Reproductive pharmacology

Question 1

GnRH actions

Answer 1

Stimulatory action: released relatively infrequently, i.e. once per hour. Each episode of GnRH release stimulates LH release. Pulsatility is key. GnRH released in protal vessels, otherwises it gets chewed up too quickly in systemic circulation.

Synthetic GnRH: fertirelin, Gonadorelin

GnRH can also inhibit gondatrophin secretion. If GnRH is given/secreted too frequently, as infusion or implant, will get inhibitory action after a while. Initial flare effect is stimulatory. Eventually LH secretion is dampened and inhibits rest of reproductive axis.

Question 2

Structure of GnRH and relative potentcy of analogues

Answer 2

analogs: substitute position 6 (glycine) and 10 (glycine)

Buserelin: D-serine at 6, N-Et at 10–20x more potent than GnRH

Deslorelin: D-Trp at 6, N-Et at 10–144x more potent than GnRH

Increased potentcy and also increased half life than GnRH

nb: GnRH half life is around 4 minutes

Question 3

Uses for GnRH in vet practice

Answer 3

Drugs: burserelin (analog), Gonadorelin (synthetic GnRH), deslorelin (analog)

Single injection (positive stimulatory effect): IM–1) diagnostic test for whether reproductive axis is working; 2)promote ovulation; 3) increase conception rates; 4) follicular cysts in cattle and bitch; 5) stripping eggs in fish

Continous: (subcutaneous implant)– 1) contraception 2) induction of abortion 3) behaviour management (inhibit T-secretion) 4) hormone dependent tumours 5)postponement of puberty- i.e. animals not growing well

Pulsatile: (using pumps) for induction of reproductive function

Withdrawal periods: nil

Adverse reactions: very few, but failure to recover repro function; hypo-estrogenism

Benefit of using GnRH: small molecule, doesn’t stimulate immune response (cf. FSH and LH)

Question 4

Single injection of GnRH: promotion of ovulation and diagnostic test for repro function

Answer 4

Gonadorelin: promote ovulation

Diagnostic test for repro function: If pituitary problem, if you give GnRH, LH, Testosterone or estrogen will not increase. If gonadal problem, LH will increase, but testosterone/estrogen will not increase. (i.e. LH not translated into androgen increase).

Question 5

Single injection of GnRH: COD

Answer 5

Treatment of cystic ovary disease in cattle (COD): cattle in post-partum period; 30-60 days after calving; 5-30% of animals that don’t come back in season. Increases calving interval by 22-65 days

Reason: persistence of dominate follicle which hasn’t ovulated and is producing high estrogen– arrests next cycle and causes behavioral problems.

No CL, low progesterone levels. Progesterone causes formation of LH receptors on dominant follicle. If there are few LH receptors, it doesn’t respond appropriately to LH. Natural levels of LH aren’t high enough to elicit a response.

Treatment: Diagnosis of follicular cyst via rectal palpation. GnRH injection ruptures dominant follicle. CL forms for 7-9 days. Then give PGF2alpha (estrumate) injection. After 3-5 days, cow goes into oestrus.

Question 6

Use of a GnRH agonist to inhibit reproduction: continuous implant or infusion

Answer 6

Deslorelin implant: Supralorin 6 or Supralorin 12–fertility control

Pros: temporary (can be removed), no surgery required, safe (no scarring), alters undesirable behavior, rapid mass sterilization, facilitate healthy monitoring. Also, can treat benign prostatic hyperplasia (stimulated by androgens)

Can also use for tx for urinary incontinence.

nb: get initial flare-up of stimulation of repro axis

Question 7

Future: GnRH antagonists

Answer 7

used in human medicine, used to lower steroid levels in certain cancers.

Uses: contraceptive, abortifacient, control of some steroid dependent cancers

Advtanges: immediate, reversible, longer half lives (hours), no flare effect (because it’s blocking the receptor)

Disadvtanges: histamine reactions (older products), lowering of gonadal steroid concentrations.

