Download Normal Menstrual cycle

Harvard-MIT Dvision of Health Sciences and Technology
HST .071: Human Reproductive Biology
Normal Menstrual cycle
Alan Penzias MD
Normal Menstrual Cycle – Alan Penzias MD
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SUMMARY OF THE NORMAL MENSTRUAL CYCLE
Teleologically, the purpose of the human menstrual cycle is the production of a fertilizable egg and the
development of an appropriate uterine environment for implantation of the resultant embryo (Figure 1).
In the human the usual course of events is the production of only one mature egg per menstrual cycle,
although occasionally twinning results from the simultaneous ovulation of two or more eggs (dizygotic).
The human menstrual cycle, therefore, can be seen as the mechanism whereby only one mature egg
(from the 7 million present at the time of maximal oocyte (egg) availability from meiotic division at 6
months of fetal life, is allowed to ovulate each lunar month. Simultaneously a hormonal environment is
created which permits implantation in the uterus 7 days after ovulation.
The human menstrual cycle is ultimately controlled by the hypothaiamic pulse generator located in the
arcuate nucleus. It is modulation of this pulse generator, either directly of through modulation of the
signal from this pulse generator at the pituitary target of the message that results in the human menstrual
cycle. The signal from the hypothaiamic pulse generator is delivered by means of a decapeptide, the
neurohormone gonadotropin releasing hormone (GnRH). Release of GnRH is pulsafile in nature and is
the result of multicircuit electrical activity in the GnRH producing cells of the arcuate nucleus. To date
no convincing evidence is available that any modulation of this multicircuit activity can increase the
synchronized firing rate of GnRH neurons above their intrinsic maximum of approximately once every
75 minutes. (Aspartic acid has been putative in this regard, but solid evidence is lacking). Thus, all
modulation of the GnRH signal at the level of the hypothalamus is by slowing of the GnRH pulse
generator from its intrinsic rate.
The effect of GnRH on the pituitary is to release two glycopeptides, follicle stimulating hormone (FSH)
and luteinizing hormone (LH). (Although these hormones are named from their functions in the
menstrual cycle, the identical hormones are present in men where they regulate testosterone production
and spermatogenesis by the testis). GnRH has been shown to possess a remarkable one to one
relationship with LH at the pituitary. That is each pulse of OnRH is accompanied by a imultaneous
pulse of LH. FSH is regulated in a more complex fashion with a combined effect of both OnRH and an
ovarian peptide called inhibin.
The resting stage of the ovarian follicle is termed the primordial follicle. This follicle consists of the
oocyte, arrested at the diplotene phase of meiosis I, and a single layer of cuboidal cells - the grannlosa
cells. The process of maturation of the follicle is initially gonadotropin (LH and FSH) independent. The
length of this gonadotropin independent phase is poorly characterized in the human but may last several
months. Follicular maturation is characterized by an increase in the number and functional capacity of
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33 the granulosa cells. These follicles almost all undergo atresia due to lack of rescue by gonadotropius
necessary for continued growth. The determinant of whether a follicle is at the appropriate stage of
development to be "rescued" from atresia is the number of FSH receptors, which is in turn dependent on
the number of granulosa cells which contain these receptors. Until just prior to its final stage of
development, the preovulatory follicle contains FSH receptor but no LH receptor. The process of
follicular development and atresia is ongoing from six months of prenatal life until the depletion of all
follicles at the time of menopause. It continues through childhood and pregnancy unabated. The precise
mechanism which signals cohorts of follicles to initiate growth is unknown, however the number
initiating growth is directly proportionate to the remaining pool of follicles. In childhood and during
pregnancy all follicles undergo atresia as a result of insufficient FSH to "rescue" these follicles. During
the course of the menstrual cycle, however, several of these follicles will have developed to a stage
where these is sufficient growth to be sensitive to the circulating levels of FSH. This cohort of follicles
are said to be recruited and of them only one will gain,dominance, and the remainder will undergo
atresia through a mechanism similar to their non-recruited counterparts. The process by which one
follicle gains dominance is the result of positive feedback within the granulosa cells of this follicle. FSH
induces its own receptor. The process of FSH induced FSH receptor in the granulosa cells is estrogen
dependent, with the predominant estrogen produced by the granulosa cell being estradiol. Thus in the
dominant follicle FSH > estradiol > FSH receptor.
