Reproductive Endocrinology Flashcards
organs/brain regions and hormones associated with Hypothalamic-Pituitary-Gonadal Axis?
Hypothalamus: Gonadotropin Releasing Hormone (GnRH) Pituitary: Follicle Stimulating Hormone (FSH) Luteinizing Hormone (LH) Ovary: Estradiol Progesterone Testes: Testosterone
What is GnRH? What results from it’s activation?
10 aa peptide
Secreted in pulsatile fashion (2-3 hr cycle)
Higher frequency stimulates FSH secretion
Lower frequency stimulates LH secretion
Sexual maturity results from activation of GnRH secretion
Describe FSH and LH. What function do they play in males and females?
Heterodimeric glycoproteins
α-subunit – shared by FSH, LH, TSH, and hCG
ß-subunit – provides unique actions of hormones
FSH - MW ~34,000
LH – MW ~28,000
Each have trophic functions in males and females
Describe sexual differentiation in embryos.
Up to 8 weeks gestation, embryos contain primordial genital ducts of both sexes:
Wolffian – male
Mullerian – female
At 8 weeks, testes begin production of:
Testosterone – supports development of Wolffian:
Epididymis, vas deferens and seminal vesicles
Anti-mullerian hormone – blocks Mullerian growth:
Fallopian tubes, uterus, upper vagina
Lack of testosterone action leads to Wolffian degeneration and Mullerian development
What happens during female puberty? Adrenarche? Menarche?
~400,000 primordial follicles at puberty
300-400 will reach maturity and ovulate
Remainder “die” by atresia throughout life
Puberty:
Adrenarche – onset of adrenal androgen synthesis
Onset at 6-7 years
Androstendione, DHEA and DHEAS
Dec. sensitivity of HP axis to negative feedback
GnRH and gonadotropin secretion
Menarche – onset of menstrual cycles
Describe the Female HPG Axis.
GnRH stimulates FSH and LH release FSH – follicular maturation and estradiol synthesis LH – follicular rupture and progesterone synthesis Estradiol (E2) Endometrial proliferation Pos and neg feedback Progesterone (P4) E ndometrial support
Name two Female hormones and their functions.
Estradiol(-17ß) – E2 18 carbon aromatic steroid Promotes secondary sexual characteristics Increases HDL, some proteins (eg, TBG) Synthesized in ovary and placenta
Progesterone – P4 21 carbon steroid Precursor of many steroids Some influence on breast development Primarily involved in pregnancy
How is Estradiol measured?
Estradiol
Reference is interval age and menstrual cycle dependent
39-375 pg/mL (follicular phase)
49-440 pg/mL (luteal phase)
How is progesterone measured?
Progesterone
Ref. interval is age, cycle & pregnancy stage dependent
0-2.7 ng/mL (follicular phase)
3.0-31.4 ng/mL (luteal phase)
Pregnancy: 11.0-45.0, 26.0-89.0, 46.0-423 ng/mL by trimester
Immunoassay (competitive)
LC-MS/MS
How is Gonadotropin measured?
Immunoassay (usually sandwich assays)
Reference ranges sex, age and cycle variable
Ultrasensitive assays available – necessary for prepubertal evaluations
What happens during an LH surge?
Release of egg from follicle
What happens during the follicular phase?
Late luteal phase (of prev. cycle) E2 and P4 decline, FSH secretion increases (loss of negative feedback)
FSH stimulates follicular proliferation and E2
Day 1-4 – several follicles recruited and develop
Granulosa cells synthesize and secrete E2
Day 5-7 – dominant follicle selected, suppressing others
E2 stimulates endometrial (uterine lining) proliferation
E2 negative feedback suppresses FSH secretion
E2 synthesis continues
Antral follicle is final product
What happens during the ovulatory phase?
Rising follicular E2 stimulates LH surge at day 12-13 via positive feedback
LH peaks 24-36 hours later
Ovulation – 10-12 hrs post LH peak (day 14)
- –Follicular rupture
- –Ovum release
LH stimulates follicular synthesis of P4
Ovum captured by fallopian tubes
What happens during the luteal phase?
