Advanced Reproduction Physiology (Lecture 1) Isfahan University of Technology College of...

Advanced Reproduction Physiology

(Lecture 1)

Isfahan University of Technology

College of Agriculture, Department of Animal Science

Prepared by: A. Riasihttp://riasi.iut.ac.ir

The syllabuses

Puberty and sexual maturity

Physiology of gamete production

Hormonal & non-hormonal secretions of reproductive

in male and female animals

Physiology of pregnancy and embryo development

Physiology of parturition

Pheromones

Abnormality of reproduction

Reproductive immunology

Recent advance associated with reproductive

physiology

The syllabuses

1. Reproductive in Farm Animals, By: E.S.E. Hafez

2. Reproduction in Dairy Cattle 1&2, By: Gietema

3. Improving the Reproductive Management of Dairy

Cattle Subjected to Artificial Insemination, By: IAEA-

TECDOC-1533

4. Review and Original Papers

References

Puberty is originated from Latin word “pubscere”

Hypothalamus control puberty in animals

Two centers in hypothalamus:

Tonic center

Surge center

Puberty and sexual maturity

SurgeTonic

SurgeTonic

Puberty

In near to puberty age:

Sensitivity of the hypothalamic tonic center

GnRH and gonadotrophins secretion

Sensitivity of GnRH surge center in hypothalamus

Puberty

Puberty

Testis

T

TE2

Surge CenterDoes notDevelop

Surge CenterDoes notDevelop

Blood BrainBarrier

Effect of testosterone on male brain

Ovary

E2

E2 E2

PlacentaE2FP + E2

Surge CenterDevelops

Surge CenterDevelops

Blood BrainBarrier

Effect of estrogen on female brain

Puberty may affected by different factors:

Heritability

Environmental factors

Birth month

Social condition

Nutritional factors

Age and weight

Factors affecting puberty

Effect of a minimum percentage of body fat

Serum leptin concentrations

Leptin does not serve as triggering signal but acts

mainly as a permissive signal that permits puberty to

occur.

Role of leptin in puberty

Role of leptin on puberty

Physiology of Testicular Function

The testes have two compartments:

Tubular compartment (tubuli seminiferi)

Interstitial compartment (interstitum)

Functional organization of testis

The interstitial compartment:

The leydig cells

Secretion of testicular testosterone

Secretion of insulin like factor 3 (INSL3)

Immune cells

Blood and lymph vessels

Nerves

Fibroblasts

Loose connective tissue


Different type of leydig cells (Ge and Hardy, 2007):

Stem Leydig cells as founder cell

Progenitor Leydig cells as a committed stem cell

Fetal Leydig cells as a terminally differentiated cell in the

fetus

Adult Leydig cells as the terminally differentiated Leydig

cell


The interstitial compartment also contains cells

belonging to the immune system:

Macrophages, probably influence the function of leydig cells:

Proliferation

Differentiation

Steroid production

Lymphocytes



Immunological compartments of the testis. Sertoli cells (S) traverse the testicular tubules, keeping in close contact with the germ cells. Together with the peritubular cells, they form the seminiferous epithelium. The blood–testis barrier (tight junctions) is built by tight junctions between neighboring S, dividing the seminiferous tubules into a basal and adluminal compartment. The interstitial space contains the Leydig cells (L) and the immune cells such as macrophages (MP), dendritic cells (D), mast cells (M), and T cells as well as blood vessels (BV) with migrating leukocytes

Spermatogenesis takes place in the tubular

compartment:

Germ cells

Somatic cells

The peritubular cells

Sertoli cells


Peritubular cells produce several factors that are

involved in cellular contractility (Holstein et al. 1996):

Panactin

Desmin

Gelsolin

Smooth muscle myosin and actin


Several regulators of cell contractions are reported:

