Animal Science 434 The Follicular Phase of the

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Animal Science 434 The Follicular Phase of the Estrous Cycle

Animal Science 434 The Follicular Phase of the Estrous Cycle

Hypothalamus Progesterone (-) Gn. RH Estradiol (-, +) Anterior Pituitary Inhibin (-) LH, FSH

Hypothalamus Progesterone (-) Gn. RH Estradiol (-, +) Anterior Pituitary Inhibin (-) LH, FSH LH CL Estradiol LH, FSH Ovary Follicle

Tonic and Preovulatory Surge of Gn. RH

Tonic and Preovulatory Surge of Gn. RH

Hypothalamus Progesterone (-) Gn. RH Estradiol (-) Anterior Pituitary Inhibin (-) LH, FSH LH

Hypothalamus Progesterone (-) Gn. RH Estradiol (-) Anterior Pituitary Inhibin (-) LH, FSH LH CL Estradiol LH, FSH Ovary Follicle

Steps Leading to the Preovulatory LH Surge P from Cl 4 Gn. RH FSH

Steps Leading to the Preovulatory LH Surge P from Cl 4 Gn. RH FSH and LH Inhibin Proestrual Follicular Development Estradiol to threshold FSH Preovulatory LH surge

Relationship of Hypothalamus, Anterior Pituitary and Ovary In the Absence of Progesterone

Relationship of Hypothalamus, Anterior Pituitary and Ovary In the Absence of Progesterone

Tonic and Preovulatory Surge of Gn. RH

Tonic and Preovulatory Surge of Gn. RH

Hormone Changes During the Folliclular Phase Progesterone LH FSH Estradiol

Hormone Changes During the Folliclular Phase Progesterone LH FSH Estradiol

Follicle Progression

Follicle Progression

Growth and Atresia of Follicles

Growth and Atresia of Follicles

Follicular Growth Gonadotropin Independent Small Antral Follicle Recruitment Initiated by FSH

Follicular Growth Gonadotropin Independent Small Antral Follicle Recruitment Initiated by FSH

Progesterone FSH Inhibin LH FSH Inhibin E 2 LH Deviation!!!

Progesterone FSH Inhibin LH FSH Inhibin E 2 LH Deviation!!!

Folliclular Waves in Cattle

Folliclular Waves in Cattle

Follicular Waves

Follicular Waves

Follicular Waves

Follicular Waves

Growing Phase • Initial growth (recruitment) is under influence of FSH • Inhibin secreted

Growing Phase • Initial growth (recruitment) is under influence of FSH • Inhibin secreted to decrease FSH and development of subordinate follicles (estrogen also; selection) • Dominant follicle becomes less dependent on FSH for growth • FSH induces LH receptors in granulosa • Dominant follicle produces estradiol androgens in response to LH and FSH • Androgens, lack of FSH may cause subordinate follicles to become atretic (dominance)

Static Phase • Inhibin production stops • FSH increase stimulates follicular wave • Estradiol

Static Phase • Inhibin production stops • FSH increase stimulates follicular wave • Estradiol from dominant follicle decreases androgens increase, this may initiate atresia of dominant follicle

Regressing Phase • Dominant follicle becomes atretic and looses steroidogenic capability

Regressing Phase • Dominant follicle becomes atretic and looses steroidogenic capability

Follicular Waves

Follicular Waves

Growing Phase • Initial growth (recruitment) is under influence of FSH • Inhibin secreted

Growing Phase • Initial growth (recruitment) is under influence of FSH • Inhibin secreted to decrease FSH and development of subordinate follicles (estrogen also; selection) • Dominant follicle becomes less dependent on FSH for growth • FSH induces LH receptors in granulosa • Dominant follicle produces estradiol androgens in response to LH and FSH • Androgens, lack of FSH may cause subordinate follicles to become atretic (dominance)

Growing Phase • LH continues to increase in response to estradiol positive feedback in

