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Scribe: Brittney Wise
Tuesday, November 10, 2009
Proof: Laura Adams
Dr. Weignent
Pancreatic Endocrinology and Regulation of Plasma Glucose
Page 1 of 5
**Slide notes are in italics**
I. [S1] The Pancreatic Islet
a. Beta Cells: 65-75%
i. these serve as the source of insulin
b. Alpha cells: ~20%
i. these are responsible for the synthesis of glucagon
c. Delta Cells
i. these are responsible for the synthesis of somatostatin which is a 14 amino acid protein; it is also
responsible for the control of growth hormone in the neuroendocrine system; somatostatin is also made in
a 28 amino acid form in the intestine
ii. not much is known about the function of somatostatin in the pancreas
1. it is known that it inhibits the synthesis of glucagon and insulin and their secretion
2. it also seems to block/inhibit/slow the secretion of other hormones important for digestion;
a. it slows the movement of food through the digestive tract allowing the body to sense what’s
there and how well it’s been degraded and how much more can be recovered and so it may
serve as a monitor for the movement of the food through the gut
iii. overall somatostatin does play a role in the islet in a regulatory way and acts as a inhibitor to digestion
d. Islets represent about 1-2% of the pancreas. There are about 1-2 million islets in the pancreas.
e. The 3 different cell types do communicate with each other. Their location within the islet is important possibly
for their regulation. Alpha cells secrete the glucagon which stimulates the beta cells to secrete insulin, whereas
the beta cells inhibit the alpha cells and the secretion of glucagon.
f. Also, the way the blood flows through here allows the nutrients to affect the cells in the periphery more.
g. Insulin: Fat, Muscle, Liver and Kidney
i. as your body digests nutrients and such, the flow goes from the intestine to the liver, however, nutrients
pick up these hormones from the pancreas along the way
ii. one of the first places these hormones go is the liver (so the [insulin] and [glucagon] seen in the liver are
the highest in the body)
iii. the liver also has enzymes to degrade these enzymes
iv. insulin is important in extra-hepatic tissues but about 50% of these hormones are lost because there are
receptors that bind up these hormones and there are enzymes that degrade these hormones; so ½ the
potency is lost in the passage through the liver
h. Glucagon: Metabolic Actions in Liver ONLY
i. it is from the liver that these substances and nutrients are moved to the rest of the body
i. The ratio of insulin to glucagon is very important. If you are eating, the glucose load and amino acid load will
stimulate insulin release, leading to insulin becoming dominant. When the blood levels are low with glucose and
your body needs it like it would in between meals, glucagon will become a big player. Depending on the
nutrients that you take in, this will determine the levels of these hormones and their biological effects.
There will be a test question from this graph (what does glucagon/insulin inhibit or promote?)
Glucagon Insulin Major Features of Metabolism
+
Glycogenolysis – breakdown of glycogen; you store glucose when you eat in the form of glycogen;
insulin is a major hormone that stimulates that process; you will hear the word anabolic (build) to
imply that it builds that reserve; this reserve is important in between meals
+
Gluconeogenesis – the synthesis of glucose from pyruvate
+
Glycogen Synthesis; making glycogen from glucose molecules
+
Glycolysis – breakdown of glucose
+
Ketogenesis – in the absence of insulin keto acids are made and can cause a diabetic coma and
some serious consequences as a result of the lack of insulin
II.
[S2] Glucagon
a. Chemistry, Secretion, and Metaboilism:
i. peptide hormone
1. this is a 29 amino acid peptide
ii. synthesized as prohormone
iii. stored in secretory granules, released by exocytosis (by the alpha cells)
iv. circulates free in the plasma and has a very short ½ life (3-4 minutes)
1. the short ½ life is due to the liver taking it out of action
H & E: 1:00 - 2:00
Scribe: Brittney Wise
Tuesday, November 10, 2009
Proof: Laura Adams
Dr. Weignent
Pancreatic Endocrinology and Regulation of Plasma Glucose
Page 2 of 5
b. Physiologic Actions of Glucagon
i. Metabolic effects are restricted to the LIVER (major effects of glucagon are in the liver!)
ii. Enzyme activity and expression
1. A lot of times these hormones will stimulate phosphorylation events which will activate or inhibit
certain enzymes. These hormones will bind to receptors on cells and stimulate synthesis/activity of
important enzymes.
iii. Stimulates hepatic production and secretion of metabolic fuels
III. [S3] Figure 4: Regulation of glucagon secretion
a. The major inducer of glucagon is low blood glucose (amino acids, epinephrine, and acetylcholine can also play
a stimulatory role here). The major inhibitor of glucagon is high blood glucose (somatostatins, free fatty acids
and ketones can also play an inhibitory role). A lot of these works through g-proteins.
b. Remember, glucagon is secreted via alpha cells.
