Gyne Rep Endo-Dr. Ona Cruz

Learning Objectives

Reproductive Endocrinology  J.ONA CRUZ,MD,MHPEd,FPOGS OBSTETRICS & GYNECOLOGY FEU-NRMF

1

Explain the Hypothalamic-Pituitary-Ovarian Interactions

2

Describe the GnRH structure and functions

3

Trace the major and alternative route route of GnRH transport

4

Describe the manner of GnRH secretion in relation to the menstrual cycle

5

Explain the regulatory mechanisms governing GnRH secretion and release

6

Explain the therapeutic value of GnRH analogues

7

Describe gonadotrophins’ gonadotrophins’ structure and function function

8

Describe the manner of gonadotropins’ secretion in relation to the menstrual cycle

1

Learning Objectives 9

Explain the two-cell-two-gonadotropin theory of steroid production

10 Tabulate the different growth factors and their effects on

gonadal gonadal function function 11 Tabulate the different eicosanoids/prostaglandins and

their role on ovarian physiology 12 Diagram ovarian steroid biosynthesis 13 State the ovarian steroids and their action 14 Describe ovarian gametogenesis gametogenesis and the development of

the dominant follicle 15 Relate the key events in the m enstrual cycle

3

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2

GnRH

Gonadotropin-releasing hormone SECRETION

Unique among releasing hormones

Regulates secretion of FSH and LH Secreted Secreted in pulsatile pulsatile manner to be effective. (Half-life: 2 to 4 minutes)

9

GnRH

Gonadotropin-releasing hormone Regulation of SECRETION

What regulates amplitude and frequency of GnRH secretion? secretion? LONG feedback loop

The control of episodic GnRH GnRH secre secretio tion n is extremely important for the maintenance maintenance of normal ovulatory ovulatory cyclicit cyclicity. y.

Stimulation and inhibition by ovarian steroids (E2, P4) Stimulation and inhibition by nonsteroida nonsteroidall secretions secretions (inhibin, (inhibin, activin, and follistatin)

SHORT feedback loop

Inhibition Inhibition by gonadotropins gonadotropins (LH, FSH)

ULTRA-SHORT feedback loop

Inhibition by GnRH

11

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Neurotransmitters and Neuromodula Neuromodulators tors and Brain peptides peptides (Catecholamines, dopamine, 12 endogenous endogenous opioid peptides) peptides)

Neurotransmitters and their Role in Regulation of GnRH secretion 1

*How do medications affect reproductive function?

Catecholamines: Catecholamines: Modulate Modulate GnRH pulsatile pulsatile release release by influencing the frequency and amplitude of the pulses Dopamine

Inhibits GnRH release, (and indirectly indirectly inhibit gonadotropins) Inhibits Pituitary prolactin secretion (Prl Inhibiting Hormone???)

Norepinephrine 2

How can some pharmacologic agents cause galactorrhea and amenorrhe amenorrhea? a?

Stimulatory to GnRH

Indolamine Serotonin

Does NOT affect GnRH GnRH release. Stimulates PRF, thus stimulating Prl ultimately inhibiting GnRH 13

14

*Neuromodulators *Neuromodulators & Brain peptides: peptides: Role in Regulation Regulation of GnRH secretion secretion Neur Neurom omod odul ulat ator ors s 1 Opiods: ↓LH, ↑Prl, ↓ GnRH 2 Prostaglandins (PG E2): ↑ GnRH 3 Catech Catechole olestr stroge ogens: ns: Inhibi Inhibits ts tyrosin tyrosine e OHlase Brain Peptides

1 Neuropeptide Y 2 Angiotensin II 3 Soma Somato tost stat atin in 4 Acti Activi vin n and and Inhi Inhibi bin n 5 Foll Follis isttati atin 6 Galanin 18

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*Learner Task : tabulate the different neuromodulators neuromodulators and brain brain peptides peptides as to their basic description and functional effects on GnRH GnRH and gonadotropin secretion.

19

GnRHa: Comparison

GnRH Analogs: Analogs: Clinica Clinicall Use

Hall JE: ClinObstetGynecol7:44,199 ClinObstetGynecol7:44,1993 3

Activation of pituitary Gonadal Gonadal function function

Agonist

Antagonist

Suppression of Gonadotropin

Desensiti itization

Competitive receptor blockade

Acute Responses

Stimu Stimulat late e LH LH / FSH

Inhibi Inhibitt LH, LH, Partia Partially lly FSH

Chronic response

Inhibit LH / FSH

Give in pulses Pituitary Pituitary - gonadal gonadal inhibition Give in bolus

Inhibit LH / FSH

Delayed puberty Cryptorchidism Functional Hypothalamic amenorrhea Hypogonadotropic hypogonadism (Kallmann’s syndrome) Precocious puberty Hormone dependent tumors

Endometriosis

Uterine leiomyomas/Fibroids Breast cancer Prostatic Prostatic cancer cancer

Suppression of ovarian fucntion in PCOS and in IVF

Experience

Extensive

Limited

Safety

Long history of safety

Effects of histamine release

Contraception

Suppression of spermatogenesis

Relatively low

high

Give in bolus

Ovulation inhibition

Cost

PMS DUB

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GnRH antagonists: mechanism of action Loy RA: Curr Opin Obstet Gynecol 6:262, 1994

