Melatonin levels are decreased in rheumatoid arthritis.

The hormone, melatonin, is a product of the pineal gland. This methoxy-indole, also known as N-acetyl-5-methoxy-tryptamine, is structurally related to indomethacin, a derivative of methylated indole. The fact that indomethacin has been used successfully in patients suffering from certain chronic inflammatory conditions (such as rheumatoid- and osteoarthritis) gives rise to the question as to whether melatonin also possesses anti-inflammatory virtues. This hypothesis has been tested by determining melatonin concentration levels by means of a radioimmunoassay in patients with rheumatoid arthritis. The daytime melatonin levels of untreated patients were significantly lower (mean concentration = 5.76 pg/ml) than the normal value (mean concentration = 15-33 pg/ml). The second part of this study showed that the administration of indomethacin (100 mg/day) to normal healthy subjects led to a 14.7 pg/ml decrease in plasma melatonin levels. This may indicate that melatonin and indomethacin act synergistically.