28 AA sequence derived from the gut that stimulates GH release -Increases before meals and decreases after meals
What is ghrelin acyltransferase (GOAT) responsible for?
Enzyme expressed in stomach that is responsible for acylating 3-serine of ghrelin with octanoate
What do GHRH injections do?
Stimulate GH release
Give an overview of the regulation of GH secretion.
SRIF neuron controls/inhibits both the GHRH neuron and the pituitary gland. GHRH neuron acts on pituitary to stimulate release of GHRH, SRIF neuron acts on pituitary to inhibit as needed Ghrelin from the stomach feeds back positively to the GHRH neuron and the pituitary GHRH acting on liver, liver negative feedbacks to pituitary via IGF-I GH from pituitary positive feedback on SRIF neuron GH on fat, free fatty acids inhibit pituitary
When does GH secretion increase?
What does pulsatility refer to?
Undergoing pulsation-cyclic increase and decrease of hormone concentrations
What hormones are involved with the regulation of prolactin secretion?
Give an overview of prolactin secretion regulation.
PRF neurons in the PVN and dopamine neurons in the Arc connect with pituitary Dopamine inhibits prolactin release from the pituitary TRH, Oxytocin, VIP stimulate PRL release from pituitary PRL stimulates breast, multiple other target organs Sucking stimulus travels up spinal afferent neuron, inhibiting dopamine neurons and stimulating PVN PRF neurons PRL stimulates dopamine neurons and inhibits itself through the pituitary Estrogen stimulates PRL release
What factors stimulate PRL release?
Estrogen TRH, oxytocin, VIP release Sucking stimulus traveling up the afferent spinal neuron to the PVN PRF neurons (also inhibits dopamine release)
What factors inhibit PRL release?
PRL release -Acts on pituitary and dopamine neurons Dopamine release
What is the thyroid system important for?
Energy balance and metabolism
Give an overview of the hypothalamo-pituitary-thyroid axis.
Temperature inputs from brain stem catecholaminergic neurons input to the TRH neurons in the PVN and the hypothalamus TRH release stimulates pituitary to convert T4 to T3, releases TSH which acts on thyroid Thyriod releases T3 and T4, both inhibit the pituitary and TRH neurons in the PVN Somatostatin inhibits TSH release
What does the TRH precursor give rise to?
6 different biologically active peptides
What does TRH stimulate?
What blocks TRH action?
T3 and T4
Give an overview of the hypothalamo-pituitary-gonadal (HPG) axis.
Stress, nutrition, exercise, seasonal cues and neuronal mediators stimulate or inhibit GnRH neuron, which projects to the hypothalamus Pituitary releases LH and FSH, which stimulate ovaries or testes Ovaries and testes release inhibin, which negatively feeds back to the pituitary Ovaries release estradiol which inhibits pituitary and GnRH neuron, and also progesterone, which inhibits neuronal mediators Testes release testosterone, which inhibits the pituitary and neuronal mediators
What inhibits the HPG axis?
Inhibin inhibits the pituitary (released from ovaries or testes) Estradiol inhibits pituitary and GnRH neuron Progesterone inhibits neuronal mediators Testosterone inhibits the pituitary and neuronal mediators
What do most species have in regards to GnRH?
Most species have two GnRHs that may have different functions that are expressed in different regions of the brain
How many peptides are in GnRH?
What are the other forms of GnRH that are expressed in other vertebrate species?
Midbrain GnRHII Telencephalic GNRHIII
What nucleus modifies GnRH output? What pattern is observed?
Suprachiasmatic nucleus (SCN)
What kind of generators are GnRH neurons?
Endogenous pulse generators
What other hormone pulse coordinates with GnRH?
One pulse of GnRH coincides with a pulse of LH in the systemic circulation
What was observed in a female rhesus monkey with bilateral lesions in the arcuate nuclei affecting GnRH neurons, who had GnRH infused at different pulse frequencies?
One GnRH pulse per 3 hr promotes FSH secretion (mimics early-mid follicular phase)
One GnRH pulse per 1 hr promotes LH secretion (mimics late follicular phase)
When given a dose of estradiol, what was observed in ovariectomized monkey treated with E2 infusion?
E2 suppresses LH secretion -Several hours after E2 treatment is stopped the LH secretion rebounds
What is E2-induced negative v. positive feedback on LH secretion determined by? Explain.
The duration of exposure to and dose of estradiol -Longer duration E2 exposure leads to positive feedback resulting in an LH surge -At first, E2 causes negative feedback, decreases LH secretion
Describe the changes in plasma E2, P4, GnRH, LH, and FSH during the menstrual cycle.
E2: negative feedback during days 0-10, positive feedback/peak through days 10-14, negative feedback during remaining cycle P4: peaks near end of menstrual cycle GnRH: peaks during ovulation (day 14) LH and FSH: peak during ovulation (day 14)
What are the key hormones involved in the hypothalamo-pituitary-adrenal (HPA) axis?