Reproductive Hormones and Their Therapeutic Uses

By

Dr. Atef Abdel-Hai Khalil SelmiProfessor of Obstetrics, Gynecology, & A.I.

Faculty of Veterinary MedicineZagazig University

Neuro-endocrine Regulation of Reproductive HormonesCerebrum

Cerebellum

Medulla Oblongata

Pituitary Stalk

Third Ventricle

Pineal Body

Optic chiasmPituitary

Gland

Hypothalamus

I - Hypothalamic hormonesHypothalamus secretes neurohumoral substance called neurohormones or releasing hormones that influence pituitary synthesis and secretion of the corresponding hormone such that: 1.Gonadotropin hormone–releasing hormone (GnRH) affect synthesis and release of gonadotropin hormones (FSH and LH) from anterior pituitary gland.2.Thyroid stimulating hormone releasing hormone (TSHRH) affect synthesis and release of Thyroid stimulating hormone (TSH) from anterior pituitary gland.

3. Adrenocoticotropic hormone releasing hormone (ACTHRH) affect synthesis and release of Adrenocoticotropic hormone (ACTH) from anterior pituitary gland.

4. Prolacten inhibiting hormone (PIH) affect synthesis and release of prolactin hormone from anterior pituitary gland.

5. Somatostatin affect synthesis and release of somatotropin or growth hormone from anterior pituitary gland.

6. Oxytocine hormone that stored in posterior pituitary gland.

1- Gonadotropin Releasing Hormone (GnRH(

Chemistry:GnRH is a decapeptide neurohumoral substance (composed of 10 amino acids) secreted by neurons located in the arcuate nucleus of the hypothalamus, then transported axonally to be stored in the median eminence until appropriate stimulation which causes its release into the hypothalamo-hypophyseal portal circulation.Biological effect:The portal circulation carries the releasing hormone to their receptors (pituitary gonadotrophs) in the anterior lope of pituitary gland, where it stimulates synthesis and secretion of gonadotropic hormones, Follicle stimulating hormone and luteinizing hormone (FSH &LH ).

Commercial Preparations :Receptal (5 ml IM) and Fertagyl (2.5 ml IM) are the preparations mostly available that can be used in cows as a single IM injection to stimulate a surge like release of FSH and LH from the anterior pituitary.

Therapeutic Uses:1-Ovarian inactivity. 2-Delayed ovulation. 3-Cystic ovary (twice the dose).4-Improve conception rate.5-Synchronization of ovulation and resumption of normal estrous cyclicity in postpartum cows. 6-Minimize incidence of cystic ovary in postpartum cows.

2- Oxytocin Hormone

Chemistry:It is a peptide neurohumoral substance synthesized by neurons located in supraoptic nucleus of the hypothalamus and transported axonally to be stored in the posterior pituitary. It is released from posterior pituitary to the general circulation following appropriate nervous stimuli (neural reflex) coming either from pelvic plexus during parturition or from other sense (visual, tactile, or auditory) during lactation.

Biological effect: It stimulate smooth muscle contraction in both the

genital tract (must be primed by estrogen) and mammary system (myoepithelial cells around milk acini and lactiferous ducts). Therefore, oxytocin has a definite functions in parturition, milk let-down, ovulation, transportation of sperm and ova in genital tract, and implicated in the control of luteal regression.

Adrenalin block the contractile effect of oxytocin on uterine muscle and myoepithelial cells in mammary tissue. Therefore, widely exited females would develop nervous inhibitory impulse during parturition and would not likely to give a good milk let-down.

Commercial Preparations:Oxytocin, Cyntocinon, hypophesin or posterior pituitary extract are the preparations mostly available that can be used as a single IM or IV injection (10-15 iu for small or 15-25 iu for large animal, respectively) to stimulate milk let-down or to stimulate uterine contraction.Therapeutic Uses:1.Stimulates milk let-down.2.Stimulates uterine contraction: A.In parturient females during weak or abolished birth pain to overcome uterine inertia, hasten placental drop, and to hasten uterine involution. B.In open pyometra to get- red uterine contents.C.In uterine prolapse to reduce size of the prolapsed uterus.