Question 8

Use of gonadotrophins in veterinary practice (i.e. FSH and LH)

Answer 8

Leutinizing hormone: LH from anterior pituitary gland

Follicle stimulating hormone: FSH from anterior pituitary gland (extracts of pituitary gland: oLH, oFSH, pFSH)

Chorionic gonadotrophin: hCG- predisposition to act through LH. complex glycoprotein from urine of pregnant women

Serum gonadotrophin (eCG/PMSG): complex glycoprotein from mare’s serum- predominantly FSH effects

Chemistry:

Glycoproteins: alpha (common to LH and FSH) and B subunits- Beta are hormone and species specific)

Chorulon (hCG)

PG 600 (hCG and PMSG)

PMSG

Question 9

Examples of use of gonadotrophins

Answer 9

A) superovulation

b) advancement and synchronization of reproductive behaviour
c) induction of ovulation
d) enhance or test male fertility
e) diagnose cryptorchidism (or incomplete gonadectomy) and treat (in specific cases)

Question 10

Superovulation using gonadotrophins

Answer 10

Superovulation prior to embryo transfer in order to produce a lot of good embryos

FSH/PMSG stimulate primordial follicles to become antral and eventually dominant follicles–>fertilize–>embryo transfer

Potential protocol: Progesterone vaginal impant to inhibit reproductive axis–>dominant follicles can’t ovulate). After 8 days, start giving injections (oFSH need to give a lot of injections, if giving PMSG, fewer injections)–> remove progesterone implant around day 10 or 11. LH surge at day 13, AI around day 14 and collect embryos around day 19.

Question 11

Advancing estrous and synchronizing ovulation using gonadotrophins

Answer 11

FSH/PMSG given for:

Bitch: anestrus 5 days, hCG for surge

Sheep and goats: advance time of follicular growth and ovulation–synchronize with progestagens

Cattle: acylic

Give FSH/PMSG at end of luteal phase (i.e. when progesterone is decreasing).

Perhaps also give LH injection to promote ovulation

Question 12

Inducing ovulation using gonadotrophins

Answer 12

hCG given as a boost to endogenous LH

Question 13

Enhancing/testing male fertility using gonadotrophins

Answer 13

hCG stimulates production of testosterone from leydig cells (remember hCG acts through LH). hCG–>interstitial cells–>increase T–>increase libido and increase spermatogenesis in seminiferous tubules.

Question 14

Decting cryptorchidism/incomplete gonadal removal using gonadotrophins

Answer 14

nb: cryptorchid testes more likely to get sertoli cell tumours; also, cryptorchid testes still produce testosterone which can cause behavioral problems.

Measure T in serum. Give hCG, if there are no testes, there will be no increase in testosterone. If animal is cryptorchid, can measure increase in serum testosterone.

Administer as a single IM or IV injection

Mainly in horses and dogs

Ethical issues: inherited condition- in dog autosomal recessive gene

nb: can have temporary inguinal crytporchidism but could go on to breed. Testosterone can help testicular descent if testes are held quite low.

Question 15

Melatonin

Answer 15

melatonin is secreted in circadian rhythym. Melatonin is only released at night, therefore melatonin is low during the day and increased at night.

Sheep are short-day breeders, therefore can use melatonin to alter breeding in sheep. Melatonin acts on G-coupled receptor in the brain.

Melatonin secreted from pineal gland of sheep (at back of 3rd ventricle)

Question 16

Use of melatonin to time the breeding season

Answer 16

Melatonin (e..g regulin) as an implant.

Introduce regulin in april- high melatonin animal sees it as an ultra-short day–> gear up repro system. Breeding season can then start in June, rather than september.

takes about 40 days for melatonin to act

Ram effect: when you introduce strange ram and measure LH, ram goes in and through olfactory system–> increase LH pulse frequency–>ovulation.

nb: melatonin can also cause an increase in progeny: synchronize and cause a couple of DFs to ovulate–> greater incidence of twins.

Question 17

Steroid hormones: estrogens, progesterones, androgens

Answer 17

steroids have actions on many tissues and processes including: repro axis, uterus, mammary tissue, bone formation (tend to close epiphysis), lipoprotein metabolism, inflammation, CNS, growth

Question 18

Oestrogenic compounds

Answer 18

repro steroids are all formed from cholesterol

Steroidal oestrogens:

oestradiol and esters (better pharmacokinetics and longer half life)

Oestradiol benzoate(EB) (Mesalin)- given IM or SC- formulated in oil

Oestradial valerate (EV)

Oestradiol cypionate (EC)

Ethinylestradiol (oral bioavailability)

Estriol (Incurin)- natural estrogen used for incontinence in spayed bitches

Receptors for estrogens: ER alpha and ER beta- nuclear hormone receptors where they affect transcription of various genes.

