The Follicular Phase of the Estrous Cycle Animal Science 434 The Follicular Phase of the Estrous Cycle

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

Tonic and Preovulatory Surge of GnRH

Hypothalamus Progesterone Estradiol (-) (-) GnRH Anterior Pituitary Inhibin (-) LH, FSH Estradiol LH, FSH LH CL Follicle Ovary

Steps Leading to the Preovulatory LH Surge P4 from Cl  GnRH FSH and LH Inhibin  FSH Proestrual Follicular Development Preovulatory LH surge  Estradiol to threshold

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

Tonic and Preovulatory Surge of GnRH

Hormone Changes During the Folliclular Phase Progesterone LH FSH Estradiol

Follicle Progression

Growth and Atresia of Follicles

Follicular Growth Recruitment Gonadotropin Independent Small Antral Follicle Recruitment Initiated by FSH

Progesterone FSH FSH FSH E2 Inhibin Inhibin LH LH Deviation!!!

Folliclular Waves in Cattle

Follicular Waves

Follicular Waves

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 and 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 from dominant follicle decreases and androgens increase, this may initiate atresia of dominant follicle

Regressing Phase Dominant follicle becomes atretic and looses steroidogenic capability

Follicular Waves

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 and 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 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 Ovulation Follicular Phase Progesterone LH FSH Estradiol

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

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

Follicular Waves

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 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 100 Days of Gestation 2.9 million Can increase with superovulation with FSH to stimulate the rescue of follicles which would have undergone atresia

Gonadotropin Action Within the Follicle

Theca Interna Granulosa

Theca Interna Selection Granulosa LH Receptor Dominant Follicle cAMP Blood Receptor LH cAMP Receptor LH Selection Dominant Follicle Express LH Receptor cAMP Cholesterol Testosterone PKA Testosterone Receptor FSH cAMP Estradiol PKA

Ovulation

Germinal Epithelium Tunica Albuginea Theca Externa Theca Interna Basement Membrane Granulosa

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

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

Preovulatory LH Surge Ovulation Cumulus Expansion Oocyte Separates From Follicular Wall Ovulation

Cumulus Expansion Hyaluronic Acid and Protein Production Unexpanded

Cumulus and Oocyte Separation

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

Types of Ovulators

Spontaneous Ovulators

Induced Ovulators

Nerve endings sensing copulation Induced Ovulators Nerve endings sensing copulation Sensory Neurons Penis Copulation

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

Nerve endings sensing copulation LH Nerve endings sensing copulation Sensory Neurons Penis Copulation

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 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

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

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

Corona Radiata Oocyte Cortical Granules Zona Pellucida Gap Junctions Cortical Granules

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

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

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