Concomitantly, estradiol is inhibitory to FSH so that levels of FSH from the pituitary gradually decrease
depriving less mature follicles of FSH necessary to prevent their atresia. In this way one dominant
pre-ovulatory follicle is produced each cycle. (Administration of excess FSH is the mechanism whereby
multiple follicles can be induced for such pregnancy enhancing procedures as in-vitro fertilization).
In the process of follicular growth during the first half of the menstrual cycle, the follicular Phase,
estradiol levels in the circulation increase approximately 10-fold largely as the result of activity of the
dominant pre-ovulatory follicle. The effects of the estradiol are not only to inhibit pituitary FSH but to
regulate the pituitary release of LH. At higher levels estradiol is inhibitory to LH, however in a critical
range of physiologic estradiol levels achieved during the first haft of the menstrual cycle estmdiol has a
unique effect on the pituitary. It increases LH synthesis in response to GnRH, but partially inhibits
GnRH-induced LH release. Thus there is in the gonadotroph an increasing "reserve pool~ of synthesized
but unreleased LH as the follicular phase of the menstrual cycle progresses. Eventually the "reserve
pool~ of LH is saturated and a massive release of LH occurs over a 36 hour period, the so called "LH
surge" which is the trigger for ovulation and marks the end of the follicular phase.
Prior to the LH surge however, there is a lower level of palsatile release of LH from the gonadotroph.
This LH acts upon a second ovarian cell type the theca cell. The theca cell synthesizes androgens,
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primarily androstenedione from LDL-cholesteml. This androgen serves as the substrate for granulosa
cell estradiol production. Thus in the menstrual cycle, the theca cell and granulosa cell operate in concert,
giving rise to the two cell theory of ovarian function. The conversion of the theca derived
androgens to estrogen is by the aromatization of the first ring of the steroid molecule. The enzyme
responsible is therefore called aromatase. Aromatase activity is directly induced by FSH action on the
granulosa cell.
LH receptor is present at all times on theca cells, and FSH receptors develop in granulosa cells during
their maturation from the primordial follicle. At high doses, FSH action on the granulosa cell induces LH
receptors. Physiologically, this high degree of FSH activity is attained only by the dominant
preovulatory follicle (as a result of a high concentration of FSH receptors) a few days before ovulation.
Thus the granulosa cell develops LH receptors a few days prior to the LH surge.
The LH surge typically occurs 14 days into the menstrual cycle (which is counted from the first day of
menstrual bleeding), although there is a normal physiologic variation in this interval (follicular phase
length) from 9-17 days.
In contrast the second half of the menstrual cycle (luteal phase) is much more precise physiologically
lasting 14 ± 2 days. (A shorter than 12 day luteal phase is considered pathological and termed lnteal
phase defect a condition seen repeatedly overseveral menstrual cycles in only 3-4% of women). The LH
surge induces proteases, collagenases and tissue plasminogen activators that digest the capsule
of the ovary and permit extrusion of the oocyte and a surrounding nest of specialized granulosa cells the
cumulus cophorus. Simultaneously, meiotic division proceeds to metaphase of meiosis II where it is
arrested until fertilization. The effect of the LB surge is to induce at partial 17 hydroxylase block in the
steroidogenic pathway resulting in the production of progesterone as well as estrogen by the remaining
theca and granulosa cells. This progesterone production results in a characteristic yellow color of the
remaining dominant follicle and from this the name corpus luteum (yellow body) is given to the remains
of what was previously the dominant follicle. This second phase of the menstrual cycle is referred to as
the luteal phase.
The follicular phase of the cycle is therefore estrogen dominated, while the luteal phase is both estrogen
and progesterone dominated. The premenstrual syndrome including, breast tenderness, bloating and
affective liability are likely to be progesterone induced. Most characteristic of the action of estrogen is
the hypertrophy of the uterine lining (endometrium) which grows severifi millimeters in height during
the follicular phase. The action of progesterone on the estrogen-primed endometrium is to convert this
endometrium into a secretory pattern. The endometrium can be accurately dated in the post ovulatory
phase by the presence of initially subnuclear vacuoles in the glandular epithelium which by 4 days past
ovulation migrate to the endothelial surface and release their contents. By day 21 of the classic 28 day
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cycle, these epithelial glands have become tortuous and there is abundant secretion in the lumina, a
condition optimal for implantation of the fertilized egg which occurs at this time. (The phases of the
endometrial cycle are termed differently than those of the menstrual cycle, with the follicular phase
being referred to in the endometrial cycle as the proliferative phase, and the luteal phase as the secretory
phase,) In the absence of pregnancy, the life span of the corpus iuteum is self limited. The mechanisms
for this are poorly indicated although responsivity to LH has been clearly shown to decline. As a result
of this during the last 7 days of the cycle estrogen and progesterone production from the corpus luteum
decline. These decreases lead to spasm of the arteries in the blood vasculature which supports the
endometrium (either by direct action or through prostaglandin mediated mechanisms) and breakdown of
the endometrium occurs leading to menses.
