Gonadotropin Releasing Hormone (GnRH)
GnRH is also known as Mother Reproductive Hormone. It is released
from the Anterior Hypothalamic Area (AHA) of hypothalamus.
Functions:
-
It induces the growth of follicles
-
It causes the release of FSH and LH
-
It induces the cyclicity in acyclic female animals
Uses:
-
Synthetic GnRH is used in delayed estrus, true anestrus, low
conception rate, estrus synchronization, etc.
-
It is used at the time of AI in delayed ovulators
Follicle Stimulating Hormone (FSH)
FSH is also called follitropin. It is released form anterior
pituitary.
Functions in Female:
-
It stimulates the growth of ovarian follicle.
-
It enhances the estrogen (estardiol-E2) production from ovarian
follicle.
-
It
also helps the formation of LH receptors on granulosa cells so that
LH can perform its function
Functions in Male:
-
It causes the growth of
seminiferous tubules.
-
It influence the
spermatogenesis (up to formation of 2nd spermatocytes)
-
It acts on the sertoli
cells and stimulate them to produce Androgen Binding Protein
(ABP).
Luteinizing Hormone (LH)
It is also called as leutropin. It is released from anterior
pituitary.
Functions in Female:
-
It has receptors on the
theca cells & mature granulosa cells of the follicles, luteal
cells of corpus luteum and interstitial cells.
-
It causes maturation of
ovarian follicles.
-
It helps in ovulation.
-
It helps in corpus
luteum formation.
-
It helps maintaining the
corpus luteum.
Functions in Male:
Prolactin (PRL)
It is released from the anterior pituitary.
Functions:
-
It influences the metabolic growth in an individual.
-
In Female, induces the milk synthesis.
-
It induces the maternal behavior in animals for caring and
nursing their offsprings.
-
It induces suppressive effects on the secretions of
gonadotrpoins.
Oxytocin
Oxytocin
is released from hypothalamus. Oxytocin target is smooth muscles of
reproductive tract.
Functions:
-
Required for delivery of fetus and helpful for expulsion of
fetal membrane
-
Causes the contraction of smooth muscles of certain organs
(particularly of reproductive system).
-
Helps in movement of the gametes to the sight of fertilization
-
Plays important role for milk letdown. Teats have tactile
receptors which send message to brain & from brain signal goes
to hypothalamus to secrete Oxytocin. This Oxytocin through blood
reaches to milk alveoli and then helps in contraction of
myothelial cells; results into milk letdown.
-
Stimulates the secretions of PGF2α and
thus helpful for killing Carpus luteum
Uses:
-
Used in milk led down
problem in animals
-
Used when there is
difficultly in parturition due to deficiency of uterine
contraction
-
Used to enhance the
postpartum uterine involution
-
Used for treating
retention of fetal membrane cases within 24 hours after
parturition.
-
To improve the
conception rate at the time of breeding
-
Used in cases of uterine
prolapse
Estrogens
Estrogens are 18 carbon steroid hormones and are responsible for the
development and maintenance of secondary sex characteristics and for
induction of estrus behavior and ovulation in female animals.
Types of Estrogens:
Estron (E1), estradiol (E2), estriol (E3), equilin, equilinen are
the major estrogens. Equilin and equilinen are only found in
equines. The principal estrogen is estrodiol (E2). The immediate
precursors of estrogens are androgens (testosterone). These are
produced by glandular as well as non-Glandular tissues.
Functions:
-
Estrogens establish the
femininity (femaleness of an individual).
-
Promotes the fetal
growth.
-
Induces secondary sex
characteristic as well as sexual behavior.
-
Causes differentiation
of neural tissue, so that there are functional differences in
several areas of brain of female compared to that of male.
-
After birth
promotes the growth of female genital organs & at puberty rate
of growth is blooming.
-
Plays important role in
the development of skeleton and to give a peculiar shape to the
body contour.
-
Plays important role in
the formation or development of duct system in mammary glands
and also causes fat deposition in mammary gland and other body
areas.
-
Induces estrous behavior
in female animals or causes the expression of heat signs.
-
Induces the release of
preovulatory LH-surge in cyclic female animals.
Uses:
-
Used for prevention of unwanted or mismated pregnancy
-
Used to cause abortion due to any medical reason.
-
Used to treat the mild endometritis in ruminants.