Growing Phase • LH continues to increase in response to estradiol positive feedback in the absence of progesterone • Dominant follicle increases in size and estrogen production • LH surge occurs to trigger ovulation of the dominant follicle

Hormone Changes During the Folliclular Phase Follicular Phase Progesterone LH FSH Estradiol Ovulation

Hormone Changes During the Folliclular Phase Follicular Phase Progesterone LH FSH Estradiol Ovulation

Follicular Size Two Follicular Waves Dominance Atresia Ovulation Selection (Deviation) Recruitment Ovulation 10 Day

Follicular Size Two Follicular Waves Dominance Atresia Ovulation Selection (Deviation) Recruitment Ovulation 10 Day After Ovulation 21

Follicular Size Three Follicular Waves Ovulation 9 16 Day After Ovulation 21

Follicular Size Three Follicular Waves Ovulation 9 16 Day After Ovulation 21

Follicular Waves

Follicular Waves

Fate of follicles and oocytes. Total # of follicles At birth 100, 000 12

Fate of follicles and oocytes. Total # of follicles At birth 100, 000 12 months 75, 000 4 -6 years 21, 000 Aged cow 2, 500 100 Days of Gestation 2. 9 million Follicles grow to tertiary characteristic and degenerate. Maximum number of oocytes ovulated for a cow 17 cycles/year x 8 year = 136 oocytes ovulated/lifespan Can increase with superovulation with FSH to stimulate the rescue of follicles which would have undergone atresia

Gonadotropin Action Within the Follicle

Gonadotropin Action Within the Follicle

Theca Interna Granulosa

Theca Interna Granulosa

LH Theca Interna Receptor Selection Dominant Follicle Express LH Receptor c. AMP Cholesterol PKA

LH Theca Interna Receptor Selection Dominant Follicle Express LH Receptor c. AMP Cholesterol PKA Testosterone LH Receptor c. AMP Testosterone c. AMP PKA Granulosa Estradiol Bloo d FSH

Ovulation

Ovulation

Germinal Epithelium Tunica Albuginea Theca Externa Theca Interna Basement Membrane Granulosa

Germinal Epithelium Tunica Albuginea Theca Externa Theca Interna Basement Membrane Granulosa

Blocking of these events in the follicle prevents ovulation. • protein synthesis • steroid

Blocking of these events in the follicle prevents ovulation. • protein synthesis • steroid synthesis • prostaglandin synthesis • plasminogen activator synthesis

Pathways of Ovulation LH increased cyclic AMP Mature follicle Increased blood flow to follicle

Pathways of Ovulation LH increased cyclic AMP Mature follicle Increased blood flow to follicle Protein synthesis Cumulus cell production (cellular differentiation) of hyaluronic acid and proteins Steroid biosynthesis Prostaglandin biosynthesis Cumulus expansion (PGE 2 and PGF 2 ) Progesterone Separation of cumulus and oocyte from granulosa cells Inactive Collagenase (theca) Plasminogen activator (granulosa) Plasmin (protease) Active Collagenase Breakdown of theca and tunica albuginea collagen and tensile strength of follicle wall PGF stimulates smooth muscle contractions around follicle Increased vascular permeability of follicle Follicle ruptures with only a slight increase in follicular pressure Expulsion of follicular contents Increased plasminogen in tissue and follicular fluid

Preovulatory LH Surge Cumulus Expansion Oocyte Separates From Follicular Wall Ovulation

Preovulatory LH Surge Cumulus Expansion Oocyte Separates From Follicular Wall Ovulation

Cumulus Expansion Hyaluronic Acid and Protein Production Unexpanded Expanded

Cumulus Expansion Hyaluronic Acid and Protein Production Unexpanded Expanded

Cumulus and Oocyte Separation

Cumulus and Oocyte Separation

Preovulatory LH Surge Cumulus Expansion Protein Synthesis in and around Follicle Plasminogen Activator Collagenase