Question 19

Pharmacology of Estrogens

Answer 19

EB,EV,EC: synthetic esters, absorbed and hydrolyzed in the body

All steroid hormones undergo rapid hepatic metabolism and urinary excretion (as sulphates or glucoronides)

Esters prolong half-life (EB/EV) to combat rapid metabolism and excretion

Ethinyl group: increases oral bioavailability

Rapidly absorbed from mucous membranes/GIT

Injections in oil or implants increase persistence (prolongs half life because they’re released slowly from oil)

Bound to plasma proteins (sex hormone binding globulin- amount of this protein can change i.e. insulin decreases amt of SHBG–> more steroid is free and able to act) and ethinylestrodiol is bound to albumin.

After administration (cows) of 17betaE, EB, EV, concentrations in plasma and milk are within physiological range.

Question 20

Uses of oestrogens in veterinary practice

Answer 20

Synchronization/induction of estrus and ovulation (also can do GnRH or LH)

Misalliance (EB): potential toxic effects- not strongly recommended for use for abortion because it’s negative effects. E stops transport of zygote down fallopian tube (need to give VERY early on);also makes uterus hostile environment for implantation. NB: can’t tell if bitch is pregnant for 28 days (measure relaxin)– may be aborting a pregnancy that’s not even there.

Urinary incontinent after spaying (estriol)

Chronic endometriosis (cow: low dose)- if used for acute, very bad news. Estrogens tend to absorb toxins. If you have a gram negative bacteria causing the endometriosis, releases toxins, E allows absorption of those toxins.

Anal adenomas, prostatic hyperplasia, libido (dog): Ethinylestradiol (under the cascade)- negative feedback actions–> lowers FSH, LH and androgens.

Question 21

Side effects of estrogens

Answer 21

thromboembolism

*Aplastic anemia (can be life threatening)- cats and dogs

Cystic endometrial hyperplasia (bitches)

Cystic ovaries (cattle and pigs)

Carcinogenic (e.g. diethylstilbestrol: prohibited in food producing animals)

Squamous metaplasia of prostate (dogs)

In pregnancy: abortion, congenital defects

in acute uterine infection, increase absorption of toxins

Question 22

Androgens: indications

Answer 22

Deficient libido

hormonal alopecias- certain androgens also can act on glucocorticoid receptors

reversal of feminisation (sertoli cell tumours)

Suppression of estrus in bitch (racing greyhounds)

Examples of androgens used in vet med: methyltestosterone e.g. Orandrone; mixed esters e.g. Durateston- long duration of activity

Side effects: aggression, impaired growth in young (by closing epiphyses), congenital defects, oedema (so not in animals with impaired kidneys/liver), virilisation in females

Question 23

Anti-androgens

Answer 23

in order to reduce potent androgens without effecting testosterone function–> no feminisation

Flutamide: non-steroidal androgen receptor antagonist- blocks effects of endogenous androgens

Finasteride: enzyme inhibitor; blocks 5 alpha reductase (T –> dihydro T (which is much more potent than testosterone).

uses: prostate hypertrophy or carcinoma

hyper sexuality

behavioral problems

Question 24

Progestagens-indications

Answer 24

synchronize/induce estrus and ovulation

prevention or suppression of estrus and ovulation

treatment of cystic ovaries

pseudopregnancy

oestrogen/androgen dependent tumours- using negative feedback

Aggression/behavioural problems

Miliary eczema (can act through glucorticoid receptors), eosinophilic granuloma (cats)

Prevention of abortion (cats and dogs): particularly those which don’t have sufficient progesterone through CL

Question 25

Pharmacology of progestagens

Answer 25

Rapid hepatic metabolism and urinary excretion- half life around 5 minutes

usually formulated as some kind of ester

slow metabolism with substitutions to A ring

Orally active with ethinyl group

Species differences in potency and efficacy

Question 26

Examples of progestagens in vet med

Answer 26

Medroxyprogesteron acetate: by injection, dogs and cats

Megestrol acetate: oral, dogs and cats

Proligestone: IM, dogs, cats, ferrets

Delmadinone acetate: SC or IM, dogs and cats

Flugestone acetate: intravaginal, sheep/goats

Altrenogest: oral, horses, pigs

Progesterone: intravaginal, cattle, sheep (CIDR) controlled internal drug release. INhibits repro axis and when it’s removed–> synchronization.

