Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

reproduction > GnRH and GnRH Analogues > Flashcards

GnRH and GnRH Analogues Flashcards

1
Q

What is GnRH?

A

-master controller of reproduction
-characterised in 1971
-GnRH coding sequence is found on chromosome 8
-23 isoforms in vertebrates , commonly GnRH I and GnRH II

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are roles of GnRH?

A

-neuroendocrine : HPG
-paracrine ( placenta/gonads)
-autocrine (prostate/ breast cancer)
-neurotransmitter (bc it is released from hypothalamus but acts in the anterior pituitary regions of the brain)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is GnRH structure?

A

-10 amino acid glycoproteins with alpha and beta chain.
-alpha chain identical in both FSH and LH but variation in beta chain and this confers unique properties.
-Pre-pro hormone
-Cleavage steps = mature GnRH and GAP
-GAP peptide - co secreted with GnRH , unknown function.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Where do the GnRH neurons originate?

A

-they originate in the olfactory neurone (outside CNS) and during embryonic development they migrate to the hypothalamus via the olfactory bulb.
- they are produced upstream of the hypothealamus
-neurones respond to genetic cues and genes which regulates migration pattern.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What causes hypogonadotrophic hypogonadism(HH)?

A

when the migration process goes wrong due to mutation in genes like KAL1 gene (Kallaman syndrome) which causes premature termination of migration

KAL1 is involved in controlling the migration process of GnRH neurone from olfactory neurones to the hypothalmus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what is Kallman syndrome?

A

-mutationin KAL-1 gene
- premature termination of migration
=> anosomia (inability to smell, as GnRH migrates from olfactory neurones)
=> hypogonadotropic hypogonadism

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

How is GnRH released?

A
  • processed and packaged into storage nucleus that are transported down the axons to the external zone of the median eminence
  • Rhythmic pulses - every 30-120 minutes (circhoral pulses)
  • GnRH pulse generator(collection of kisspeptin neurones in the arcute nucleus)
  • short half life and stimulates synthesis and secretion of FSH/LH
    -different frequency and amplitude which alter the pattern of FSH and LH secretion
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What gonadotrophin release does fast frequency of GnRH favour?

A

LH

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What gonadotrophin release does slow frequency of GnRH favour?

A

FSH

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what are two types of GnRH receptors?

A
  • G- protein coupled receptor
    -two variants type I and Type II GnRH
    -type I = full length has protein that can bind
  • type II is missense bc the actual protein to bind to the GnRH is not available.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is different about GnRH receptor?

A

no carboxyl terminal tail (COOH) on receptor
evolutionary benefit - makes it resistant to disensitisation.
COOH is normally phosphorylated to allow dissensitisation in other receptors but in this case no need.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How does GnRH regulate which gonadotrophin is produced (LH/FSH)?

A

=>rhythmic pulsatility
slow frequency or low amp GnRH pulse => increased FSH beta expressed
high frequency of GnRH pulse => increased LH beta transcription

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What determines unique biological actions of the gonadotrophins (FSH/LH)?

A

beta chain of the glycoprotein is unique to FSH and LH
alpha chain is identical in both FSH and LH

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What else does rhythm and pulsitility of GnRH determine?

A
  • dimerisation of subunits
    -glycolyation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

How does GnRH and gonadotrophin release differ in males and females due to different pulses?

A

males: constant GnRH pulses , every 2 hours but amplitude is variable in LH pulses and testosterone.

females: higher frequency GnRH pulse (every 30 mins)= favours LH secretion
lower frequency and amplitude (every 90-120 mins) = favours FSH synthesis and secretion.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What mechanism provides evidence for how GnRH differently regulates LH and FSH?

A

=> ERK signalling pathway in the pituitary
- ERK is required for fertility in females but not in males
- major mediator of GnRH dependent pathway

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What experiment provides evidence for ERK 1/2 being important in producing LH so important in menstrual cycle

A
  • saline in cervix epithelial cells in control
  • pituitary specific deletion of ERK1/2 to investigate reproductive consequence in male and female mice, corpus luteum was found.
  • controlled mice consistent pattern in epithelial cell count in MC whereas in DKO mouse theres a decreased epithelium cells and no corpus luteum to suggest MC.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What did ERK 1/2 pathway experiment conclude about LH?

A

deletion mutation in ERK1/2 caused decreased expression of LH beta
ERK activation essential for LHb transcription and translation suggesting LH is very much GnRH driven compared to FSH as no LH was sen in DKO mouse whereas some FSH still seen.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

How did this experiment lead to ERK mechanism pathway of GnRH?