Ruptured follicle transforms to corpus luteum
Corpus luteum (CL) synthesizes P4 and E2
-P4 rises ~3 days post ovulation
-P4 suppresses LH and FSH secretion
-P4 peaks about 8-9 days post ovulation
Fertilized ovum implants in uterine lining
-hCG synthesis by trophoblast maintains CL
-CL P4 maintains endometrium
Without hCG, CL begins regression ~day 9
-Decreasing P4 promotes endometrial sloughing
What is menopause?
Defined as 12 months of amenorrhea
—Mean age at 51 years
—No correlation with age of menarche
Primary depletion of ovarian follicles
Decreased estradiol (10% of normal levels)
Increased FSH & LH (no negative feedback)
—FSH 10-15x due to longer half-life (4 hrs)
—LH 4-5x (half-life 30 minutes)
Disorders of Female Reproduction.
Pseudohermaphroditism:
- –Gonadal sex different than genital sex
- –46,XX karyotype with ambiguous genitalia
- Congenital adrenal hyperplasia (CAH)
Precocious puberty:
- –Secondary sexual characteristics before age 8
- –GnRH-dependent – early activation of HP axis
- ——-nc. LH using ultrasensitive immunoassay
GnRH-independent:
- Usually CAH
- Tumors of adrenals or ovaries
- Steroid measurement, imaging
Primary amenorrhea
- –No menses by age 16
- –Turner’s syndrome (45,X(O) karotype)
- –Pure gonadal agenesis
- –Mullerian duct agenesis/dysgenesis
- -Absent uterus or vagina
- –Androgen insensitivity (testicular feminization)
- –Congenital adrenal hyperplasia
- —Hypothalamic or pituitary
Elevated FSH indicates ovarian non-response
Chromosomal testing indicated
Low FSH/LH suggest 2° or 3° issue
What is Andogen Insensitivity Syndrome
X-linked defect of androgen receptor Lack of androgen cellular effects Wolffian development fails ---Testosterone ineffective Mullerian development “normal” --Anti-mullerian factor present -------Blocks upper genital tract development Genotypic XY, phenotypic female Intra-abdominal testes Normal to high testosterone, high LH
Describe secondary amenorrhea.
Secondary amenorrhea
Loss of normal menses for ≥6 months
Pregnancy
Polycystic ovary syndrome (PCOS)
Ovarian tumors, premature ovarian failure
Late-onset CAH, Cushing’s syndrome, adrenal tumors
Pituitary disorders, incl. hyperprolactinemia
Hypothalamic, excessive exercise, stress
Drugs
History very important
Lab testing similar to primary amenorrhea except no genetic testing
What is PCOS?
Polycystic Ovary Syndrome (PCOS)
May comprise 80-90% of anovulatory infertility
Prevalence up to 20%
More common in Hispanic and South Asian women
Less common in women of Chinese or Japanese descent
Diagnosis requires two of the following:
Presence of hyperandrogenism and/or hyperandrogenemia
Irregular or absent ovulation
Presence of polycystic ovaries by ultrasound
Describe Hyperandrogenism in PCOS
Hyperandrogenism:
Hirsutism – male hair pattern (beard, trunk)
Virilization – inc. muscle mass, deepening voice
More common in androgen-secreting tumors
Describe Hyperandrogenemia in PCOS
Hyperandrogenemia: ASD, DHEA and/or testosterone increased DHEA-S normal; elevated indicates adrenal origin 50% are obese, many have acne Insulin resistance LH elevated, FSH normal to low LH:FSH >2.5 suggestive (with symptoms)
Describe the male HPG Axis
GnRH stimulates FSH and LH release FSH – Sertoli cells -Spermatogenesis -Inhibin secretion (dont worry about it) (↓ FSH) LH – Leydig cells -Synthesize testosterone Testosterone -2° sexual characteristics -Anabolic actions -Spermatogenesis
What are the male steroids? (Androgens)
Testosterone (T) -Secondary sexual characteristics -Inc. muscle and bone mass (anabolic) -Libido -Promotes spermatogenesis Dihydrotestosterone (DHT) -5α-reductase in prostate and skin -Biologically active form of testosterone ---Similar to T3 ---Rarely measured Dehydroepiandrosterone (DHEA) Androstanedione (ASD) ----Both are precursors to T and DHT
Testosterone (bound vs free)
Bound to plasma proteins
Sex-hormone binding globulin (SHBG) – ~60%
Low capacity, high affinity
Estradiol also bound
Albumin – high capacity, low affinity - ~35%
Free – 2-3%
Controversy as to whether only free (2-3%) or weakly bound (37-38%) are biologically active
How is Testosterone measured?
