Synthesis and biological activity of Schiff and Mannich bases bearing 2,4-dichloro-5-fluorophenyl moiety.

Central α-adrenergic systems as targets for hypotensive drugs

α-Adrenoceptor subclassification

1. Low frequency (0.1 Hz) electrical stimulation of the rat isolated vas deferens produced regular contractions that were inhibited by low concentrations of clonidine. 2. The inhibition of the vas deferens produced by clonidine was presynaptic in origin and involved alpha-adrenoceptors. 3. Presynaptic alpha-adrenoceptor antagonist activity was assessed by studying the effects of increasing concentrations of the antagonists on cumulative clonidine dose-response curves on the stimulated vas deferens. 4. Postsynaptic alpha-adrenoceptor antagonist activity was assessed by comparison of control cumulative noradrenaline dose-response curves with those in the presence of increasing concentrations of antagonists in the rat anococcygeus muscle. 5. The results indicate that yohimbine and phentolamine are more potent in blocking presynaptic than postsynaptic alpha-adrenoceptors. Phenoxybenzamine and prazosin block postsynaptic alpha-adrenoceptors preferentially. 6. The findings support the view that presynaptic and postsynaptic alpha-adrenoceptors differ in their sensitivity to alpha-adrenoceptor antagonists.

SELECTIVITY OF BLOCKING AGENTS FOR PRE- AND POSTSYNAPTIC α-ADRENOCEPTORS

Presynaptic α-autoreceptors

Results of animal studies indicate that the hypotensive effect of prazosin is due to vasodilatation which is dependent on two discernible components of drug action: (1) direct relaxation of vascular smooth muscle and (2) interference with peripheral sympathetic function at a site distal to the alpha-adrenergic receptor.

Analysis of the hypotensive action of prazosin.

Analysis of the cardiovascular effects of 2-(2,6-dichlorophenylamino)-2-imidazoline hydrochloride (Catapres).

Prazosin and presynaptic alpha-receptors in the cardioaccelerator nerve of the dog

4 neue Aminoquinazolin-Derivate, die den Blutdruck von Hunden und Katzen herabsetzen, werden beschrieben. Ihre wirksamen Dosen liegen im Bereiche von 20 bis 300µg/kg peroral. Diese Substanzen setzen den peripheren Widerstand herab und reduzieren die blutdrucksteigernde Wirkung von Adrenalin, unterscheiden sich aber von den typischenα-Sympatholytika.

Pharmacological studies with some new antihypertensive aminoquinazolines.

Quinterenol (1-[5-(8-hydroxyquinolyl]-2-isopropylaminoethanol) antagonized histamine-, acetylcholine-and serotonin-induced bronchoconstriction and prevented egg albumin-induced anaphylaxis in guinea pigs. Orally and by inhalation quinterenol was as potent as isoproterenol; by i.v. and s. c. routes it was less potent. The onset of action was slower and the duration of action was considerably longer for quinterenol than for isoproterenol. In dogs, quinterenol, 0.5 mg/kg i.v., increased heart rate, cardiac output and stroke volume and lowered peripheral vascular resistance. In dog open chest preparations quinterenol increased cardiac output without elevating myocardial oxygen consumption and lowered blood pressure without reducing coronary arterial blood flow. In dog hind limb preparations quinterenol increased femoral arterial blood flow; in this respect it was as potent as papaverine, but it had considerably longer duration of action. All cardiovascular effects of quinterenol were blocked by propranolol. Chlorpromazine blocked quinterenol-induced tachycardia, but not the hypotensive effect. Quinterenol-induced cardiac acceleration in dogs was not abolished by vagotomy and sectioning of the spinal cord at the level of the second cervical vertebra, or by pretreatment with reserpine. Quinterenol relaxed isolated guinea-pig tracheal strips and abolished the spontaneous contractile activity of isolated rat uteri. These effects were antagonized by propranolol. At single doses up to 4 mg quinterenol had no positive inotropic or chronotropic effects on isolated perfused hearts of various species; it had no positive inotropic activity on isolated cat heart papillary muscles at concentrations up to 10 -5 g/ml. The data indicated that the positive chronotropic effect of quinterenol is probably not due to its direct interaction with beta adrenergic receptors.

Quinterenol, a new beta adrenergic stimulant

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