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. Ý GHRH and ¯ somatostatin,  \  Ý 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. Ý amino acids	building blocks for growth
								

			b. ¯ blood sugar,  ¯ FFA,  ¯ obesity


				i. some forms of diabetes


				ii. Ý glucagon


			c. VIP ® ¯ somatostatin

				i. substance P,   neurotensin ® Ý somatostatin


			d. motilin & bombesin stimulate somatotropes directly


		4. Ý androgens and estrogens	  also anabolic


		5. ¯ hypothyroidism (results in Ý 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