Melatonin (N-acetyl-5-methoxytryptamine) is an endogenous growth hormone produced in many body tissues, including the pineal gland, retina and the gastrointestinal tract of dogs.
The biological clock, which determined longevity in dogs is dictated by daily (circadian) and seasonal (circannual) time. These time changes are mediated by the alteration of levels of melatonin, an evolutionary ancient hormone, which follows a circadian rhythm.
Melatonin production is controlled by nerve impulses from the suprachiasmatic nuclei. Melatonin synthesis, which is inhibited by light on the mammalian retina, peaks in plasma concentrations during the night.
Melatonin, synthesized from dietary tryptophan, affects physiological parameters within the dog, specifically immune-status (by regulation of neutrophil and lymphocyte activity), reduction in oxidative stress and production of estradiol, androstenedione, thyroxine and cortisol, extracellular water transport, cellular apotosis, seasonal hair growth, reproductive cycles and fertility, sleep cycles and stimulation of osteoblast activity.
Exogenous melatonin has been used pharmacotherapeutically for a number of canine diseases, including:
- Alopecia X
- Follicular dysplasia
- Sleep disorders associated with chronic renal disease
- Noise phobia
- Separation anxiety and other anxiety disorders
- Post-operative adhesions
Recommended dose rate in dogs is 0.1 - 0.3 mg/kg daily orally.
Minor side-effects include skin allergies and disruption of normal corticosteroid production at higher doses.
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