoholhypersensitive Japanese individuals as well as in disulfiram-treated alcoholics.
Immunocytofluorescent and microautoradiographic methods were applied to measure met-enkephalin-like immunoreactivity (MELI) and ME receptor binding (MERB) levels in cerebral nuclei of serial brain slices from SHR which received clonidine, α-methyldopa and hydralazine at equivalent hypotensive doses. All three drugs increased both MELI and MERB levels in the caudal part of the n. tractus solitarii and its functionally related dorsomedullary nuclei and decreased them in the n. accumbens septi, in accordance with the correspondent change in glucose utilization rates in these nuclei as reported previously. Both CNS-active agents (not hydralazine) also increased MELI and MERB levels in the n. intercalatus and substantia grisea centralis, and they decreased them in the n. ventromedialis hypothalami. Differences in both CNS-active agents were minor. Vasodilative hydralazine alone decreased these levels both in the n. reticularis medialis and n. tegmenti ventralis, and it increased them slightly in the area lateralis hypothalami. The present studies indicate that ME neurons of these dorsomedullary and supramedullary nuclei may act as direct as well as homeostatic controls of blood pressure.
Our study was designed to evaluate the effects of the K+ channel blocker tetraethylammonium TEA (20 mM), Ca++ ionophore A23187 (6.9 μM), the Ca++ channel blocker verapamil (2 μM), and CaCl2 (6 mM) on a model of heart damage, hypoxia/reoxygenation of isolated guinea-pig hearts. The right ventricular papillary muscles maintained at 37°C and paced at 60 beats/min were perfused with Ringer solution equilibrated with 95% O2-5% CO2 (normoxia) or 95% N2-5% CO2 (hypoxia). After stabilization of the electrical and mechanical activity, 60 min of hypoxia was induced and then followed by 15 min of reoxygenation. During hypoxia, there was a significant decrease in the action potential duration (APD) and the contractile force (CF). The decrease in APD in the TEA-treated muscle was significantly less than that in the non-treated muscle. However, CF declined at the same rate in both groups. Neither A23187, CaCl2 nor verapamil prevented the decline in both APD and CF. To study the slow responses, the fast Na+ current was first voltage-inactivated by partial depolarization to about -40 mM using an elevated K+ solution. The rate of hypoxia-induced blockade of the slow response was not slower in the presence of 20 mM TEA. These data demonstrate that TEA significantly prevented the decline of APD in hypoxia, but this resistance in APD did not affect the rate of inhibition of mechanical activity.
Antiarrhythmic effects of intravenous coronary vasodilators (verapamil, diltiazem, bepridil, trimetazidine and nicorandil) were evaluated using two canine ventricular arrhythmia models (halothane-adrenaline arrhythmia and digitalis arrhythmia), and the minimum effective plasma concentrations of the drugs were determined for each arrhythmia model. Verapamil (0.1 mg/kg), diltiazem (0.1 mg/kg), bepridil (1 mg/kg) and high dose trimetazidine (10 mg/kg) were effective on halothane-adrenaline arrhythmia; and the minimum effective plasma concentrations of the above drugs were less than 30±10 ng/ml, less than 18±5 ng/ml, 0.38±0.11 μg/ml and 7.0±1.5 μg/ml, respectively. Nicorandil (1 mg/kg) did not suppress halothane-adrenaline arrhythmia. Verapamil, diltiazem and bepridil must have suppressed the halothane-adrenaline arrhythmia by blocking the Ca channel. Verapamil (1 mg/kg), diltiazem (1 mg/kg), bepridil (5 mg/kg), trimetazidine (3 mg/kg) and nicorandil (3 mg/kg) were ineffective on digitalis arrhythmia, even though their maximum hypotensive doses were used.
The stainless steel cannula inserting method was used to examine the effects of periarterial electrical nerve stimulation and intraluminal norepinephrine in the isolated and perfused mesenteric artery of the dog. The optimum conditions for inducing an increase in perfusion pressure over 50 mmHg to periarterial electrical stimulation were 3-5 msec duration, 40-50 volts and 10-20 Hz. After the treatment with phentolamine or prazosin, the vasoconstrictor response to norepinephrine was readily inhibited completely at a relative small dose of 0.3-3 μg. Periarterial stimulation-induced vasoconstriction was also significantly suppressed by a relatively large dose of 100 μg of phentolamine or prazosin in concentrations 30 to 100 times larger than that required for blocking the norepinephrine-induced constriction. Yohimbine in relatively small doses potentiated the stimulation-induced vasoconstriction, but rather suppressed it in a large dose. The constrictor response to periarterial stimulation was significantly suppressed by 1 and 10 μg of intraluminal tetrodotoxin. It is concluded that periarterial electrical stimulation in the cannula inserting method is useful for studying autonomic pharmacology and physiology in vasculature with due regard to the characteristics.
