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Toronto Notes 2019 Pituitary Gland Table 16. The Physiology and Action of Pituitary Hormones (continued)
Endocrinology E17
Hormone Function
LH/FSH Stimulate gonads via cAMP Ovary:
LH: production of androgens (thecal cells) which are converted to estrogens (granulosa cells); induces luteinization in follicles
FSH: growth of granulosa cells in ovarian follicle; controls estrogen production
Testes:
LH: production of testosterone (Leydig cells) FSH: production of spermatozoa (Sertoli cells)
Prolactin Promotes milk production Inhibits GnRH secretion
TSH Stimulates growth of thyroid and secretion of T3 and T4
via cAMP
ADH Acts at renal collecting ducts on V2 receptors to
cause insertion of aquaporin channels and increases water reabsorption thereby concentrating urine
Oxytocin Causes uterine contraction Breast milk secretion
Physiology
Polypeptide
Glycoproteins (similar α subunit as TSH and hCG) Secreted in pulsatile fashion
Polypeptide Episodic secretion
Glycoprotein
Note: hCG can act like TSH and react with TSH receptor
Octapeptide
Secreted by posterior pituitary Osmoreceptors in hypothalamus detect serum osmolality
Contracted plasma volume detected by baroreceptors is a more potent stimulus than osmolality
Nonapeptide
Secreted by posterior pituitary
Inhibitory Stimulus
Estrogen Progesterone Testosterone Inhibin Continuous
(i.e. non-pulsatile) GnRH infusion
Dopamine (only pituitary hormone under tonic inhibition of secretion)
Circulating thyroid hormones (T3, T4) Opiates, dopamine
serum osmolality
EtOH
Secretory Stimulus
Pulsatile GnRH (low frequency pulsation = FSH release, high frequency pulsation = LH release)
Sleep
Stress, hypoglycemia Pregnancy, breastfeeding Mid-menstrual cycle Sexual activity
TRH
Drugs: psychotropics, antihypertensives, dopamine antagonists, opiates, high dose estrogen
TRH Epinephrine Prostaglandins
Hypovolemia or effective circulatory volume
serum osmolality Stress, pain, fever, paraneoplastic
Lung or brain pathology
Suckling
Distention of female genital tract during labour via stretch receptors
Growth Hormone
GH DEFICIENCY
• causeofshortstatureinchildren(seePediatrics,P26)
• adultsexhibitincreasedfatanddecreasedleanbodymass,decreasedbonemineraldensity,andless
energy (fatigue)
• diagnosismadewithlowserumIGF-1levelsorbyfailuretoincreaseGHwithaprovocativetest
• GHreplacementifadultpatientwithchildhoodonsetGHdeficiency,andsomepatientswith
hypopituitarism
GH EXCESS
Etiology
• GHsecretingpituitaryadenoma,carcinoidorpancreaticislettumourssecretingectopicGHRH resulting in excess GH (very rare)
Pathophysiology
• normallyGHisacatabolichormonethatactstoincreasebloodglucoselevels
• inGHexcessstates,secretionremainspulsatilebutthereislossofhypoglycemicstimulation,glucose
suppression, and the nocturnal surge
• proliferationofbone,cartilage,softtissues,organomegaly
• insulinresistanceandIGT
Clinical Features
• inchildren(beforeepiphysealfusion)leadstogigantism • inadults(afterepiphyisealfusion)leadstoacromegaly
Risks Associated with GH Excess
• Cardiac disease (e.g. CAD, cardiomegaly, cardiomyopathy) in 1/3 of patients, with a doubling of risk of death from cardiac disease
• HTN in 1/3 of patients
• Risk of cancer (particularly GI) increased
2-fold to 3-fold