LECTURE 2
SECTION 2
ENDOCRINOLOGY
INTRODUCTION
Cell to Cell Communication
Locally
Direct Physical Contact
Chemical or Electrical Contact
At Distance
Chemical or Electrical Contact
nervous system
circulatory system
Hormones (classical definition)
Chemical agents synthesized and secreted by
specialized ductless glands and carried by the blood
stream to specific target tissues where they evoke
physiological adjustments
Glands
Endocrine glands -- ductless glands which secrete
directly into blood stream (have a larger blood supply
then other glands)
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Exocrine glands-- ducted glands which secrete
externally, not into the blood stream
Receptor sites--specific sites located on the cell
membrane or within the cell which have a high affinity
for a specific hormone (lock and key)
General properties of hormones
Effect specialized tissues containing receptors
Do not initiate reactions
Are not chemically unique
Have variable speeds of reaction
Active at very low concentrations
-9
(10 grams = nanograms (ng) or ppb)
(10-12 grams = picograms(pg) or ppt)
Reproductive Hormone Classes
Neurohormones -- peptides
Gonadotropic hormones -- proteins
Gonadal hormones -- steroids, peptides & proteins
Uterine and placental hormones -- proteins, steroids & lipids
HORMONES FROM ANTERIOR PITUITARY (AP)
Gonadotropins
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Follicle stimulating hormone (FSH)
Glycoprotein hormone
MW - 32,000
t½ - 2 to 2½ hours
Structure
About 210 amino acids in a and ß subunits
Actions in female
Stimulates Follicle growth
Stimulates Estrogen production (in conjunction with
LH)
Stimulates Inhibin production
Actions in male
Stimulates Spermiogenesis
Stimulates Inhibin production
Stimulates Androgen-binding protein
Uses by Man
Stimulation of follicular development to induce multiple
ovulations
Luteinizing hormone (LH)
Glycoprotein hormone
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MW - 30,000
t½ - 30 min
Structure
About 215 amino acids in a and ß subunits
Actions in female
Maturation of follicle
Ovulation
Corpus luteum (CL) formation
Progesterone production (luteotropic effect)
Actions in male
Testosterone production
Uses
Induces ovulation
Treatment of cystic ovaries
Human Menopausal Gonadotropins (hMG)
Recovered from urine of menopausal women
Both LH and FSH units (1:1)
Use
superovulation
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Prolactin (Prl)
Not a "gonadotropin" in domestic animals
Protein hormone
MW - 24,000
Structure
About 198 amino acids
Actions in female
Milk synthesis
Development of mammary gland
Maternal behavior
Adrenocorticotropic hormone (ACTH)
Polypeptide hormone (MW - 4,500)
Action in female and male
Release of glucocorticoids from adrenal
gland
HORMONES FROM OVARY
Estrogens
Major estrogens
Estradiol-17 beta (E2ß)
Estrone (E1)
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Estriol (E3)
Estradiol-17 alpha (E2a)
Structure (FIGURE 1)
Steroid hormones
18 carbons
MW for estrogens varies (272 to 288)
Site of production
Theca and granulosa cells in follicle
Actions
Estrus
Uterine contractions
Positive and negative feedback on
gonadotropins
Duct growth of mammary gland
Secondary sex characteristics
Growth of female reproductive tract
Calcium uptake and ossification of bones
Anabolic effects
Uses
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Induction of behavioral estrus
Induction of uterine contractions
Promotes growth in domestic animals
Birth control pills for humans
Progestins or Progestogens
Major progestogens
Progesterone (P4)
17a-Hydroxyprogesterone
20ß-dihydroprogesterone
Structure (FIGURE 1)
Steroid hormones
21 carbons
MW for progesterone - 314
Site of production
Luteal cells of corpus luteum
Actions
Maintenance of pregnancy
Inhibits uterine contractions
Inhibition of estrus
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Alveolar growth of mammary glands
Secondary sex characteristics
Growth of female reproductive tract
Stimulates endometrial secretion
Negative feedback on gonadotropins
Uses
Prevents abortion
Birth control pills
Synchronization of estrus and ovulation
Inhibin (Folliculostatin)
Structure
Glycoprotein hormone
MW - 32,000
Contains a and ß subunits
Site of production
Granulosa cells of follicle
Found in follicular fluid
Action
Selectively suppresses release of FSH from AP
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Relaxin
Structure
Polypeptide hormone
MW - 5,700 to 6,500
Site of production
Luteal cells of corpus luteum during pregnancy
Also produced by placenta and uterus
Actions
Acts on tissues after presensitization to estrogens
Relaxation of pelvic ligaments
Softens connective tissue in uterine muscles
Softens connective tissue of cervix at parturition
HORMONES FROM TESTIS
Androgens
Major androgens
Testosterone (T)
Androstenedione (A)
Dihydrotestosterone (DHT)
Structure (FIGURE 1)
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Steroid hormones
19 carbons
MW for testosterone - 288
Site of production
Leydig cells of testes
Actions
Spermatocytogenesis
Male sexual behavior (libido)
Secondary sex characteristics
Maintains accessory sex organs
Negative feedback on gonadotropins
anabolic effects
Uses
Prepare teaser animals for estrous detection
