Effects of the beta-receptor antagonists propranolol, oxprenolol and labetalol on human vascular smooth-muscle contraction

1. Spiral strips of human digital arteries have been studied in vitro to investigate whether DL-propranolol, D-propranolol, oxprenolol and labetalol have peripheral vascular effects in man. 2. Labetalol was a potent inhibitor of contractile responses to noradrenaline, but had less effect on responses to 5-hydroxytryptamine and barium chloride. 3. DL-and D-propranolol were equally effective inhibitors of responses to barium chloride. They were only weak antagonists of noradrenaline responses, but stronger, non-competitive antagonists of 5-hydroxytryptamine responses. 4. Oxprenolol was only a weak inhibitor of the responses to both noradrenaline and 5-hydroxytryptamine and had little effect on responses to barium chloride. 5. It is concluded that labetalol has specific alpha-adrenoreceptor-blocking properties, which are probably relevant to its therapeutic action in man. Propranolol has non-specific inhibitory effect on vascular smooth muscle, which might contribute to its hypotensive activity at high concentrations, but oxprenolol has only slight peripheral effects that are probably therapeutically insignificant.

[Pharmacological studies of loperamide, an anti-diarrheal agent. III. Interaction between loperamide and various agonists in the guinea pig intestine (author's transl)]

To clarify the mode of action of loperamide, the interaction with various agonists was investigated in guinea pig intestines. The following results were obtained. Prostaglandin E1 (0.1 microgram) or acetylcholine (1 approximately 3 microgram) injection into the mesenteric artery at 10 min intervals caused a constant rise of intraluminal pressure of the intestinal loop in situ. Loperamide (0.01 approximately 0.1 mg/kg i.v.) markedly suppressed the response induced by prostaglandin E1. Morphine (0.1 approximately 1.0 mg/kg i.v.) and atropine (0.01 mg/kg i.v.) also suppressed the response. The intestinal response induced by acetylcholine was inhibited markedly by atropine and slightly by loperamide (0.1 mg/kg i.v.) but not by morphine. Contractions of the isolated ileum induced by coaxial stimulation, BaCl2, nicotine and serotonin were suppressed by loperamide (10(-9) approximately 2 X 10(-7) g/ml). Morphine, methadone and codeine showed the same effect as loperamide but the activity was weaker than that of loperamide. Contractions of isolated ileum induced by acetylcholine, histamine and bradykinin, and Ca-contraction in the depolarized taenia coli were inhibited by relatively high concentrations of loperamide (2 X 10(-7) g/ml or above). These results suggest that loperamide suppresses the function of cholinergic neurons in the intestines.

The action of prazosin in human vascular preparations

To identify the mode of action of prazosin, its effects on isolated human vascular preparations were studied. Isometric tension was recorded from spiral strips of dorsal metacarpal veins, common palmar digital arteries and uterine, splenic and ileocolic arteries. Prazosin was a potent antagonist of noradrenaline, but not 5-hydroxytryptamine or barium chloride in the metacarpal veins. Higher concentrations of prazosin were necessary to antagonize noradrenaline in the visceral arteries. The digital arteries were resistant to its sympatholytic effect. It is concluded that prazosin acts as an alpha-adrenoceptor antagonist of different potency in various vascular beds. It is postulated that the initial cardiovascular side effects of prazosin are due to venous pooling and that the long term antihypertensive effect is the result of reduced peripheral resistance because of interference with arterial sympathetic tone.

Pharmacologic studies on W10,294A, a new bronchodilator

W10,294A (1,2,3,4-tetrahydro-8,9-dimethoxy-3(2-piperidinoethyl)-5H-[1] benzopyrano [3,4-c] pyridin-5-one dihydrochloride) is a potent antagonist of the bronchoconstriction induced by histamine, methacholine or acetylcholine. In vitro evaluation on guinea pig trachea indicated that W10,294A had both direct smooth muscle relaxant activity and modest antihistaminic properties. Resistance and dynamic compliance measurements in anesthetized dogs indicated that W10,294A prevented or reversed bronchoconstriction due to histamine or pilocapine. Bronchodilator activity of long duration was observed in dogs after oral administration. W10,294A was compared with aminophylline in several tests. W10,294A was 6 times more potent than aminophylline in relaxing isolated guinea-pig trachea. In the anesthetized dog W10,294A was more potent and longer acting than aminophylline in reversing pilocarpine-induced bronchospasm. The bronchodilator activity of W10,294A was not blocked by the beta adrenoceptor antagonist bunolol. Comparative studies in dogs and guinea pigs, using identical doses, showed that W10,294A had considerably less effect on the cardiovascular system than did aminophylline.

