Endocrine versus exocrine pancreas
(3 cells
- Insulin
- Amylin
- TRH
a cells
- Glucagon
- GLP-1
Pancreatic Islet
(human adult pancreas)
endocrine/ '
insulin glucagon
nuclei
exocrine
8 cells
somatostatin
PP cells
- Pancreatic polypeptide
Scharfmann eta I., 2008 PMID189582B9
Pancreatic islets represent 1 - 2 % of pancreas, but blood flow through them represents 10 - 15 %.
^ CGRP
cu c
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Substance P (sensoric n.)
Pancreas innervation
0
Uncinate process
Sup. mesenteric vein and artery
Basal secretion I Glu-stimulated secretion I (a-AR)
Somatostatin
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O
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fD OJ O
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Glucagon PP
nsulin
Characteristics
- Polypeptide
- Secretory granules - free insulin and C-peptide
- Two types of secretory granules:
- Quickly secretable (5 %)
- Reserve pool (95 %)
- Half-time 3 - 8 min
- Degradation - liver ( up to 50 %), kidneys, target tissues (insulin proteases)
p chiii-i V. !
Fast-acting analogues
InsuJin lisprn Insuii
Long-acilng analogues
kisuin glargjna     A) D&temf insulin
Coflfilitul^e pathway
Reg^ted C*S membrane pathway
secretion
Secretion of insulin is pulsatile and shows rhytmicity. Stimulation of insulin secretion by glucose is biphasic. Glucose exhibits incretin effect.
51
secretion - „normal" and obese
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•—i Obese
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51
Regulation of insulin secretion
Glucose
(3 cells = neuroendocrine integrator, response to:
- Plasmatic concentrations of substrates (AA, Glu)
- PC of hormones (insulin, GLP-1, somatostatin, adrenaline)
- PC of neurotransmitters (noradrenaline, acetylcholine)
Endoplasmic reticulum
AA - Leu, Arg, Lys
- Generation of ATP
- Direct depolarization of plasmatic membrane
Modification of mRNA translation -   Glu-(+) mRNA
Other: - GH, VIP, secretin, gastrin, glucocorticoids, prolactin, placental lactogene, sex hormones
Glucose is the main stimulus for insulin secretion. Glucose has a permissive effect on secretion of other insulin secretion modulators.
Glucose
17 Glucose transporter
j Glucokinase G lucose-6 - phosph ate
1
Glycolysis
Mitochondrion
Intracellular,. Ca2+ stores <
Insulin
O Ca' containing p.
granules
Amino acids Ketoacids
Acetylcholine {+) CCK (+)
Glucagon (+} GLP-1 (+)
Epinephrine (-) Norepinephrine (-) Somatostatin (-)
Voltage-dependent A NCa2+ channel
ATP-sensitive K* channel
^ Ca2+
)
Depolarization
Characteristics
- 2 a and 2 (3 subunits
- TK activity
- Phosphorylation of IRS 1-4 (insulin receptor substrate)
- Interaction with other cell substrates
- PI3K (phosphatydylinositol-3-kinase)
- MAPK (mitogen-activated protein kinase)
a subunits = Ligand binding
(3 subunits = TK activity
Endocytosis of IR
Endosome acidification
Insulin dissociatio
■=>
Phosphorylation
Degradation of insulin
IRS4
IRS3
Number of available IR is influenced by exercise, diet, insulin itself and by other hormones. Obesity and chronic hyperinsulinemia causes significant decrease in number of IR, exercise and starvation significant increase in number of IR.
r-*-
T Glucose uptake & T Glycolysis t Glycogen synthesis & \ GEuconeogenesis t LipogenGsis & I Lipolysis T Protein synthesis & 4- Proteolysis
Ceit surviva [/growth__j
Physiologie effects of insulin
Immediate effects
- Seconds
- Modulation of K+and Glu transport
Early effects
- Several minutes
- Regulation of metabolic activity
Medium-term effects
- Minutes to hours
- Regulation of metabolic activity
Delayed effects Hours to days Cell growth Cell differentation
Effect of insulin on target tissue is anabolic and is mediated by insulin receptor.
mmediate effects of insulin on target tissues
Utilization of glucose
- Approx. 40 % of glucose in body
- Approx. 80-90% skeletal muscles
- Adipose tissue - adipocytes
- GLUT4
While GLUT1 is responsible Tor basal uptake of glucose by skeletal muscles and adipocytes, GLUT4 is stimulated by insulin and is responsible for insulin-stimulated uptake of glucose.
Transporter	Expression	Function
GLUTI	- Ubiquitous - Ery, endothelial cells (CNS), placenta, kidneys, colon - Skeletal muscles and adipocytes	-   Basal uptake of Glu
GLUT2	- (3 cells of pancreas - Liver, small intestine, kidneys	- Glu sensor - Uptake of Glu during high concentrations of circulating Glu
GLUT3	- Primarily neurons - Placenta, liver, epithelial cells of GIT	- Basal uptake of Glu - Essential role in CNS
GLUT4	- Skeletal muscles and adipocytes - Vesicles!	- Insulin-stimulated uptake of Glu
	-  Jejunum, sperms	-  Transport of Fru
Utilization of glucose is the main immediate effect of insulin.
