Reproductive Hormones Overview - Anatomy & Physiology

Introduction

Reproductive hormones often have multiple roles and operate via negative feedback systems. The information below will provide the main reproductive hormones in domestic species and their functions.

Reproductive Hormones

Gonadotropin Releasing Hormone (GnRH)

GnRH is a neuropeptide (a decapeptide) that is produced in the hypothalamic surge and tonic centres. In the male and the female, the target tissue is the anterior pituitary gland, specifically Gonadotroph cells. In males and females, secretion of GnRH results in the release of Follicle Stimulating Hormone (FSH) and Leutinising Hormone (LH) from the anterior pituitary gland.

GnRH-producing neurons are stimulated into production in response to spontaneous rhythms and by sensory impulses from sensory inputs derived from the external environment. Alterations in the internal conditions of the body can also result in altered GnRH production. For example in some species such as the sheep, there is seasonal sexual activity and the cerebral cortex, hypothalamus, pituitary and testes interact to regulate functions further along the signalling chain.

GnRH in Males

In males there are between 4-12 GnRH peaks per day. Plasma concentrations of LH peak approximately 10mins post GnRH surge.

Leutinising Hormone (LH)

LH is a type of glycoprotein that is produced in the Anterior Pituitary via gonadotroph cells. Their target tissue in the male are Leydig cells in the testes and in the female their target are Theca interna cells and luteal cells within the ovary. In the male LH stimulates testosterone production whilst in the female it stimulates ovulation and the formation of the corpora lutea together with progesterone secretion.

Follicle Stimulating Hormone (FSH)

FSH is a type of glycoprotein that is produced in the Anterior Pituitary via gonadotroph cells. Their target tissue in males are Sertoli cells within the testes and in the female Granulosa cells of the ovary. In the male FSH stimulates the secretion of inhibin which has a negative feedback directly in the anterior pituitary, whilst in the female it stimulates follicular development and oestradiol synthesis.

Prolactin (PRL)

PRL is a protein that is produced from the Anterior Pituitary via lactotroph cells. In males the target tissues are the testes and the brain whilst in females the target tissue are cells located within the mammary tissues and the corpus luteum in rodents. In the male PRL induces maternal behaviour whilst it also does this in the female together with lactation and ensuring functionality of the corpora lutea in some species.

Oxytocin (OT)

OT is a neuropeptide (a octapeptide) which is synthesised in the hypothalamus and stored in the posterior pituitary. OT can also be synthesised by the corpus luteum. In males the target tissue for OT is smooth muscle within the epididymal tail, ductus deferens and the ampulla. In females OT targets the uterine myometrium and endometrium together with cells of the mammary glands. In the male OT stimulates PGF2α synthesis and facilitates the pre-ejaculatory movement of spermatozoa. In females, OT stimulates uterine motility and the synthesis of PGF2α from the uterus. It also begins milk 'let-down' or ejection.

Oestradiol (E₂)

E₂ is a steroid that is produced by the granulosa cells of a follicle, the placenta and the testes. In males the target tissue is the brain for maturation of the male brain during foetal development. E₂ in the male also inhibits long bone growth. In females the target tissues are the hypothalamus, the entire female reproductive tract and the mammary glands. The primary action of E₂ in males is the appropriate development of male sexual behaviours whilst in females it influences sexual behaviour, GnRH levels, the secretory activity of the reproductive tract and enhances uterine motility.

Progesterone (P₄)

Progesterone is a steroid hormone that is produced by the corpus luteum and the placenta. In males the target tissues are the accessory sex glands, the tunica dartos (scrotum), the seminiferous tubules and skeletal muscles. In females the target tissues are the uterine endometrium, the mammary gland, the myometrium and the hypothalamus. Progesterone results in increased endometrial secretions and inhibits the release of GnRH in females. It also inhibits female reproductive behaviour as well as acting to maintain a pregnancy. Progesterone has no primary action in the male.

Testosterone (T)

Testosterone is a steroid hormone that is produced in the leydig cells within the testes and also via theca interna cells within follicles. In males the target tissue for testosterone are the anterior pituitary gland, specifically the gonadotroph cells. In females the target tissues are the brain, skeletal muscle and granulosa cells. This is because testosterone acts as a substrate for estradiol. The synthesis of testosterone rather than estradiol can lead to abnormal masculinisation in females. In males the primary action of testosterone is anabolic growth, spermatogenesis promotion and promotion of secretion from the accessory sex glands.

Inhibin

Inhibin is a type of glycoprotein that is synthesised within the granulosa cells in females and in sertoli cells in the male. In both males and females the target organ for inhibin is the anterior pituitary, specifically the gonadotroph cells. In the male inhibin inhibits FSH secretion whilst in females it stimulates FSH secretion.

Activin

Activin is a glycoprotein that is produced within granulosa cells in females and sertoli cells in the male. The target tissue for activiin in the male is the epididymis whilst in the female it is the anterior pituitary gland, specifically gonadotroph cells. In males and females activin stimulates FSH secretion.

Prostaglandin F2α

Prostaglanin is a C₂O fatty acid and is produced within the uterine endometrium and vesicular glands. The target tissue in the female is the corpus luteum, uterine myometrium and ovulatory folicles. In the male foetus prostaglandin affects the the metabolic activity of spermatozoa and epididymal contractions. In the female prostaglandin results in luteolysis, the induction of tone and contractions within the uterus and ovulation.