[Derivatives of 1,3-bis-(methlendioxyphenoxy)propane with antispastic activity]

A number of amines derived from 1,3-bis(3,4-methylen-dioxyphenoxy)propane have been prepared from 1,3-bis-(3,4-methylendioxy-phenoxy)propan-2-one. The acute toxicity and the activity of these compounds on isolated guinea pig ileum have been studied. The majority of the compounds showed clear antagonist activity towards BaCl2, histamine and acetylcholine contracting responses, generally grater than that of papaverine; on the contrary, their antagonist activity towards 5-HT responses was slightly lower.

Pharmacological evaluation of new calcium antagonists: 2-substituted 3-dimethylamino-5,6-methylenedioxyindenes

Calcium antagonists are valuable pharmacological tools for the study of stimulussecretion and excitation-contraction coupling mechanisms. Two 2-substituted 3-dimethylamino-5,6-methylenedioxyindene hydrochlorides were tested for antagonism of the spasmogenic action of various agonists on isolated smooth muscle preparations. The 2-n-propyl and 2-n-butyl aminoindenes (5 X 10(-5) to 10(-4) M) blocked the spasmogenic action on the estrogen-treated rat uterus of prostaglandin E2 (10(-7) M), prostaglandin F2alpha tromethamine salt (10(-7) M), oxytocin (10(-3) U/ml), barium chloride (BaCl2-2H2O; 2.2 X 10(-4) M), acetylcholine chloride (10(-6) M) and ergonovine maleate (7.5 X 10(-4) M); they also blocked the contractile effect on the ileum of acetylcholine chloride (10(-6) M; rat) and histamine hydrochloride (10(-6) M; guinea pig). In further experiments on rat uterus using the agonists acetylcholine chloride (10(-6) M; which presumably acts by increasing influx of extracellular calcium into cells) and barium chloride (2.2 X 10(-4) M; which presumably contracts smooth muscle by releasing intracellular calcium), a progressive increase in extracellular calcium concentration (from 9 X 10(-4) to 7.2 X 10(-3) M CaCl2-2H2O) was paralleled by progressive reversal of the blockade produced by both 2-substituted aminoindene antagonists. In studies on the perfused bovine adrenal medulla, the 2-n-propyl aminoindene (10(-4) M) completely blocked the calcium-dependent catecholamine secretion evoked by 0.1 and 3.3 mM carbachol, without affecting the calcium-independent catecholamine secretion evoked by 33 mM acetaldehyde. These findings suggest that the aminoindene antagonists interfere with the action of calcium and that in smooth muscle the antagonism is at an intracellular site involved in excitation-contraction coupling.

Characterization of the oxybutynin antagonism of drug-induced spasms in detrusor

Oxybutynin chloride exerts a moderate anticholinergic effect on rabbit detrusor in vitro, which is reversible and competitive in nature (KB = 4.7 x 10(-9), and midway in potency between atropine and papaverine. In addition, oxybutynin strongly antagonizes BaCl2-induced spasms of detrusor with a potency equivalent to that of papaverine and 10 times that of atropine. This musculotropic spasmolytic effect is slightly greater in rabbit than human or monkey tissue, and noncompetitive (pD2 = 5.5). This direct relaxant effect, unlike that of papaverine, is not mediated by the inhibition of tissue phosphodiesterase, but probably reflects oxybutynin's local anesthetic properties and associated effects on Ca++ fluxes and binding.

Bladder muscle contractility. Comparative effects and mechanisms of action of atropine, propantheline, flavoxate, and imipramine

The anticholinergic and antispasmodic activity of atropine, propantheline, imipramine, and flavoxate were judged by each drug's ability to inhibit bethanechol chloride and barium chloride-induced canine detrusor contractions. In this in vitro model, atropine and propantheline are pure anticholinergic agents. Imipramine significantly decreases both bethanechol and barium-induced contractions, while flavoxate only minimally inhibits the response to either stimulant.

[Pharmacological analysis of effects of perimetazine on isolated smooth muscle]

Effects of perimetazine on the motility of the isolated smooth muscle of guinea pig (ileum, taenia coli, uterus, vas deferens and trachea) and the ileum of rabbit were studied. The results obtained are as follows: Perimetazine showed a specific antihistamine, antiadrenaline and antiserotonin action. Moreover, antiacetylcholine and anti-BaC12 actions were observed with high doses of perimetazine as well as chlorpromazine and such actions were attributed to the nonspecific direct action on the smooth muscle. Both the spontaneous movement and the tonus of guinea pig taenia coli were also inhibited by a high concentration of perimetazine. The spontaneous membrane action potentials of the taenia coli recorded by the use of the sucrose-gap method were inhibited by a high concentration of perimetazine both in frequency and in amplitude with relaxation of the tonus. The action potentials were abolished however and change in the resting membrane level was not clearly observed.

