Tonic and Preovulatory Surge of GnRH
Animal Science 434
The Follicular Phase of the Estrous Cycle
Hypothalamus Tonic and Preovulatory Surge of GnRH Progesterone Estradiol (-) (-) GnRH
Anterior Pituitary
LH, FSH Inhibin (-) Estradiol LH LH, FSH CL Follicle Ovary
Follicular Phase Hypothalamus Progesterone Estradiol (-) (-) GnRH
Anterior Pituitary
LH, FSH Inhibin (-) Estradiol LH LH, FSH CL Follicle Ovary Follicular Phase Hypothalamus Estradiol (+) GnRH
Anterior Pituitary
LH, FSH Inhibin (-) Estradiol LH, FSH
Follicle Ovary
Follicular Progression Growth and Atresia of Follicles
Primordial Primary
Secondary
Atresia Tertiary
Fate of follicles and oocytes Fate of follicles and oocytes
Total # of follicles Total # of follicles At birth 100,000 At birth 100,000 100 Days of Gestation 12 months 75,000 12 months 75,000 2.9 million 4-6 years 21,000 4-6 years 21,000 Aged cow 2,500 Aged cow 2,500
Follicles undergo atresia at all stages of development. Follicles undergo atresia at all stages of development.
Maximum number of oocytes ovulated for a cow Maximum number of oocytes ovulated for a cow
17 cycles/year x 8 year = 136 oocytes ovulated / lifespan 17 cycles/year x 8 year = 136 oocytes ovulated / lifespan Superovulation; rescue follicles from undergoing atresia with FSH treatment. Initial Follicular Growth Follicular Waves in Cattle
Small Antral Atresia Follicle Recruitment Dominance
50 - 60 days Selection
Gonadotropin
FSH Size Follicular Independent
FSH Sensitive Pool
Recruitment Ovulation 9 16 21 Day After Ovulation
Follicular Waves in Cattle Follicular Waves in Cattle Progesterone Progesterone Atresia estradiol FSH Atresia Recruitment inhibin Dominance Dominance FSH estradiol (-) Selection inhibin (-)
Selection FSH estradiol (-) inhibin (-) Follicular Size Follicular Size Follicular
Recruitment FSH Sensitive Pool FSH estradiol (-)
Ovulation 9 16 21 Ovulation 9 16 21 Day After Ovulation Day After Ovulation
Follicular Waves in Cattle Follicular Waves in Cattle Progesterone Progesterone
Atresia
Dominance
Selection Follicular Size Follicular Size Follicular
Recruitment
Ovulation 9 16 21 Ovulation 9 16 21 Day After Ovulation Day After Ovulation Follicular Waves in Cattle Follicular Waves in Cattle Progesterone Progesterone
Dominance
Selection Follicular Size Follicular Size Follicular
Recruitment
Ovulation 9 16 21 Ovulation 9 16 21 Day After Ovulation Day After Ovulation
Two Follicular Waves Progesterone Follicular Wave Emergence • Recruitment = Emergence • FSH always controls emergence • Increase in FSH precedes emergence Follicular Size Follicular
Ovulation 10 21 Day After Ovulation
Species Variation in Follicular Waves • Cattle - 2 or 3 / cycle Cl-progesterone • Sheep - 4 or 5 / cycle Gonadotropin Action • Pigs - 1 / cycle Within • Horses - 1 / cycle Cl-progesterone, inhibin the Follicle • Human - 1 / cycle Theca Interna Antral Follicle LH Receptor cAMP Theca Internal Cholesterol PKA Testosterone FSH
Granulosa Receptor cAMP Testosterone PKA Estradiol Granulosa
Theca Interna LH Selection Receptor Dominant Follicle cAMP Express LH Receptor Cholesterol PKA Ovulation Testosterone LH FSH Receptor Receptor cAMP cAMP Testosterone PKA Estradiol Granulosa
Blocking of these events in the follicle prevents ovulation. • protein synthesis • steroid synthesis Germinal Epithelium • prostaglandin Tunica synthesis Albuginea Theca Externa • plasminogen activator synthesis Theca Interna Basement Membrane
Granulosa Preovulatory LH Surge Cumulus Expansion
Cumulus Hyaluronic Acid and Protein Expansion Production
Oocyte Separates From Follicular Wall Unexpanded Expanded Ovulation
