Exam 2

Question 1

Under high levels of ______ and low levels of ________ Krebs cycle will be inhibited

Answer 1

NADH; ATP

Question 2

Surgical methods, specifically surgical ablation, is a technique that affects hormone levels.
Provide an example of surgical ablation and its effect on hormone levels while including the concept of compensatory hypertrophy.

How would you confirm your example of surgical ablation.

Answer 2

• Surgical ablation if the removal of an organ. For example, orchidectomy is the removal of the male gonads. When one testes is removed, at first, there will not be a large negative feedback on the anterior pituitary and hypothalamus. They will continue to stimulate the production of testosterone until the one testis becomes enlarged and reaches homeostasis.
• Monitor changes in testosterone level within the blood

Question 3

Alloxan, also known as Streptozotocin (STZ), destroys ______ of pancreatic islets while cobalt chloride destroys _____ of pancreatic islets.

Answer 3

Beta
Alpha

Question 4

If action of a hormone is inhibited by actinomycin D, it can be implied that this hormone works through ______ process.

Answer 4

a transcriptional RNA synthesis - this hormone uses genomic effects via changing gene expression to carry out its function - most likely a steroid hormone or thyroid hormone
actinomycin D inhibits RNA production

Question 5

If action of a hormone is inhibited by puromycin and cycloheximide, it can be implied that this hormone works through _____ process.

Answer 5

a translational protein synthesis - this hormone uses genomic effects via changing protein synthesis to carry out its function - most likely a steroid hormone or thyroid hormone
puromycin and cycloheximide inhibit protein synthesis `

Question 6

Some drugs interfere with cell transport mechanism, thus inhibit protein hormone secretion. For example, colchicine destroys _______ and cytochalasin B destroys ___________.

Answer 6

Microtubles
Microfiliments

Question 7

In genetic engineering, the leptin receptors in POMC neurons can be excised using Cre-mediated tissue-specific knockout. Describe how Cre recombinase and Lox P are used to excise the leptin receptors.

Answer 7

Lox P sites flank the leptin receptor gene. In order to remove the leptin receptor gene only in the POMC neurons, the Cre gene will only be expressed in POMC neurons. When Cre recombinase is expressed in POMC neurons, it lines up with lox P sites and excises DNA sequence between two loxP sequences. As a result, the leptin receptors are not able to be made in POMC neurons only. Leptin receptors are normal in all other cells and tissues.

Question 8

A hormone uses cAMP as a second messenger as signal transduction mechanism to induce cellular responses.
Which enzyme is activated to produce cAMP? Briefly describe how you measure activity of this enzyme?

Answer 8

Adenylyl cyclase. Use enzyme assay, label ATP with radioisotope tritium [3H], trace label to cAMP to quantitate conversion of ATP to cAMP. If radioisotope labeled cAMP level is high, adenylyl cyclase enzyme activity is high.

Question 9

Can you measure cAMP level to indicate the activity of this enzyme? Why or why not?

Answer 9

No. Because cAMP level is also altered by phosphodiesterase activity, which is unrelated to cyclase activity and cAMP formation

Question 10

When discussing exogenous hormone production, specifically replacement, what are things that should be taken into consideration?

Answer 10

Not very specific or sophisticated - not replaced to specific cells or tissues or organs because the replaced hormone would reach all cells/tissues/organs.
Effect of hormone will regulate complete suite of hormone-dependent traits in vivo
Treatment with “standard” amount of hormone could have very different effects in different individuals
Need to manipulate animals within normal physiological range not to produce pharmacological (e.g. toxic) effects

Question 11

____________ is the increase in size of a cell, while _______ is the decrease in the size of a cell

Answer 11

Hypertrophic
Hypotrophic/ atrophic

Question 12

___________ is the increase in the number of cells present in the sample, while ___________ is the decrease in the number of cells present in the sample.

