Reproductive Endocrinology

Reproductive Endocrinology

Melatonin

• Melatonin is a hormone secreted by the pineal (epiphysis) gland located at the back of hypothalamus.

• It displays its effect by starting and ending the sexually active season in poliestric animals (sheep, goat, horse).

• The impulses regarding light in the eyes are transformed into neurological impulses in the retina and these neurological impulses travel to the suprachiasmatic nucleus located in front of hypothalamus which determines the secretion rhythm of the pineal gland directly by retino- hypothalamic pathway.

Reproductive Endocrinology

Melatonin

• Signals emenating from the suprachiasmatic nucleus are transferred through the preganglionic and postganglionic fibers to the pineolocytes which are the main cells of the pineal gland.

• The pineal gland changes the melatonin secretion levels in accordance with duration of daylight depending on the neural information coming from the eyes.

• Darkness increases the sympathic neural activity on the pineal gland, thus increasing melatonin secretion rate.

• Estrus (heat) is one of the main characteristic events and it is a state in which female animals show physiological and psychological effects and accept the male.

• Sexual cycle is the time passed from the start of one heat to the start of the next heat.

Sexual Cycle in Female

Animals

• The sexual cycle varies among species and consists of 5 stages; proestrus, estrus, metaestrus, diestrus and anestrus.

• Proestrus and estrus are follicular phase,

metaestrus and diestrus are luteal phase.

Sexual Cycle in Female

Animals

Animals are divided according to their cyclic activities;

• Monoestric animals

- Dog and carnivore wild animals

• Polyestric animals - Cattle and swine

• Seasonal Polyestric animals

- Horse, sheep, goat and cat