Anterior Pituitary Hormones Flashcards
What hormones are in the glycoprotein family?
Follicle-stimulating hormone
Luteinizing hormone
Thyroid-stimulating hormone
Human chorionic gonadotropin (hCG)
What are the two subunits of the glycoprotein family hormones?
a-subunit - Identical in all proteins in this family
B-subunit - Unique for each protein and responsible for conferring biological activity
Both subunits required for binding and biological activity
What signaling pathway do glycoprotein hormones activate?
cAMP signaling pathway
What hormones are in the somatomammotropin family?
Growth hormone (two different forms can be made from the same gene)
Prolactin
Placental GH and Chorionic somatomammotropin/placental lactogen share significant homology to these hormones
What hormones are in the proopiomelanocortin family?
Adrenocorticotropin
All peptides in this family are products of a single gene that encodes for a large precursor molecule, POMC
What is GH binding protein?
Binds about half of GH in circulation
Same molecular structure as external portion of the GH receptor
What is the result of GH action on target tissue?
Production of IGF-1 that induces most of the growth promoting actions of GH
What mediates GH action on skeletal growth?
IGF-1
What are the metabolic effects of GH?
Stimulates lipolysis
Inhibits glucose uptake and oxidation
Increases whole body protein synthesis
What may be caused with the decrease in GH secretion that occurs with aging?
Age-related muscle wasting
What signaling pathway does the GH receptor activate
JAK-STAT pathway
What are the sources of IGF-1?
Major source for circulating IGF-1 is the liver
Locally produced IGH-1 by target cells also mediates action
What part of the bone expresses receptors for GH and IGF-1?
Chondrocytes in the epiphyseal growth plates
Synthesize and release IGH-1 in response to GH stimulation
What are the functions of IGF binding proteins?
Provide a circulating reservoir for IGF
Increase half life of IGF
Modulate IGF bioavailability
Potentiate or inhibit IGF action
How is most IGF in the blood transported?
Large molecular weight complex composed of:
IGF
IGFBP-3
ALS (glycoprotein)
What is the function of IGFB proteases?
Degrade IGFBPs, increasing the affinity of IGF-1 for its receptor
What is the mechanism of action of IGF-1?
Receptor tyrosine kinase that activates the Ras/Map Kinase pathway
What are the specific effects of IGFs?
Stimulation of DNA, RNA and protein synthesis
Cell proliferation
Insulin-like effects on adipose tissue and muscle
What is growth hormone releasing hormone (GHRH)?
Stimulates the synthesis and release of GH via G-protein mediated activation of adenylyl cyclase
Actions enhanced by ghrelin
What is the function of somatostatin (as it relates to growth hormone)?
Blocks basal and GHRH-stimulated GH release
Mediated by Gi protein
Describe the negative feedback control of GH secreiton
Negative feedback inhibition exerted primarily by the actions of IGF-1
Gh inhibits its own release via short feedback loop to the hypothalamus
What is the pattern of GH release?
Released in secretory pulses
Released in a circadian pattern that occurs about 1-2 hours after the onset of deep sleep
What are the physiological stimuli of GH secretion?
Stress
Postprandial hypoglycemia (fast)
Protein meal
Sex steroids
Ghrelin
What conditions have an inhibitory effect on GH secretion?
Hyperglycemia
Elevated levels of FFAs
