Alterations in nociception after intracisternal administration of prostaglandin D2, E2 or F2 alpha to conscious mice.

The effect of intracisternal administration of three major prostaglandins on nociceptive responses was evaluated in mice. Prostaglandin D2 had biphasic effects on pain thresholds (hot plate and acetic acid writhing tests) when given in a dosage range of 5 ng to 5 micrograms per mouse. Lower doses of prostaglandin D2 (less than or equal to 15 ng) increased the sensitivity to pain stimulation. Higher doses (greater than or equal to 50 ng) caused hypoalgesia, which was completely blocked by intracisternal injection of 500 pg of naloxone. Prostaglandin E2 (5 ng-5 micrograms) also had a biphasic effect on pain thresholds, similar to the effect of prostaglandin D2. However, the hypoalgesia caused by a higher dose of prostaglandin E2 (5 micrograms) was not blocked at all by naloxone doses of up to 500 ng. Prostaglandin F2 alpha had little effect on pain thresholds. These results indicate that each prostaglandin has a specific effect on the modulation of nociception.