Question 27

Adverse effects of progesterones

Answer 27

cystic endometrial hyperplasia

pyometra

mammary hypertrophy

weight gain

diabetes mellitus

Contraindications (small animals): diabetes mellitus, liver disease, mammary tumours

Question 28

Progesterone receptor antagonists

Answer 28

Blocks receptor for progesterone.

Mifepriston (RU 486)- no vet license– morning after pill

Aglepristone (RU 534)- licensed for misalliance in bitch

Alizine

Misalliance: 2 injections, subcutaneous 24h apart, up to 45 days after mating.

P high for 60d in pseudopregnant animals as well as if pregnant.

Question 29

Prostaglandins

Answer 29

PGF2alpha causes regression of the CL (after refractory period)–> decrease in progesterone

PGF2alpha goes to ovary via special counter-current exchange–> causes regression of CL 1) animal will return to cycling or 2) if animal is pregnant, will lose pregnancy

Refractory period in cow, mare, ewe and dose is 5 days after ovulation. If you give before 5 days, no PGF2alpha receptors, no effect.

Pig refractory period=11 days

Bitch is unresponsive to PGF2alpha- need to give multiple injections- support for CL in bitch is due to trophic hormone (LH or Prl).

Question 30

Prostaglandins in vet practice- indications

Answer 30

synchronization of oestrus

prolonged disestrus in mare

luteal cysts in cow

pyometra (open)- if closed, can cause rupture- PGF2 alpha will cause contraction of uterus and expel contents.

Termination of pregnancy: Cows- before 150 days, sheep before 50 days, mares before endometrial cups (day 35), bitch after day 30 (repeated doses, not a good idea).

Induction of parturition in cows and pigs (incl. mummified fetus)- towards v. end of pregnancy i.e. overterm or dead fetus

Pseudopregnancy in goats

Question 31

Pharmacology of prostaglandins

Answer 31

very rapid metabolism- synthetics have a longer half life

compounds: synthetic: dinoprost; analogues (closprostenol, luprostiol)

Administration: single IM injection- be very careful as administer because it can cause bronchospasms and contractions of other muscles- can cause abortion in women

Side effects: smooth muscle constriction (bronchospasm); sweating/colic/vomiting/tachycardia; vasconstriction; severe cellulitis at injection site; miscarriage.

Question 32

Dopamine receptor agonists

Answer 32

Serotonin inhibits dopamine secretion. Dopamine inhibits Prl.

Prl responsible for: mammary development, milk production, support of canine and feline CL.

Dopamine receptor agonists: Bromocriptine (under cascade) –> terminate pregnancy of bitch (can get into brain and cause nausea/vomiting)

Cabergoline–> terminate pseudopregnancy

Metergoline (anti-serotonin action)–>suppress lactation.

CL in bitch supported by LH and Prl. Release of Prl is stimulated by TRH and inhibited by dopamine. D receptor will suppress Prl release and will withdraw support for canine/feline CL.

Question 33

Oxytocin

Answer 33

uterus contractions and milk let down

Myometrial stimulants: oxytocin

Nonapeptide, stored in posterior pituitary; ferguson reflex; estrogen induced receptors.

Metabolism is very rapid; half life is 1-5 minutes (alter NH2 or position 8)

Compounds: extracts of posterior pituitary (also contain vasopressin ADH); synthetic (non-contaminated)

Admin: IM or IV (S.c. may cause abscess)

Pulsatile vs. low-dose continuous

Examples: oxytocin S, carbetocin (much more active, less quickly metabolised).

Question 34

Indications of uterine stimulants: parturition

Answer 34

dystocia: no physical obstruction

postpartum hemorrhage: contractions clamp down on bleeding vessels

removal of retained placenta

uterine infection (open)

induce parturition- after a certain point in time

Initiation of milk ejection

OT needs OT receptors. only present in uterus at v. end of pregnancy (won’t cause abortion in mid-pregnancy). Estrogen causes OT receptor formation in myometrium and endometrium and mammary tissue. Estrogen rises at the end of pregnancy.

Question 35

Myometrial relaxants

Answer 35

Delay parturition

facilitate uterine manipulation

ringwomb in sheep

B2 adrenoceptor agonists: relax smoothe muscle and coordinate contractions

clenbuterol, vetrabutine

nb: handling and sotrage because they can cause contractions.

Question 36

Contraceptive methods in wild populations

Answer 36

contraceptive vaccines: GnRH vaccine, porcine zona pellucida vaccine

bird fertility control: nicarbazin, diazacon