Pituitary-ovarian axis suppression without flare effect

Action

Compete with with GnRH for its receptors Prevent synthesis and release of LH/FSH Induce immediate and transient hypogonadism Suppress Suppress gonadal steroidogenes steroidogenesis is

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Structure: FSH and LH Glycoproteins of high molecular weight. [LH 28,000 and FSH 37,000 daltons] α subunit

14,000 daltons, 90 amino acids Similar to TSH & hCG

Different β subunits

Carb Ca rboh ohyd ydra rate tes s

Biol Biolog ogic ic acti activi vity ty

Amino acids Sialic ac a cid

Half life

LH

1 or 2

30 min

FSH

5

3.9 hrs

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Functions: LH 1

2

3

Stimulate Stimulates s horm hormone one production production by activating activating cP450SCC  a

Andr Androg ogen en in thec theca a cell cells s

b

Proges Progester terone one in the the corp corpus us lute luteum um

Acts Acts syne synergi rgist stica ically lly with with FSH FSH A

on the granulosa cells to help follicular maturation

B

to increase LH receptors receptors and luteinization of follicle (thus increasing progesterone production)

Indu Induce ces s ovu ovula lati tion on a

stimulating a plasminogen activator that decreases decreases tensile strength of the follicle wall before follicular rupture occurs.

b

Stimul Stimulate ates s prosta prostagla glandi ndin n synthe synthesis sis..

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Functions: FSH 1

2

3

Stimu Stimulat lates es hormon hormone e produc productio tion n a

Estrogen (E1, E2) in granulosa granulosa cells by activating aromatase  enzyme

b

Interconversion of Androstenedione and Testosterone in the th theca eca cells by activating 3ß-OHSD 

Acts Acts syn syner ergi gist stic ical ally ly wit with h LH A

on the granulosa cells to help follicular growth growth & maturation

B

to increase LH receptors and luteinization of follicle (thus increasing progesterone production)

Rescue Rescue of follicles follicles from from degenerat degeneration ion (achiev (achieved ed by reducing reducing androgenicity of environment) a

indirectly by stimulating stimulating activin production

b

directly metabolizing LH-induced thecal thecal androgens to estrogens 29

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STEROIDOGENESIS Luteal phase OVARIAN OVARIAN STEROIDOGENESIS : LUTEAL PHASE LDL THECA GRANULOSA Acetate

Acetate

LH

Cholesterol

Cholesterol

LH

Pregnenolone

Pregnenolone 17-OH pregnenolone DHA

LDL

Progesterone

Estradiol

FSH

Estrone

Androstenedione

Androstenedione

Testosterone

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Acti Ac tivi vin n & Inhi Inhibi bin n Involvement in ovarian steroid synthesis Inhibins Inhibins stimula stimulate te progesterone and inhibit estradiol production Activins Activins inhibit inhibit progesterone and stimulate estradiol production Mathews LS. Endocrine Rev 15:310, 1994

OVARY Cholesterol Pregnenolone Inhibin

+

-

Activin

Progesterone Androstenedione Activin

+

-

Inhibin

Estradiol

36

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Inhibin

Activin

Production is regulated by FSH Preferentially inhibits FSH over LH release Action Actions: s:

Stimulates FSH release but NOT LH. Action Actions: s: 1 stimul stimulati ation on of the thecal cal and androg rogen en production

1 stimul stimulati ation on of the thecal cal and androg rogen en production

2 Inhi Inhibit bits s oocy oocyte te ma matu tura rati tion on

2 Inhi Inhibit bits s oocy oocyte te ma matu tura rati tion on

Decline Decline in inhibin inhibin levels levels in the  perimenopau  perimenopause se and menopause menopause is  probably the permissive factor in the rise of FSH levels at these times.

Decline Decline in inhibin inhibin levels levels in the  perimenopau  perimenopause se and menopause menopause is  probably the permissive factor in the rise of FSH levels at these times. 37

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Follistatin Ovarian peptide

*Learner Tasks:

aka: FSH-suppressing protein Action Actions: s:

1 inhibit inhibition ion of FSH synthe synthesis sis and secretion 2 Inh Inhibit ibition ion of FSH FSH resp respons onse e to GnRH

Tabulate the different growth factors and prostaglandins and their functions.