Oxytocin

Oxytocin-like substances

Prostaglandins

Androgenic steroids

Endothelins

Endothelin converting enzymes

Endothelin receptors


These cells also secrete extracellular matrix and factors

typically expressed by connective tissue cells:

Collagen

Laminin

Vimentin

Fibronectin

Growth factors

Fibroblast


Sertoli cells synthesize and secrete a large variety of

factors:

Proteins

Cytokines

Growth factors

Opioids

Steroids

Prostaglandins

Modulators of cell division


The Cytoplasm of sertoli cells contains:

Eendoplasmic reticulum

Smooth type

Rough type

A Prominent Golgi apparatus

Lysosomal granules

Microtubuli and intermediate filaments


Another important functions of Sertoli cells:

Final testicular volume

Sperm production


Hormonal control of testicular function

Pituitary gonadotropes are the central structure

controlling gonadal function.

In turn, are regulated by the hypothalamic

gonadotropin-releasing hormone (GnRH).

GnRH secretion depends on the activation of the

GPR54 receptor.


GnRH receptors are located on the surface of the

GnRH neurons and stimulated by the peptide

kisspeptin.

The pituitary function is also under the control of

gonadal steroids and peptides that influence its activity

both directly and through the hypothalamus.


The Gonadotropin-producing cells constitute

approximately 15% of the adenohypophyseal cell.

The same cell type is believed to secrete both

gonadotropins.

Pituitary gonadotropes are often found in close

connection with prolactin cells.


Dramatic changes by pubertal activation:

The proximity of several stimulated endocrine cells types to

each other and to the germinal cell line.

Central feedback actions:

FSH

LH

Testosterone


In male testosterone is major the hormone controlling

GnRH secretion

Testosterone can act as such or after metabolism to

DHT or estradiol.


During spermatogenesis gonadotropes regulate

testicular function.

Testosterone and FSH affect the seminiferous tubules

and enhance spermatogenesis

LH affect the release of sperm from germinal

epithelium (spermiation)

Hormonal control of spermatogenesis

High concentration of testosterone may find in

seminiferous tubules, rete testis, afferent tubules and

epydidymis.

Effect of inhibin and activin on FSH secretion and

spermatogenesis


The other hormones may affect testicular funtion:

Prolactin

GH and IGF-I

Insulin

Glucocorticoids

Thyroid hormones

PGE2

Testicular GnRH


Androgens are essential for:

The development and function of testes

Maturation of secondary sexual characteristics

Masculinization of the bone-muscle apparatus

Libido

Stimulation of spermatogenesis

Testicular androgens

Physiological effects of androgens depend on different

factors:

Number of androgen molecules

Distribution of androgens and their metabolites inside the

cell

Interaction with the receptors

Polyglutamine number of the amino acid sequence in the

androgen receptor

Receptor activation


In turn, androgen concentrations in the blood depend

on:

The synthesis rate

Balanced by metabolic conversion and excretion.


The main site of androgen production in the testis is the

Leydig cell.

Since Leydig cells cannot store androgens, de novo

biosynthesis takes place continuously.

LH as the central regulatory factor controls both

steroidogenesis and Leydig cell cholesterol homeostasis

in vivo.


Cholesterol is stored in cytoplasmic lipid droplets.

The number of lipid droplets is inversely related to the

rate of androgen synthesis in the Leydig cell.


Testosterone moves from the leydig cells into:

Blood vessel

Lymphatic vessel

Seminiferous tubules


Testosterone also give rise to two other potent

androgens:

Dihydrotestosterone (DHT)

5α-androstandiol


Circulating testosterone is found in three forms

Free

Bounded with a liver-drived sex steroid-binding globulin

(SSBG)

Bounded with albumin and other proteins


Testosterone is excreted by urine:

As glucronide (1% of daily production of testosterone)

17-ketosteroids products


Testosterone (T) is synthesized in the testis. After entering the target cells (in the hypothalamus, pituitary, testis and wolffian duct) T is directly bound to the androgen receptor (AR) and the complex T-AR binds to specific DNA sequences and regulates gene transcription, which can result different works.


