Involvement of melatonin metabolites in the long-term inhibitory effect of the hormone on rat spinal nociceptive transmission

Distribution and colocalization of melatonin 1a-receptor and NADPH-d in the trigeminal system of rat

Melatonin and nitric oxide (NO) are involved in orofacial signal processing in the trigeminal sensory system. The aim of the present study was to examine the distribution of melatonin 1a-receptor (MT1) and its colocalization with nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) in the spinal trigeminal nucleus (STN), the trigeminal ganglion (TG), and the mesencephalic trigeminal nucleus (MTN) in the rat, using histochemistry and immunohistochemistry. Our results show that MT1-positive neurons are widely distributed in the TG and the subnucleus caudalis of the STN. Furthermore, we found that MT1 colocalizes with NADPH-d throughout the TG and MTN, most extensively in the TG. The distribution pattern of MT1 and its colocalization with NADPH-d indicate that melatonin might play an important role in the trigeminal sensory system, which could be responsible for the regulation of NO levels.

Melatonin and their analogs as a potential use in the management of Neuropathic pain

Melatonin (N-acetyl-5-methoxytryptamine), secreted by the pineal gland is known to perform multiple functions including, antioxidant, anti-hypertensive, anti-cancerous, immunomodulatory, sedative and tranquilizing functions. Melatonin is also known to be involved in the regulation of body mass index, control the gastrointestinal system and play an important role in cardioprotection, thermoregulation, and reproduction. Recently, several studies have reported the efficacy of Melatonin in treating various pain syndromes. The current paper reviews the studies on Melatonin and its analogs, particularly in Neuropathic pain. Here, we first briefly summarized research in preclinical studies showing the possible mechanisms through which Melatonin and its analogs induce analgesia in Neuropathic pain. Second, we reviewed research indicating the role of Melatonin in attenuating analgesic tolerance. Finally, we discussed the recent studies that reported novel Melatonin agonists, which were proven to be effective in treating Neuropathic pain.

Preoperative anxiolytic effect of melatonin and clonidine on postoperative pain and morphine consumption in patients undergoing abdominal hysterectomy: a double-blind, randomized, placebo-controlled study

Recent evidence has demonstrated analgesic, anti-inflammatory, and anxiolytic properties of melatonin. Taking into account that higher anxiety makes the control of postoperative pain more difficult, one can hypothesize that melatonin anxiolytic and analgesic effects improve the control of postoperative pain. Thus, we conducted a randomized, double-blind, placebo-controlled study with 59 patients undergoing abdominal hysterectomy to test the hypothesis that melatonin is as effective as clonidine and that both are more effective than placebo in reducing postoperative pain. Additionally, we compared their anxiolytic effects on postoperative pain. Patients were randomly assigned to receive oral melatonin (5 mg) (n = 20), clonidine (100 microg) (n = 19), or placebo (n = 20) orally. In addition to primary outcomes of pain intensity and analgesic consumption, secondary outcome measures included postoperative state anxiety. In anxious patients 6 hours after surgery, the number of patients needed to be to prevent moderate to intense pain during the first 24 hours after surgery was 1.52 (95% CI, 1.14 to 6.02) and 1.64 (95% CI, 1.29 to 5.93), respectively, in the melatonin and clonidine groups compared with placebo. Also, the anxiolytic effect of melatonin and clonidine resulted in reduced postoperative morphine consumption by more than 30%. However, in the mildly anxious, it was not observed the treatment effect on pain.

PERSPECTIVES

The preoperative anxiolysis with melatonin or clonidine reduced postoperative pain and morphine consumption in patients undergoing abdominal hysterectomy. The effects these 2 drugs were equivalent and greater than with placebo.

The clinical impact of preoperative melatonin on postoperative outcomes in patients undergoing abdominal hysterectomy

BACKGROUND

Melatonin has sedative, analgesic, antiinflammatory, antioxidative, and chronobiotic effects. We determined the impact of oral melatonin premedication on anxiolysis, analgesia, and the potency of the rest/activity circadian rhythm.

METHODS

This randomized, double-blind, placebo-controlled study included 33 patients, ASA physical status I-II, undergoing abdominal hysterectomy. Patients were randomly assigned to receive either oral melatonin 5 mg (n = 17) or placebo (n = 16) the night before and 1 h before surgery. The analysis instruments were the Visual Analog Scale, the State-Trait Anxiety Inventory, and the actigraphy.

RESULTS

The number of patients that needed to be treated to prevent one additional patient reporting high postoperative anxiety and moderate to intense pain in the first 24 postoperative hours was 2.53 (95% CI, 1.41-12.22) and 2.20 (95% CI, 1.26-8.58), respectively. The number-needed-to-treat was 3 (95% CI, 1.35-5.0) to prevent high postoperative anxiety in patients with moderate to intense pain, when compared with 7.5 (95% CI, 1.36-infinity) in the absence of pain or mild pain. Also, the treated patients required less morphine by patient-controlled analgesia, as assessed by repeated measures ANOVA (F[1,31] = 6.05, P = 0.02). The rest/activity cycle, assessed by actigraphy, showed that the rhythmicity percentual of 24 h was higher in the intervention group in the first week after discharge ([21.16 +/- 8.90] versus placebo [14.00 +/- 7.10]; [t = -2.41, P = 0.02]).

CONCLUSIONS

This finding suggested that preoperative melatonin produced clinically relevant anxiolytic and analgesic effects, especially in the first 24 postoperative hours. Also, it improved the recovery of the potency of the rest/activity circadian rhythm.