Effect of desipramine on the depolarized isolated renal artery

Inhibition of contractions by tricyclic antidepressants and xylamine in rat vas deferens

The effects of noradrenaline uptake inhibitors on contractions evoked by electric field stimulation, noradrenaline, clonidine. 5-hydroxytryptamine, ATP, high K+, and BaCl2 in the epididymal half of rat isolated vas deferens were examined. Protriptyline, amitriptyline and xylamine concentration-dependently inhibited monophasic contractions induced by low frequency electrical stimulation (0.3 Hz, 1 ms duration, 60 V). Protriptyline and xylamine inhibited in a noncompetitive manner the contractile response induced by noradrenaline (3 x 10(-8)-3 x 10(-5) M) and the inhibitory effect of protriptyline was reversible, while xylamine produced long-lasting inhibition. All three noradrenaline uptake blockers inhibited the clonidine (3 x 10(-6) M) or 5-hydroxytryptamine (10(-5) M)-induced contraction. Protriptyline and amitriptyline at concentrations of 3 x 10(-6)-3 x 10(-5) M reversibly inhibited the ATP (10(-4) M)-induced monophasic contraction. In contrast, xylamine ((1-3) x 10(-5) M) had no effect. Protriptyline and amitriptyline but not xylamine concentration-dependently reduced the high K+ (6 x 10(-2) M)-induced sustained contraction with respective IC50 values of 1.81 x 10(-6) M and 8.6 x 10(-7) M. Protriptyline and amitriptyline at 10(-5) M reversibly inhibited BaCl2 (3 x 10(-3) M)-induced phasic contractions and xylamine (10(-5) M) had no effect. These findings demonstrate that tricyclic antidepressants might exert direct inhibitory action on mechanical contraction pathway, whilst xylamine, a structurally different inhibitor of noradrenaline uptake, may act mainly at alpha-adrenoceptors and other amine receptors on the smooth muscle of the rat vas deferens as a long-lasting nonselective antagonist, and it at least in part blocks sympathetic transmission.

Inhibitory effect of noradrenaline uptake inhibitors on contractions of rat aortic smooth muscle

1 The effects of noradrenaline (NA) uptake inhibitors on contractions induced by NA, high K+, and 12-O-tetradecanoylphorbol-13-acetate (TPA) in rat isolated aorta were investigated. 2 Protriptyline (0.3 microM) and amitriptyline (0.3 microM) produced an approximately parallel shift to the right in the dose-response curve to NA. Protriptyline (> 0.3 microM), amitriptyline (> 0.3 microM) and xylamine (0.01-1 microM) significantly reduced the maximal contractile response to NA. The IC50 values for inhibition of the contractile response to 3 microM NA were 1.58 microM for xylamine, 1.70 microM for amitriptyline and 2.57 microM for protriptyline. 3 Protriptyline and amitriptyline dose-dependently inhibited the high K+ (60 mM)-induced contraction (IC50 = 0.69 microM for protriptyline and IC50 = 3.15 microM for amitriptyline). In contrast, xylamine did not affect the high K(+)-induced contraction. 4 Protriptyline and amitriptyline dose-dependently inhibited TPA (1 microM)-induced contraction in calcium-free solution; xylamine (up to 30 microM) was without effect. Staurosporine (10 nM) completely inhibited the TPA- and NA-induced contraction. 5. Protriptyline (3 microM) and amitriptyline (3 microM) caused about 54% and 60% inhibition, respectively, of aortic contractions caused by endothelin-1 (10 nM) in the absence of endothelium. Xylamine (10 microM) was without effect. 6 Inhibitory effects of NA uptake inhibitors on contractions were independent of the presence of endothelium and were unaffected by the K+ channel blockers, tetraethylammonium ions (up to 3 mM) and glibenclamide (up to 30 microM). 7 These results indicate that tricyclic antidepressant drugs such as protriptyline and amitriptyline could act as both postsynaptic adrenoceptor antagonists and direct inhibitors of muscle contraction; whereas, xylamine, a structurally distinct NA uptake blocker might principally exert its action only at alpha-adrenoceptors on rat aortic smooth muscle.