In the event pregnancy occurs, a hormone analogous to LH (sharing an identical first 121 amino acids)
human chorionic gonadotropin (hCG)is released by the developing embryo into the maternal circulation,
hCG has additional scialic acid residues on the C terminal amino acids (not shared by LH) which greatly
prolong its half-life and permit maintenance of the corpus luteum and consequently the absence of
menses.
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Learning Objectives
Describe the hypothalamic control of the menstrual cycle
Understand the role of the pituitary gland in regulating ovarian response
Appreciate the steroidogenic capacity of the ovarian follicular unit
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Reasons to learn about the normal menstrual cycle:
You have one
You know someone who has one
As a physician, you will be a lightening rod for medical questions on any topic including this one
Menstrual Cycle Length
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Age 21-39:
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98% CI: 21-35 days
Only 15% with 28 day cycle
Age 25: 40% with 25-28 day cycles
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Age 25-35: 60% have 25-28 day cycles
o Age < 20 and > 40
Highest incidence of anovulation
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Elements of cyclic menstruation
 Hypothalamic Control
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GnRH pulse generator
Pituitary Response
Differential release of LH and FSH
Ovarian Compliance
The foUide unit
Theca, Gmnulo, Oocyte
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Gonadotropin Releasing Hormone
(GnRH)
10 Amino Acids (decapeptide)
Primarily produced in Arcuate Nucleus
T1/2:90 seconds
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Pulsatile Release
Pulse generator located in medial basal hypothalamus (MBH)
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GnRH Antagonists
Hypothalamic Control
GnRH Pulsatility
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Central Modulation
α-Adrenergic
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Norepinephrine
Dopaminergic
Opioids
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Hypothal
GnRH
Central Modulation
 α-Adrenergic
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Norepinephrine
 Dolmminergic
 Opioids
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Hypothslamic Control
GnRI-I Puisatility
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Central Modulation
α-Adrenergic System
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Norepinephrine - STIMULATORY FFFECT
HOW would you test this hypothesis?
Block the adrenergic receptor
Look for anatomic connection
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Dopaminergic Input
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 Dopamine – INHIBITORY EFFECT
Cycling and postmenopausal women
Mechanism
Direct Effect
Indirect effect via ENDOGENOUS OPIOIDS
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Hypothalamic Control
GnRH Pulsatility
Central Modulation
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α-Adrenergic System
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Norepinepbrine - STIMULATORY EFFECT
PROPOSED MECHANISM
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NE neuron inhibits the inhibitory GABA neuron
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 Central Modulation
Endogenous Opioid Peptides
β-endorphin- INHIBITORY EFFECT
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Evidence
Naloxone (an opioid ANTAGONIST)
DA stimulates hypothalamic j3-endorphin release
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Proopiomelancirtiun (POMC)
GnRH Pulsatility
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Actions of Pulsatile GnRH
 Synthesis and storeage of LH and FSH
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Activation mid movement of LH and FSIi from reserve pool to acutc rclc, asablc
pool
Direct secretion of LH and FSH
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PITUITARY RESPONSE
Regulators of Gonadotropins (LH and FSH)
Estrogen
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Progesterone
FSH as a market of reproductive aging
Cyclic Gonadotropins
The LH Surge
Luteal phase temperature shift
Hormonal Mediation
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Estrogen:
Modulates LH amplitude
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Negative feedback on LH (early folllcular)
Change to STIMULATORY to induce LH surge
(or attenuation of negative feedback)
Propsed Mechanism
Under influence of E2 GnRH receptor conoentration increases near mid-cycle
(self-priming)
Critical estradiol level for critical length of time
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LH Surge
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Estradiol:
Critical concentration
(>150 pedna)
Critical length of time
(>50 hours)
Precise Mechani$.m
Unknown
Surge rarely seen under above conditions during fertility therapy
Cyclic Gonadotropins (LH/FSH)
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Hormonal Mediation
 Progesterone:
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Modulates LH frequency
At Iow levels, with E2, augments LH surge
Induces small FSH surge
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At post-ovulatory levels: POWERFUL suppressant of LH and FSH
o Sites of Action
Direct inhibition of GnRH at hypothalamus
 Antiestrogenic at pituitary
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Thermogenic Shift
Luteal phase (after ovulation) rise in core body temperature
Rise of 0.40 -0.6o C
Caused by PROGESTERONE
o MECHANISM
Set point changein thermoregulatory center of hypothalamus
Thought to be mediated byopioids, serotonJn and IL-1
Thermogenic shift
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Hormonal Mediation
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Progesterone:
Clinical application of gonadotropin (LH/FSH) suppression
Progestin compounds
Birth control pills
Depot Provera
E2 Regulation of FSH
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Signs of Reproductive Aging
What else regulates FSH level (other than E2)?
