Lecture 15 - Melatonin and Erythropoietin

Which gland secretes melatonin?

- pineal gland (epithalamus)

Where is the pineal gland located?

- in the diencephalon

- epithalamus

What type of organ is the pineal gland?

- neuroendocrine transducer involved in control of photoperiodism

What is the chemical nature of melatonin?

- derived from tryptophan

What hormone is typically confused with melatonin?

- α-MSH (melanocyte-stimulating hormone)

What initiates melatonin secretion?

- darkness (light expisure inhibits secretion)

How is light information conveyed to the pineal gland?

- retina

- suprachiasmatic nucleus

- superior cervical ganglion

- pineal gland

What happens when daylight duration increases?

- melatonin secretion decreases

What is melatonin's main physiological role in seasonal breeders?

- regulation of reproduction via control of GnRH

What is melatonin's effect on gonads in most species?

-antigonadal (suppresses reproductive activity)

What species are exceptions to the antigonadal effect?

- goat and sheep

What is melatonin's effect in long-day breeders?

- suppresses reproduction during darkness

Why does artificial light induce breeding in mares during winter?

- light decreases melatonin

- activates gonads in long-day breeders

What is an example of a long-day breeder?

- horse and cat

What is an example of short-day breeders?

- goat and sheep

What are examples of nonseasonal breeders?

- cow

- pig

- human

- llama

Does melatonin show circadian rhythmicity?

- yes

- high at night

What brain structure does melatonin entrain?

- suprachiasmatic nucleus (circadian clock)

What is the effect of melatonin on puberty?

- Circulating melatonin decreases by 75% between ages 7-12 in humans

What is the effect of melatonin on stress response?

- affects pineal function via SNS and glucocorticoids

What is the effect of melatonin on sleep?

- strong influence on sleep-wake and arousal cycles

What is the effect of melatonin on immune function?

- enhances immune function

What is the effect of melatonin on free radicals?

- reduces free radical formation

What is the effect of melatonin on hair?

- inhibits hair growth in mice

- induces white winter coats in weasels

What is the effect of melatonin on the adrenal cortex?

- inhibits cortisol release

What is the effect of melatonin on the thyroid?

- reduced thyroid function (via reduced TRH)

What is the effect of melatonin on lactation?

- enhances hypothalamic dopamine

- reduced prolactin release

What is the effect of melatonin on melanocytes?

- antagonizes alpha-MSH

What is the effect of melatonin on the cardiovascular system?

- vasopressor activity

What is erythropoietin?

- glycoprotein hormone

Where is erythropoietin produced?

- fetal liver

- adult kidney

What is the main physiological effect of EPO?

- stimulates erythropoiesis

Where does erythropoiesis occur?

- fetal liver

- adult bone marrow

What controls EPO production?

- PO2 of blood perfusing the kidney

What stimulates EPO release?

- renal hypoxemia

What are the major triggers of EPO secretion?

- decreased renal blood flow

- cardiopulmonary disease

- decreased hemoglobin concentration

- hemorrhage

- high altitude

- hypotension

- pregnancy

- placnetal lactogen

What happens when EPO is deficient?

- anemia

What commonly causes anemia in cats and dogs?

- renal disease

- decreases EPO

What are the treatments for EPO deficiency anemia?

- human recombinant EPO

- iron supplementation

- transfusion

What is EPO abuse associated with?

- blood doping

- greyhounds and racing horses