Early and medium-term effects of insulin
-   Determined by phosphorylation of enzyme connected to metabolic pathways. Skeletal muscles, adipose tissue, liver
Production of ketone bodies (-)
Dephosphorylation of hormone-sensitive lipase = inhibition of triglyceride utilization
Activation of acetylcoenzyme A carboxylase (lipogenesis) Antagonization of catecholamines effect on lipolysis
Utilization of glucose
- liver
- Stimulation of expression of enzymes connected to Glu utilization (glucokinase, pyruvate kinase) and lipogenic enzymes
- Inhibition of enzymes connected to Glu production (phosphoenolpyruvate carboxykinase, glucose-6-phosphatase)
- Synthesis of glycogen
- Inhibition of production of keto bodies
T Glycogen j I synthase
Glycogen Phosphorylase TG
Glucose-1-P
Gluconeogenesis
{2) Pyruvate
I
(2) Ofcaioacetate
I I    I PEP cartoxykinase f G (2) PEP
I
(2) 3-Phosphoglycerate
t
12} 1,3-Bisphosphoglycerate
Fructose-1,6-Diphosphate
^ Fruetose-1,6-bisphosphate f(j Fructose-6-phosphate
t
Giucose-6-phosphate
' '    |. QIUiBOWrtSB'8 |G
GI ucose-6-ph osphate
:
Fructose-6-phosp hate
*TP Phospho- -
ADP-<-^ I Iruclokiriaae t«
Fructose-1,6-bisphosphate
Dihydroxyacetone phosphate
:
Gl ycer a Ide hyde-3 - pho sp h ate
1:3-Bisphosphog!ycerate
3- Ph os phcglyce rate
2-Phosphoglycerate
Phosphoenolpyruvate
tl
Glucose
Pyruvate j ^ kinase    T w
Pyruvate
nsulin and skeletal muscles
(+) uptake of glucose (GLUT4)
(+) glycogen synthesis
(+) transport of AA
(+) translation of mRNA
(-) degradation of proteins
(+) preference of fat reserves
mechanism - mTOR phosphorylation
nsulin and liver
Direct effects of insulin
IGlycogenolysis IGluconeogenesis
Indirect effects of insulin
I Decrease free fatty acid
flux to liver I Glucagon secretion
Adipose tissue
Glucose
State versus fasted-state
Fed-state
Insulin *
Fasted-state; Exercise
Epinephrine
Glycerol Lactate
L Amino acids
-Glucagon
Norepinephrine?
NEFA
Hypoglycemia
(-) insulin secretion (+) glucagon and adrenaline secretion (liver)
(+) GH and Cortisol (decreased utilization of Glu)
Neurogenic
Sweaty Hungry Tingling
Shaky/tremulous Heart pounding Nervous/anxious
Blood sugar low (p< 0.001)
2-
oH
±
\        I T
EU     ADB PAB
Neuroglycopenic
Warm Weak
Difficulty thinking/confused
Tired/drowsy
Faint
Dizzy
Difficulty speaking Blurred vision
Hypo
Catecholamines and glycaemia
Decreased glucose
Decreased Increased
insulin glucagon
I I
(Lost in F1 DM) (Lost in MDM)
(PNS)
f Increased sympathoadrenal outflow
'.■■■—[•■'- i (SNS' i
it    Adrenal r\ A A,
medulla V * Increased NE      Increased ACh
<------A   J (palpitations,    (sweating, hunger)
X_J tremor, arousal)
Increased Increased
epinephrine neurogenic symptoms
I I
(Often attenuated in T1 DM)   (Often attenuated in T1 DM)
Do
increased glucose production
Decreased .
, Increased
ingestion of carbohydrates clearance        s . '
Y Increased ,
glucose
Vegetative nervous system represents an important mechanism preventing hypoglycemia.
t Epinephrine
r
Liver
I
Pancreatic islets
I Insulin t Glucagon
I
Muscle
ß2
Fat
ßi,ß2 (?ß3)
* t Glycolysis \ Glucose tLipolysis
/ J transport
t Glycogenolysis "\ &_      t Lactate r
tGluconeogenesisj ^   and Alanine
t Glucose production
I Glucose utilization _I
fu
At
)oh
I
Glycerol NEFA
I
t Glucose
Adrenaline prepares body to immediate performance, it mobilizes energetic substrate - glucose - as a source of energy.
Diabetes mellitus type 1
Muscle
Lactate Amino acids
Glucose Ketones
Kidney
Glucose Ketones
Triglyceride
FFA
Adipose tissue
w <n CO
E
"ČĎ Ü i
CD.
Genetic predisposition
Environmental trigger (virus?)
I
100 -i
50-
Islet cell-directed antibodies
T-cell-mediated ß-cell injury
Regulatory -T-cells?-
DKA trigger (illness?)