A

GnRHR - GaS and Gaq/11 coupled binding activates PKA (via GaS) or PKC (via Gaq) which diverge to activate ERK1/2 which causes up regulation of Egr1 which binds to promoter of LH beta increasing production.
so in DKO mouse eliminating ERK1/2 causes down regulation of LH beta.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

what is the current GnRH receptor signalling pathway when there is a high GnRH pulse favouring LH production?

A

GnRH binds to GnRHR which is Gaq which activates PLC beta - activates PKC - activates MEK 1/2 - activates ERK 1/2 which increases ICER in FSH and Egr in LH

=> LH: has a secondary pathway:
GnRH binds to GnRHR which is Gaq coupled this binding activates PLC beta which activates two pathways - the IP3 -calmodulin-?

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

How does Egr promote LH production?

A

Binds to LH promoter increasing LH beta

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

How does ICER regulate FSH and promote LH production?

A

inhibits FSH transcription
CREB is required to bind to promoter for FSH transcription
ICER binds to promoter to inhibit CREB binding

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

How does low GnRH pulse favour FSH?

A

LH: too little GnRH not enough Egr1 produced so no LH transcribed
FSH: not enough GnRH to produce enough ICER so CREB can bind to promoter (not inhibited) causing up regulation of FSH.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

How do GnRH pulse change frequency during menstrual cycle alternating the release of FSH and LH?

A
  1. early follicular phase pulses are slow every (90 - 120 mins)
  2. mid - late Follicular phase pulse frequency increases every hour - LH
  3. After ovulation pulses slow (every 3- 5 hrs) - FSH
  4. end of luteal phase GnRH pulse secretion is higher than early follicular phase but still slow enough to release FSH preparing for the start of a new cycle.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What is gonadal feedback in males?

A

LH- testosterone from leydig cells reduces LH secretion
FSH- inhibin decreases secretion and activin increases secretion.

26
Q

What is gonadal feedback in females?

A

Oestrogen and progesterone negative feedback on the pituitary and hypothalamus but when high levels of E2 is sustained (48hrs) switches to positive feedback during ovulation.

27
Q

where is the site of steroid feedback?

A

either in pituitary or hypothalamus:
-oestrogen and progesterone receptors on anterior pituitary and hypothalamus
-inhibin receptors found only in pituitary

28
Q

How does steroid feedback occur both directly and indirectly?

A

-anterior pituitary by direct regulation of GnRH receptors
- In hypothalamus by directly affecting GnRH neurones or indirectly by changing activity of other neural system that influence GnRH release.

29
Q

Evidence for site of sterioid feedback to be anterior pituitary using Rhesus monkeys?

A

-lesion in hypothalamus(to decrease GnRH) and removed ovaries (Ovx)
- give exogenous GnRH this increased LH/FSH release negatively feedbacking to the anterior pituitary
- inject E2 which also negatively fed back to the anterior pituitary decreasing FSH/LH
- also injected alot E2 which caused positive feedback
=>this shows the role of anterior pituitary involvement exerting both positive and negative feedback

30
Q

What is the mechanism of positive feedback in pituitary?

A

-E2 induces and maintains GnRHR by increasing GnRHR mRNA in pre-ovulatory phase
- E2 sentisises ‘self- priming’ effect ie. enhances interaction between GnRH and GnRHR

31
Q

what is the mechanism of negative feedback in pituitary?

A

E2 and inhibin may affect stability of GnRHR
Progesterone decreases GnRHR mRNA also evidence of P4 response element in GnRHR gene

32
Q

Evidence of hypothalamus being the site of feedback - Dolly the sheep

A
  • OVx and inject large bolus E2
  • normally use LH as a proxy bc its difficult to get sample from the hypophyseal circulation but scientists were skilled enough to get blood sample directly from the portal blood in hypothalamus
    => in response to injecting a large bolus of oestrogen showed increased frequency of GnRH in hypothalamus.
33
Q

GnRH neurones can only be involved in negative feedback because…

A

GnRH neurones only express ER beta
need ER alpha for positive feedback and positive feedback is crucial in reproduction (ovulation)
so E2 must act on other afferents that express ER alpha that project into GnRH neurones.
This is indirect stimulation and include neuronal inputs such as kisspeptin and GABAnergic neurones.

34
Q

Which neuronal inputs express ER alpha for positive feedback?

A
  • kisspeptin
  • GABAnergic
35
Q

What shuts down FSH and LH?

A
  • continuous release
  • continuous low dose/ single high dose
  • this leads to down regulation of gonadotrophin secretion, important when gonadotrophin inhibition required
    =>pulsatile release upregulates
36
Q

How can native GnRH vs GnRH analogues be used to upregulate or down regulate HPG axis?