Reproduced from Reproductive endocrinology Edited by Samuel S.C and Robert B. Jaffe( W.B. Saunders Company, Philadelphia)

oxytocin

GnRH

II - Pituitary Gonadotropin HormonesChemistry:Gonadotropins are glycoprotein in nature (carbohydrates-containing proteins), that are secreted from pituitary gonadotrophs under the stimulatory effect of hypothalamic GnRH. They are composed of two polypeptide subunits,α and β that are bound in non-covalent association of very high affinity.Both FSH and LH within the same species have a common α subunit that possess the same amino acids sequence (species specific), but β subunit is a hormone specific subunit that has a different amino acids sequence.

Carbohydrate groups located in both subunit influence the stability and ability of the hormone to combine with and activate their receptor sites in testis and ovary.

The half-life of gonadotropin hormones in circulation depends upon their sialic acid content (see next table).

Characteristics of gonadotropic hormones

HormoneMolecular weight

Carbo-hydrate

Sialic acid

Half-life

LH28 - 3400012- 24 %

1 – 2% <30 min.

FSH32 - 3700025% 5% 2 hr.

HCG3800032%8.5% 11 hr.

PMS (eCG)6800048% 10.4% 26 hr.

1 - Follicle stimulating hormone (FSH )Biological effect: 1.Stimulate folliculogenesis: It reach the specific receptor sites on the granulosa cells surrounding the primordial follicle and stimulate their mitosis with a consequent proliferation and follicular fluid formation that result in increased follicular size and development.2.Stimulate follicular maturation that ocurrs under a certain balance between FSH, LH, Estrogen, Progesteron, and Androgen hormones.3.Stimulate luteinization : by increasing LH receptors on both thecal cells and granulosa cells.

4. Stimulate steroidogenesis: the steroidogenic activity of the follicle depends upon FSH and LH that acting synergistically on both thecal cells (androgen) and granulosa cells (estrogen) with a consequent increase in follicular estrogen production (two cell theory).

Steroid cocentration in follicular fluid in relation to follicular development and atresia:

Follicular diameter (mm)Estradiol (Pmol/ml)

Progesterone(Pmol/ml)

Testosterone(Pmol/ml)

2-3mm (small, nonatretic) 14040280

3-6 mm (large, nonatretic)10015070

3-6 mm (large, atretic)860120190

Commercial preparations:Anteron, Prolan A, Gestyl, and Folligon.Biological preparations:Anterior pituitary extract, Pregnant mare serum gonadotropin (PMS) Or equine chorionic gonadotropin (eCG), and Menopausal urine gonadotropin (MUG). Therapeutic dose:A.200 - 500 i.u. for Small animal. B.500 -1500 i.u. for large animal.NB: Over dosing causes super-ovulation.

Therapeutic uses:1.It is used mainly to activates the ovary in cases of ovarian inactivity or to induce follicular growth either for super-ovulation purposes or for out-of-seasone breeding. 2.Repeated injections are required owing to short half-life, but repeated administration has a refractory results due to antibodies formation that neutralize the injected hormone. Moreover, anaphylactic reaction may be developed in treated cases.

2 - Luteinizing hormone (LH) Biological effect:1.Stimulate follicular steroidogenesis: the steroidogenic activity of the follicle depends upon FSH and LH that acting synergistically on both thecal cells (androgen) and granulosa cells (estrogen) with a consequent increase in follicular estrogen production (two cell theory), since androgen well be aromatized to estrogen during diffusion through granulosa cells (aromatase enzyme).2.Stimulate follicular and ovum maturation through increased progesteron production by granulosa cells in antral follicle.

1. Induce ovulation by increasing intrafollicular concentration of proteolytic system ( proteolytic enzymes, collagenase-like enzyme, plasminogen ).

2. Stimulate CL formation and maintain its steroidogenic activities.

Commercial preparations:

Premogenyl, Prolan B, and Pregnyl.

Biological preparations:

Human chorionic gonadotropin(HCG).

Therapeutic dose : • 500-1000 i.u. for small animals.• 1000-5000 i.u. for large animals.

Therapeutic uses:

1. Luteinization of follicular cysts (cystic ovary).

2. Induction of ovulation.

3. Delayed ovulation.

NB: Repeated administration has a refractory

results due to antibodies formation that neutralize

the injected hormone.

3 - Prolactin or Leutotrophic hormone(LTH(Biochemistry: Its molecules are very similar to growth hormone.It is composed of single polypeptide chain that contains 198 amino acid with a molecular weight of 27000.It have specific receptor sites on the ovary, liver, adrenal gland, and mammary gland.The wide spread of prolactin receptors and wide range of action (osmoregulation, metabolic, and reproduction) classify prolactin as a metabolic rather than a gonadotropic hormone.

Biological effect: It inducing mammary growth (mammogenic

action). It initiates milk secretion after parturition

(lactogenic action). It stimulates continuation of established milk

secretion (galactogenic action). It has luteotropic action and increased number of

LH receptors on the ovary. It maintain CL function with consequent

cessation of estrous cycle in high lactating cows. It stimulate maternal behavior in nursing females.

III – Ovarian HormonesA – Ovarian Steroid Hormones Biochemistry: The ovary, among the steroid synthesizing glands, has the unique capacity to secrete significant amount of estrogens.

Plasma cholesterol is the precursor of steroid nucleus (cyclopentano-perhydro-phenantherin nucleus).Conversion of cholesterol in the ovarian tissues to steroid hormone is accelerated by LH through cAMP.

1- EstrogenIt is generally accepted that follicular estrogen is synthesized by collaboration of two cell layers (theca interna cells and granulosa cells) through what is called two cell theory.LH stimulate theca interna cells to synthesize and secrete androgens. Whereas, FSH stimulate the granulosa cells to aromatize the diffused androgens into estrogen with a cosequent rise in concentration of estrogen in intrafollicular fluid.

Biological action:1. Growth of sexual organs through its anabolic

effect.2. Development of secondary sexual characters in

females.3. Induce the clinical and behavioral signs of estrum.4. induce proliferation of the duct system of the

udder.5. Favors calcium deposition and closure of epiphysis

in long bones.6. Prepare receptors on uterine muscle to oxytocin.7. Favors deposition of glycogen in endometrial

glands.8. Anabolic steroid.

Commercial preparations: Diethyl stibesterol, Premarine, Cyren B,Triphynyl etheline, Hexesterol, and Folone 1&5.Therapeutic dose:The preparations are oily and injected IM or SC (Average dose is 30 mg).A.Small animals Up to 20 mg.B.Large animals Up to 50 mg.

Therapeutic uses: 1.To induce abortion in cases of unwanted pregnancy.2.To open cervical canal to get red of uterine contents during treatment of closed pyometra or mummified fetus.

3. To induce hormonal castration and fattening of males.

4. To treat ovarian inactivity through multiple injection of small minute doses to initiate FSH secretion.

5. To help in treatment of vaginal prolapse.NB: Estrogen treatment may lead to

hypocalcaemia. Therefore, calcium preparation should be injected together with estrogen.

Disadvantages of estrogen application:1. Reduce milk yield and lactation may be inhibited

or even stopped.2. Excessive amounts causes relaxation of the pelvic

ligaments and may leads to vaginal or rectal prolapse together with development of genital tract infection.

3. Prolonged use might causes nymphomania, cassation of estrous cycle and atrophy of the ovary due to its inhibitory effect on FSH secretion and release.

2-ProgesteroneBiological action:

1.Play an important role in follicular maturation,

ovulation, fertilization, and implantation.

2.Necessary to maintain pregnancy.

3.Favors deposition of glycogen in endometrial glands

and stimulate uterine milk secretion

4.Proliferate the alveolar system of mammary gland.

5.Anabolic steroid .

6.Inhibit folliculogenesis.

Commercial preparations:1.Methyl acetoxyprogesterone (MAP).2.Chlormadinone acetate progesterone (CAP).3.Medroxy progesterone acetate (MPA). Therapeutic doses:Small animals 10-20 mg.Large animals 50 mg.Therapeutic uses:1.To prevent or control habitual abortion.2.Synchronization of estrous. 3.To counter act the effect of estrogen in cows suffer cystic ovary (nymphomania).4.In cases of vaginal prolapse .

B - Ovarian Protein Hormones1 – InhibinIt is a protein hormone made by the ovary (granulosa cells) and testis (Sertoli cells) that is secreted into the blood stream to control (inhibit) the secretion of follicle stimulating hormone by the pituitary gland. It also limits the release of gonadotropin-releasing hormone. There are two functional forms of inhibin, A and B forms. Both inhibin A and B has two protein subunits, (an αA and a βA subunits & αB subunit and a βB subunit).The two forms and subunits are almost of the same size and are held together by covalent linkages.

Inhibin A is secreted by the granulosa cells of the dominant follicle as it grows, causing blood inhibin A levels to gradually increase toward midcycle, with the main peak occurring after ovulation.

Inhibin B is produced by small follicles at the start of the cycle, with minimal secretion during the luteal phase. Elevated levels of follicle stimulating hormone in menopause women may be due to reduced inhibin B owing to decreased follicular reserves.

Serum inhibin levels fell during gonadotropin suppression and were partially and approximately equally restored by either FSH or LH treatment.

However, bilateral ovariectomy decreased plasma immunoreactive inhibin and increased plasma FSH significantly.

These findings indicates that the ovary is the main source of inhibin secretion and that the inhibin is a major regulator in the follicular development through FSH secretion.

FSH presumably acts directly on the Sertoli cell to increase inhibin secretion in males, whereas LH may act via increased intratesticular Testosterone levels and/or other factor(s).

The relationship between inhibin and follicle-stimulating hormone represents a typical negative feedback servomechanism

2 - ActivinIt is a polypeptide hormon produced in the gonads, pituitary gland, placenta, and other organs.It has an action in the body opposite to that of inhibin. Levels of these two hormones tend to fluctuate in both males and females in response to a number of cues (include changes in hormone levels triggered by natural biological processes, environmental pressure, and other factors).In the ovarian follicle, activin increases FSH binding and FSH-induced aromatization.It participates in androgen synthesis, enhancing LH action in the ovary and testis.

3 - BradykininIt is a polypeptide hormone. It is found in the follicular fluid of Graffian follicle of bovine, rabbit and human.It reaches the fallopian tube after ovulation and help in trapping the ovum by infundibulum.4 - RelaxinIt is a polypeptide in nature secreted from CL in late pregnancy, and by the placenta and uterus. It aids in the dilatation of the cervix and causes relaxation of the pelvic ligaments, separation of the symphysis pelvis thereby preparing the birth way for the act of parturition.

Mechanism of Hormonal Control

1. Neurohumoral mechanism: A neurohumoral substance reaching the

endocrine gland through circulating blood such as Gonadotropin releasing hormone secreted from the hypothalamus and reaching anterior pituitary gland through hypothalamo-hypophysial portal circulation to stimulate synthesis and secretion of Gonadotropin.

Neurohumoral mechanism

2. Nervous mechanism: An appropriate nervous impulse is necessary

to release the hormones such as nervous impulse necessary to release oxytocin from posterior pituitary gland following visual or tactile or auditory stimulation during milking. Vaginal stimulation in conditioned ovulators (she camel and female rabbit) is necessary to induce surge-like release of LH to induce ovulation.

Nervous mechanism

3. Feed-back mechanism (servo-mechanism): Such that reported between FSH and inhibin

hormone. FSH stimulate follicular growth and stimulate steroidgenesis. FSH secretion will be decline or inhibited as the follicle reaching the mature size and secrete high amounts of inhibin hormone ( negative feed back regulation), but high level of estrogen will stimulate release of high amounts of LH necessary to induce ovulation (positive feed back regulation).

Therefore, a negative feed back is found between inhibin and FSH, but a positive feed back is developed between estrogen and LH.

In another wards, inhibin will feed back to anterior pituitary gland to inhibit secretion of FSH (negative feed back) and estrogen stimulate secretion of LH (positive feed back).