Cumulus and Oocyte Preovulatory LH Surge Separation Cumulus Expansion Protein synthesis changes in and around Follicle
Progesterone Plasminogen Prostaglandin Activator Synthesis PGE and PGF
Oocyte Separates From Follicular Wall
Ovulation
Histamine Histamine
Preovulatory LH Surge PGE2 Preovulatory LH Surge PGE2
Cumulus Increased Blood Cumulus Increased Blood Protein synthesis changes Protein synthesis changes Expansion Flow to Ovary and Expansion Flow to Ovary and in and around Follicle in and around Follicle Follicle Follicle
Progesterone Plasminogen Prostaglandin Vascular Progesterone Plasminogen Prostaglandin Vascular Activator Synthesis Permeability Activator Synthesis Permeability PGE and PGF Collagenase (inactive) PGE and PGF Plasminogen Plasmin Plasminogen Oocyte Oocyte Collagenase (active) Separates Separates From Edema From Follicular Wall Edema Follicular Follicular Weakens Wall Wall Follicular Follicular pressure pressure Ovulation Ovulation Histamine
Preovulatory LH Surge PGE2
Cumulus Increased Blood Protein synthesis changes Expansion Flow to Ovary and in and around Follicle Follicle
Progesterone Plasminogen Prostaglandin Vascular Activator Synthesis Permeability Types of Ovulators Collagenase (inactive) PGE and PGF Plasmin Plasminogen Oocyte Collagenase (active) Separates Contraction Follicular Wall From of Smooth Edema Weakens Follicular Muscle Wall Follicular pressure Ovulation
Spontaneous Induced Ovulators Ovulators
Hypothalamus Induced Ovulators Blood LH
Time (hr) GnRH Posterior Pit. Stimulation Nerve LH endings Sensory Neurons sensing Anterior Pit. copulation
Copulation Penis Spinal Chord Cats • Induced Ovulators • Single copulation – Only works 50% of the time LH • Multiple copulations – Higher LH surge
Nerve endings Sensory Neurons sensing copulation
Copulation Penis
Spontaneous Ovulators Oogenesis Migration to germinal ridge Primordial Germ Cells • Retain some neural control of Mitotic divisions Oogonia Follicle Cells ovulation Initiation of Meiosis Interphase Prophase of Meiosis – heifers can alter the timing of the LH Primary leptotene DNA synthesis Oocyte Meiotic prophase begins zygotene surge by clitoral stimulation pachytene diplotene – human rape cases result in higher than dictyotene Growth Meiotic Arrest expected pregnancy rates Gonadotropin Independent zona pellucida formation mRNA production protein synthesis cortical granule formation Gonadotropin Dependent nuclear maturation cytoplasmic maturation
Oogonia in Egg Nest Oogonia and Primary Oocytes
Fetal Pig Ovary Primary Oocytes in Primordial Follicles Primary Oocyte in Primary Follicle
Fetal Oocyte Development Ovulation of Tertiary Follicle
Mitosis Meiosis Fertilization Birth
Cow 280 d
Sow
114 d
Mouse
19 d
Formation of the Zona Pellucida Corona Radiata Zona Pellucida Oocyte Corona Radiata
Oocyte
Zona Pellucida Gap Junctions During Oocyte Growth and Before the LH Surge The LH Surge
• OMI - Oocyte cAMP Maturation Inhibitor OMI cAMP • MPF - Maturation GV PKA promoting factor
pre-MPF MPF • GV - germinal vesicle (nucleus)
Gap Junctions Allow Cell to Cell Communication! Gap Junctions are Destroyed!
First polar body The LH Surge Resumption of emitted, arrest at LH Surge Meiosis metaphase II of meiosis
4N 4N 2N cAMP GVBD Resumption of Meiosis Primary Oocyte PKA Secondary Oocyte GV Ovulation pre-MPF MPF (most species)
Zygote (pronucleate egg)
N N Sperm 2N Penetration
Gap Junctions are Destroyed!
First polar body Resumption of emitted, arrest at LH Surge Meiosis metaphase II of meiosis
4N 4N 2N
Primary Oocyte Sperm Secondary Penetration Oocyte Ovulation Ovulation • Dog • Dog (most species) • Fox • Fox
Zygote (pronucleate egg)
N N Sperm 2N Penetration