Endocrinology, lecture on Growth Hormone
USD Department of Biology
Endocrinology
Summers
Hormones
Endocrine Glands
Receptors
Homeostasis
2nd Messengers
Nuclear Receptors
Genetic Regulation
Hormone Synthesis
Receptor Regulation
Hypothalamo-Hypophysial Communication
Tropic Hormones
Neurohypophysial Nonapeptides
Thyroid Axis
Steroids
Adrenal Axis
Adrenal Medulla
Osmotic-Pressure Balance
Reproductive Endocrinology
Prolactin
Somatic Axis
Growth Factors
Immune Factors
Ca++, PO4 Homeostasis
Pancreatic Hormones
GI Hormones
Guts 'n Brains
Brain Hormones
Neurosteroids
Neuropeptides
Endocrine Evolution
Figures for Endocrionology
text:Vertebrate Endocrinology5th Edition - David O. Norris:
Read pages 130-131, 143-145 for this lecture
acronyms    end
XXII.  Somatic Growth Axis 	video		


	A. Somatotropes (GH) are stimulated by GHRH   (= GRH = GRF = somatocrinin)
	                   via Gs / cAMP


		1. inhibited by somatostatin (GHRIH) via Gi


		2. 35 - 45% of all anterior pituitary cells


			a. found mostly in the lateral wings


			b. have very large secretory granules (vesicles) containing GH


		3. GH secretion pulsatile


	B.  GHRH and ¯ somatostatin,  \   GH caused by:


		1. Sleep


			a. ¯ REM


		2. stress, exercise and emotional state
	

			a. a-adrenergic stimulation, b-adrenergic inhibition, ¯ B/F


				i. opiates, NE, Epi, DA, even l-DOPA 


		3. nutritional status & digestive effectors


			a.  amino acids	building blocks for growth
								

			b. ¯ blood sugar,  ¯ FFA,  ¯ obesity


				i. some forms of diabetes


				ii.  glucagon


			c. VIP ® ¯ somatostatin

				i. substance P,   neurotensin ®  somatostatin


			d. motilin & bombesin stimulate somatotropes directly


		4.  androgens and estrogens	  also anabolic


		5. ¯ hypothyroidism (results in  T3)   synergistic


		6. ¯ IGF1 (insulin-like growth factor 1 = somatomedin)  
		                                               mediate growth effects
							

	C.  GH Function

		1. tissue growth 

			a. mediated by IGF1 

				i. protein synthesis, cell growth,
				   chondrogenesis, osteogenesis 

			b. antagonized by B/F


		2. GH stimulates JaK2 ® STAT3+5 ® the production of  IGFs

			a. IGFs are similar in structure to proinsulin		


			b. 2 receptors for IGFs found

				i. one binds insulin weakly


			c. IGFs are strong mitogens


		3. GH directly effects carbohydrate and lipid metabolism


			a. opposed to the effects of insulin
			   (i.e.. diebetogenic (hyperglycemia) & lypolytic)


			b. synergistic with B/F


	D. Feedback


		1. IGF1


			a. GH stimulates IGF1  production in the liver

	
			b. IGF1  inhibits GH by inhibiting GHRH or stimulating somatostatin


		2. GH inhibits itself also by inhibiting GHRH or stimulating somatostatin


		3. exercise, emotional and/or nutritional status

XXIII. Growth Factors