Transcript Reproductive hormones

Reproductive hormones
What is a hormone?
Definition of hormone
• Hormone
– Greek “I excite” or “I arouse”
• First used by Starling in 1895
– Classical definition
• Chemical signals that travel via bloodstream to
affect the function of the distant organ
– Regulatory factor
• Secretory organ
• Target organ/tissue
Definition of hormone
• Hormones
– Contemporary definition
• Much broader
• Local factors (produced and used without being
carried in the bloodstream)
– Autocrine (produced and used by the same cell/tissue)
– Paracrine (produced by the neighboring cells and
transported via the interstitial fluid)
GnRH
Hypothalamus
LH
FSH
Estradiol
Pituitary
gland
Ovary
Granulosa cells
Basement
membrane
Antrum
Oocyte
Theca interna
Theca externa
Granulosa
cells (GC)
Basement membrane
Theca
cells (TC)
Classes of hormones
• Three general classes
– Lipids
• Cholesterol derivatives (steroids)
• 12-C fatty acid derivatives (eicosanoids)
– Proteins and polypeptides
– Monoamines
Cholesterol and its derivatives
• Cholesterol
– Large molecule
• Hydrocarbon ring
– Highly hydrophobic
– Source
• Diet
• De Novo synthesis
– Found in cell
membrane
Cholesterol and its derivatives
• Derivatives
– Vitamin D
– Bile acid
• Lipid digestion
– Steroid hormones
• Sex steroids
• Adrenal steroild
– All cholesterol
derivatives contain
sterol ring
Steroid hormones
• Commonly called sex steroid hormones
– Produced mainly by the gonads
• Ovaries and testis
• Some production by placenta, adrenal gland, and
brain
– Water-insoluble but lipid soluble
• Easily move across the plasma membrane
• Bound to Steroid hormone-binging globulin during
transport
• Three classes of sex steroid hormones
– Progestin/progestagens
– Estrogens
– Androgens
• Produced through metabolic process
– Steroidogenesis
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Steroidogenesis
• Source of cholesterol
– Acetate
• De Novo Synthesis
– Lipoproteins
• HDL (humans and rodents)
• LDL (cattle)
• Common pathway
– Conversion of cholesterol to pregnenolone
• Splits into two different pathway with the
same outcome
– Delta-4 pathway
• Conversion of pregnenolone to progesterone
• Conversion of progesterone to androstenedione
– Delta-5 pathway
• Conversion of pregnenolone to androstenedione
• Production of estrogens
– Final destination of steroidogenesis in the
ovary
• Conversion of androgens (testosterone) to
estradiol-17 beta
– Some species (i.e. rats) use delta-4 pathway,
whereas others (i.e. cows) prefer delta-5
pathway
General function of steroid
hormones
• Development of physical characteristics
– Male and female sex characteristics
• Primary (reproductive organs)
• Secondary (physical)
• Reproductive success
– Sexual behavior and libido
– Fertility
– Pregnancy
Eicosanoids
• Derivative of 12-C fatty acid (Arachidonic acid)
– Prostaglandins (more important for reproduction)
– Leukotriens
• Arachidonic acid released from phospholipid
component of the cell membrane
– Phospolipase A
– Phospholipase C
• Prostaglandins
– Produced from leukotriens through
cyclooxygenases
– No specific organ of production
• Originally isolated from prostate gland
• Many reproductive organs produce prostaglandins
– Quickly metabolized
• Lungs
Protein hormones
• Three subclasses
– Glycoproteins
– Proteins
• Growth hormone
• Prolactin
• Placental lactogens
– Cytokines (immune system)
– Polypeptdes
Glycoproteins
• Produced by the anterior pituitary
– Gonadotropins
• Follicle-stimulating hormone (FSH)
• Luteininzing hormone (LH)
– Thyroid-stimulating hormone (TSH)
• Less important for regulation of gonadal function
• Produced by placenta
– Chorionic gonadotropins (CG)
• Human (hCG)
• Horse (eCG/PMSG)
• Structural similarity
– Two subunits
• Alpha
– Universal
• Beta
– Unique to each hormone
• Linked together non-covalently (disulfide bridges)
– Glycosylated
• Attachment of carbohydrate moiety onto the
subunits
– Unique among hormones
Proteins
• Pituitary hormones
– Growth hormone (GH)
– Prolactin (PRL)
• Placental hormones
– Unique to humans, rodents, and ruminants
• Placental lactogen (PL)
• GH-Variant (GH-V)
• Affect metabolism and lactation
• Affect ovarian functions
Cytokines
• Different from hormones
– No specific organ/cells produce
• Immune response
• Inflammation
– Multiple targets
– Interactions to modulate activities of other
cytokines
– Redundant functions
– Auto/paracrine factor rather than endocrine
factor
• Ovarian proteins
– Inhibins
– Activins
– Mullerian inhibitory substance/hormone (MIS)
– Two subunits (alpha and beta)
• Different combination determines the nature of
proteins
Polypeptides
• Small proteins
– Short in length compared to proteins
– Produced by cleaving large preprohormone
peptides
• Hypothalamic
neuropeptides
– Gonadotropinreleasing hormone
(GnRH)
• Regulates secretion of
LH and FSH
• Composed of 10 amino
acids
• Posterior pituitary hormones
– Oxytocin
• Composed of 9 amino acids
• Produced by the neurons within the hypothalamus
but secreted by the posterior pituitary gland
• Induces contraction of smooth muscles
• Critical for milk let-down