Answer 12

Hyperplasia
Hypoplasia

Question 13

Double-labeling immunohistochemistry is a type of Immunohistochemistry (IHC) in which two specific antibodies can detect and label two different receptors in one tissue.
Provide an example of a double-labeling immunohistochemistry experiment.
- describe the procedure

Answer 13

.
Two specific primary antibodies to detect and label estrogen receptor and progesterone receptor in one tissue.
-
Tissue to be examined is treated with a fixative, sectioned into thin slices. Primary antibody for estrogen receptor is added to the tissue; Excess primary antibody for estrogen receptor is rinsed from the tissue. Secondary antibody (for estrogen receptor’s primary antibody) conjugated to an enzyme or a fluorescent dye. Then, primary antibody for progesterone receptor is added to the tissue; Excess primary antibody for progesterone receptor is rinsed from the tissue. Secondary antibody (for progesterone receptor’s primary antibody) conjugated to another enzyme or another fluorescent dye.

Question 14

____________ method labels cells expressing mRNA of nucleic acid sequence.

Answer 14

In Situ Hybridization (ISH)

Question 15

Immunoblot/Western Blotting allows researchers to analyze the amount of ______.

Answer 15

protein

Question 16

A sample was injected with the radioisotope tritium [3H]-labeled thymidine (autoradiographic method) into the anterior pituitary of rats that had one testicle removed. Describe what the researchers should have observed.

Answer 16

In rats with a testicle removed, the autoradiographic results would have shown a silver color/grains showing mitotic division in the anterior pituitary gonadotrophs, due to reduced long-loop negative feedback → increased gonadotroph activity to synthesize and secrete gonadotropins, which leads to compensatory hypertrophy of the remaining testis.

Question 17

_____ measure levels of a hormone based on biological activity.

Answer 17

bioassay

Question 18

In radioimmunoassays (RIA), which is a type of ____________ inhibition assay, the ____________ hormone (Unknown - what you will measure) competes with ____________ hormone (*Hormone) for binding to antibody. The amount of each of these hormones is ________ proportional to each other.

Answer 18

Competitive
Unlabeled
Radiolabeled
Inversely

Question 19

Enzyme linked immunosorbent assays (ELISA) measures the amount of hormones _______ and also measures ________, not radioisotopes.

Answer 19

Directly
Absorbance

Question 20

You will compare insulin receptor number and affinity between a healthy person and a type 2 diabetic patient.
- Which assay would you use?
- What is your possible result? Explain your results

Answer 20

• Use radioreceptor assays (aka radioligand binding assay)
  It tests the physiological regulation of hormone receptor number or affinity.
• Chronic hyperinsulinemia: Chronic hyperinsulinemia as seen in type 2 diabetes mellitus patients reduce plasma membrane insulin receptor number (due to internalization and degradation of receptors in target cells) and reduce insulin receptor binding, therefore reduce responsiveness of target tissues to insulin.
  decrease number of insulin receptor – as condition 2 in (a)
  reduce insulin receptor binding affinity – as condition 1 in (b)

Question 21

Neurons that produce hormones are _______ cells. Whereas, hormones released by neurons are _______.

Answer 21

Neuroendocrine
Neurohormones

Question 22

Magnocellular neurons within the hypothalamus consist of cell bodies in ________ and ________. These neurons project into the _______ pituitary to release the neurohormones, _______ and _______, into the blood.

Answer 22

supraoptic nucleus (SON)
paraventricular nucleus (PVH)
Posterior
Vasopressin (AVP) or Antidiuretic Hormone (ADH)
Oxytocin (OXY)

Question 23

Parvicellular neurons within the hypothalamus have cell bodies located in the ________, _________, and ________ regions. These neurons release neuropeptides (releasing factors) into pituitary portal vessel to ________ pituitary.

Answer 23

periventricular (PeVH)
paraventricular nucleus (PVH)
arcuate nucleus (Arc)
anterior

Question 24

Hypothalamic projection neurons within the hypothalamus have cell bodies located in the ________, __________, and _________ regions. These neurons terminate at synapses on other neurons.

Answer 24

paraventricular nucleus (PVH)
arcuate nucleus (Arc)
lateral hypothalamic area (LHA)

Question 25

Innervation by __________nervous system stimulates pancreatic beta cells to _______ insulin before, during, and after a meal.