Competitive immunoassay
Suitable for adult males (ref. int. 260-1000 ng/dL)
Direct immunoassay not recommended for females or prepubertal males
Cross-reactivity with other steroids
Req. extraction and chromatography before immunoassay
LC-MS/MS preferred
LC-MS/MS
Requires enhanced sensitivity instrument (>$300K)
Free vs Bioavailable Testosterone?
Free testosterone
Equilibrium or direct dialysis (cf free T4)
Mass action calculation
Measured testosterone
Measured SHBG (sandwich immunoassay)
Measured or assumed (4.3 gm/dL) albumin
Known binding constants: Testo:SHBG and Testo:Alb
Bioavailable testosterone
As for free except albumin-bound and free testo are both considered to be bioavailable
Is the 17-Ketosteroids (Urine) test still used?
Obsolete test for androgens
Performed on 24 hr urine
Chemical summation of all by Zimmerman reaction
Many drug interferences, positive and negative
Occasionally fractionated by chromatography
Serum DHEA-S preferred
Disorders of male reproduction.
Hypogonadotropic hypogonadism
- Panhypopituitarism (2°)
- Hypothalamic syndromes (3°)
- GnRH deficiency (3°)
- Hyperprolactinemia (suppresses GnRH, 3°)
- Malnutrition, anorexia
- Characterized by decreased testosterone (120 mIU/mL)
What is hCG
Human Chorionic Gonadotropin
Heterodimeric protein (α- same as FSH, LH, TSH; ß)
Synthesized by syncytiotrophoblastic tissue (placenta)
-Also synthesized in pituitary (minimal)
Maintains corpus luteum function during pregnancy
As a laboratory test:
—Detect pregnancy
—Evaluate quality/viability of pregnancy
—Evaluate possible ectopic pregnancy
—Monitor choriocarcinoma and germ cell tumors
“Beta” hCG – an ambiguous term denoting specificity to hCG (w/o LH cross-reactivity)
Superfluous with current assays
Describe hCG Metabolism
Intact – α:ß native heterodimer
Nicked – cleaved bonds in ß-chain
—May affect Ab recognition
Free subunits – some assays detect only intact
ß-core fragment – primary urinary form
—-Serum assays must be validated to detect hCG in urine
Two types of pregnancy tests
Serum tests: -Cutoff 25 mIU/mL -Detection 3-5 days before missed period Urine tests -Cutoff 20-25 mIU/mL -Detection period highly variable Depends on urine specific gravity (~osmolality) ---Dilute urine = lower sensitivit
What is ectopic pregnancy?
A pregnancy with an abnormal implantation site
May spontaneously abort or rupture
Ruptured ectopics are medical emergencies
hCG discriminatory zone –
hCG >1000-1500 mIU/mL - should be able to see intra-uterine pregnancy by transvaginal ultrasound
hCG
What can produce non-placental hCG?
Tumors Pituitary – increases with age Peri-menopausal woman (41-55 yrs) Reference interval: 5.0-14.0 mIU/mL FSH >20 mIU/mL makes pregnancy unlikely Clin Chem 51(10):1830-35(2005)
