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Why do we need to be aware of the hormonal control of the estrus cycle when considering use of reproductive drugs?
many drugs are or mimic the hormones that regulate the estrus cycle. also, many reproductive drugs need to be administered during certain stages of the reproductive cycle to achieve the proper effect
Name the 2 main phases of the estrus cycle.
follicular phase and luteal phase
Briefly, what happens during the follicular phase?
a follicle (on the ovary), containing an ovum (egg, oocyte), matures and also produces estrogen.
What hormone does the hypothalamus release, which stimualtes the pituitary gland to produce FSH and LH?
GnRH - gonadotrophic releasing hormone.
What does FSH stimulate the ovary to do?
What do follicles contain?
eggs (ova, oocytes)
What hormone does follicular tissue produce? What does this hormone do?
estrogen - produces the behavioral and physical changes associated with estrus
When the follicle matures and ruptures, it releases its oocyte, and then changes into a what? (Under the influence of LH from the pituitary gland.) (This begins the luteal phase).
corpus luteum - CL
What is the main hormone produced by the corpus lutem (CL)?
progesterone - "the hormone of pregnancy"
What is "the hormone of pregnancy"?
In general, what does progesterone do?
gets the uterus ready to be pregnant. non-contracting, thickened uterine lining, increased secretions, etc. also provides negative feedback to the hypothalamus - inhibits release of GnRH, FSH, and LH, to prevent a new estrus cycle from starting up.
What happens to the corpus luteum of the animal does not get pregnant?
it degenerates, progesterone levels drop, removes negative feedback to the hypothalamus, GnRH is released, which causes FSH and LH to be released, which initiates a new estrus cycle.
What happens to the corpus luteum if the animal does get pregnant?
the CL stays throughout the pregnancy, providing progesterone to maintain the pregnancy.
How is parturition normally initiated at the end of pregnancy?
the fetus produces ACTH, which causes both the baby's and the mom's corticol levels to increase - this causes estrogen and prostaglandin levels to increase - this causes the uterus to become more prone to contraction, by increasing the number of oxytocin recptors ont he uterus. these prostaglandins also cause the lysis of the CL, which stops the production of progesterone
List the 5 main categories of reproductive drugs.
gonadotropin - releasing hormone (GnRH) and its synthetic analogs; gonadotropins; progestins, progestagens, and progestatinal hormones; estrogen; and prostaglandins
What is the main use now of GNRH (gonadotropin - releasing hormone) analogs?
lyse persistent ovarian follicles in cattle.
List 2 natural gonadotropins.
- FSH - follicle - stimulating hormone
- LH - luteinizing hormone
List 2 pharmaceutical sources of gonadotropins
- hCG - human chorionic gonadotropin
- eCG - equine chorionic gonadotropin
What are chorionic gonadotropins used for in veterinary medicine?
induce superovulation in food animals, induce estrus in dogs and cats, stimualte testes to descend in cryptorchids.
Name 2 drugs in the progestin category.
altrenogest - Regu-mate, medroxyprogesterone - Depo-Provera
List the main problems associated with progestin use.
infection, pyometra, cystic endometriosis, mammary hyperplasia, insulin antagonism.
List 2 estrogen type drugs.
- ECP - estradiol cypionate
- DES - diethylstilbestrol
What problems can estrogen administration cause?
- bone marrow suppression
What is "pyometra"? List some clinical signs associated with pyometra.
- infected uterus.
- PU/PD, lethargy, anorexia, may have vulvar discharge, high WBC count
List 2 prostaglandin type drugs.
- dinoprost tromethamine - Lutalyse
- cloprostanol - Estrumate
List the main problems associated with prostaglandin use. How should people protect themselves when handling these drugs?
- abortion, bronchoconstriction.
- wear latex gloves when handling.
- pregnant women and asthmatic should avoid altogether
For what purposes are reproductive durgs used in veterinary medicine?
control estrus cycling, delay foal heat, treat anestrus, maintain pregnancy, prevent pregnancy, terminate pregnancy, etc.
Why is it useful to get all of the cow in a herd to come into estrus at the same time?
artificial insemination, efficiency of caring for the mothers and calves, labor, more uniform calf crop
What is "foal heat"? Why is it useful to delay foal heat?
the first heat period after the mare give birth. delaying the first heat improves conception rates
What species is altrenogest - Regu-Mate used in? For what purposes?
horses. control estrus cyclying, delay foal heat, treat anestrus, maintain pregnancy.
Do people have to take any precautions when handling altrenogest - Regu-Mate? If so, what?
yes - altrenogest can be absorbed through the skin. waer latex gloves when handling. women who are pregnant, or people with certain reproductive problems or cancers, or certain blood vessels disorders, should avoid handling altrenogest
What is the best method of pet contraception?
surgery - spay and neuter
List 2 drugs that are used to prevent pregnancy, and the species that they are used in.
- megestrol acetate - Ovaban (dogs and cats)
- mibolerone - Cheque (dogs)
List the risks associated with us of megestrol acetate - Ovaban.
- mammary hyperplasia
- insulin antagonism
- if used in a pregnant animal, can masculinize female fetuses, delay parturition
Megestrol acetate - Ovaban was once used for a non-reproductive purpose - name it. Why is it not used for this purpse much any more?
behavior modification. too many risks, better drugs available.
What type of drugs is used to terminate pregnancy?
What prostaglandin drug is approved for termination of pregnancy in mares?
dinoprost tromethamine - Lutalyse
What side effects can prostaglandins cause in dogs?
- respiratory distress
- lasts about 20 minutes, can give atropine.
Is it possible for corticosteroids induce labor? Are corticosteroids reliable for this purpose?
What are the normal effects of naturally released oxytocin?
uterine contraction, milk let-down
What is oxytocin used for in clinical veterinary medicine?
treat uterine inertia. May be used after birth to help expel uterine contents and decrease hemorrhage
What is "uterine inertia"?
lack of uterine contraction during labor - due to exhaustion, anxiety, stress, etc.
What do "anabolic" and "catabolic" mean?
- anabolic - enhanced production of body tissues
- catabolic - wasting of body tissues
What are anabolic steroids used for in veterinary medicine?
enhance production of muscle and body tissue in debilitated patien. have been used to increase weight and muscling in cattle
List 3 anabolic steroids.
- stanozolol - Winstrol - V
What 2 drugs are used to treat "spay incontinence"?
- sometimes DES - diethylstilbestrol
What is a "mismate shot", and what drug is used for this purpose?
- a drug given to a bred dog to prevent pregnancy
- ECP - estradiol cypionate
Is this "mismate shot" recommended? Why or why not?
no - high incidence of pyometra
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