16.8.3: Principles of contraception Flashcards
Which drugs can act at point 2 in this diagram?
Diagram = female
GnRH agonists
Effect of GnRH agonists
Depends on the time frame
Short term
* e.g. buserelin injection, deslorelin implant
* Causes stimulation of LH and FSH release
Long term
* Deslorelin (suprelorin) implant
* Causes initial stimulation and then receptor down-regulation (there is a block at the level of the pituitary, so there is then no stimulation of the ovary and testes)
What might we use long-acting GnRH implants (e.g. deslorelin; Brand name= Suprelorin) for?
- Control and fertility in male dogs
- Temporary suppression of oestrus in bitches
- Delaying puberty in bitches
- Treatment of anal adenomas (testosterone stimulates this)
GnRH agonist can be used to inhibit reproduction in males and females of aff species (dose-dependent).
What can deslorelin be used for?
Deslorelin = GnRH agonist
* Short-term: can be used to induce ovulation
* Long-term: can be used to inhibit reproduction/control behaviour
* Ferrets: can be used in the management of adrenal disease
Effects of progestogens
- Progestogens exert a powerful negative feedback effect upon the hypothalamus/pituitary
- Central sedative effects
- Closes cervix
- Stimulates endometrial proliferation
- Suppresses myometrial activity
- Mammary enlargment
Examples: proligestone, osaterone
Proligestone is a:
a) prolactin inhibitor
b) GnRH agonist
c) progestogen
d) prostaglandin
c) progestogen
Adverse effects of progestogens
- Increased appetite/weight gain
- Mammary enlargement ± benign nodules/neoplasia
- Risk of cystic endometrial hyperplasia
- Diabetogenic (insulin antagonism)
- Acromegaly
- Coat changes esp local reactions following SC injections
- Masculinised female pups and cryptorchic pups if given in pregnancy
- Suppression of spermatogenesis
Adverse effects are less in newer generation compounds. We are moving away from using progestogen now we have GnRH agonists like deslorelin.
How can we use progestogens to control oestrus?
If progestogens are given in anoestrus, the occurence of oestrus is prevented through negative feedback
How can we use progestogens for pseudopregnancy?
- Progestogens given as depot therapy e.g. proligestone, delmandinone
- Normally, a fall in progesterone stimulates a rise in prolactin which causes the pseudopregnancy
- When progestogens are given, they inhibit the release of prolactin from the pituitary gland, thereby preventing pseudopregnancy
What can we use progestogens for in males?
- Anything relates to high concentration of testosterone e.g, antisocial behaviour, prostate disease, anal adenoma
- Progestogens will result in reduction of FSH and LH secretion
- Lower LH -> Leydig cells affected -> lower androgens
- Lower FSH -> Sertoli cells affected -> reduced spermatogenesis
What are the possible adverse effects of oestrogens?
- Potentiate the effects of progesterone on the uterus -> pyometra
- Dose-related bone marrow suppression -> anaemia, thrombocytopaenia -> death
- Stimulate signs of oestrus
- Non-pruritic bilaterally symmetrical alopecia and hyperpigmentation
- If given during pregnancy, may cause abortion
Examples of oestrogens used in practice
- Oestradiol benzoate
- Estriol (Brand name= Incurin)
What can we use oestrogens for in practice?
- Oestrogens have a negative feedback effect but are predominantly used for their target tissue effects
- They cause oedema of the repro tract, pheromone producton, changes in function of the uterine tube and uterus (support sperm transport and the environment for fertilisation)
- Used for management of unwanted mating or incontinence
- Use carefully, at low doses or topically
How can oestrogens be used for unwanted mating?
- Licensed: oestradiol benzoate. Not currently on sale but still in some practices.
- This prevents implantation and/or interferes with the transport of zygotes
- Animals may continue to show signs of oestrus; if re-mated, unlikely to become pregnant
How can oestrogens be used to treat urinary incontinence?
- Oestrogens (e,g. estriol, brand name= Incurin) have a direct effect on the reproductive tract
- This increases urethral mucosal thickness
What effect do androgens have on males and what could they be used for?
- Androgens mimic the action of testosterone and so have a negative feedback effect
- This leads to less LH and FSH production -> less testosterone production and reduced spermatogenesis)
- This has an effect on target tissues (testicular atrophy) -> induce temporary infertility in males
- e.g. Durateston
What are the clinical uses of eCG in dogs?
There are none.
You’d imagine that it would mimic FSH and stimulate oestrus, but it doesn’t do this in practice.
What are the clinical uses of hCG in dogs?
- hCG = LH-like in activity
- Can use hCG to force a follicle, or follicular cyst, to ovulate if the animal is in oestrus; i.e. to hasten or force ovulation
- Can use hCG to stimulate a gonad if you are trying to work out if it is present. e.g. if ovary present -> oestrogen will rise; if testis present -> testosterone will rise)
Adverse effects of prostagladins
- Restlessness
- Hypersalivation
- Vomiting
- Abdominal pain
- Diarrhoea
True/false: we can use prostaglandins to induce oestrus in the dog.
False
* We can use prostaglandins to induce oestrus in the polyoestrus animal.
* The dog is monoestrus - if we try to use prostaglandin to unduce oestrus, we will just end up pushing her into anoestrus.
What effect do prostaglandins have on the CL in the bitch and queen? From when do they have this effect?
- Prostaglandins cause lysis of the CL but the early CL will usually not respond
- In the bitch and queen, the CL is autonomous for the first 15 days of the luteal phase
- Practically, prostaglandins are of little use before Day 20
How would you use prostaglandins to terminate a pregnancy?
- Use low doses 2x daily for 5-10 days
- Commence after day 20
- Termination occurs by resorption or abortion
The above protocol is for prostaglandins alone - we can use prostaglandins with prolactin inhibitors.