Improve performance in feedlot animals
Inhibin
Structure
Glycoprotein hormone
MW - 32,000
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Contains a and ß subunits
Site of production
Sertoli cells of testes
Function
Selectively suppresses release of FSH from AP
HORMONES FROM PLACENTA
Estrogens -- Same as for ovary
Progestins -- Same as for ovary
Relaxin -- Same as for ovary
Human chorionic gonadotropin (hCG)
Structure
Glycoprotein hormone
MW - 40,000
a and ß subunits with 237 amino acids
Site of production
Syncytiotrophoblastic cells of placenta
Actions
Converts CL of menstrual cycle to CL of pregnancy
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LH-like
Uses
Human pregnancy test kits
Induces ovulation
Source -- Urine of pregnant women
Treatment of cystic ovaries
Pregnant mare serum gonadotropin (PMSG or eCG)
Structure
Glycoprotein hormone
MW - 28,000
t½ - several days
Site of production
Endometrial cups of mare's placenta
Actions
Formation of accessory CL in mare during pregnancy
FSH-like in domestic animals other than mare
Use
Stimulates excessive follicular development in domestic animals
other than mare
Source -- Isolated from mare's serum
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Placental lactogen
Structure
Protein hormone
MW - 22,000 to 23,000
About 192 amino acids
Similar to prolactin and growth hormone
Highest concentrations
Last trimester of pregnancy
Higher concentrations in dairy than beef cows
Site of production
Placenta
Possible functions
Development of mammary gland for milk production
Regulation of maternal nutrients to fetus
Regulation of fetal growth
Protein B
Structure
Protein hormone
t½ - 7 days
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Site of production
Placenta of bovine and ovine
Function
Unknown
Possible use
Pregnancy test substance in cow and ewe (Detectable
22 days after conception in cow)
HORMONES FROM UTERUS
Relaxin
Same as for ovary
Prostaglandin (PG) F2_
Structure
Lipid hormone (Figure 2)
20 carbons
Arachidonic acid precursor
MW - 355
Source
Endometrial cells of uterus
Also produced by vesicular glands of male
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Actions
Regression of CL (luteolytic)
Causes constriction of blood vessels
Stimulates smooth muscle contraction for
sperm transport, ovum transport, parturition
and ovulation
Stimulates gonadotropin release
Practical uses
Synchronization of estrus and ovulation in
cows and mares
Luteolytic effect on CL
Abortion in feedlot heifers
Aids in treating uterine infections in dairy
cows
PGF2_ compounds commercially available
Lutalyse (Upjohn)
Estrumate (Haver-Lockhart)
Bovilene (Syntex)
Equimate (ICI United States)
Prostaglandin (PG) E2
Structure
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Lipid hormone
20 carbons
Arachidonic acid precursor
MW - 352
Source
Same as PGF2_
Actions
Smooth muscle stimulator
Effects on CL are opposite to that of PGF2_
Antiluteolytic action may be a factor in
maintenance of CL during pregnancy
Involved in process of ovulation
Involved in gamete transport
HORMONES FROM ADRENAL GLAND
Glucocorticoids
Cortisol
Structure
Steroid hormone
MW - 362
Site of production
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Adrenal cortex
Actions
Initiation of parturition
Synergizes with prolactin to
initiate milk synthesis
Reduces inflammation
OTHER HORMONES
Compudose
Implant
Contains estradiol-17ß
Increases weight gain and feed efficiency
For steers
Synovex-H
Implant of estradiol benzoate and testosterone
propionate
Increases weight gain and feed efficiency
For heifers
Synovex-S
Implant of estradiol benzoate and progesterone
Increases weight gain and feed efficiency
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For steers
STEER-oid
Generic equivalent implant to Synovex-S
Diethylstilbestrol
Commonly called DES (Figure 3)
No longer approved by FDA
Anabolic, promotes nitrogen retention
Increases weight gain and feed efficiency
Ralgro
Zeranol (Figure 3)
Plant extract with estrogen activity
Binds to estradiol receptor
Increases weight gain and feed efficiency
Norgestomet
Trade name is Syncro-Mate-B (Figure 3)
Progestin compound for synchronization of
estrus and ovulation in cows
Melengestrol Acetate
Progestin compound (Figure 3)
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For use in feedlot heifers to suppress estrus
Increases weight gain and feed efficiency
Regumate
Progestin compound (Altrenogest)
Suppresses estrus in mares
MECHANISM OF ACTION OF HORMONES
Gonadotropins (Figure 4)
Gonadotropic hormone (first messenger) binds to
membrane receptor
Receptor activates adenylate cyclase which converts
ATP to cyclic AMP (cAMP)
cAMP (second messenger) stimulates steroidproducing enzymes to produce estrogen, progestogen
or androgen
Hormone secreted into blood stream
Steroids (Figure 5)
Steroid hormone (S) passes through cell membrane
Steroid binds to a protein receptor (R) in cytoplasm
Steroid-receptor complex translocates to nucleus
Stimulates synthesis of mRNA
Messenger RNA translocates to cytoplasm
Synthesis of specific proteins
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New proteins responsible for action of steroid hormone
on target tissue
Back to ASFT 3401 Index
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