LH is also a glycoprotein of molecular weight about 26,000 (in human). It is secreted apparently by the same basophilic cells of adenohypophysis which secrete FSH.
It is identical with the interstitial cell stimulating hormone (ICSH) of males.
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In the female, the luteinizing hormone works with FSH and is responsible for the final maturation of the ovarian follicles and ovulation.
These two gonadotropins are also responsible for the stimulation of the ovaries to produce estrogens (female sex hormones) and for the stimulation of the testes to produce androgens (male sex hormones).
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The luteinizing hormone alone, however, induces luteinizing of the ruptured follicle and stimulates the secretion of progesterone.
In the male the interstitial cell stimulating hormone stimulates the interstitial cells (Leydig cells) of the testes and also induces the secretion of the male hormone, testosterone.
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Although the pituitary is the prominent source of gonadotropins, some of the gonad-stimulating hormones are secreted by the placenta and other tissues too. These may be classified as follows:
(1) Human chorionic gonadotropin (present in blood, urine and tissues of pregnant woman),
(2) Human nonchorionic gonadotropin (present in blood and urine of ovariectomized and post-menopausal woman), and
(3) Equine gonadotropin (present in blood and placental tissue of the pregnant mare).
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The placenta is also said to be a site for the production of ACTH. It is known that pregnant woman exhibits great remission in symptpms of asthma and other allergic signs during their pregnancy, but soon after delivery these symptoms return. ACTH has been found to alleviate greatly the asthmatic condition.
Define Prolactin or luteotropin hormone:
Riddle was the first who discovered this hormone. This hormone appears to be a pure protein with an isoelectric point of 5 7 and a molecular weight of about 25,000.
It is secreted by a special group of acidophilic cells in the adenohypophysis. Its original name (lactogenic hormone or prolactin) was given because of its role in milk production by the mammary glands.
The functions controlled by this hormone are diverse but all have some connection with reproduction.
In mammals the development of mammary glands depends on stimulation by the female sex hormones estrogen and progesterone, and by prolactin.
The secretion of milk depends on the thyroid hormone, the steroids of the adrenal cortex and prolactin, and the actual ejection of milk on oxytocin. Prolactin is clearly not alone in this complex process.
The name luteotropin hormone (LTH) refers to the stimulation of secretion of progesterone by the corpus luteum of the mammalian ovary, formed after ovulation under the influence of the luteinizing hormone (LH or ICSH).
LTH also has marked effects on behaviour, stimulating the characteristic maternal behaviour in vertebrates from fishes to mammals.
It stimulates the crop glands of the pigeons to form the milk on which the young ones are nourished for a time; it induces the newt Triturus viridescens to return to the water on approach of the breeding season, and it aids in the development of the sexual colouration pattern in certain fishes.
There is as yet no known cellular basis for these varied actions, and one wonders if there can be a single common basis.
From the biological point of view, LTH offers the first of several examples of the diversity of actions of a single hormone, in this case all directed toward the same biological end of reproduction.