3 Bind Binds s tto o act activ ivin in and and in in thi this s manner decreases the activity of activin. 39

Ovarian Steroids:

GONADAL STEROIDOGENESIS Cholesterol

P450c17 17a OHlase

Pregnenolone

4 pathway Progesterone pathway

17-Hydroxypregnenolone

3 -OHSD isomerase

17 -OHSD

Liver Kidneys

Transport proteins

SHBG: Estrogen & Androgens

Testosterone

17 HSD

CBG: Progesterone Clinical application:

Estradiol, obesity and hyperthroidsm increases SHBG. Androgens Androgens and hypothyroidism decreases them

P450arom

P450arom Estrone

Metabolism

17-Hydroxyprogesterone P450c17 17, 20 lyase

Androstenedione Speroff L, et al. ClinicalGynecologic Endocrnolgy and Infertility, ed 6, Lippincott, 1999

the corpus luteum)

P450c17 17a OHlase

Dehydroepidandrosterone 5,4

3 -OHSD 5,4 isomerase

Progesterone

P450c17, 20 lyase

Estrogen &

Progesterone Daily estradiol: 0.1 to 0.5 mg (lowest during menses, highest just before ovulation) Secretion progesterone: 0.5 mg (follicular phase, by the adrenals) to 20mg (luteal (luteal phase, phase, by

Acetate

P450scc 5 pathway DHEA pathway

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Estradiol 41

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Functions of Ovarian Steroids

OVARIAN DEVELOPMENT: CHRONOLOGY

Estrogen

stimulation of synthesis of estrogen and progesterone receptors in target tissues such as the endometrium Progesterone inhibition of synthesis of estrogen and progesterone receptors increase intracellular synthesis of estrogen dehydrogenase (converts estradiol to less potent estrone

Primordial germ cells

6 weeks

migrate Genital ridge 12-24 weeks 1

ST

Meiotic Division

Meiotic Division Diplotene Diplotene Stage (Prophase)

Birth Puberty

Reproduction span

43

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Primary Primary oocytes in meiotic arrest 2,000,000 oocytes

Resumption of the Miotic Miotic Division Division

7,000,000

Oogonia proliferation

400,000 oocytes 400 oocytes

A T R E S I A

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The dominant follicle The dominant follicle established by day 7 of the cycle.

1 Secret Secretes es highes highestt amou amount nt of estrogen 2 Most sensitive to FSH 3 Has greatest number of

receptors 4 Has the greatest mitotic activity

and number number of granulosa granulosa cells 5 More vascularize vascularized d theca cells cells so

more FSH reaches its receptor 52

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THE END 

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THE MENSTRUAL CYCLE

KEY EVENTS OF THE MENSTRUAL CYCLE (Dr. Alenzuela’s Note)

At the start of each menstrual cycle, gonadal hormones are low and has been declining since the end of the luteal phase of the previous cycle. With the demise of the corpus luteum of the previous cycle, FSH levels begin to rise and follicular recruitment of  the next cycle begins. Under t he influence of FSH, these follicles grow and each secrete increasing amounts of  estradiol. The rising estrogen causes proliferation of the endometrium. Estrogen stimulate growth and differentiation of the functional layer of the endometrium and work synergistically with FSH for follicular development. Rising levels of estradiol sends a negative feedback the pituitary and hypothalamus resulting into inhibition of FSH release and FSH declines at midpoint o f the follicular phase. Also, the granulose cells secrete inhibin which help suppress FSH. LH on the otherhand, is initially stimulated by secretion of estrogen throughout the follicular phase. The midpoint decline of FSH causes atresia of all except one folliclefo llicle- the dominant follicle. The dominant follicle produces about 80% of the daily estradiol production of 500 µg. The rapid rise of estradiol and small amounts amounts of  progesterone from the dominant follicle is the HPO signal that the follicle is ready to be ovulated. When a critical estradiol level isreached (200pg/ml or more for two or more days), the initial negative feedback reverses into a positive one and causes the LH and FSH surge at midcycle. The LH surge initiates ovulation.

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At the end of the follicular phase just before ovulation, FSH-induced receptors appear on the granulose cells. LH stimulation modulates progesterone secretion. LH surge initiates germinal vesicle disruption disruption and metaphase I is completed. The oocyte enters metaphase II and the first polar body appears. (It is only upon sperm penetration into the zona pellucida when meiosis is completed and the second polar body is extruded). Prior to rupture, LH stimulates synthesis of PGF2 α and PGE and collagenase. FSH stimulates production of  plasminogen activator which converts plasminogen to plasmin, a proteolytic enzyme. These facilitates follicular rupture and egg extrusion. extrusion. After extrusion of the oocyte, there is a decrease in follicular fluid , the follicular wall convolutes and there is a marked decrease in diameter and volume of the follicle. The granulosa cells become vascularized allowing LH to reach more receptors. Both granulose gr anulose and theca cells become luteinized and acquire yellow coloration. Under LH, the cor pus luteum produces significant amounts of progesterone. Estradiol levels meanwhile decreases  just before ovulation and continues to lower in the early luteal phase. Its levels pick up at midluteal phase as a consequence of corpus luteum production (second estradiol peak). The decrease in LH frequency in the luteal phase is due to the negative feedback effect of progesterone on the hypothalamus which decreases GnRH release. (Increased β-endorphin levels probably mediates this event). The decrease in LH amplitude is due to the negative feedback of progesterone on the pituitary. Estradiol and progesterone levels remain elevated throughout the lifespan of the c orpus luteum. However, its existence is dependent on LH. With co ntinuing decline in LH levels, there is demise of the corpus luteum and sex steroid levels delines. In 4-6 days after this fall menstruation ensues and the next cy cle begins. If however, fertilization occurs, there is rescue of the corpus luteum as a consequence of HCG production which acts as a surrogate for LH.

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