4-Hydroxy-2-methyl-4-phenyl-1,2,3,4-tetrahydroisoquinoline (PI-OH): a new potentiator of sympathomimetic amines on the rat anococcygeus muscle

1. The potentiating effects of racemic 4-hydroxy-2-methyl-4-phenyl-1,2,3,4-tetrahydroisoquinoline (PI-OH), cocaine, desipramine and nomifensine on the concentration-response curves of the rat anococcygeus muscle to noradrenaline (NA) and field stimulation were examined. 2. PI-OH and cocaine concentration-dependently potentiated the responses of anococcygeus muscle to NA and field stimulation, but the activity of PI-OH was stronger than that of cocaine on both responses. 3. At high concentrations the potentiating activities of desipramine and nomifensine were less, a fact that was explained by their postsynaptic inhibitory properties; the actions of nomifensine and desipramine as antagonists against NA were competitive and non-competitive, respectively. 4. It is concluded that PI-OH may be an ideal potentiator of the response to NA in adrenergically-innervated tissues because it has no side effects such as postsynaptic inhibition.

Antagonism of noradrenaline and histamine by desipramine in the isolated artery of the rabbit ear

1. The effects of desipramine (DMI) were examined on the vasoconstrictor responses of the isolated perfused artery of the rabbit ear to noradrenaline (NA) and to histamine. Innervated and sympathetically denervated arteries were used.2. In innervated arteries, DMI in concentrations of 1 x 10(-8) to 1 x 10(-7)M enhanced the responses to NA; higher concentrations reduced the responses. In sympathetically denervated arteries, DMI caused only reduction of the responses to NA.3. Responses to histamine were reduced by DMI in both innervated and denervated arteries. DMI was considerably more potent as an antagonist of histamine than of noradrenaline.4. The reduction by DMI of the responses to NA and histamine in both innervated and denervated arteries was associated with a parallel shift to the right of the concentration-response curves of the agonist and a depression of the maximal response. These effects of DMI were reversible.5. Analysis of the data by the method of Arunlakshana & Schild (1959) showed the following: the antagonism of the action of NA by DMI on denervated arteries fulfilled the requirements for competitive antagonism; antagonism of the action of NA on innervated arteries was not competitive; antagonism of the actions of histamine on innervated and denervated arteries was not competitive.6. It is suggested that DMI antagonizes the action of NA and histamine on the perfused artery of the rabbit ear in two ways: (i) reversible specific antagonism which is competitive for NA and not competitive for histamine; (ii) reversible non-specific antagonism which is non-competitive for both agonists.

Blockade or reversal of the contraction induced by calcium and adrenaline in depolarized arterial smooth muscle

1. Mesenteric arteries immersed in a depolarizing solution contract in the presence of calcium. These contractions are proportional to the calcium concentration and are reversible.2. Mesenteric arteries immersed in a calcium-free depolarizing solution contract in the presence of adrenaline. Under the experimental conditions reported here, this response develops only about one-third of the contractile tension developed in polarizing solution (modified Krebs bicarbonate).3. Cinnarizine and chlorpromazine inhibit the contractile response to calcium and induce relaxation of depolarized muscle previously contracted by calcium; cinnarizine was 4 times more potent than chlorpromazine in such activity.4. Chlorpromazine inhibits the response to adrenaline in both polarizing and calcium-free depolarizing solutions, whereas cinnarizine inhibits the response in polarizing solution but not that in calcium-free depolarizing solution.5. The significance of these results is discussed.

The effect of drugs on the constriction of isolated depolarized blood vessels in response to calcium or barium

1. The rat isolated anterior mesenteric artery was perfused at a constant rate with a calcium-free depolarizing solution. Injection close to the cannula of 0.05-0.1 ml. of solutions of CaCl(2) (117 mM) or BaCl(2) (100 mM) caused a rise in perfusion pressure.2. The responses to injected CaCl(2) solution could be obtained repeatedly but those to successive injections of BaCl(2) solution slowly declined. When the responsiveness to barium had almost disappeared, it could be restored by the addition to the perfusing fluid of a small amount of calcium (0.05 mM).3. The contractile effects of calcium or barium were antagonized by the addition to the perfusing fluid of several anti-inflammatory substances, certain local anaesthetics and certain spasmolytic drugs.4. Perfusion of the mesenteric artery with a depolarizing solution containing 0.2 mM-CaCl(2) caused a persistent rise of the perfusion pressure. This was rapidly and completely reversed by the addition of indomethacin (4 mg/100 ml.) or cinchocaine hydrochloride (2 mg/100 ml.) to the perfusing fluid.5. The uptake of (45)Ca by rat aorta depleted of calcium was reduced by amethocaine hydrochloride (10 mg/100 ml.) or cinchocaine hydrochloride (2 mg/100 ml.) but not by indomethacin (10 mg/100 ml.) or desipramine hydrochloride (1 mg/100 ml.).