THE ANALGESIC AND HYPNOTIC ACTIONS OF BARBITURATES

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Abstract
The pain sensitivity of 130 rats was determined with a modification of the D''Amour - Smith technic and expressed as the response time to the exposure of the terminal cm. of the rat''s tail to heat of constant intensity. Following the intraperiton. admin. of phenobarbital Na (75 and 100 mg./kg.), pentobarbital Na (25 and 40 mg./kg.) seconal Na (25 and 40 mg./kg.), and thiopental Na (30, 35, and 40 mg./kg.) analgesia, as expressed by an increase of 2 or more sec. of the response time, developed in 36 of the 130 rats. Only 11 (8%) showed analgesia without concurrent hypnosis. The max. incidence of analgesia without hypnosis (19%) developed when thiopental Na was given in 30 mg./kg. doses. Hypnosis without analgesia developed in 30% of all cases. The overall mortality was 7.5%. Using the same method analgesia could be detected with all the clinically used analgesics tested. The above expts. indicate that anesthesia (simultaneous hypnosis and analgesia) can not be produced safely with barbiturates in rats. This is probably true also for man, because barbiturates, unlike ether, do not depress the electrical activity of the brain cortex as measured by electro-encephalo-graphic technics. While barbiturates in therapeutic doses do not affect pain perception, the reaction to pain might be influenced by them.