Preovulatory LH Surge Cumulus Expansion Protein Synthesis in and around Follicle Plasminogen Activator Collagenase (inactive) Progesterone Increased Blood Flow to Ovary and Follicle Vascular Prostaglandin Permeability Synthesis PGE and PGF Plasmin Oocyte Collagenase (active) Separates Follicular Wall From Weakens Follicular Wall Ovulation Plasminogen Contraction of Smooth Muscle

Types of Ovulators

Types of Ovulators

Spontaneous Ovulators

Spontaneous Ovulators

Induced Ovulators

Induced Ovulators

Induced Ovulators Nerve endings sensing copulation Copulation Sensory Neurons Penis

Induced Ovulators Nerve endings sensing copulation Copulation Sensory Neurons Penis

Hypothalamus Blood LH Time (hr) Gn. RH Posterior Pit. Stimulation LH Anterior Pit. Spinal

Hypothalamus Blood LH Time (hr) Gn. RH Posterior Pit. Stimulation LH Anterior Pit. Spinal Chord

LH Nerve endings sensing copulation Copulation Sensory Neurons Penis

LH Nerve endings sensing copulation Copulation Sensory Neurons Penis

Cats • Induced Ovulators • Single copulation – Only works 50% of the time

Cats • Induced Ovulators • Single copulation – Only works 50% of the time • Multiple copulations – Higher LH surge

Spontaneous Ovulators • Retain some neural control of ovulation – heifers can alter the

Spontaneous Ovulators • Retain some neural control of ovulation – heifers can alter the timing of the LH surge by clitoral stimulation – human rape cases result in higher than expected pregnancy rates

Manipulating Ovulation • will cover latter in class

Manipulating Ovulation • will cover latter in class

Oogenesis Migration to germinal ridge Mitotic divisions Primordial Germ Cells Oogonia Initiation of Meiosis

Oogenesis Migration to germinal ridge Mitotic divisions Primordial Germ Cells Oogonia Initiation of Meiosis Interphase DNA synthesis Meiotic prophase begins Gonadotropin Independent Gonadotropin Dependent Primary Oocyte Growth Follicle Cells Prophase of Meiosis leptotene zygotene pachytene diplotene dictyotene Meiotic Arrest zona pellucida formation m. RNA production protein synthesis cortical granule formation nuclear maturation cytoplasmic maturation

Fetal Oocyte Development Mitosis Fertilization Meiosis Birth Cow 280 d Sow 114 d Mouse

Fetal Oocyte Development Mitosis Fertilization Meiosis Birth Cow 280 d Sow 114 d Mouse 19 d

Corona Radiata Oocyte Cortical Granules Zona Pellucida Gap Junctions Cortical Granules

Corona Radiata Oocyte Cortical Granules Zona Pellucida Gap Junctions Cortical Granules

During Oocyte Growth and Before the LH Surge • OMI - Oocyte Maturation Inhibitor

During Oocyte Growth and Before the LH Surge • OMI - Oocyte Maturation Inhibitor c. AMP OMI c. AMP GV PKA pre-MPF • MPF - Maturation promoting factor • GV - germinal vesicle (nucleus) Gap Junctions Allow Cell to Cell Communication!

The LH Surge c. AMP GVBD PKA GV pre-MPF Gap Junctions are Destroyed! Resumption

The LH Surge c. AMP GVBD PKA GV pre-MPF Gap Junctions are Destroyed! Resumption of Meiosis

LH Surge 4 N Primary Oocyte Ovulation • Dog • Fox Resumption of Meiosis

LH Surge 4 N Primary Oocyte Ovulation • Dog • Fox Resumption of Meiosis First polar body emitted, arrest at metaphase II of meiosis 4 N Sperm Penetration Secondary Oocyte • Dog • Fox 2 N Ovulation (most species) Zygote (pronucleate egg) N N 2 N Sperm Penetration