A
  • native GnRH is exactly the same structure as GnRH produced in the hypothalamus and bind to GnRHR to upregulate HPG axis
  • GnRH agonist is slightly different structure but initially upregulates but then continuous release of gonadotrophins switches the HPG axis off.
    -GnRH antagonist binds and blocks the gonadotrophins binding inhibiting function and shutting down the HPG axis.
37
Q

What is native GnRH?

A
  • synthetic GnRH which has the same protein structure as natural GnRH unlike agonists which are slightly different.
38
Q

Why do we use GnRH analogues?

A
  1. GnRH has a short half life 2-4 mins
  2. to increase potency and duration of GnRH - analogues created = agonist or antagonists
  3. manipulate the HPG axis in clinical practice - eg. IVF you want to increase FSH for a while to enable follicle maturation.
39
Q

How is the GnRH structure manipulated to make analogues?

A
  • substitution of Gly by D- amino acids - for stability and enhanced activity
  • Replacement of Gly - NH2 ethylamide binding to pro (pos 9/10)- to avoid proteolytic cleavage
40
Q

What is the structure of GnRH analogue and function of different amino acids?

A
  • horse shoe
  • 1-4 are crucial in receptor binding and activation of GnRH, 9-10 are also important in receptor binding , greatest variation amongst species in AA 8 arginine as this is determines binding site of ligand.
  • 1-4 and 9-10 AAs are conserved in all species but variation in AAs 5- 9, mostly in AA 8.
  • 5 - 7 are variable to manipulate antagonist structures so they are potent , specially glycine which is the 6 amino acid .
    Glycine -> d amino acid to increase stability and enhance activity
41
Q

why is the 6th AA (Gly) substituted with D amino acid?

A
  • natural form is L amino acids
  • D amino acid is stereoisomer which is used to manipulate GnRH structure to make analogues to enhance activity and stability.
42
Q

What does the addition of the ethylamide(Et) group in analogues help?

A
  • avoids proteolytic cleavage, injecting exogenously has that risk of breaking down and digestion
43
Q

What are examples of GnRH agonists?

A
  • Lupron (TAP) - GLY replaced with LEU makes it x10 potent.
    -Buserelin (hoescht) - put NEt group on 9 and 10 and GLY replaced with amino acid SER makes it x100 potent and used in IVF.
44
Q

What is the history of GnRH antagonist?

A
  • took 30 yrs
    -1st gen replaced HIS and TRP at position 2 & 3 but low suppressive activity
  • 2nd gen potency increased by D-aa substitution in position 6 but anaphylaxis by histamine release
    3rd gen replaced D rg by D - ureidoalkayl aa
45
Q

What are the mechanisms of action of GnRH?

A
  1. GnRH binds to receptor
  2. activation of signalling
  3. stimulation of gonadotrophin synthesis and secretion
  4. dissociation of GnRH from GnRHR
  5. GnRH responsive to next GnRH pulse
46
Q

What are the mechanisms of action of GnRH agonist?

A
  1. Agonist binds to GnRHR
  2. activation of signalling
  3. stimulation of gonadotropin
  4. desensitisation of GnRHR so continuous release of gonadotropin
  5. GnRHR non - responsive to GnRH
47
Q

What are the mechanisms of action of GnRH antagonist?

A
  1. Antagonist binds to receptor
  2. blockage of receptor
  3. No downstream effects
48
Q

What is the clinical use of native GnRH?

A

used as a diagnostic test :
to identify hypogonadotrophic hypogonadism defined as impaired gonadal function with resultant decreased sex steroid (primary and secondary hypogonadism)
- treat patients with delayed puberty (14 y/o boys with testicular volume and girls with no menarche at 15- 18 and no breast till 13)

49
Q

What is the clinical test for hypogonadism?

A

Test:
GnRH is administered intravenously or subcutaneously and plasma LH and FSH is measured at 0, 15, 30, 45 and 60 minutes.

50
Q

How does primary and secondary gonadism arise?

A

primary = arises from gonadal failure
-> gonads produce low levels of oestrogen/testosterone negative feedback increases LH and FSH levels but still low levels of oestrogen.
Therefore individuals with primary hypogonadism present with low levels of gonadal steroids and NORMAL TO HIGH levels of FSH/LH.

secondary = arises from abnormalities of hypo- pituitary axis
-> lower levels of FSH and LH so less acts on gonads and negative feedback should cause increased release of GnRH and FSH/LH but abnormalities means low levels and hypogonadism
Therefore individuals with secondary hypogonadism present with low levels of gonadal steroids and LOW levels of FSH/LH.

so when diagnosing LH and FSH levels are measured in regular intervals to see if its higher than normal = primary hypogonadism
If levels are low = secondary hypogonadism - (pituitary tumour could be a cause)

51
Q

What is hCG used for in IVF?

