Pharmacological control of reproduction Flashcards
Label the hormonal control of reproduction in the female
Describe the hormonal regulation of the oestrous cycle in females
Hypothalamus releases Gonadotropin-Releasing Hormone (GnRH), which stimulates the anterior pituitary.
The anterior pituitary secretes Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH).
FSH stimulates follicular development in the ovary, leading to the release of oestrogen from the follicle.
Oestrogen acts on target tissues to induce behavioural and physiological changes for reproduction.
The growing follicle also secretes activin (enhancing FSH release) and inhibin (inhibiting FSH release).
A surge in LH triggers ovulation, forming the corpus luteum from the ruptured follicle.
The corpus luteum secretes progesterone, preparing the body for pregnancy and inhibiting further ovulation.
If no pregnancy occurs, the uterus releases prostaglandin, causing luteolysis (regression of the corpus luteum), lowering progesterone, and allowing the cycle to restart.
How can the female reproductive cycle be halted?
Give progesterone or oestrogen/testosterone (androgens) => negative feedback on hypothalamus => decreased GnRH production
What is the risk of controlling the reproductive cycle using progesterone or androgens in females?
Progesterone
- mammary enlargement and possibility of tumours
- increased risk of pyometra
Testosterone
- clitoral enlargement
Oestrogen
- cause bone marrow suppression
Label the hormonal reproductive control in males
What is the consequence of giving testosterone or progesterone in males?
-ve feedback on hypothalamus => decreased GnRH => decreased FSH and LH => gonads are not stimulated, no stimulation of spermatogenesis => tiny testicles, poor sperm quality and decreased sperm production, possible behavioural changes (cycle can be blocked in entire males to change behaviour by lowering testosterone e.g., if aggressive)
How can benign peri-anal adenoma in males be treated?
Adenomas are stimulated by testosterone
By giving progesterone => -ve feedback on hypothalamus => decreased GnRH etc => decreased testosterone production => decreased size of adenoma
How do GnRH agonists work?
Cause an initial stimulation => followed by receptor down-regulation => act as a GnRH antagonists => decreasing testosterone and sex drive
Why does giving GnRH, FSH or LH have a limited impact on improving fertility?
because we cannot mimic the way in which they are released naturally (where the amplitude and pulse frequency of concentration is important for the biological effect)
What is the use of exogenous GnRH and hCG (LH-like activity) in males?
Used to confirm the presence of functional testicular tissue - if testosterone increases after exogenous hormone = functional testicular tissue present
Describe the hormonal regulation of spermatogenesis in male animals.
Hypothalamus releases Gonadotropin-Releasing Hormone (GnRH), stimulating the anterior pituitary.
The anterior pituitary secretes Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH).
LH stimulates Leydig cells in the testes to produce testosterone, which acts on target tissues to support male reproductive function.
FSH acts on Sertoli cells, promoting spermatogenesis and the production of androgen-binding protein (ABP), which helps maintain high testosterone levels in the testes.
Sertoli cells also produce oestrogen, inhibin, and activin:
- Activin enhances FSH release.
- Inhibin inhibits FSH secretion, regulating sperm production.
Testosterone and oestrogen exert negative feedback on the hypothalamus and anterior pituitary, regulating hormone levels and preventing excessive sperm production.
In what ways can we pharmacologically control reproduction in females?
Why might we stimulate oestrus/ovulation?
For optimal/controlled mating:
- Synchronisation of a group of animals
- Induction of ovulation
- Hasten return of cyclicty (i.e. after parturition, season, lactation)
Why might we want to suppress oestrus/ovulation?
prevent breeding
How is oestrus/ovulation controlled?
Influencing photoperiod or its control (season)
Mimicking release of gonadotrophins for stimulatory or down-regulation purposes
Lengthening or mimicking the luteal phase
Blocking progesterone
Shortening the luteal phase (PGF2A or Prolactin inhibitor) - enables animal to come back into follicular phase
Describe the control of oestrus and ovulation in sheep
Stimulate onset of cyclicity earlier in breeding season:
- Melatonin
- Progestogen sponges for ~14 days in combination with ECG/GnRH
- Ram effect - ram induces female into oestrus earlier
Synchronisation of breeding for management purposes
How does a progesterone sponge work?
The sponge releases progesterone, mimicking the luteal phase and preventing ovulation.
After several days (commonly 12–14 days), the sponge is removed, causing a drop in progesterone.
This triggers the animal to come into oestrus (heat) within a few days, allowing for timed breeding or artificial insemination.
Describe control of oestrus and ovulation in pigs
Aid oestrus detection / management of mating
Multiple protocols e.g.
- Ovsynch (with or without P4)
- Progestogen plus PGF
May with fixed-time AI
Describe the control of oestrus and ovulation in cattle
Synchronisation of a group of sows or gilts that enables batch farrowing
- Progestogen (oral) for 14-18 days with or without ECG just before P4 removal
Limited hormonal use after weaning
Two doses of PGF ineffective as CL only responsive d11-16
What are the different hormonal control protocols in cattle?
- P4 for >7 days plus PGF
Followed by fixed-timed AI - prostaglandin => GnRH => prostaglandin => AI (Ovsynch)
- GnRH => progesterone device => Prostaglandin => GnRH => AI
Describe the control of oestrus and ovulation in horses
Suppression of oestrus to enable training and performance
- Repeated treatment of progestogen for 10-15 days
Stimulate onset of cyclicity in early breeding season
- Daylight
- Oral progestogen for ~10 days
Management of AI/mating
- Progestogen
- PGF if active CL is present
- Hasten ovulation with HCG/GnRH
Describe the control of oestrus and ovulation in dogs
Prevention of oestrus
Suppression of oestrus
- Progestogen depots for 6+ months (increased risk of pyometra if started in pro-oestrus or oestrus)
- GnRH agonist implant (takes time to act)
- Testosterone in Greyhounds
Induction of oestrus (delayed puberty / prolonged lactational anoestrus)
- Prolactin inhibitors for 2-5 weeks
- GnRH agonist implant
- HCG to induce ovulation
Describe the control of oestrus and ovulation in cats
Prevention of oestrus
Suppression of oestrus
- GnRH agonist implant
-GnRH antagonists
- Melatonin implants
Induction of oestrus
- Exposure to daylight
- HCG to induce ovulation
How can anovulatory anoestrus be resolved?
Make sure animals in “breeding” window to maximise chance of timely conception
Stimulate follicular development to ensure ovulatory follicle is mature
Control time of ovulation to enable use of fixed time mating
Ensure the induced CL is functionally normal
Ovsynch (GnRH-PGF-GnRH)
Ovsynch plus progestogen
Progesterone plus eCG (and/or GnRH, PGF)