IV. [S4 and 5] Figure 2: hepatic glucose metabolism
a. What does glucagon do? The red in the graph is inhibitory and the green is stimulatory. With regard to
glucagon, it inhibits the glycogen synthase and stimulates the glycogen phosphorylase. You end up with a
break down in glycogen or you have glycogenolysis. In addition, it stimulates the breakdown of glucose-6-P
through the actions of phosphatase to release glucose (in the liver) and inhibits the hexokinase.
b. It particularly becomes a player when you are hungry, starving or fasting. In between meals glucagon levels will
begin to rise and begin to draw upon those reserves. He thinks that glucagon is important particularly during
stress times and when the levels of glucose are really low.
c. As you continue down the glycolytic pathway, you see the stimulation of fructose-1-6-bisphosphatase and an
inhibition of the important regulator phosphofructokinase (PFK). The net effect here is that it’s stimulating
gluconeogenesis. Glucagon here is breaking down glycogen to push glucose into your blood and its
synthesizing glucose so that again it can raise blood glucose levels.
V. [S6] Liver Ketogenesis: The Carnitine Shuffle
a. The idea here is normally one of the products of glycolysis is acetyl-CoA. This is converted by acetyl-CoA
carboxylase to malonyl CoA. Malonyl CoA is then converted to long chain fatty acids (in the liver, aka liver
ketogenesis or Carnitine shuffle). The long chain fatty acids are then converted to triglycerides from which you
will then get LDL’s which now are secreted in the blood and transported to the adipose where they are acted
upon by a lipase and taken up and stored.
b. At the time it’s doing that, the malonyl CoA, as it accumulates, also has the ability to inhibit another set of
proteins called carnitine acetyl transferase and some other proteins. The whole process is a little more complex
than what he can share with us here. By this inhibition, it facilitates the movement of acetyl-CoA and the
building of fatty acids and the movement of triglycerides into storage and prevents the movement of this
substrate into the mitochondria here, and it’s conversion to fatty acetyl-CoA. Two acetyl-CoA can then convert
to acetoacetic acid which can be transformed into beta-hydroxybutyric acid (these last 2 are ketone bodies).
i. Ketone bodies are good news and bad news. The bad news is that they change the pH of the blood which
ultimately could lead to a coma. The good news is that these ketone bodies in some regards spare the
muscle (when the body has to have substrate to make glucose, if it doesn’t use these then it’s got to break
down muscle to get protein and draw out amino acids to make glucose).
ii. In addition and most importantly, under conditions where your glucose levels are low and this cycle is
stimulated, you are not making the malonly CoA so you have relieved this inhibition. Ketone bodies can be
used by other tissues particularly the brain. Your body is interested in sparing glucose and it sets itself up
to do that in several ways. This is a major way that it does that. So it preserves glucose for the brain by
various mechanisms so when it gets low on that and can’t survive under those conditions then it goes
ahead and makes these ketone bodies which now can be utilized by the brain for energy.
iii. What happens under those conditions is that the other tissues, the liver the muscle, and the adipose they
use free fatty acids. You don’t get a lot of glycogen made by the muscle or the adipose tissue (maybe more
by muscle than adipose). Muscle and adipose tend to use fatty acids for energy.
c. Glucagon is a major ketogenic hormone or it stimulates ketogenesis. It inhibits the acetyl CoA carboxylase
which allows malonyl CoA to accumulate. When you lose the inhibition it draws those fatty acids into the
mitochondria and you get the formation of ketone bodies.
d. On the other hand insulin stimulates that enzyme. Some think that it alters the phosphorylation of this acetylCoA carboxylase. Some think that it alters the subunit polymerization (dimer or trimer) and in the process of
doing that they alter the activity of this important enzyme. In the process of stimulating this enzyme and
promoting this pathway you build the inhibitor up and you block the pathway to ketone bodies and you now are
building long chain fatty acids to triglycerides to the LDL’s and you are going to put it in the fat. This is an
anabolic pathway which will build reserves because you can’t eat all the time.
e. So, glucagon inhibits processes that won’t give you glucose & stimulates processes that will give you glucose.