Inhibin:
o Produced by ovarian granulosa cells
o Potent inhibitors of FSH
Activin
o Stimulates FSH release
o Much lower quantifies than of inhibin
Follistatin
o A pituitary single chain glycosylatcd polypetide
o Binds activin (therefore favors FSH suppression)
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Inhibins and Activins
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Inhibin:
o Inhibin A-Mature Follicles, Corpus Luteum
o lnhibin B - Smaller Pre-ovulatory follicles
(marker of OVARIAN RESERVE)
Activin
o Activin A & B - Observed in nature
o Activin AB - Not observed to occur
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Reproductive Aging
See Santoro N. et al. Fertil Steril 1999, 71 : 658-62.
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Reproductts Aging
Fewer follicledoocytes left in re-serve
Less Inhibin B (less suppression of FSH)
More lnhibin A (stimulation of FSH release)
Inhibin comprised of α ＆ β subunits
Activin comprised ofβdimers
? Lessαsubunit therefore moreβdimers
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Result: Higher FSH Levels
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GnRH Smnmary
Pulsatile release from Arcuate Nucleus
Pulse Generator; Medial Basal Hypothalamus
oMODULATORS
 adrenergic: NE – STIMULATORY
 GABA – INHIBITORY
 Opioids - INHIBITORY
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Summary of Key Points
Pulsatilc GnRH: critical range for frequency and amplitude
GnRH: Positive action on Anterior Htuitary
Synthesis, Storeage and
Release of LH/FSH
LH/ FSH Summary
Difti~renfial release to Pulsatile GnRH
MODUL ATORS
o Estrogen: Inhibitory then STINULATORY
o Progesterone: Inhibitory
o Inhibin: FSH Inhibitor
o Activin: FSH Stimulator
o Follistatin: Binds Activin (Favors FSH Inhibition)
Summary: Key Points
 LOW ESTROGEN
o Enhances synthesis and storeage of LH/FSH
o Inhibits RELEASE of LH/FSH
 HIGH ESTROGEN
o Induces LH Surge at midcycle
o Sustained elevation of LH
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Summary: Key Points
 LOW PROGFSTERONE
o Enhances LH response to GnRH at midcyde
o Responsible for midcycle FSH surge
 HIGH PROGESTERONE (Post-ovulatory)
o Powerful inhibitor of LH/FSH release
o Direct inhibition of OnRtl at hypothalamus
o Antiestrogenie at pituitary
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Recommended Texts and Investigators
 Physiology of Reproduction (Knobil and Neill)
Clinical Gynecologic Endocrinology and Infertility (Speroff, Glass and Kese)
 Reproductive Endocrinology: Physiology, Pathophysiology, and Clinical
Management (Yen, Jaffe & Barbieri)
 Investigators
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Gary Hodgen
AV Schaliy
Ernst Knobil
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IGF, IGF-BP & PAPP-A
Products of granulosa cc!Is
IGFs stimulate slcroidogcncsis and folliclc development along with Lli and FSII
IGF-BP4 modulates the effects of IGF by modulating its bioavailability; low
IGF-BP4 means more free IGFs
IGF-BP4 proteolysis decreases IGF-BP4 thereby increasing free IGFs
IGF-BP4 protcasc rcgcntly identified as PAPP-A (pmggmncy associated se. mm
prolein A)
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IGF and IGF-BP
Granulosa ccUs arc the source of' PAPP-A!
