Reproductive pharmacology Flashcards
A mare is brought to stud. She has been cleared of veneral disease and you need to induce luteolysis. What drug class would you use?
- Prostaglandin F2a receptor agonist
- causes CL regression and luteolysis.
- This is given to synchronise oestrus.
Which of these drugs is the most appropriate to inject to induce ovulation in mares?
GnRH, eCG, hCG, LH
All these drugs would potentially induce ovulation, but hCG is the most appropriate
- GnRH is not the most appropriate as in mares the GnRH surge lasts for several days, so a GnRH implant would be required, not an injection
- eCG is not the most appropriate as it results in a higher FSH release than LH release
- hCG is the most appropriate as it results in the highest LH release, longer t1/2 than LH and cheaper
- LH is not the most appropriate as it has a very short half-life (0.5 hrs) and is expensive
Mechanism of action of GnRH agonist. Both naturally and pharmacologically
- Endrogenous GnRH released in PULSES from hypothalamus.
- Binds to specific receptors on anterior pit, releasing LH and FSH
- Pharmacologically given in pulsatile injections
- Continuous will cause downregulation and inhibit LH and FSH!
How do we administer GnRH agonist?
injectible continuous release implants
When would you use GnRH agonist
- To improve conception rates and improve synchronisation of oestrus/ ovulation
- To suppress repro function e.g. used in sexually mature male dogs and ferrets: deslorelin implant
Main effect of GnRH agonist pulsitile
• Stimulate short surge in FSH & LH and thus ovulation if there is a pre-ovulatory follicle. In mares the gonadotropin surge lasts for several days so use implants rather than single injection
warning when using GnRH and why
Pregnant women should not administer GnRH agonists. They can be absorbed through the skin
You are trying to synchronize a 3 year old dairy cow ready for AI using PGF2 alpha and GnRH. What is the correct order for the Ovsynch programme?
- 2nd dose of GnRH
- 1st GnRH dose
- AI
- Prostaglandins
- progesterone
2, 4, 1, 3
You are trying to synchronize a 3 year old dairy cow ready for AI using PGF2 alpha and GnRH. What happens on: Day 0 Day 7 Day 9 Day 10 for the Ovsynch programme?
On day zero = GnRH will be given to start off the development of a new follicular wave
Day 7 = Prostaglandins (PGF2 alpha) will cause the luteolysis of a CL
Day 9 = GnRH second dose to cause ovulation of the tertiary follicles
Day 10 = AI will be done once they have ovulated
Progesterone would not be used in Ovsynch but may be used to help synchronize a group of animals so they come into heat at the same time- this may be used in sheep flocks such as a progesterone sponge to prolong the current cycle and prevent ovulation temporarily
GnRH Vaccines Mechanism of action
- 2 doses of GnRH analogue protien conjugate (vaccine) given 2 weeks apart
- Induces antibodies against GnRH
Route of GnRH vaccine administration
Injectible
Main effects and example of use of GnRH vaccine
- Induces antibodies against GnRH and can thus be used to chemically castrate pigs (prevent boar taint)
WARNING: self-injection can disrupt reproductive function. Should not be administered by pregnant women
What are gonadotropins?
How do we administer
Anterior Pituitary Hormones
1. Glycoproteins = peptide and CHOs
Administer: Injection
2. They are LH/ FSH receptor agonists - stimulating the release of sex steroid hormones from the testis adn ovary
How resistant to breakdown are gonodotropins? and what are the half lives of the respective hormones?
- More resistant to breakdown than peptides/proteins
- The more CHO in the structure, the more resistant to breakdown by proteases and thus longer
Half life:
(LH - 0.5 hrs)
(FSH - 1 hr)
hCG = 8 hrs
eCG = 25 hrs
List the gonadotropings
PMSG, eCG, hCG
Main effects of eCG/ PMSG
Where produced
- Produced from the endometrial cups of pregnant mare 40 – 120d pregnancy. 2. Mostly FSH activity but some LH. Longer T1/2 than FSH and cheaper.
- promote recruitment of follicles and can be used for superovulation programmes
HCG main effects in males and females
- HCG in the female can be used to promote maturation of the follicle, ovulation & the formation of the CL.
- In the male it stimulates the production of testosterone. And can therefore be used to determine whether testicular tissue is present e.g. in cryptorchid animals (rig test).
WARNINGS og HCG and eCG
eCG have teratogenic effects – should NOT be handled by women who could be pregnant and are exogenous proteins for species other than humans or horses and can therefore promote an antigen – antibody reaction
List the Gonadal steroid receptor agonists and antagonists
- Oestrogen receptor agonist estriol
- Progestogen receptor agonist and antagonist (Aglepristone )
- Androgens & anti-androgens
Name the only licenced oestrogen receptor agonist
ESTRIOL
Where is endrogenous oestrogen released. Where does it bind
Endogenous hormone is released from the ovarian follicular cells, the placenta and to a lesser degree the adrenal cortex. It binds to specific receptors which are largely found in the brain, uterus & mammary gland.