Answer 25

cholinergic/ parasympathetic release

Question 26

Innervation by __________nervous system to the pancreatic beta cells _______ insulin secretion as well as prevent glucose uptake by non-muscle cells.

Answer 26

Sympathetic Inhibits

Question 27

Provide an example of how the nervous system controls or modifies the function of endocrine glands?

Answer 27

- Three types of neural cells of the central nervous system regulate neurosecretion of tropic hormones or neurohormones. a. Neural cells at PVN and SON in the hypothalamus regulate posterior pituitary hormone release. b. tropic hormones (hormones 1 and 2 regulate endocrine gland secretion). - Sensory and autonomic nervous system of the peripheral nervous system regulate endocrine glands. c. Adrenal gland, pancreas, pineal glands (and many others) are regulated through direct innervation (noradrenergic and cholinergic neurotransmission) from autonomic (sympathetic and parasympathetic) nervous system.

Question 28

The pituitary gland gland is often referred to as the ______ ______, and it is located just below the _______. These two structures are connected by the _______ which contains nerve fibers and blood vessels (hypothalamic-pituitary portal system). Together, they make up the ________ unit.

Answer 28

Master gland Hypothalamus Infundibulum Hypothalamic-pituitary

Question 29

When describing the composition of the Hypothalamic-pituitary unit, the _______ lobe consists of Pars Distalis and Pars Tuberalis, the ______ lobe consists of the Pars Intermedia, and the _______ lobe consists of the Pars Nervosa.

Answer 29

Anterior Intermediate Posterior

Question 30

The posterior pituitary is an outgrowth of the hypothalamus which is derived from the ________ ________, whereas the anterior pituitary is derived from the _________ _________.

Answer 30

Neural ectoderm Oral ectoderm

Question 31

Hormones released from anterior pituitary are _________ unless directed to be released by the hypothalamus via ________ ________.

Answer 31

Dormant Releasing factors

Question 32

What is the main function of the Hypothalamic-pituitary unit?

Answer 32

Secretes a number of hormones Most of the hormones are released from the anterior pituitary Two protein hormones (oxytocin & vasopressin) are released from posterior pituitary

Question 33

What are the 6 major hormones released by the anterior pituitary?

Answer 33

FSH - follicle stimulating hormone LH - Luteinizing hormone TSH - Thyroid stimulating hormone ACTH - Adrenal corticotrophic hormone GH - Growth hormone PRL - prolactin

Question 34

Do hormone isoforms exists? If so, why?

Answer 34

Yes, this is due to differential splicing of mRNA, post-transcriptional, or post-translational modifications. Multiple hormones can be produced from one gene transcript.

Question 35

Describe the structure, metabolism, release, actions of growth hormone.

Answer 35

It is a protein that binds to a receptor on the cell membrane. The pulsatile patterns of release greatly increases during adolescence. Release is stimulated by GHRH and inhibited by Somatostatin (SST). GH stimulates body growth (both bone and tissue growth).

Question 36

What causes acromegaly? What results from it? What is a common metabolic defect of acromegaly patients?

Answer 36

Increased GH production After epiphyseal closure, increased GH production causes enlargement of hands/feet with thick toes and fingers; proliferation of connective tissue and interstitial fluid (thicken skin and facial features); enlarged viscera and organs (lung, liver, heart, kidney); changed metabolic rates; double vision; irregular periods; a release of breast milk; increased sweating Chronic overproduction of growth hormone (GH) often leads to insulin resistance, glucose intolerance and, ultimately, diabetes mellitus.

Question 37

What are the actions of prolactin?

Answer 37

Mammotropic Lactotropic Luteotropic

Question 38

The most common pituitary tumor is prolactinoma. Describe three physiological symptoms you might observe in patients with a prolactinoma (2) What method could confirm the presence of high level of prolactin? (3) Surgical removal of suspected prolactinoma. Which method could confirm prolactinoma?