A
  • for final maturation
52
Q

what are GnRH agonists used for in IVF and major benefits?

A

GnRH agonist + gonadotrophin used for follicle growth stimulation in IVF
-improved follicular recruitment => larger no. oocytes recovered (not in all patients)
-prevent prmature LH surge -> lower cancellation rate
- improvement in routine organisation

53
Q

GnRH agonists and breast cancer?

A
  • premenopausal women -> chemical castration (reduce oestrogen output) bc agonist enables shut down of HPG reducing oestrogen levels - cancer is associated to excess levels of oestrogen.
  • GnRHR present in breast cancer tissue (50-60%) so agonist can bind and have direct anti-proliferative effect.
54
Q

GnRH agonist and prostate cancer

A
  • 80% of prostate cancers are androgen dependent
  • GnRH agonist - desensitisation/HPG shuts down - decreased testosterone from testis
  • ‘flare-effect’ bc agonists initially give micro surge of T, LH , FSH before HPG shuts down
    -Agonist co- administered with anti- androgen drugs
55
Q

GnRH agonists and fertility preservation

A
  • many women exprerience premature ovarian failure (POF) due to follicular damage, bc chemotherapeutic agents directly attack DNA dividing and dormant germ cells
  • to preserve fertility either freeze embryos or oocyte after IVF and before chemotherapy or freeze ovarian tissue f(cryopreserve)
  • GnRH agonist can be a co- therapy to minimise gonadal damage ( agonist shuts down hpg axis, so less stimulation of oocytes) before chemotherapy
56
Q

Evidence : mice study to show GnRH agonist and minimised gonadal damage

A

-two groups
- control : not administered GnRH agonist before chemo
- participants : administered agonists before chemo
Results: controlled mice had alot of follicular damage and resulted in POF and in agonist group less damage and retained ovarian function.

57
Q

Limitations of GnRH agonists

A
  • temporary treatment, symptoms can return
  • side effects - pseudo menopasue in women
  • reduced libido, erectile function
  • extra pituitary sites of action
  • flare effect
  • chronic treatment , over 6 months - risk of oestroporesis bc oestrogen is used in maintaining bone density.
58
Q

What are advantages of GnRH antagonist over agonist in prostate cancer?

A
  • no ‘flare’ or micro surges
  • reduces testosterone to castrate levels by day 3
  • rapid reversal
  • shorter treatment regime compared to 7-10 days for pituitary down regulation with agonist
  • dose dependent : partial pituitary - gonadal inhibition , can adjust level of hypogonadism as desired.
59
Q

What are examples of antagonists?

A
  • 1st antagonist Abarelix withdrawn due to systemic allergic reaction
  • Degarelix => rapid and sustained reduction in testo and PSA routinely used now in advanced prostate cancer.
60
Q

What are disadvantages of GnRH antagonists?

A
  • limited licenses available for wider use
  • more expensive than agonists
  • need higher dose than agonist 100mg/month versus 3-5 mg
  • competitive inhibitor therefore less effective over time.
61
Q

Q: A prostate cancer patient is administered a treatment regimen containing a combination of Lupron (GnRH analogue) and Flutamide (androgen receptor agonist).
(a) what class of GnRH analogues does Lupron belong to and what is it mechanism action?
(a) lupron belongs to the agonist group of GnRH analogues
1. bind to GnRH receptor
2. activation of signaling
3. stimulation of gonadotropin synthesis and secretion
4. desnsitisation of GnRHR causes GnRH non-responsive to GnRH - reducing testosterone levels

(b) why was flutamide prescribed?
When androgen binds it sends negative feedback to the HPG causing less LH release from the pituitary and less acting on leydig cells so less testosterone released

80% of prostate cancer is androgen dependent so reducing testosterone levels can reduce prostate cancer.

A

(a) what class of GnRH analogues does Lupron belong to and what is it mechanism action?
(a) lupron belongs to the agonist group of GnRH analogues
1. bind to GnRH receptor
2. activation of signaling
3. stimulation of gonadotropin synthesis and secretion
4. desnsitisation of GnRHR causes GnRH non-responsive to GnRH - reducing testosterone levels

(b) why was flutamide prescribed?
When androgen binds it sends negative feedback to the HPG causing less LH release from the pituitary and less acting on leydig cells so less testosterone released

80% of prostate cancer is androgen dependent so reducing testosterone levels can reduce prostate cancer.

62
Q

How do steroids feedback to the GnRH?

A

In the hypothalamus they release less GnRH
In the pituitary they cause desensitised GnRH receptors

reproduction (29 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions