Neuroendocrine Regulation of Reproduction

By

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

& A.I.Faculty of Veterinary Medicine

Zagazig University( 1 )

Neuroendocrine Regulation of Reproduction

Mammalian hormones

Neuro-endocrine Regulation of Reproductive HormonesCerebrum

Cerebellum

MedullaOblongat

aPituitary Stalk

Third Ventricle

Pineal Body

Optic chiasm

Pituitary Gland

Hypothalamus

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-Improvement of 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 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. Therefore, oxytocin has a definite functions in parturition, milk let-down, 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 and Cyntocinon are the preparations mostly available that can be used as a single IM or IV injection (10-15 iu or 15-25 iu for small or 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. B- to overcome uterine inertia. C- to hasten placental drop. D- to hasten uterine involution. E- to get- red uterine contents in open pyometra. F- to reduce size of the prolapsed uterus.

Pituitary Gonadotropin Hormones

Chemistry: 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 bound in noncovalent association of very high affinity. Both FSH and LH wthin 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. Whereas, 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. However, half-life of glycoprotein hormones in circulation depends upon their sialic acid content.

Characteristics of gonadotropic hormones

Hormone

Molecular 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.

A- Follicle stimulating hormone (FSH:(Biological effect: 1-Stimulate folliculogenesis: It reach the specific receptor sites on 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 luteinization : by increasing LH receptors on both granulosa cells and thecal cells. 3- Stimulate steroidogenesis: the steroidogenic activity of the follicle depends on FSH and LH that acting on both granulosa cells (estrogen) and thecal cells (androgen) with a consequent increase in follicular estrogen production (two cell theory). 4- Stimulate follicular maturation: a certain balance between FSH, LH, Estrogen, Progesteron, and Androgen hormones is needed to stimulate follicular maturation.

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

Follicular diameter (mm)

Estradiol (Pmol/ml)

Progesterone(Pmol/ml)

Testosterone(Pmol/ml)

2-3 (small, nonatretic)

14040280

3-6 (large, nonatretic)

10015070

3-6 (large, atretic)860120190

Commercial Biological preparations: - Anteron -Anterior pituitary extract.- Prolan A -Pregnant mare serum gonadotropin (PMS).- Gestyl Or equine chorionic gonadotropin (eCG).-Folligon -Menopausal urine gonadotropin (MUG).

Therapeutic dose:

-200 - 500 i.u. for Small animal. -500 -1500 i.u. for large animal.-Over dosing causes super-ovulation.

:Therapeutic uses- 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. Repeated injections are required owing to short half-life. - Repeated administration has a refractory results due to antibodies formation that neutralize the injected hormone. Moreover, anaphylactic reaction may developed in treated cases.

(LH :( B- luteinizing hormone Biological effect:1- Stimulate follicular steroidogenesis: the steroidogenic activity of the follicle depends on FSH and LH that acting on both granulosa cells (estrogen) and thecal cells (androgen) with a consequent increase in follicular estrogen production (two cell theory), since androgen well be aromatized to estrogen during diffusion through granulosa cells.2- Stimulate follicular and ovum maturation. 3- Induce ovulation by increasing intrafollicular concentration of proteolytic system ( proteolytic enzymes, collagenase-like enzyme, plasminogen ). 4- Stimulate CL formation and maintain its steroidogenic function.

Commercial Biological preparations: - Premogenyl - Human chorionic gonadotropin(HCG) - Prolan B -Pregnyl

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.4-Repeated administration has a refractory results due to antibodies formation that neutralize the injected hormone.

C- prolactin or Leutotrophic hormone(LTH(:Chemistry: 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 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 metabolic rather than gonadotropic hormone.

Biological effect:It has mammogenic action: inducing mammary growth.It has lactogenic action: initiates milk secretion after parturition. It has galactogenic action: stimulates continuation of established milk secretion.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 mature females.

Ovarian Steroid hormones1-Estrogen :

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

Biological action:Growth of sexual organs through its anabolic effect.Development of secondary sexual characters in females.Induce the clinical and behavioral signs of estrum.induce proliferation of the duct system of the udder.Favors calcium deposition in long bones.Prepare receptors to oxytocin.Favors deposition of glycogen in endometrial glands.

Commercial preparations:-Diethyl stibesterol -Premarine. -Cyren B .-Triphynyl etheline.-Hexesterol.-Folone.They are oily preparations and injected i.m. or s.c.

Therapeutic dose:-Small animals Up to 20 mg.-Large animals Up to 50 mg.-Average dose 30 mg.

Therapeutic uses:

1. Induce abortion in case of unwanted pregnancy.2.To open cervical canal to get red of uterine contents during treatment of closed pyometra or mummified fetus.3.To treat ovarian inactivity through injection of small minute doses to initiate FSH secretion. 4. To induce hormonal castration and fattening.5- To help in treatment of vaginal prolapse.

Disadvantages of estrogen application:

1- Reduce milk yield and even stop its secretion.

2- Excessive amounts causes relaxation of the pelvic ligaments and may leads to vaginal or rectal prolapse.

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

2-ProgesteroneBiological action:

1- Inhibit folliculogenesis.2- Proliferate the alveolar system of mammary gland.3- Necessary to maintain pregnancy.4-Favors deposition of glycogen in endometrial glands and stemulate uterine milk secretion.5-Anabolic steroid .

Commercial preparation: Methyl acetoxy progesterone (MAP).Chlormadinone acetate progesterone (CAP).Medroxy progesterone acetate (MPA).

Therapeutic doses:Small animals 10-20 mgLarge animals 50 mg

Therapeutic uses:1. To prevent or control habitual abortion.2. Synchronization of estrous. 3.  In cystic ovary (nymphomania) to counter effect of estrogen.4. Vaginal prolapse .

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 trapping of the ovum by infundibulum.

4-Relaxin:It is a polypeptide in nature secreted from C.L. in the 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.

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.

3-Feed-back mechanism (servo-mechanism): such that reported btween Gonadotropin hormones and estrogen hormone. FSH stimulate follicular growth and stimulate steroidogenesis. FSH secretion will be decline or inhibited as the follicle reaching the mature size and secrete high amounts of estrogen 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 estrogen and FSH, but a positive feed back is developed between estrogen and LH. In another wards, estrogen will feed back to anterior pituitary gland to inhibit secretion of FSH (negative feed back) and stimulate secretion of LH (positive feed back).

Mechanism of Hormonal Action

Protein/Peptide HormonesATP = Adenosine Triphosphate

cAMP = Cyclic Adenosine MonophosphatePP = Pyrophosphate

Granulosa Cell

FSH

Enzyme Cytoplasm

DNASteroid

enzymes

Estrogensynthesis

PhosphodiesteraseInactivates

by conversion

Caffeine inhibitsenzyme and allows

prolonged activation

CapillaryProtein

HormoneHormoneReceptor

AdenylateCyclase ATP cAMP + PP

ProteinKinase

5 ’AMP

NucleusmRNA

Protein

Releasedfrom cell

Bilaminar Cell Membrane

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

Endometrial hormones Prostaglandin

Chemistry:Arachidonic fatty acid is the precursor of Prostaglandin series ( A, B, C, D, E, F, G, H).Biosynthesis of Prostaglandin (PG) is mediated by a microsomal complex of 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.

:Synthesis and secretion Progesterone stabilize phospholipase enzyme that is responsible for hydrolysis of phospholipids. However, estrogen labilize this enzyme. Thus, decline in progesterone cocentration in the plasma and ascendence 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), but 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 preparationsEstrumate (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-Treatment of pyometra, endometritis, and mummified or macerated fetus (opening the cervix and repeated estrum).