Pharmacological Research 2002-08-01

Verification of protector effect of the norepinephrine and felypressin upon the cardiovascular system under action of the lidocaine hydrochloride and prilocaine hydrochloride in anesthetized rats.

L D Araújo, G Singi, R Gazola

Index: Pharmacol. Res. 46(2) , 107-11, (2002)

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Abstract

Vasoconstrictor substances, as norepinephrine and epinephrine, were mixtured to local anesthetics to decrease their toxic effects and to prolong the depth of the anesthesia. However, these catecholamines produce systolic and diastolic hypertension. The effects of felypressin, a synthetic vasoconstrictor, upon arterial blood pressure and heart are lesser than those of norepinephrine or epinephrine, but due to its effects like oxytocin these catecholamines are yet the most used vasoconstrictors in association with lidocaine or another anesthetic salt. These vasoconstrictors are contraindicated for some physician, mainly for cardiac patients. But, are the catecholamines or is the salt the most dangerous components of the local anesthetic? The effects of the salt and catecholamines are opposite, but which of these exercises their effects first when inside blood vessel? Singi et al. [Pharmacol. Res. 44 (2001)] demonstrated that the first effect is always of the salt and that norepinephrine promotes protector effects upon guinea-pig isolated heart against lidocaine action. But, is this true for in vivo animals? The present study was performed with the aiming to answer this question and to verify if felypressin can induce the same effect of the norepinephrine. Fourteen Rattus norvegicus albinus, weighing 350g on average, were used. After being anesthetized with sodic thiopental, they were tracheostomizeds and one jugular and one carotid were cannuled for application of substances and to record the blood arterial pressure, respectively. The ECG was gotten through electrodes located in the front and back paws of the animals. The animals were separated in two groups, each one with seven rats. The lidocaine hydrochloride 2% in the doses of 600 microg and 3% in the doses of 900 microg acted on the cardiovascular system reducing the arterial pressure and modifying the electrocardiogram, while the prilocaine hydrochloride, in the same doses, also reduced the arterial pressure, but did not modify the electrocardiogram. When norepinephrine was associated to lidocaine 3% hydrochloride, it was possible to observe that this salt always exercised its effect first and a protective effect against the fall of pressure produced for the lidocaine. The same protective effect did not occur when felypressin was associated with prilocaine hydrochloride 3%.