Gonadotropins ( FSH & LH)
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Two hormones from the adenohypophysis, the follicle‑stimulating hormone (FSH) and luteinizing hormone (LH/ICSH) in females/males affect the gonadal activity.
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The basal or tonic output of FSH and LH is pulsatile during the reproductive functions in males and females.
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FSH output is under hypothalamic control by GnRH and a negative feedback mechanism involving the gonadal hormones, rising levels of estrogen and inhibin production.
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Follicle stimulating hormone (FSH) is a glycoprotein made up of α- (92 amino acids) and β- (118 amino acids) subunits with carbohydrate moiety.
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Luteinizing hormone (LH) or Interstitial-cell stimulating hormone (ICSH) - LH in female and ICSH of the male is the same hormone.
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LH is a glycoprotein made up of α- and β- subunits having 92 and 115 amino acids with carbohydrate moiety.
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The pituitary content of LH is highest in cattle, sheep and cat but lowest in horse and man.
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Environmental conditions like changing seasons and day light length is mediated from exteroceptors like eye to the hypothalamus to influence GnRH output.
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Basal pulsatile FSH secretion stimulates follicular growth and estrogen secretion in ovaries.
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FSH acts synergistically with LH to effect ovulation.
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In the male FSH acts on the seminiferous tubules and stimulates spermatogenesis.
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The actions of LH and FSH are synergistic.
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Increased production of estrogen by the Graafian follicle stimulates LH surge to effect ovulation by positive feedback effect.
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LH secretion is increased greatly 24 to 48 hours before ovulation to effect ovulation but the increase in FSH is to a lesser extent.
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In induced ovulators e.g., cat and rabbit, LH secretion is stimulated by neuroendocrine reflex of the hypothalamus.
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In male LH stimulates interstitial cells of testis and causes testosterone production .
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The regulation of LH output from the pituitary gland is dependent upon the hypothalamic GnRH by a negative-feedback control mechanism.
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During pregnancy, placenta also secretes placental luteotropic hormone.
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Estrogen and progesterone in large amounts inhibit FSH and LH release from the adenohypophysis and the feedback effect operates through the hypothalamus and anterior pituitary.
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In addition inhibin secreted from the large graafian follicles in females and Sertoli cells in males inhibits FSH to a major extent and LH to a lesser extent.
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Last modified: Tuesday, 24 April 2012, 10:47 AM