H & E: 1:00 - 2:00
Scribe: Brittney Wise
Tuesday, November 10, 2009
Proof: Laura Adams
Dr. Weignent
Pancreatic Endocrinology and Regulation of Plasma Glucose
Page 3 of 5
VI. [S7] Insulin (5 points)
a. Administered therapeutically
b. Amino acid sequence and tertiary structure
c. Membrane mechanism of action; discovered to be through cyclic AMP
d. First to be measured by RIA (Radio-immuno assay)
e. Biosynthesis in bacteria
VII. [S8] Insulin (Structure of the alpha and beta chains of insulin and 5 points)
a. 1953 sequence determined by Fred Sanger and colleagues
b. Before Edman procedure, took 10 years
c. Demonstrated proteins contained all L-amino acids
d. All linkages were peptide bones
e. Sanger got Nobel Prize (1st of 2)
f. The picture of insulin shows that it is 2 separate amino acid chains (one is 21 amino acids and the other is 30
amino acids) combined via disulfide linkages. There is also a connecting peptide that goes from a glycine to an
alanine.
VIII. [S9] 9-Step Pathway
a. What you see here is representative of a beta cell which is the source of the insulin. They have what are called
GLUT-2 receptors which are not insulin dependent. When people have diabetes some of this breaks down.
You can see problems not only in production of the hormone but also problems where that hormone acts.
b. Step 1: glucose has to bind to the GLUT-2 receptor which is insulin independent
c. Step 2: metabolized through the glycolytic pathway
d. Step 3: the cell knows that it is metabolizing and that something is going on
e. Step 4: this will increase the ration of ATP to ADP
f. Step 5: you have reducing equivalents in NADPH
g. Step 6: the combination of the above steps is what signals the potassium channel to close; that causes a
depolarization in the cell which allows the potassium not to influence the open nature of the calcium channel
h. Step 7: once calcium comes in you have activation now of calmodulin and calcium kinase and this facilitates the
movement of these granules to the surface of the membrane so they can dump insulin out
i. Step 8: there are other aspects of control over this cell that aren’t subject to glucose (although glucose is the
major regulator)
i. at the bottom of the slide you can see that there are g-proteins (g-inhibitory [aka Gi] and g-stimulatory [aka
Gs]) along with the hormones somatostatin and alpha-adrenergic pathways that act as g-inhibitory
(glucagon is a g-stimulatory)
ii. these bind and increase or decrease the levels of these 2nd messengers in the cell
iii. because of an increase in PKA there is an increase in the movement of granules to the surface of the cell
j. Step 9: you also see Acetylcholine (ACH) or Cholecystokinin (CCK)
i. Remember when you think about food or hunger CCK beings to stimulate some of the juices for the
delivery of nutrients and it prepares the intestines
ii. They work through these pathways that are Gq centered
iii. You then have IP3 and DAG that activate protein kinase C (PKC)
iv. As you can see you have a number of PKA and PKC channels all contributing to the net/sum of the
movement of these granules to the surface and the release of insulin.
IX. [S10] Pathway involving Amino Acids, Insulin, Glucose at the top of the slide
a. You won’t see this slide again except in this power point. This slide shows the effects of insulin on target cells.
b. What you can see at the very top is the insulin molecule that was “released” from the previous slide and now is
binding to a receptor of alpha and beta subunits. It’s a tyrosine kinase receptor and it activates a number of
second messengers including the insulin receptor substrates which are IRS-1 and IRS-2. Then there is an
activation of phospholipase C and uptake of calcium both of which contribute to a number of 2nd messenger
systems.
c. You have the PI3 kinase activated, you have protein kinase B activated, you have a lot of things that are getting
very busy with the idea of stimulating the synthesis of transcription factors acting at insulin response elements
making proteins that are going to induce/suppress the target enzymes to explain the actions of insulin in the
cells. In some cases that is going to be stimulating the glycogen synthetase. In some cases that is going to be
inhibiting the glycogen phosphorylase.
d. Another important point is the insertion of transporter molecules for glucose in the membrane. As he recalls
these are preformed but it takes the binding of insulin and the inner workings here to insert the insulin
dependent transporter called the GLUT-4.
i. You will see GLUT-4 on muscle and fat.
ii. You will see GLUT-2 on one that is not insulin dependent like the liver and the beta cell.
