Let’s Cure Robert Wadlow The Growth Axis Hypothalamus Somatostatin hypothalamus GHRH hypothalamus Group 1 (-) (+) Pituitary GH pituitary Group 2 Liver IGF-I liver Group 3 This slide illustrates the GH axis in humans. Each group has to devise a way to cure Robert. T3/T4 cortisol Bone Growth Plate bone Group 4 E2/T nutrition

Endocrine Secretion: Products, Pathways and Regulation Overview and Quick Review General Cell Biology Regulation One Example in More Depth Glucose Regulation of Insulin Secretion Neil Gesundheit, M.D., and Stephen J. Smith, Ph.D. neil7@stanford.edu, sjsmith@stanford.edu

Endocrine Signaling Depends on the Regulation of Hormone Secretion Analyte or substrate regulation

Peptides Amines Steroids Hormones and Corresponding Secretory Pathways and Regulation Mechanisms Fall into Three Broad Patterns (almost…) Peptides Amines Steroids (The somewhat exceptional case of thyroid hormones will be treated at length in later lectures)

Synthesis and Secretion of the Peptide Hormones Examples: Growth Hormone Prolactin TSH, LH, FSH, hCG Somatostatin Hypothal. Releas. Horm. Insulin Glucagon Parathyroid Hormone Many, many others Transcription Translation Glycosylation Processing Packaging Storage Exocytosis Circulation DNA mRNA Prehormone Prohormone Hormone

Alpha and Beta Cells of Pancreatic Islets

How Do Vesicles Fuse? [Ca++] [Ca++] SNARE complex of proteins merge the synaptic vesicle to the plasma membrane. Free intracellular Ca++ activates the process. “SNARE” is an acronym derived from "SNAP (Soluble NSF Attachment Protein) REceptors” Thomas Sudhof is Stanford scientist and Nobel laureate who worked out many of these mechanisms [Ca++] [Ca++]

Synthesis and Secretion of Peptide Hormones: the Anterior Pituitary Cell Examples: Growth Hormone Prolactin TSH, LH, FSH, hCG Somatostatin Hypothal. Releas. Horm. Insulin Glucagon Parathyroid Hormone Many, many others Regulated Secretion Transcription Translation Glycosylation Processing Packaging Storage Exocytosis Circulation DNA mRNA Prehormone Prohormone Hormone

GHRH Administration Produces Rapid Secretion of GH from the Anterior Pituitary 30 GHRH (2 mcg/kg IV bolus) GH Concentration (mcg/L) 20 10 (Adapted from Maccario et al, J Clin Endo Metab 2001; 86:167-171)

Synthesis and Secretion of Amine Hormones Primary Regulation (acetylcholine from preganglionic fibers via nicotinic receptors, leads to increases in free Ca++) Sympathetic neurons and sympathetic ganglia (PNMT) Sympathetic neurons Sympathetic ganglia Adrenal medulla

Ultrastructure of Catecholamine Secretory Cells Cat Adrenal Chromaffin Cells Sympathetic Nerve Ending on Rat Chromaffin Cell

Steroid Secretion and Regulatory Pathways: the Adrenal Cortical Cell Cholesterol has 27 carbons. Pregnenolone has 21 carbons. The side-chain cleavage enzyme works through 3 enzymatic steps – 2 hydroxylations and one hydrolysis/cleavage – to remove 6 carbons. Side-chain cleavage is the rate-limiting step in the biosynthesis of the steroid hormones. ACTH increases cholesterol uptake into mitochondrion ACTH increases side-chain cleavage in mitochondrion, to produce pregnenolone

Steroid Secretion and Regulatory Pathways: Side-Chain Cleavage in the Mitochondrion of the Adrenal Cortical Cell Cholesterol Pregnenolone Side-chain cleavage enzyme Cholesterol has 27 carbons. Pregnenolone has 21 carbons. The side-chain cleavage enzyme works through 3 enzymatic steps – 2 hydroxylations and one hydrolysis/cleavage – to remove 6 carbons. Side-chain cleavage is the rate-limiting step in the biosynthesis of the steroid hormones. ACTH increases cholesterol uptake into mitochondrion ACTH increases side-chain cleavage in mitochondrion, to produce pregnenolone

Cortisol concentrations after SQ injection of synthetic ACTH Cosyntropin (synthetic ACTH) administration at time 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Time (hours)

Let me challenge you… How would you predict that the beta cell would regulate the secretion of insulin? How does the beta cell sense high and low glucose concentrations?

The Regulation of Insulin Secretion from Pancreatic Beta Cells by Glucose In spite of long and intensive searching, no beta-cell “glucose receptor” has been identified Glucose metabolism itself is the glucose “sensor” (Frances Ashcroft) Electrophysiological and ionic mechanisms couple intracellular ATP to insulin secretion

K Channel Closure is Linked to Insulin Secretion via Closing of ATP-Sensitive K Channels and Consequent Opening of Voltage-Dependent Ca Channels The biology of ATP-mediating glucose sensing and how it regulates insulin secretion is largely the work of Frances Ashcroft, PhD., a famous Oxford scientist.

Sulfonylurea Oral Anti-Diabetic Drugs Act By Promoting the Closing of ATP-Sensitive Potassium Channels

Take Home Points Secretion of peptides and amines occurs via secretory vesicles (they are “pre-packaged”), is regulated, and Ca++ from intracellular sources is the key signaling molecule for secretion Secretion of steroid and thyroid hormones occurs by increasing substrate; these hormones are not packaged/stored in secretory vesicles Secretion of insulin is unique: sensing is by changing concentrations of a by-product of glycolyis, ATP; Ca++ triggers secretion and is from extracellular sources Goal of this module is to have you engage in joyful learning!