Answer 38

1. (1) Mammotropic abnormal development of large mammary glands -> breast enlargement (2) Lactotropic excess production and discharge (spontaneous flow) of milk from breast (3) Luteotropic stimulate progesterone secretion from corpus luteum (negative feedback on hypothalamus and pituitary) -> absence of menstrual cycle and inhibition of ovulation - infertal 2. RIA or ELISA 3. Removed tumor tissue: western blot – high protein level of prolactin; IHC – show high immunohistochemical labeling for prolactin.

Question 39

_________ and __________ are two hormones released from the anterior pituitary that use a Tyrosine kinase associated receptor in their mechanism of action.

Answer 39

GH Prolactin

Question 40

Predict pattern of prolactin secretion of a woman who nurses her baby and a woman who does not during postpartum period. Provide a mechanistic explanation for the likely difference in prolactin levels between these two women.

Answer 40

Non breast-feeding mom: Prolactin level remains high for ~1 week post-partum (even in the absence of suckling). Non breast-feeding mom lacks neuroendocrine reflex stimulates PRL secretion. Breast-feeding mom: Prolactin level remains high for ~1 week post-partum. Then prolactin secretion would be stimulated by suckling. Breast-feeding mom receives suckling stimulus. Neural afferents from areolae area, inhibit dopaminergic neurons in the hypothalamus increase prolactin secretion.

Question 41

The cessation of menstrual cycles during lactation (lactation amenorrhea) is referred to as ‘nature’s own contraception’. Provide a hypothesis as to the possible mechanisms that mediate the inhibitory effects of nursing on menstrual cyclicity. Design an experiment that could be used to test your hypothesis in experimental animals.

Answer 41

-Hypothesis: High prolactin level during lactation leads to low level of gonadotropins, which has inhibitory effects on menstrual cyclicity. Mechanisms: Prolactin level remains high during lactation → high prolactin level has luteotropic effects → stimulates corpus luteum to produce high levels of progesterone → inhibits gonadotropins → low FSH/LH -------Low FSH → no ovarian follicular development occurs → nature’s own contraception -------Low LH and low E2 → need LH surge for ovulation and need E2 for proliferative phase of uterine cycle – no ovulation, no menstrual cyclicity -Administration of gonadotropins LH and FSH to lactating animals → induce menstrual cyclicity. Any methods that could reduce prolactin level or increase gonadotropins → induce menstrual cyclicity.

Question 42

Glycoproteins are a class of proteins that have carbohydrate groups attached to the polypeptide chain. The ____ chain is almost identical in all glycoproteins whereas the ____ chain has functional and immunological specificity.

Answer 42

ɑ Β

Question 43

Describe the role of LH and FSH in both males and females

Answer 43

MALES: LH binds to receptors on Leydig cells, stimulating synthesis and secretion of testosterone. FSH works on Sertoli cells to support sperm cell maturation in the seminiferous tubules. FSH enhances LH action by stimulating the synthesis of LH receptors on Leydig cells FEMALES: LH stimulates the production of estrogen and the LH surge causes ovulation of mature follicles FSH works on Granulosa cells to stimulate maturation of ovarian follicles and oocytes (gametogenesis). It also stimulates aromatase activity in granulosa cells → estrogen synthesis and secretion

Question 44

What signals are for FSH and androgen?

Answer 44

FSH: Endocrine Androgen: Paracrine

Question 45

During moderate levels of estrogen, there is _______ feedback on LH secretion. During elevated levels of estrogen, there is a ______ feedback on LH with causes the LH ______.

Answer 45

Negative Positive surge

Question 46

Would androgen treatment be potentially useful as a male contraceptive strategy? How might it work?

Answer 46

High level of testosterone → negative feedback decreases GnRH → lower FSH decrease spermatogenesis; High level of testosterone → negative feedback decreases LH lower testosterone production → decrease spermatocyte maturation Spermatogenesis depends on FSH and testosterone.

Question 47

Most hormone pregnancy tests indicate the presence or absence of human chorionic gonadotropin (hCG) in a woman’s urine. - Why is this an accurate indicator of pregnancy?