-
Used for dilatation of cervix, in certain cases of dystocia.
Progesterone
It is a 21 C atom steroid hormone which is responsible for
maintaining pregnancy in all female animals. In females it is mainly
secreted from C.L (G.F, placenta & adrenal gland also secrete small
amount of progesterone). In males it is secreted from the testes.
Since progesterone is changed into the testosterone, some
unconverted progesterone comes in blood.
Functions:
-
It maintains the
pregnancy.
-
It primes the brain
center for the action of estrogen for behavioral signs.
-
It reduces (inhibits)
the contractility of the uterus.
-
It causes the closure of
cervical rings and thickening of the cervical mucus.
-
It stimulates growth of
uterus during pregnancy.
-
It prepares the uterus
for implantation of the zygote.
-
It stimulates the
secretary activity of uterine glands.
-
It suppresses the local
immune mechanism of uterus because fetus is 50% foreign body.
-
It forms the milk
alveoli of the mammary glands.
-
It plays important role
in inducing maternal behavior.
-
It has strong negative
feedback effect on GnRH and gonadotropins.
Uses:
Progesterone Sponges:
1.
PRID
(Progesterone releasing
intravaginal device)
2.
CIDR
(Controlled internal
drug release)
Androgens
Naturally occurring androgens are 19 carbon steroid hormone
responsible for the maintenance and development of Masculine
characteristics.
The main androgens are testosterone, androstenedion,
dihydroepiendrosteron (DHEA), 5-androstenediol. Testosterone is the
important one.
Testosterone is converted into 5α-dihydro-testosterone (5α-DHT)
which is the metabolite of testosterone. This 5α-DHT is needed by
prostate gland, penis and scrotum; is more common in humans
and dogs and less common in farm animals.
Functions:
In Fetus:
At Puberty:
-
Testosterone causes
pubertal growth of male genital organs including the accessory
sex organs.
-
It causes
hypertrophy of vocal cords (voice of male changes at
puberty).
-
Hair growth at certain areas.
-
Stimulates growth of skeletal muscles especially shoulders.
-
It enhances
spermatogenesis (especially maturation of sperm).
-
It stimulates secretary
activity and growth of accessory sex glands.
In
Adults:
-
It maintains the
pregnancy.
-
It maintains the
secretary activity of accessory sex glands.
-
It favors the baldness.
-
It maintains the libido
(sexual desire).
-
It favors the RBC
synthesis i.e. males have 10-15% more RBCs
Uses:
-
It is used to
androgenize the infertile cows so that they have the male
characteristics and with the help of them heat detection of
other animals could be made possible.
-
It
is used to descend the testes in scrotum if not descended.
-
It
is used to improve the debilitating effect of costly animals.
-
Certain androgens have
been developed which have more anabolic effect than sexual
effect.
Prosaglandins (PGs)
PGs are hormone like chemicals occurring naturally in all mammals.
These are not secreted by the glands but are secreted by the cells
scattered throughout the body.
These are derivatives of fatty acids, mainly arachidonic acid.
Arachindonic acid is a 20 Carbon polyunsaturated essential fatty
acid that has cyclopentane ring in its structure. Prostaglandins are
not stored in the cell, but when physical or chemical or hormonal
stimuli come, they are secreted in many body parts. PGs are involved
in inflammatory processes, gastric secretion, respiratory system,
blood clotting and also perform important reproductive functions.
PGA, PGB, PGE, PGF
are different kinds of PGs. They perform different function in the
different species.
Functions:
-
Act as the
leuteotropic hormone.
-
Cause strong contraction
of smooth muscles of reproductive tract.
-
PGF2α is the most
important PG in female because it determines the length of
estrus cycle. In females PGF2α is secreted by the endometrium,
myometrium, fetoplacental unit (placentome), and graffian
follicle.
-
PGF2α regresses the C.L.
We can shorten the estrus cycle length by intravenous
administration of PGF2α which kills the corpus luteum. PGF2α
does not come in the general circulation. PGFM is the metabolite
of PGF2α which comes in general circulation.
-
Myometrial cells in
grafian follicle are also contracted by PGF2α.
Uses:
-
Abortificiant, used to
terminate the pregnancy.
-
Used for synchronization
of heat (squeeze the estrus cycle length)
-
After parturition used
for removal of pathological contents from the uterus (in case of
pyometra and mummified fetus)
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