Abstract
Evidence has been presented in the following experiments that morphine analgesia is not mediated by the release of epinephrine from the adrenal medulla. Adrenalectomy and adrenal demedullation did not decrease the pain reaction threshold of rats to morphine.
The threshold dose in rats for the hyperglycemic effect of morphine, a sensitive index for release of epinephrine from the adrenal medulla, was 10-30 times that required for elevating the pain reaction threshold.
Tetraethylammonium chloride (TEA) did not reverse the effect of morphine on pain reaction time in rats.
Although morphine produced hyperglycemia and elevated plasma "sympathin" levels in dogs, the absolute changes in "sympathin" levels were much less than could be expected to raise the pain reaction threshold. Near lethal doses of epinephrine and norepinephrine were required to raise the pain reaction threshold in mice.
Footnotes
- Received January 10, 1955.
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