Repro endocrinology and regulation Flashcards
Hormone composition categories
Peptides: GnRH, oxytocin
Proteins: FSH, LH
Steroids: estrogen, progesterone, testosterone
Fatty Acids: prostaglandin F2α
All hormone receptors (peptide, protein, and steroid) are composed of…
Proteins
Peptide and protein hormone receptors are located on the cell surface
Steroid hormone receptors are located in the cytoplasm or nucleus
Hormone binding to a receptor is influenced by…
Shape and charge
Steroid Hormones
Estrogen, progesterone, testosterone
Cholesterol based
Produced by Gonads (Ovary/Testes), adrenal, placenta
Steroid hormones have a neutral charge
Hormone-receptor binding depends on:
-Presence of hydrophobic domains in the receptor
-Determined by hydrophobic amino acids in the receptor
Steroid hormone receptors
Located in the nucleus
Are transcription factors
Steroid-bound receptors bind to DNA and modulate transcription
-Upregulation of LH, FSH receptors in follicle cells by mitogens (estrogen)
Upregulation of LH, FSH receptors in follicle cells happens by…
Mitogens (estrogen)
Peptide-Protein Hormone Receptors
These receptors are TRANSMEMBRANE proteins
Hormone binding domain in the extracellular region
Activates an intracellular signaling pathway
Energy needed
Signaling pathway mediates the hormone’s effect
Reproductive signaling pathways include:
Phospholipase C
Adenyl cyclase
Protein Hormone mechanism of Action
FSH + LH bind to follicle cells in the ovary
Result in synthesis of a new product, Estradiol
Protein Kinase C
Example: GnRH -> LH and FSH
Activated in response to binding of a peptide or protein hormone to its receptor (GnRH)
Phospholipase C activates Protein Kinase C
PKC upregulates expression of specific genes (LH, FSH)
Leading to exocytosis of LH and FSH
Adenyl Cyclase
Example: LH/FSH -> estrogen/testosterone/ progesterone
AC is activated in response to binding of a peptide or protein hormone to its receptor
AC catalyzes the conversion of ATP to cAMP
cAMP activates Protein Kinase A, which stimulates gene expression and protein synthesis (steroidogenic enzymes)
Primary reproductive regulatory systems of the Hypothalamic-Pituitary-Gonadal Axis
Puberty
Seasonality
Cyclicity
Hypothalamic-Pituitary-Gonadal Axis
Gonadotrophin Releasing Hormone (GnRH)
Synthesized and secreted by hypothalamic neurons
Peptide (10 amino acids, decapeptide)
Travels “locally” to pituitary via a portal vein
Travel systemically to gonads via general circulation
Gonadotropins
Follicle stimulating hormone (FSH)
Leutinizing hormone (LH)
Synthetized and secreted in the anterior pituitary “gonadotroph” cells
Glycoproteins (protein core + carbohydrate side chains) = Inhibin, Activin
Gonadal hormones
Testis
Leydig cells (interstitial cells)–>Testosterone (steroid)
Sertoli cells–> Inhibin (protein)
Ovary
Follicle
-Estrogen (steroid)
-Progesterone (some) (steroid)
-Inhibin (protein)
Corpus luteum
-Progesterone (most) (steroid)
Ovarian Hormones and feedback
Estrogen (follicle: granulosa cells)
Low levels: positive feedback on GnRH, FSH, LH
High levels: negative feedback on GnRH, FSH, LH
Inhibin (follicle: granulosa cells)
Negative feedback on FSH
Progesterone (corpus luteum)
Negative feedback on GnRH, FSH, LH
Testicular hormoens and feedback
LH -> Leydig cells that make T and feedback to ant. pit. to suppress FSH
FSH -> Sertoli cells
Convert T to DHT and E2 which can feedback to hypothalamus and suppress GnRH
Secrete Inhibin for neg. feedback on FSH
Effect of Gonadectomy on levels of gonadotropins
VERY HIGH due to lack of feedback from the gonads
