The protein fraction isolated from blood of seal, Phoca groenlandica, has been found to produce hyperalgesic effect on rats exposed to thermic or electrocutaneous nociceptive stimulation, but fail to affect writhes provoked by intraperitoneal injection of acetic acid solution on mice. When combined with morphine, the fraction lowered completely its narcotic analgetic action in the above mentioned tests. On the contrary, these same proteins combined with promedol or fentanil enhanced and prolonged analgetic effect of the latter. Tested in vitro the protein showed neither opioid nor anti-opioid activity. Therefore it is reasonable to suppose that neurophysiological activity of the isolated fraction is due to the peptides formed on enzymatic hydrolysis of proteins in vivo rather than these proteins as such.
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