Specific actions of Dihydrotestosterone (DHT). After entering the T to target cells (in the urogenital sinus, urogenital tubercle, and several additional androgen target tissues) T is metablized to 5α-Dihydrotestosterone (DHT) by the enzyme 5α-Reductase type 2. DHT binds directly to the androgen receptor (AR) and the complex DHT-AR interacts to specific DNA sequences and regulates gene transcription, which can result in differentiation and development of the prostate, the external genitalia and at puberty in several secondary male characteristics.


The major role of testosterone:

Stimulates of differentiation of the wolffian ducts into the

epididymis, vas deferens and seminal vesicles.

With or without DHT causes enlargement of the penis and

seminal vesicles.

Causes enlargement of the larynx and thickening of the

vocal cords.



Local hormone required for initiation and maintenance of

spermatogenesis.

Cessation of linear growth by closure of the epiphyseal

growth center.

Enlargement of the muscle mass during puberty.

Important effect on lipid metabolism.



Initiation of sexual drive.

Suppression of mammary gland growth.

Stimulation hematopoiesis.

Stimulation of renal sodium reabsorption.

Stimulation of aggressive behavior

Suppression of hepatic synthesis of SSBG, cortisol-binding

globulin and thyroxin-binding globulin.


The major role of DHT and 5α-androstandiol:

DHT is specifically required in the fetus for differentiation

of the genital tubercle, genital swellings, genital folds and

urogenital sinus into penis, scrotum, penile urethra and

prostate respectively.

DHT is required during puberty for growth of scrotum and

prostate and stimulation of prostatic secretion.


The major role of DHT and 5α-androstandiol:

DHT and 5α-androstandiol stimulate the hair follicles.

DHT and 5α-androstandiol increase production of sebum.

DHT influence the spermatogenesis.


Semen volume is controlled by different factors:

Animal species

Breed

Individual properties

Season of year

Semen collection time

Semen properties

Sperm collection times for different animals

LivestockNumber of Collections

BullTwo times per week

RamDaily for weeks

BoarTwo times per week

StallionNatural - two times per day

Artificial - every other day

RoosterDaily

Semen properties

Semen liquid produced by:

Sertoli and rete testis

Genital tract secretions

Accessory glands secretion

Semen properties

Special proteins in semen liquid:

Androgen binding protein (ABP)

Acrosin inhibitor protein

Glycoproteins

Semen properties

Different ions in semen liquid

Na+

Cl-

K+

Ca++

Mg++

Hco3-

Semen properties

Other components in semen liquid:

Hormones

Vitamins

Lipids and fatty acids

Immunoglobulin A

Energy sources

Semen properties

Energy metabolism in sperm:

Fructose production by sorbitol dehydrogenase

Fructolysis

Role of membrane Plasmalogens

Semen properties

Factors may affect sperm metabolism rate:

Temperature

pH

Osmotic pressure

Sperm concentration

Hormones

Gases

Light

Semen properties

Some research papers associated to this lecture

1. Asadpour, R. et al. The effect of antioxidant supplementation in semen extenders

on semen quality and lipid peroxidation of chilled bull spermatozoa. Iranian

Journal of Veterinary Research, Shiraz University, 2012, 13: No. 3, Ser. No. 40.

2. Umut Tasdemir. et al. Effects of various cryoprotectants on bull sperm quality,

DNA integrity and oxidative stress parameters. Cryobiology xxx (2012) xxx–xxx.

3. Gaffari Tu¨rk. et al. Effects of pomegranate juice consumption on sperm quality,

spermatogenic cell density, antioxidant activity and testosterone level in male

rats. Clinical Nutrition, 2008, 27: 289-296.

Advanced Reproduction Physiology (Lecture 1) Isfahan University of Technology College of...

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