Endocrinology:Melatonin
melatonin in clinical veterinary medicine -decrease in GnRH prescribe?
-Use in Alopecia X in Dogs Mechanism unclear- Decreases GnRH which in turn decreases LH/FSH effects on Adrenal Androgen Precursors??? -Decreases Anxiety -Decreases Seizure activity -Effects of prolonged administration unknown but short term side effects are minimal Sedation Inco-ordination Tx-melatonin
melatonis affects on aging and cancer
-aging-melatonin decreaes w/ age -may decrease cell damage cancer-pinealectomy enhances tumor grwoth, melatonin-inhibits tumorigenesis caused by carcinogens -low levels in women w/ breast cancer & men w/ prostate
circadian rhythm of melatonin secretion -controlled by? -what alters timing? -secretion starts at? -increase at what age? -shift in endogenous melatonin occurs in?
-endogenous pacemaker in suprachiasmatic nucleus -environmetnal lighting -after dark, peaks at 2-4 a.m. -increase 1-3 years -flight passengers & night shift workers
synthesis of melatonin
-neuroendocrine rxn photic info from retina->suprachiasmatic nucleus-> hypothalamus& sympathetic NS (via superior cervical ganglion) to pineal gland
biological fx that may be affected by melatonin
-sleep, circadian rhythm,mood, sexual maturation, reprod. cancer, immune response, aging
how is sleep affected by melatonin? mood?
-sleep-affects speed of falling asleep, duration, quality, hypnotic effect -mood-abnormal cir. rhy. in mood disorders, depression SAD, bright light therapy decreases depression
melatonins affect on sexual maturation, reprod, puberty,
Effects vary with Species & Age In some species has anti-gonadal effect Changes in hours of darkness/season linked to reproductive activity Barn lighting to control Mare estrous cycles May affect Puberty Decreases in Melatonin activate Pituitary-Gonadal function Melatonin may normally decrease GnRH or sensitivity to GnRH May affect Sex Steroid Production or vice versa May directly modulate Ovarian function Receptors for Melatonin on Ovaries Stimulates Progesterone production
melatonin secreted by? stimulated by?
pineal gland -darkness
secretin of melatonin:stim. & inhib?
stimulated:darkness -retinal photoreceptors release NE, activate receptors on pineal, convert serotonin to melatonin inhibited:light -retinal photoreceptors hyperpolarized, in hibit NE release
