Lecture 4 -- Pharmacology of the Reproductive Tract

These flashcards cover major concepts, drug classes, mechanisms of action, and effects related to pharmacology of the reproductive tract, aiding in exam preparation.

What type of hormone is GnRH?

Peptide hormones

Why is GnRH not given orally?

GnRH is a peptide hormones = Protein

• Once the drug is given orally and enter in the gut, it would be digested 

• Usually is given by injection

What is the effect of a single bolus injection of GnRH?

• Causes a short surge of LH from the anterior pituitary → When given to an animal with a dominant follicle (which has LH receptors), it induces ovulation

• Causes a short surge of FSH → Initiate a new follicular wave

Give one example of a GnRH agonist

Receptal

Why is short-acting GnRH ineffective in mares?

Preovulatory gonadotropin surge lasts several days → Single short dose is insufficient

What are the alternatives to induce ovulation in mares?

• Frequent doses used

• Deslorelin slow release implants e.g. ovuplant

What happens with persistent (continuous) GnRH stimulation?

Persistent stimulation causes GnRH receptor desensitization -> Receptors are internalised and down-regulated -> LH and FSH secretion decreases -> Sex hormone production is suppressed

What are the clinical uses of continuous GnRH administration?

• Chemical castration of ferrets

• Human IVF (suppression of endogenous hormone production)

Give one example of a continuous-dose GnRH product

Suprelorin (slow-release GnRH implant)

Give an example of a GnRH analogue–protein conjugate vaccine.

Improvac

What is the mechanism of action of Improvac?

Induces antibodies against GnRH → Block GnRH activity → Reduce LH and FSH → Reduce sex hormone

What are the clinical uses of Improvac?

Chemical castration of pigs

• Prevents sexual maturity

• Avoids unpleasant meat smell (boar taint)

What is the chemical nature of gonadotropins?

Glycoproteins (peptide + carbohydrate)

Do gonadotropins (FSH and LH) have a longer half-life than GnRH?

Yes

• Carbohydrate (CHO) content makes them more resistant to breakdown

• More CHO = Longer half-life

How do progestogen receptor agonists affect the oestrus cycle?

They prolong the luteal phase and inhibit oestrus.

How is cabergoline used in veterinary medicine?

As a prolactin inhibitor to manage false pregnancy.

What reproductive change does oxytocin induce?

It accelerates parturition but cannot induce it alone.

What are beta-adrenergic agonists used for in veterinary practice?

To relax smooth muscles and delay parturition.

What is a key adverse effect of glucocorticoid receptor agonists?

They can induce abortion and impair immune response.

What can lead to retained placenta in animals receiving glucocorticoids?

High incidence of retained placenta due to glucocorticoid effects.

Which hormone's secretion is inhibited by dopamine?

Prolactin secretion.

What is the impact of melatonin on seasonal breeding?

Melatonin affects GnRH pulse frequency, influencing oestrus cycles.

Explain the mechanism by which GnRH vaccines work.

They induce antibodies against GnRH, preventing its action.

In which species is Proligestone used for oestrus suppression?

Cats, dogs, and ferrets.

What happens during the initiation of parturition?

Foetal stress triggers a release of oxytocin and other hormones.

What is the role of FSH and LH in the female reproductive cycle?

They stimulate the growth of ovarian follicles and mediate ovulation.

Why is progesterone important in maintaining pregnancy?

It maintains the corpus luteum and inhibits GnRH release.

What is the effect of excess glucocorticoids on the reproductive system?

They can cause abortion and suppress reproduction.

Name a reproductive hormone that has both stimulant and inhibitory effects.

Oestrogen, as it affects both LH and FSH.

What is the consequence of administering prostaglandin receptor agonists to early pregnant animals?

It can terminate pregnancy by inducing luteolysis.

What effects does testosterone have on females?

Substrate for oestradiol synthesis and potential for abnormal masculinisation.

What is the effect of administering a bolus of GnRH?

It causes a sharp increase in LH secretion.

Describe the role of glucocorticoids in stress response.

They mimic cortisol, affecting metabolism and immune response.

What is the main function of prolactin in the female?

It is involved in lactation and reproductive behavior.

What is one use of melatonin supplements in dogs?

To manage seasonal breeding rhythm.

What secondary effects are observed from long-term use of anabolic steroids?

Potential suppression of natural testosterone production.

What is a common method for administering progestogens?

Implants or injections, not orally.

Discuss the importance of receptor regulation in hormone therapy.

Receptor downregulation can lead to diminished drug effects.

How is the luteal phase manipulated in veterinary practice?

Through the administration of progesterone.

What is the pharmacological role of oxytocin?

Facilitates milk ejection and can aid in contractions during parturition.

When is the timing of GnRH agonist administration critical?

During mating to synchronize ovulation.

How does high oestrogen impact the reproductive tract?

It enhances blood flow, secretions, and prepares the genitalia.

What is an adverse effect of high doses of synthetic androgens?

They can lead to feminisation in males.

Describe the long-term effects of androgens on the female reproductive system.

Potential masculinisation and hormonal imbalance.

What is the purpose of using melatonin in sheep and goats?

To advance the breeding season based on light exposure.

Why is continuous administration of glucocorticoids contraindicated in pregnant animals?

Due to risk of abortion.

What can happen if oxytocin is administered outside of parturition situations?

It may cause complications and does not induce labor.