Answer 47

- hCG is secreted by syncytiotrophoblast cells. Only after implantation of fertilized egg, trophoblastic cells invasively proliferate into the endometrium of the uterine wall and become syncytiotrophoblast cells that release hCG

Question 48

- Would a pregnancy test that is based on the detection of hCG be useful within the first week following fertilization? Why or why not? Would it still be likely to indicate the presence of hCG during the third trimester of pregnancy? Why or why not?

Answer 48

Not useful within the first week following fertilization. hCG level is low during 1st week. hCG rises to highest 8th -14th week of pregnancy, then luteal function begins to decline, hCG declines and reaches nadir at 20th of gestation - Not likely to indicate presence of hCG during the third trimester of pregnancy.

Question 49

-What is the function of hCG?

Answer 49

hCG maintains corpus luteum; stimulates progesterone synthesis by luteal cells of corpus luteum - plays crucial role in early pregnancy

Question 50

hCG is often used in hormone regimens that are designed to induce ovulation. Why would hCG be effective in this regard (how does it work)?

Answer 50

hCG is a glycoprotein with α and β subunits, and β subunits of LH and hCG are closely related. hCG activates LH receptor → ovulation (follicle final maturation, follicle ruptures, and oocyte expulsion).

Question 51

Ectopic pituitary transplants provide evidence for hypothalamic control of pituitary hormone secretion. What happens after removal of the pituitary gland?

Answer 51

Atrophy of all target organs (adrenal cortex, thyroid, gonads, mammary gland) – no exception.

Question 52

What happens after ectopic pituitary transplantation?

Answer 52

Pituitary transplant is well vascularized in an ectopic site. Initially, adrenal, thyroid, gonad gland, and mammary gland start to develop. But after a while, adrenal, thyroid, gonad gland become atrophy, due to lack of tropic hormones from the hypothalamus. Exception: selectively maintain mammary gland and corpus luteum of ovary, but remainder of ovary atrophies – PRL secretions from pituitary transplant due to lack of DA inhibition- mammotropic and luteotropic

Question 53

What happens after transplantation of the pituitary back under hypothalamus? (ectopic pituitary trasplant)

Answer 53

Pituitary revascularization with the hypothalamus → reactivation of pituitary to release anterior pituitary hormones (e.g., adrenal, thyroid, gonad gland start to develop; female rats cycles, ovulates, etc).

Question 54

What happens after transplantation of the pituitary back under hypothalamus? (ectopic pituitary trasplant)

Answer 54

Pituitary revascularization with the hypothalamus → reactivation of pituitary to release anterior pituitary hormones (e.g., adrenal, thyroid, gonad gland start to develop; female rats cycles, ovulates, etc).

Question 55

What happens after transplantation of the pituitary back under hypothalamus? (ectopic pituitary trasplant)

Answer 55

Pituitary revascularization with the hypothalamus → reactivation of pituitary to release anterior pituitary hormones (e.g., adrenal, thyroid, gonad gland start to develop; female rats cycles, ovulates, etc).

Question 56

What can you do to reactivate pituitary function after ectopic pituitary transplantation?

Answer 56

Infusion of hypothalamus (or median eminence) extracts. Because hormones of hypothalamus (released at median eminence) control functions of anterior pituitary

Question 57

The _______ _______ of the hypothalamus is part of the hypophyseal portal system

Answer 57

Median Eminence

Question 58

Concentrations of hypophysiotropic hormones are _________ in portal vessels than in systemic circulation

Answer 58

higher

Question 59

Cells of origin of hypothalamic hormones (hypophysiotropins) reside mostly within _____-_____ tissues. =

Answer 59

MBH (Medial Basal Hypothalamus) POA (Preoptic Area)

Question 60

______ hormones act in the fetal brain to program sexual orientations. This action is ________ and _______.

Answer 60

Steroid Irreversible Chronic

Question 61

differentiation of a male hypothalamus occurs when testosterone is synthesized into estradiol by aromatase. Knowing this, why isn't the female brain masculinized?