High PAPP-A conccrttrations seen in dominant follicle l
PAPP-A gene expression is restrictcd to hcalthy follicles and corpora lutea2
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Follicle development
Gonadotropin Independent Phase
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Tonic growth phase
Occurs Independent of LH / laSH
 Oral contraceptive use
 Pregnancy
Class 1 to Class 4 follicles
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Follicle development
Gonadotropin Dependent Phase
Requires LH / FSH
Class 5 to Class 8 follicles
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Follicle development
Gonadotropin Independent Phase
o Tonic growth phase
o Occurs independent of LH / FSH
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Oral contraceptive use
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Pregnancy
o Class 1 to Oass 4 follides
 Gonadotropin Dependent Phase
o Requires LH / FSH
o Class 5 to Class 8 follicles
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 Intraovarian Follicle Development
Gonadotropin independent development
Gonadotropin dependent development
LH dependent thecal androgen production
FSH dependent granulosa estrogen conversion
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Intraovarian Follicle Development
"Selected" follicle is more efficient at aromatizing estrogen
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Remaining follicles accumulate androgens
o Aromatase cannot keep pace with androgen production
o Androgen excess induces atresia
o Atresia occurs via apoptosis
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Intmovarian Follicle Development
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Gormdotnmin theeapy
o ResoJes follicles destined for alresia
o FSH component Induces aromatase
o MulUple follicles develop
 Follicle Threshold
o Level of FSH required for efficient conversion of androgen to estrogen
o Higher close of hMG rescues more follicles
o More follicles is not necessarily better
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Normal Menstrual Cycle
Cyclic GnRH
 Differentiai production of L.H and FSH
 Ovarian Response
 Continuous production of inhibin
 Conversion of androgens to estrogen
 About 1550 BCE an Egyptian described how lint (fctet)
 inserted into the vagina could prevent conception.
Is this the first description of a tampon?
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The Abnormal
Menstrual Cycle
Alan S. Penzias, MD
Div. Reproductive Endocrinology
Beth Israel Deaconess Medical Center
Boston IVF
Harvard Medical School
Hypothalamic Dysfunction
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Endogenous Opioids
Examples
o Anorexia Nervosa
o "Stress Induced"
o Depression
Mechanism
o High cortisol states
o Increased ACTH production
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Proopiomelanocortin (POMC)
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Abnormal menstruation
Hypothalamic amenorrhea
o Pituitary Disease
o Prolactin production
o Stalk compression
Ovarian Dysfunction
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o Failure: lack of estrogen / inhibin
Hyperandrogenicity
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Prolactin Regulation
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Pituitary Disease
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Hyperprolactinemia
o Microadenoma
o Prolactin producing macroadenoma
o Other macroadenoma with stalk compression
Psychotropics
Hypothyroidism
Prolactin Regulation
Prolactin Regulation
Harvard-MIT Dvision of Health Sciences and Technology
HST .071: Human Reproductive Biology
Disorders of Ovulation
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Peripheral Disorders
Thyroid Hypofunction
o Associated hyperprolactinemia
o Low SHBG
Thyroid Hyperfunction
Excess SHBG
Sex Hormone Binding Globulin
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Decreased by:
o Androgens
o Low T4
o Obesity
Increased by:
o Estrogen
o High T4
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Impact of SHBG
Normal female testosterone level:
50 ngldl (range: 20 - 80 ngldl)
Normal mid-cycle female estradiol
level: 200 pg/ml (range: 100 - 300)
Impact of SHBG
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1 ng = 10-9 grams
1 pg = 10-12 grams
50 ng/dl = 50000 pg / 100 mi
= 500 pg/ml
Impact of SHBG
Normal female testosterone level:
500 pg/ml
Normal mid-cycle female estradiol level:
200 pg/ml
On average, circulating T is 2.5 x higher than circulating estradiol
Harvard-MIT Dvision of Health Sciences and Technology
HST .071: Human Reproductive Biology
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Impact of SHBG
Testosterone: 99% bound; 1% free
Estradiol: 97% bound; 3% free
Decreasing the quantity of SHBG present in circulation therefore has a
significant impact on the quantity of free testosterone available
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Impact of Androgens
High androgens: adrenal or ovarian feedback on the hypothalamus
DECREASING GnRH pulsatility
Abnormal Menstruation
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Peripheral Disorders
o Thyroid hypofunction
 Associated with hyperprolactinemia
 Low SHBG
o Thyroid Hyperfunction
 Excess SHBG
o Adrenal Dysfunction
 Hyperandrogenism
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Based on underlying etiology
o e.g. PRL, Thyroid, CAH
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Based on specific goals
o Fertility
o Cyclicity
o Cancer prevention (periodic withdrawal)
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Based on specific needs
o Contraception
o Side effect profile
o Lifestyle