[Bradykinin]

Homologous tachyphylaxis to bradykinin and its interference with allergic pleurisy in actively sensitized rats

After recovery from a first intraplantar or intrathoracic stimulation with bradykinin, repeated daily provocation with this peptide resulted in a progressive loss of its ability to cause paw or pleural oedema, reaching 0-20% of the control within seven and four consecutive provocations, respectively. The phenomenon was shown to be time reversible, since the unresponsiveness ceased when stimulations were discontinued, and localized, since paw oedema evoked by the peptide was not modified after desensitization of either the contralateral paw or the pleural cavity. Furthermore desensitization to bradykinin did not influence the pleurisy elicited by either histamine (200 micrograms/cavity), 5-hydroxytryptamine (5-HT) (100 microgram/cavity) or platelet-activating factor (PAF) (1 microgram/cavity), suggesting that the desensitization was selective. In contrast, when actively sensitized animals were submitted to bradykinin-induced tachyphylaxis, pleural exudation and leukocyte influx induced by antigen were drastically reduced, strongly implying bradykinin in this process. We demonstrated that repeated daily stimulation with bradykinin cause selective, local and reversible auto-refractoriness, which may be useful as a tool in attempting to evaluate the role of this peptide in inflammation.

The effects of prostaglandin E1, bradykinin and histamine on canine synovial vascular permeability

1 The relative effects of prostaglandin E1, bradykinin and histamine on canine synovial vascular permeability were investigated by a method based on the measurement of the amounts of radiolabelled dextran (molecular weight 20,000) leaking from the circulation into the synovial cavity. 2 Bradykinin, prostaglandin E1 and histamine in that order of potency all increased synovial vascular permeability. Threshold concentrations were 0.3 micrometer, 3 micrometer and 30 micrometer respectively. 3 The effects of infusion of prostaglandin E1 combined with either bradykinin or histamine were greater than mere summation.

The action of ranatensin, a new polypeptide from amphibian skin, on the blood pressure of experimental animals

1. The blood pressure response to ranatensin, an undecapeptide from the skin of the frog, Rana pipiens, has been studied in various experimental animals.2. Ranatensin raised blood pressure in the dog and rabbit. The response was not altered by atropine, phentolamine, propranolol or hexamethonium, suggesting a direct peripheral vasoconstrictor action. In both animals ranatensin was about one-tenth as potent as angiotensin. Tachyphylaxis to ranatensin did occur, but there was no cross-tachyphylaxis with angiotensin, bradykinin, or noradrenaline.3. The peptide lowered blood pressure in the monkey, being as potent as eledoisin. The response was not altered by atropine, phentolamine, propranolol, tripelennamine, tetraethylammonium, bretylium, or methysergide. This again suggests a direct peripheral action on vascular smooth muscle. There was no tachyphylaxis to the depressor action, nor was there cross-tachyphylaxis with angiotensin, eledoisin, bradykinin, or noradrenaline.4. Ranatensin did not alter the blood pressure in cats and had a variable action in the guinea-pig with a rapid onset of tachyphylaxis.5. Ranatensin has a variable effect on the blood pressure in the rat that is related to the basal level of blood pressure. When the blood pressure is high, the response to the peptide is hypotension. Ranatensin raises blood pressure in the rat when the basal blood pressure is low. The pressor response to ranatensin appears to be due, in part, to the release of noradrenaline from peripheral sympathetic nerve endings.6. The composite action of ranatensin on blood pressure of various experimental animals is unlike that of any other peptide. Its hypertensive action in the dog or rabbit, together with a potent hypotensive action in the monkey, readily distinguishes it from all other vasoactive peptides.

Effects of Bradykinin on Forearm Venous Tone and Vascular Resistance in Man

The effects of intravenous injections of synthetic bradykinin on the vascular dynamics of the forearm were studied in nine normal subjects. A plethysmographic technique was used to measure forearm blood flow and to estimate forearm venous tone. Bradykinin decreased mean systemic arterial pressure, elevated forearm blood flow, and reduced calculated forearm vascular resistance and also venous tone. The venodilatation was preceded by brief venoconstriction which was prevented in five subjects pretreated with the antiadrenergic agent, guanethidine. It is postulated (a) that this venoconstriction is one of the compensatory reflex actions that accompany reduction of systemic arterial pressure, and (b) that the prime effect of bradykinin on both the arterial and the venous beds of the forearm is a direct vasodilatation.

General Circulatory Alterations Induced by Intravenous Infusion of Synthetic Bradykinin in Man

The general hemodynamic effects induced by a continuous intravenous infusion of synthetic bradykinin were studied in ten patients submitted to simultaneous right- and left-heart catheterization. A significant drop in systemic arterial pressure and in total peripheral resistance was observed, coincident with an increase of the cardiac output, heart rate, and stroke volume. There was no consistent change of the pulmonary arterial and left atrial pressures, but the pulmonary vascular resistance decreased significantly.