Prostaglandin (PGE₂)

PGE₂ is another form of prostaglandin that is produced by the ovary, uterus and embryonic membranes. It's target tissue in females is the corpus luteum and the oviduct where it helps induce ovulation and the secretion of progesterone from the corpus luteum.

Human Chorionic Gonadotrophin (hCG)

hCG is a form of glycoprotein that is synthesised within the trophoblast cells of a blastocyst. In females the target tissue is the ovary where it results in the ovarian production of progesterone. In males hCG increases the growth of the foetal testes.

Equine Chorionic Gonadotrophin (eCG)

eCG is a form of glycoprotein that is produced from chorionic girdle cells. In females the primary target organ are the ovaries where they faciliate the formation of the accessory corpora lutea.

Placental Lactogen (PL)

Placental lactogen is a form of protein that is produced by the placenta. It's primary

Name of Hormone	Gonadotrophin Releasing Hormone	Leutinizing Hormone	Follicle Stimulating Hormone	Prolactin	Oxytocin	Oestradiol	Progesterone	Testosterone	Inhibin	Activin	Prostaglandin F2α	Human Chorionic Gonadotrophin	Equine Chorionic Gonadotrophin	Placental Lactogen
Abbreviation	GnRH	LH	FSH	PRL	OT	E2	P4	T			PGF2α	PGE2	hCG	eCG	PL
Biochemical Classification	Neuropeptide (decapeptide)	Glycoprotein	Glycoprotein	Protein	Neuropeptide (Octapeptide)	Steroid	Steroid	Steroid	Glycoprotein	Glycoprotein	Prostaglandin (C20 fatty acid)	Prostaglandin (C20 fatty acid)	Glycoprotein	Glycoprotein	Protein
Source	Hypothalamic Surge and Tonic Centres	Anterior Pituitary (Gonadotroph Cells)	Anterior Pituitary (Gonadotroph Cells)	Anterior Pituitary (Lactotroph Cells)	Synthesized in the Hypothalamus, Stored in the Posterior Pituitary, Synthesized by the Corpus Luteum	Granulosa Cells of Follicle, Placenta and Sertoli Cells of Testes	Corpus Luteum and Placenta	Interstitial Leydig Cells of Testes, Theca Interna Cells of the Follicle	Granulosa Cells (female), Sertoli Cells (male)	Granulosa Cells (female), Sertoli Cells (male)	Uterine Endometrium, Vesicular Glands	Ovary, Uterus, Embryonic Membranes	Trophoblast Cells of the Blastocyst (Chorion)	Chorionic Girdle Cells	Placenta
Male Target Tissue	Anterior Pituitary (Gonadotroph Cells)	Testes (Leydig Cells)	Testes (Sertoli Cells)	Testes, Brain	Smooth Muscle of Epididymal Tail, Ductus Deferens, Ampulla	Brain, Inhibits Long Bone Growth	Accessory Sex Glands, Tunica Dartos (Scrotum), Semniferous Epithelium, Skeletal Muscle	Anterior Pituitary (Gonadotroph Cells)	Anterior Pituitary (Gonadotroph Cells)	Epididymis
Female Target Tissue	Anterior Pituitary (Gonadotroph Cells)	Ovary (Theca Interna and Luteal Cells)	Ovary (Granulosa Cells)	Mammary Cells, Corpus Luteum in Rodents	Uterine Myometrium and Endometrium, Myoepithelial Cells of Mammary Glands	Hypothalamus, Entire Tract, Mammary Gland	Uterine Endometrium, Mammary Gland, Myometrium, Hypothalamus	Brain, Skeletal Muscle, Granulosa Cells	Anterior Pituitary (Gonadotroph Cells)	Anterior Pituitary (Gonadotroph Cells)	Corpus Luteum, Uterine Myometrium, Ovulatory Follicles	Corpus Luteum, Oviduct	Ovary	Ovary	Mammary Gland
Male Primary Action	Release of FSH and LH from the Anterior Pituitary Gland	Stimulates Testosterone Production	Sertoli Cell Function	Induce Maternal Behaviour	PGF2α Synthesis, Pre-Ejaculatory Movement of Spermatozoa	Sexual Behaviour		Anabolic Growth, Promotes Spermatogenesis, Promotes Secretion of Accessory Sex Glands	Inhibits FSH Secretion	Stimulates FSH Secretion	Affects Metabolic Activity of Spermatozoa, Epididymal Contractions		Increased Growth of Foetal Testes
Female Primary Action	Release of FSH and LH from Anterior Pituitary Gland	Stimulates Ovulation, Formation of Corpora Lutea and Progesterone Secretion	Follicular Development, Oestradiol Synthesis	Lactation, Maternal Behaviour, Corpora Lutea Function (some species)	Uterine Motility, Uterine PGF2α Synthesis, Milk Ejection	Sexual Behaviour, GnRH, Elevated Secretory Activity of Tract, Enhanced Uterine Motility	Endometrial Secretion, Inhibits GnRH Release,Inhibits Reproductive Behaviour, Maintenance of Pregnancy	Substrate For E2 Synthesis, Abnormal Masculinization	Inhibits FSH Secretion	Stimulates FSH Secretion	Luteolysis, Uterine Tone and Contraction, Ovulation	Ovulation, Corpus Luteum Secretion of Progesterone	Facilitates Ovarian Production of Progesterone	Formation of Accessory Corpora Lutea	Mammary Stimulation