Relationship between vasoconstriction and histamine induced vasodilation

Histamine produced significantly greater vasodilation in rabbit ear arteries constricted by noradrenaline than when the same arteries were constricted by either caffeine or barium. Histamine dilation in the presence of caffeine was also significantly greater than that in the presence of barium. These results suggest that histamine may produce vasodilation through at least two different modifications of intracellular calcium mobilisation.

[Action mechanism of dibenamine on the tonus and inhibition of drug-induced contraction of the isolated guinea pig ileum, with special reference to its relationship to Ca]

Dibenamine (DB) produced contraction due to influx and release of Ca in normal medium, whereas it produced relaxation of the K-induced contraction due to depression of the activity of the muscle cell membrane. DB inhibited active influx, passive influx and release of Ca induced by ACh in this order as the concentrations were increased and also inhibited the contraction by histamine selectively as compared with the contractions by ACh, K and Ba, the inhibition of the ACh-, K- and Ba-contractions being almost to the same degree. In addition, DB inhibited to much the same degree the phasic contraction(PC) and tonic contraction(TC) by histamine, whereas it inhibited TC in preference to PC induced by ACh, K and Ba. Irreversible inhibition by DB of ACh-, K- and Ba-induced contractions were protected by Ca, whereas those of histamine-induced contraction were selectively protected by histamine and antihistamine, but not by Ca. These results indicate that the antagonism of DB and its irreversibility against histamine may be due to blockade of the histaminergic receptor, whereas those against ACh, K and Ba may be due to inhibition of the Ca-site. Evidence has been obtained suggesting that the irreversible parallel shift to the right of the log concentration-action curve of histamine after washout of DB may be due to spare receptors, whereas that of ACh, K or Ba may be due to inhibition of the Ca-site.

Action of six commonly used benzodiazepines on isolated guinea-pig ileum preparation

The spasmolytic activity of six commonly used benzodiazepines was investigated on isolated guinea-pig ileum preparation. All six substances proved to be non-competitive antagonists of carbachol and barium chloride, the pD'2 values ranging between 3.23 and 4.37 in the presence of either agonist. The significance of these findings is discussed.

[Pharmacological action of cattle prostate extracts (PE). V. Effect on the bladder]

As the extract of cattle prostate (PE) is clinically effective in treating prostatic hypertrophy, a study was carried out on urinary bladders of rat, guinea pig, rabbit and dog as well as on guinea pig ileum. Muscle strip of rat and/or dog bladder contracted with PE with increasing spontaneous movement, and was unaffected by atropine. The isolated ileum of guinea pig also contracted with PE, and the contraction was inhibited by papaverine, but not by atropine. A rise in intravesical pressure was observed with increasing spontaneous movement in guinea pig bladder treated with PE, as well as in rabbit bladder in vitro or in situ. The sphincter vesica of guinea pig was dilated by PE as well as by ACh and methacholine.

[Pharmacological action of [ethyl p(6-guanidinohexanoyloxy)benzoate] methanesulfonate (FOY)]

General pharmacological effects of [Ethyl p-(6-guanidinohexanoyloxy)benzoate] methanesulfonate (FOY), a new antiproteolytic agent, were studied and the following results were obtained. Acute administration of large doses of FOY in conscious dogs and rabbits caused a decrease in spontaneous motility, ataxia, cyanosis, collapse, mydriasis, and respiratory paralysis. The agent had no effect on the central nervous system and exhibited hypotensive effects in dogs in doses of more than 1 mg/kg. Hypotensive responses were not inhibited by treatment with atropine or hexamethonium. FOY had no effects on ECG in the rabbit at doses of less than 30 mg/kg and at doses from 10(-6) to 10(-4)g/ml, distinctly reduced the amplitude of the spontaneous and rhythmic contractions of the isolated rabbit ileum, guinea-pig ileum and rat uterus preparation. The contractile response to nerve stimulation, noradrenaline and barium was suppressed in isolated guinea-pig vas deferens. FOY had no effects on the twitch response of gastrocnemius muscle to sciatic nerve stimulation in rats. The drug caused local irritant effects in rabbits and rats.

Spasmolytic activity of two synthetic anilide local anaesthetics

Two basic anilides EA-7 and EA-8 were investigated for their antispasmodic activity against a variety of spasmogens on different tissues from different species of animals and comparison was made with lignocaine. EA-8 was found to be the most potent in this respect, followed by EA-7 and lignocaine. The antispasmodic potency does not correspond to their local anaesthetic potency. This suggests a direct depressant effect on tissues.