Whereas, high level of progesterone will inhibits FSH secretion and stop estrous cycle.

NB: Typical negative feedback mechanism is recorded for FSH and Inhibin.

Feed-back mechanism (servo-mechanism)

Reproduced from Reproductive endocrinology Edited by Samuel S.C and Robert B. Jaffe( W.B. Saunders Company, Philadelphia)

Mode of Action of Protein/Peptide Hormones

ATP = Adenosine TriphosphatecAMP = Cyclic Adenosine Monophosphate

PP = Pyrophosphate

Granulosa Cell

FSH

Enzyme Cytoplasm

DNASteroid

enzymes

Estrogensynthesis

PhosphodiesteraseInactivates

by conversion

Caffeine inhibitsenzyme and allows

prolonged activation

Capillary

ProteinHormone

HormoneReceptor

AdenylateCyclase ATP cAMP + PP

ProteinKinase

5 ’AMP

NucleusmRNA

Protein

Releasedfrom cell

Bilaminar Cell Membrane

Mode of Action of Steroid Hormones

UterineGlandularEpithelial

Cell

Progesterone

Diffuses in cytoplasm

Secretion intouterine lumen

SteroidCapillary

Release from bloodcirculation

SteroidDNA

Nucleus

ReceptormRNA

Rough Endoplasmic

Reticulum

ProteinSynthesis

Bilaminar Cell Membrane

Chromatin

IV-Endometrial hormonesProstaglandinBiochemistry:Arachidonic fatty acid is the precursor of all Prostaglandin series ( A, B, C, D, E, F, G, H).Biosynthesis of Prostaglandin (PG) is mediated by a complex of microsomal enzymes (prostaglandin synthetase enzymes).These enzymes are demonstrated in a wide number of organs, but the rate and type of prostaglandin biosynthesis differ widely among organs. Prostaglandin E (PGE) is the predominant product in many tissues, but PGF is the product frequently identified in the genital tract.

PGF often display the opposite biologic activity to that of PGE, but PGF can be converted directly to PGE and vice versa. The consequent biologic activity can also be reversed or modified by direct conversion.

Synthesis and secretion: Progesterone stabilize phospholipase enzyme that is

responsible for hydrolysis of phospholipids. However, estrogen labilize this enzyme.

Thus, decline in progesterone concentration in the plasma and ascendance of estrogen during the terminal period of pregnancy are responsible to induce release of such enzyme to induce hydrolysis of phospholipids and produce the precursor of PG (arachidonic fatty acid).

Increased estrogen concentration during the last 15 days of pregnancy was associated with increased PGF2α concentration in both fetal fluid and endometrial caruncles.

Mode of action on smooth muscle: PGF (smooth muscle contraction) often display the

opposite biologic activity to that of PGE (smooth muscle relaxation).

PGF can be converted directly to PGE and vice versa. The consequent biologic activity can also be reversed or modified by direct conversion.

PGF2α has an ecopolic effect and luteolytic effect. It increases calcium release from sarcoplasmic

reticula, and calcium-induced activation of glycogen phosphorylase system through cAMP with cosequent formation of glucose (nessesary to support the metabolic needs of the contractile muscle).

PGE2 induce smooth muscle relaxation through Guanilate cyclase activity (inhibition) through cGMP.

Commercial preparations:Estrumate (2 ml IM), Lutalyse (5 ml IM), Illerine (2.5 ml IM), Prosolvine (2 ml IM), Equamate (2 ml IM for mares).Therapeutic uses:1.Estrus synchronization (Three programs or regimens):A-Clinical examination, detection of CL, single dose, breeding for responders. B-Single dose, heat, followed by another dose after 12 days from the first injection for refractory cases. C-Two successive injection with 12 days intervals, then application of two successive insemination.

2. Induction of parturition.3. Induction of abortion.4. Opening the cervix and get red uterine

contents in cases of closed pyometra, endometritis, and mummified or macerated fetus.

5. Reduce length of estrous cycle, with a consequent induction of recurrent estrous during a short period.