Inflammatory response modulated by pinealectomy: effect of light.

In view of the known interactions between pineal and adrenal glands and the importance of glucocorticoids on the acute phase of inflammatory process, we investigated the effect of the pineal gland on the paw edema response induced by carrageenin in female Wistar rats, weighing 170-220 g, measured by the pletysmographic method. Adrenalectomy increased the rate of the inflammatory response (149.02 +/- 2.93%, N = 7 vs 113.48 +/- 2.99%, N = 7) whereas pinealectomy and sham-pinealectomy under white light had an inhibitory effect (81.73 +/- 2.16%, N = 15 and 80.21 +/- 1.85%, N = 14 vs 113.48 +/- 2.99%, N = 7). Sham-pinealectomy under red light did not modify the rate of the inflammatory response. These results indicate that the pineal gland can be affected by light during sham-pinealectomy. In view of the unaltered adrenal gland weight and corticosterone levels among the different groups, we propose an antagonism between melatonin (pineal hormone) and glucocorticoids at the peripheral level. The predominant effect of glucocorticoids over melatonin may explain the inhibition of the inflammatory response caused by pinealectomy.