H & E: 1:00 - 2:00
Scribe: Brittney Wise
Tuesday, November 10, 2009
Proof: Laura Adams
Dr. Weignent
Pancreatic Endocrinology and Regulation of Plasma Glucose
Page 4 of 5
e. Once glucose gets into cells it can be modified and you can get energy and all the other functions it serves.
f. As a result of the IRS activations you get a stimulation of PDE (phosphodiesterase – an enzyme that degrades
cAMP). This decline in cAMP is important in fat because in the fat cell when you have a decrease in the cAMP
you have a decrease in the hormone sensitive lipase.
i. Insulin allows you to put triglycerides away. It builds lipogenesis where as hormone sensitive lipase is
lipolytic. So insulin inhibits the activity of hormone sensitive lipase.
g. Potassium uptake is also stimulated (along with some amino acids). The intracellular levels of potassium are
high and the extracellular levels of potassium are low.
i. When you eat you take up a bunch of potassium and that is not necessarily good news unless you can take
care of it. High potassium causes muscle issues and causes the heart to struggle. The human body takes
care of this potassium load and prevents hyperkalemia through the actions of insulin.
X. [S11] Figure 9: Insulin’s effects in adipose tissue
a. #1 - as insulin binds to the adipocyte you get the insertion of the GLUT-4 transporters which allows glucose to
be taken up from the blood.
b. #2 – you have the stimulation of various pathways that allow the synthesis of alpha-glycerol phosphate and the
activation of acetyl-CoA carboxylase system set up to synthesize the triglyceride; this is what you want to do
because you want to put triglycerides away and store them for another day.
c. #3 – it stimulates lipoprotein lipase; when those fatty acids arrive from the liver it is a mess because it has
cholesterol, lipoproteins, and triglycerides in it; this enzyme stimulated by insulin allows you to break off the
piece that you needs, takes it up into the cell, and utilizes it for triglyceride synthesis
d. #4 - from the previous slide where he mentioned the decrease in cAMP, the value of lowering cAMP is that you
inhibit this enzyme (hormone sensitive lipase) which breaks down the triglyceride; by blocking this enzyme you
promote lipogenesis
XI. [S12] Figure 10: Insulin’s effects on hepatic glucose metabolism
a. What is insulin’s effect in the liver? Just the opposite of what he mentioned about glucagon.
b. It stimulates glycogen synthesis. Insulin in the liver will stimulate glycogen synthetase and glucokinase while
inhibiting the phosphorylase and the glucose-6-P. It also stimulates glycolysis and you see that through its
actions on PFK (phosphofructokinase) and the pyruvate kinase.
XII. [S13] Pathway starting with Fructose-1-6 bisP
a. In this diagram you see this cycle that he just went over regarding the synthesis of ketone bodies. Again, acetylCoA carboxylase is stimulated by insulin. Via insulin’s process you are encouraged to make the fatty acids into
triglycerides and put them into the adipose tissue.
XIII. [S14] Figure 11: Effects of Insulin on overall fuel homeostasis
a. In muscle it stimulates protein synthesis, amino acid uptake, glucose utilization, glycogen synthesis and inhibits
protein degradation. Overall it builds, it’s anabolic.
b. As a result of that you have a decrease in amino acids in the fat. We just mentioned a number of issues where
it stimulates the glucose uptake or fatty acid uptake (lipogenesis) and inhibits lipolysis.
c. In the liver, you have a decrease in gluconeogenesis but an increase in the storage of glucose via the glycogen
pathway and the generation for intermediates for triglyceride synthesis through the increase in glycolysis and
the inhibition of ketogenesis.
XIV.
[S15] Interaction of hormones to maintain blood glucose levels
a. Insulin isn’t the only player. Epinephrine, Glucagon, Glucocorticosteroids, and Growth Hormone are also
players. The top of the diagram is showing the production of glucose, it’s release into the blood and it’s pathway
to the tissues (muscles/adipose). Here you will see the counter-regulatory effects of all the hormones on the
right with insulin’s effects on the left. Early on insulin stimulates glucose consumption by muscle and adipose
and it inhibits the glucose production.
i. The counter-regulatory hormones have a particular regulation of this system during the inter-digestive
phases.
ii. Epinephrine and Glucagon stimulate glucose production. Glucocorticoids either stimulate or inhibit the
production of glucose depending on what tissues you are in.
iii. Growth hormone is diabetogenic. And works to decrease the uptake of glucose into muscle and adipose.
b. There are situations and times when you don’t want glucose to go into cells you want to spare it (i.e. for the
brain). Under these conditions when the brain needs glucose the muscles and adipose don’t need it.
