Melatonin: an ancient molecule that makes oxygen metabolically tolerable.

Melatonin is remarkably functionally diverse with actions as a free radical scavenger and antioxidant, circadian rhythm regulator, anti-inflammatory and immunoregulating molecule, and as an oncostatic agent. We hypothesize that the initial and primary function of melatonin in photosynthetic cyanobacteria, which appeared on Earth 3.5-3.

Endogenous opioid antagonism in physiological experimental pain models: a systematic review.

Opioid antagonists are pharmacological tools applied as an indirect measure to detect activation of the endogenous opioid system (EOS) in experimental pain models. The objective of this systematic review was to examine the effect of mu-opioid-receptor (MOR) antagonists in placebo-controlled, double-blind studies using 'inhibitory' or 'sensitizing', physiological test paradigms in healthy human subjects. The databases PubMed and Embase were searched according to predefined criteria.