Answer 61

FEBP (Fetoneonatal Estradiol (E2) Binding Protein) binds estrogen with high affinity in female during development

Question 62

When examining the Interstitial nuclei of anterior hypothalamus (INAH 3), also known as Sexually dimorphic nucleus (SDN) of POA, its volume is ______ in normal males and _______ in normal females.

Answer 62

larger / smaller

Question 63

Activational Effects of steroid hormones in the adult brain regulate reproductive events, and these events are ______ and ______.

Answer 63

reversible / acute

Question 64

The Anteroventral periventricular nucleus (AVPV) is _______ in females then in males. In females, the pulsatile GnRH release is _______. In males, the pulsatile GnRH release is _______ because AVPV does not respond to neuroendocrine signals.

Answer 64

Larger Cyclic Constant

Question 65

For each scenario determined the sexual behavior (lordosis or mounting), Gonadotropin sectretion (constant or cyclic), SDN size (small or large), and AVPV size (large or small), respectfully based on the treatment the receive on the day following their birth. 1. XY, castration 2. XX, castration

Answer 65

SAME ! Lordosis, constant, small, small

Question 66

For each scenario determined the sexual behavior (lordosis or mounting), Gonadotropin sectretion (constant or cyclic), SDN size (small or large), and AVPV size (large or small), respectfully based on the treatment the receive on the day following their birth. 1. XX, testosterone

Answer 66

Mounting, cyclic, large, large

Question 67

For each scenario determined the sexual behavior (lordosis or mounting), Gonadotropin sectretion (constant or cyclic), SDN size (small or large), and AVPV size (large or small), respectfully based on the treatment the receive on the day following their birth. 1. XY, castration plus testosterone 2. XY, castration plus estrogen`

Answer 67

SAME ! Mounting, constant, large, small

Question 68

What is the general function for each of the following input tracts. Nucleus of the solitary tract (NTS)

Answer 68

Collects visceral sensory information (e.g. blood pressure and gut distension) via vagus nerve

Question 69

general function for each of the following input tracts.; Reticular formation (RF)

Answer 69

In the brainstem collects information from spinal cord (e.g., skin temperature)

Question 70

general function for each of the following input tracts.; Suprachiasmatic nucleus (SCN)

Answer 70

In the hypothalamus collects information of light and darkness from retina and optic nerve. Helps regulates circadian rhythms/ light-dark cycles related sleep, metabolism, hormone production, etc.

Question 71

general function for each of the following input tracts.; Circumventricular organs

Answer 71

Collects information from blood (e.g., osmolality and concentrations of various substances in CSF)

Question 72

general function for each of the following input tracts.; Limbic system

Answer 72

Including hippocampus, amygdala, and olfactory cortex, projects to the hypothalamus involving neurotransmitters and neuromodulators to regulate behaviors (e.g., emotion, learning, memory, motivation, reward and fear, reproduction, appetite).

Question 73

general function for each of the following input tracts.; Intrinsic receptors

Answer 73

e.g., thermoreceptors, osmoreceptors, glucose-sensing cells

Question 74

The hypothalamus has two main outputs. The _______ output acts via autonomic nervous system which controls heart rate, vasoconstriction, digestion, sweating, etc. The ______ output acts via pituitary which synthesizes and releases hypothalamic hormones.

Answer 74

Neural Endocrine

Question 75

Which primary hormone does not have a long negative feedback loop and is an amine hormone?

Answer 75

Dopamine - PRL target tissue does not secrete hormone

Question 76

T3 and T4, and TSH regulate TRH secretion via negative feedback regulation. What would happen to negative feedback regulation of TRH in the presence of actinomycin or cycloheximide?

Answer 76

actinomycin blocks mRNA synthesis; cycloheximide inhibits protein synthesis T3 and T4 do not have negative feedback (long-loop) regulation on TRH; but TSH still has negative feedback (short-loop) regulation on TRH.