XV. [S16] Interdigestive Period (Fast)
a. Nutrient levels (i.e., glucose) in blood fall several hours after a meal, thereby leading to lower levels and effects
of insulin secretion.
b. Larger glucagon to insulin ratio in the liver activates glycogen phosphorylase and inhibits glycogen synthetase
(glycogenolysis).
i. So the net effect is that here you are seeing glycogen lysis.
H & E: 1:00 - 2:00
Scribe: Brittney Wise
Tuesday, November 10, 2009
Proof: Laura Adams
Dr. Weignent
Pancreatic Endocrinology and Regulation of Plasma Glucose
Page 5 of 5
c. Gluconeogenic enzymes are increased over glycolytic enzymes in the liver (gluconeogenesis). Catecholamines
are released that amplify the effects of glucagon in the liver.
i. The idea here is to gather what you have stored and deliver it to the system.
d. Muscle: Increased proteolysis and release of amino acids and lactate for liver glucose synthesis.
i. In the absence of insulin you don’t have this increase in protein synthesis and you don’t have the amino
acid uptake.
ii. Instead the muscle starts to break down and it starts to give you amino acids that can be transported to the
liver and utilized for gluconeogenesis. The muscle now becomes a source through proteolysis and the
release of amino acids.
iii. Ultimately if things get bad enough your muscles can experience anaerobic glycolysis resulting in the
production of lactate which can contribute to this process.
e. Adipose: Activation of hormone-sensitive lipase (catecholamine, phosphorylation) and release of FFA and
glycerol (glucose-sparing role by FFA in muscle, liver, and adipose). Acetyl-CoA carboxylase is inhibited in the
liver facilitating ketone body synthesis.
i. Acetly-CoA is being inhibited because glucagon is present.
XVI.
[S17] Diabetes
a. He thinks based off of what he’s read that diabetes is caused by problems with the beta cell itself. At first when
you can’t take glucose up, the beta cell starts to make a little more insulin. After a while, he believes that it
wears out and gets tired and ultimately it struggles to keep pace. Eventually you make more ketone bodies as a
result of insulin resistance. Not only do the insulin levels eventually get low but there are problems in the
tissues themselves. It is post-receptor events that are probably tied into what the fatty acids are doing in cells,
probably tied to some phosphorylation in cells, which probably influence the glucose transporters.
Age of Onset
Islet auto-antibodies
Plasma Insulin
Plasma Glucose
Body Mass
Ketone Bodies
Insulin resistance
Treatment
XVII.
Type 1 (Juvenile)
< 20 years
Yes
Absent to low
High
Low to Normal
High
No
Insulin
Type 2
> 35 years *****
No
Normal to high
High
Obese (80%)
Low
Yes
Diet, then insulin or sulfonylureas
[S18] Symptoms
a. Hyperglycemia and Hyperkalemia
i. If you can’t take up glucose because of the issues at the insulin receptor then you have high levels of
glucose in the serum and you have a hyperkalemia develop.
b. Glucosuria – amount of glucose filtered exceeds the Tm of the renal glucose transporter. Therefore, filtered
amount exceeds the capacity for reabsorption and glucose “spills” into the urine.
c. Polyuria (excess urine) – excess filtered load of glucose exerts and osmotic effect in the tubular lumen, results
in an osmotic dieresis (excess of urine).
d. Polydipsia – dehydration from excessive urination and plasma hyperosmolarity activates the thirst reflex
i. this stimulates ADH which now promotes a thirst reflex
e. Polyphagia – excessive food consumption
i. There is a point where the body realizes its losing calories and not being fed because it’s still hungry and
so the person continues to eat.
XVIII. [S19] Diabetes
a. Retinopathy – most common cause of blindness in people of working age
b. Nephropathy – 16% of all new patients needing renal replacement therapy
c. Erectile Dysfunction – may affect up to 50% of men with long-standing diabetes
d. Coronary and cerebrovascular disease – 2-4 fold increased risk of coronary heart disease and stroke; 75% have
hypertension
e. Foot problems – 15% of people with diabetes develop foot ulcers; 5-15% of people with diabetic foot ulcers
need amputations
f. In general there is a non-enzymatic glycosylation of proteins and they are called AGE (Advanced Glycation End
products). There are a lot of problems in membrane transport and membrane functions. As a result, people will
develop a retinopathy in the eye which will lead to a blindness etc. (see above for rest of symptoms)
[End 43:58 minutes]