Veterinary Physiology-III

GnRH (GONDOTROPIC RELEASING HORMONE)/(LHRH)

• It is a decapeptide that stimulates the release of both FSH and LH.
• The frequency of GnRH stimulus is the major regulator of the relative proportions of FSH and LH synthesis and release i.e., less frequent GnRH pulse leads to FSH secretion and more frequent GnRH pulse causes LH secretion.
• When estradiol predominates GnRH favours the LH surge to effect ovulation.
• Under the influence of high progestrone level GnRH induces FSH to stimulate folliculogenesis and steroidogenesis.
• Inhibin is a glycoprotein hormone from ovarin follicle and testicular seminiferous tubules inhibit GnRH secretion.
• Prolactin and LH inhibit GnRH via short‑loop negative feed back effect.
• GnRH secretion is also influenced by light‑ dark cycle, phero­mones and stress.
• Dopamine, endorphins and increased levels of ovarian steroids provide inhibitory influence on GnRH release.
• In sheep and goat increased production of melatonin during longer dark periods / short day length of autumn initiates GnRH synthesis, thus the puberty in young ones and breeding season in adult. In contrast, lengthening days of spring results in minimal melatonin production and beginning of breeding season in horse.