Interactions of several muscarinic drugs with their receptors were studied in the ciliary body smooth muscles of the rabbit. The ciliary body smooth muscles responded to carbachol, a muscarinic full agonist, with concentration-dependent contractions, and the pD2 value of carbachol was 5.16±0.05. Atropine, a competitive antagonist of muscarinic receptors, produced a parallel shift to the right in the concentration-response curves for carbachol. Pilocarpine which is a wellknown partial agonist on muscarinic receptors in most smooth muscles did not cause any contraction in this tissue. The drug, however, behaved as a competitive antagonist on the muscarinic receptors in the ciliary body smooth muscles. The pA2 values of atropine and pilocarpine versus carbachol obtained from the Schild plot are 8.97±0.25 and 5.17±0.09, respectively. On the other hand, arecoline and oxotremorine acted as a partial agonist in this tissue. The intrinsic activity, and pD2 and pA2 values were 0.41±0.02, 4.93±0.05 and 5.32±0.05 for arecoline respectively, and were 0.26±0.02, 5.64±0.08 and 6.12±0.16 for oxotremorine, respectively. The pA2 values of these drugs were significantly larger than the corresponding pD2 values of the drugs. The values of the negative log molar dissociation constant of carbachol, arecoline and oxotremorine estimated by the method of partial irreversible blockade of spare receptors with 3×10-6 M phenoxybenzamine were 4.53±0.08, 5.20±0.09 and 6.02±0.06, respectively. These values were practically equal to those obtained from other peripheral tissues, suggesting that the muscarinic receptors in rabbit ciliary body smooth muscles were qualitatively the same as those of other smooth muscles. However, the density of muscarinic receptors in this tissue is lower than that in other peripheral tissues, and the threshold phenomenon lay between the occupation of muscarinic receptors and the tissue responses. Therefore, the pA2 values of partial agonists were different from their pD2 values, and pilocarpine, a partial agonist with lower intrinsic efficacy, behaved as a competitive antagonist in this tissue. These results suggest the importance of the receptor density and the threshold in the tissue as well as the affinity and the intrinsic efficacy of the drug as a determinant of agonist potency.
The pharmacological properties of β-adrenoceptors in rat ascites hepatoma cells were compared with those in normal rat liver cells which were cultured for 24 hr after collagenase digestion. Adenylate cyclases in the homogenates of cultured normal rat liver cells and rat ascites hepatoma cells, AH44, AH66, AH109A, AH130 and AH7974, were all activated by isoproterenol or NaF to different degrees. The enzyme in rat liver cells was activated by several β2-agonists but those in all hepatoma cells hardly responded. Furthermore, salbutamol, a β2-partial agonist, antagonized the cyclase activation by isoproterenol in AH130 cells. The Kact value of isoproterenol for the activation of adenylate cyclase in AH1 30 cells was smaller than that in rat liver cells. A comparison of the Ki values of β-antagonists for the inhibition of isoproterenol-stimulated cyclase activity shows that while the Ki values of propranolol and butoxamine in AH130 cells were similar to those in rat liver cells, a significant difference was observed in the values for β1-selective antagonists between AH130 cells and rat liver cells. The Ki values of metoprolol and atenolol for AH130 cells were 137- and 90-fold lower, respectively, than for normal rat liver cells. From these findings, it is strongly suggested that β-adrenoceptors in rat ascites hepatoma cells including AH130 cells have similar properties to the mammalian β1-receptor.
An intracoronary administration of lonomycin A, a K-selective ionophore, produced coronary vasodilatation in the presence of pindolol in anesthetized dogs. Coronary vasodilatation induced by lonomycin A, KCl and nifedipine was inhibited by pretreatment with an intracoronary injection of ouabain. This result suggests that lonomycin A-induced coronary vasodilatation may be partly due to a stimulation of Na+, K+-ATPase as well as KCl and/or a decrease in Ca2+ influx as well as nifedipine.
A marked potentiation of the antinociceptive action of morphine was produced by haloperidol, but apomorphine had no effect on the antinociceptive action of morphine in acute experiments. Following chronic treatment with haloperidol, the antinociceptive action of morphine was significantly suppressed by apomorphine, and apomorphine shifted the dose-response curve of morphine to the right and increased the ED50 value of morphine by 2.3-fold. These results suggest that the suppressive action of apomorphine on the antinociceptive effect of morphine in chronic haloperidol-treated mice may be due to an increased sensitivity of postsynaptic dopaminergic receptors to apomorphine.
A novel sesquiterpene anticomplementary agent, K-76COONa, if locally applied, was revealed to have an activity to prevent histamine release from rat connective tissue mast cells not only in a zymosan-induced inflammation of the air pouch type (zymosan-air-pouch inflammation) but also in compound 48/80-induced air-pouch inflammation. Moreover, K-76COONa inhibited in vitro histamine release from rat peritoneal mast cells induced by compound 48/80.