Question 77

Describe the neural pathway that deliver stimulatory signal to hypophysiotropic neuron AND which hypophysiotropic hormones and pituitary hormone it regulates, is released in response to: Cold temperature

Answer 77

INPUTS: Cold temperature exposure → lower skin temperature → activate thermoreceptors (intrinsic receptors) → activate reticular formation → project to hypothalamus (via CNS center neurons using NE or via stimulating TRH-stimulating neurons in the PVN and POA) Central themoreceptors → project to hypothalamus OUTPUTS: Hormonal output: Increase TRH → increase TSH → increase thyroid hormone to increase body temperature Neural output: activate PVN neurons → activate sympathetic outflow to intermediolateral cell column (IML) of spinal cord → peripheral organ

Question 78

Describe the neural pathway that deliver stimulatory signal to hypophysiotropic neuron AND which hypophysiotropic hormones and pituitary hormone it regulates, is released in response to: STRESS

Answer 78

INPUTS: Stress → activates vagus nerve → activates NTS → axons projected to PVN → neurotransmitters Ach and NE → stimulate CRH release from PVN OUTPUTS: Hormonal: activated CRH at PVN → increase CRH → increase ACTH → cortisol release Neural output: activated PVN → activate sympathetic outflow to intermediolateral cell column (IML) of spinal cord → peripheral organs

Question 79

Describe the neural pathway that deliver stimulatory signal to hypophysiotropic neuron AND which hypophysiotropic hormones and pituitary hormone it regulates, is released in response to: Circadian Rhythm

Answer 79

INPUT Suprachiasmatic nucleus of hypothalamus (SCN) → PVN (CRH), POA (GnRH, SST), ARC (GnRH, GHRH, SST), VMN (GHRH, SST)

Question 80

Why is a constant infusion of GnRH often used as antifertility, contraceptive agents?

Answer 80

GnRH releases in a pulsatile manner, which has critical importance in maintaining continued responsiveness of gonadotroph at anterior pituitary to GnRH stimulus. Constant infusion of GnRH would cause desensitization or down-regulation of processes responsible for gonadotropin release, and thus fail to reestablish LH and FSH secretion.

Question 81

During menopause, the ovaries produce declining levels of estrogen and progesterone. Which anterior pituitary hormones might be measured as a sensitive indicator for menopause?

Answer 81

Anterior pituitary hormone LH - as a sensitive indicator for menopause. Low estrogens during menopause → has less negative feedback; activates GnRH neurons in the hypothalamus → acceleration of pulsatile GnRH secretion by increasing frequency of GnRH pulse → LH β chain gene transcription → preferential for LH secretion.

Question 82

Which hypophysiotropin would be secreted at a higher rate in a postmenopausal woman than a premenopausal woman?

Answer 82

GnRH is secreted at a higher rate in a postmenopausal woman (no negative feedback inhibition by gonadal steroids).

Question 83

GH deficiency and resultant short stature can be due to hyporesponsiveness of pituitary somatotrophs, or secondary to insufficient neurohormone secretion. Hyporesponsiveness of somatotrophs – there is GHRH (GHRH level is normal or higher than normal), but somatotrophs do not response to GHRH to release GH Insufficient neurohormone secretion – not enough GHRH (GHRH level lower than normal) What diagnostic tool might be used to differentiate between these two possibilities? How would it be used? What would be measured and what would be the outcome of the tests in each scenario?

Answer 83

- using administration (intravenous) of GHRH (GHRH needs to reach the anterior pituitary). If increase GH after administration = Insufficient neurohormone secretion - RIA or ELISA measure plasma GH before and after administration of GHRH. OR quantify GHRH-immunoreactive staining with immunohistochemistry using hypothalamus section, OR quantify GHRH protein amount with western blot using protein extracted from the hypothalamus, together with measuring GH level from plasma. Intermittent administration of GHRH to prime somatotroph → stimulate GH synthesis and release. Measure circulating GH from systemic blood samples (from large veins). (in animal models may measure GH secretion from pituitary somatotrophs). Low GHRH and low GH suggests insufficient neurohormone secretion; High GHRH and low GH suggests hyporesponsiveness of pituitary somatotrophs.

Question 84

Low GHRH and low GH suggests

Answer 84

insufficient neurohormone secretion;

Question 85

High GHRH and low GH suggests

Answer 85

hyporesponsiveness of pituitary somatotrophs.