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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

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Reproductive hormones

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  1. Reproductive hormones

  2. What is a hormone?

  3. 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

  4. 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)

  5. GnRH Hypothalamus FSH LH Estradiol Pituitary gland Ovary

  6. Granulosa cells Basement membrane Antrum Oocyte Theca externa Theca interna

  7. Granulosa cells (GC) Theca cells (TC) Basement membrane

  8. Classes of hormones • Three general classes • Lipids • Cholesterol derivatives (steroids) • 12-C fatty acid derivatives (eicosanoids) • Proteins and polypeptides • Monoamines

  9. Cholesterol and its derivatives • Cholesterol • Large molecule • Hydrocarbon ring • Highly hydrophobic • Source • Diet • De Novo synthesis • Found in cell membrane

  10. Cholesterol and its derivatives • Derivatives • Vitamin D • Bile acid • Lipid digestion • Steroid hormones • Sex steroids • Adrenal steroild • All cholesterol derivatives contain sterol ring

  11. 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

  12. Three classes of sex steroid hormones • Progestin/progestagens • Estrogens • Androgens • Produced through metabolic process • Steroidogenesis

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  14. Steroidogenesis • Source of cholesterol • Acetate • De Novo Synthesis • Lipoproteins • HDL (humans and rodents) • LDL (cattle) • Common pathway • Conversion of cholesterol to pregnenolone

  15. 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

  16. 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

  17. 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

  18. 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

  19. Prostaglandins • Produced from leukotriens through cyclooxygenases • No specific organ of production • Originally isolated from prostate gland • Many reproductive organs produce prostaglandins • Quickly metabolized • Lungs

  20. Protein hormones • Three subclasses • Glycoproteins • Proteins • Growth hormone • Prolactin • Placental lactogens • Cytokines (immune system) • Polypeptdes

  21. 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)

  22. 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

  23. 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

  24. 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

  25. Ovarian proteins • Inhibins • Activins • Mullerian inhibitory substance/hormone (MIS) • Two subunits (alpha and beta) • Different combination determines the nature of proteins

  26. Polypeptides • Small proteins • Short in length compared to proteins • Produced by cleaving large preprohormone peptides

  27. Hypothalamic neuropeptides • Gonadotropin-releasing hormone (GnRH) • Regulates secretion of LH and FSH • Composed of 10 amino acids

  28. 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

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