Effect of carrageenin-induced pedal edema on rat brain prostaglandins

Carrageenin-induced pedal inflammation in rats, was found to significantly enhance brain levels of prostaglandin (PG) E2 and PGF2 alpha. PG levels increased after 30 min of induction of the inflammation, peaked at 1 h, and attained normal levels by 4 h. Bilateral adrenalectomy had little effect on carrageenin-induced increase in rat brain PGs. The pattern of elevation of central PGs and the time course of carrageenin inflammation were at variance, the latter peaking between 3 and 4 h. The findings lend credence to the postulate that inflammatory hyperalgesia involves participation of central pain circuits, and that fever accompanying inflammation is caused by the central release of PGs. The central nociceptive and hyperthermic actions of PGs are well documented. However, the increase in central PG levels may well be caused by stress induced by the peripheral inflammation, since the pattern of elevation in either case is qualitatively similar.