Impaired 1st-phase insulin secretion
M-►
Stable diabetes
■> Unstable diabetes
«-►
I
3
I
5
I
6
I
7
8
10
Time (yrs)
DM1 is associated with mobilization of substrates for gluconeogenesis and ketogenesis from muscle and adipose tissue, increased gluconeogenesis and ketogenesis in the liver, as well as disturbed substrate intake by peripheral tissues.
Diabetes mellitus type 2
Clinical relevance
Insulin resistance
- Mutation in IR gene
Defects in insulin secretion
- Mutation in insulin gene (proinsulin)
- Mutation in mitochondrial genes
- MODY (Maturity-onset diabetes of the young)
- HNF-4a (MODY 1)
- Glucokinase (MODY 2)
- HNF-la (MODY 3)
- IPFl(MODY4)
- HNF-lß (MODY 5)
- NeuroDl/BETA2 (MODY 6)
Glucose
Endoplasmic reticulum
ATP-sensilive K+ channel
DM2 is multifactorial disease connected with resistence of peripheral tissues (muscles, adipose tissue) to insulin, disturbed insulin secretion (under glycemia influence) and increased glucose production in liver.
■
What are the
Proteins
Protein catabolism Negative nitrogen balance
Lipids
- Lipid catabolism with production of ketone bodies
- Decreased synthesis of FA and triglycerids
- Increased concentration of free FA
- FA catabolism, production of ketone bodies
Hyperglycemia
- Glycosuria, osmotic diuresis and polyuria
- Increased plasma osmolality, polydipsia, ADH
- Dehydratation
- Decreased blood pressure and volume of ECF Polyphagy
Ketoacidosis
- Metabolic acidosis
- Hyperventilation
- Acidification of urine
- Hyperkalemia
Ě100
IjJ
50-
/ subject	
	
Fasting plasma
glucose concentration
T me after oral glucose [hi]
KEY
I
Range for diagnosis of pre-diabetes
blucagon
Characteristics
- Peptide hormone (29 AA)
- Syntesized as proglucagon
- Pancreas
- Enteroendocrine eels in GIT
- CNS
- Alternative splicing creates other peptides, most important GLP-1
- Short half-life (5-10 min)
- Degradation in liver
Secretion (+) AA
(+) hypoglycemia Receptors
- Liver, (3 cells, kidneys, heart, adipose tissue, blood vessels, CNS, stomach, adrenal glands
Functions
- Glucose homeostasis - insulin antagonism
Glucagon release is stimulated
■ Hypoglycemia
■ Epinephrine (fe)
■ Vagal stimulation
Glucagon release is inhibited by:
* Hyperglycemia
* Somatostatin
I    ^>   Mobilisation of Ca2
PGC-t -* PEPCK G-6-Pase
Cytoplasm
a *
i Glycolysis I Glycogenesis    T Gluconeogenesis
Phosphatase t Glycogenosis ,
T Phosphorylase Kinase |
—V
Glucagon t Hepatic glucose output
Proglucagon - alternative splicing
Glicentin - L-cells (small intestine) Preproglucagon
- Stimulation of insulin secretion
- Inhibition of stomach secretion
- Trophic effect in intestine Proglucagon
Oxyntomodulin - colon (anorexigenic factor)
- Postprandial secretion
- Increased energy expandituree
- (+) glucose tolerance
GRPP
(inhibition of Glu-stimulated insulin secretion, modulator of energy metabolism)
IP-1,IP-2 L-cells
(modulation of insulin secretion?)
a-cell
Glicentin-related pancreatic peptide
Intervening peptide 1
Major proglucagon fragment
GLP-1
Psck2 dominant
Glucagon
GRPP
IP1
IP2
GLP-2
Psck1/3 dominant
GLP-1
GLP-2
] PS	GRPP	Glucagon	IP1	GLP-1	IP2	GLP-2
						
	GRPP _i	Glucagon	IP1	GLP-1	IP2	GLP-2 _/
Glucagon
IP1
Oxyntomodulin
IP2
GRPP    Glucagon     IP1 Glicentin
GLP-1 and GLP-2
Charakteristics
- Neuroendocrine L cells
Functions- GLP-1 (GLP1R)
- (+) insulin secretion
- (-) glucagon secretion
- (+) neogenesis and proliferation of pancreatic isles
- (-) ß cell apoptosis
Functions-GLP-2 (GLP2R)
- (-) antrum motility
- (-) of gastric juice secretion stimulated by food
- Trophic effect (small intestine, colon)
- (-) enterocyte apoptosis
- (+) blood flow and nutrient absorption
CNS
- Caudal NTS-viscerosensoric information
- Activation of POMC neurons
- Inhibition of food intake (anorexigenic factor)
- Induction of satiety = quick modification of food intake based on metabolic substrates (glucose), hormones (leptin) and neuropeptides.
Clinical relevance
- Agonists of GLP1R- treatment of DM2
- Exenatid, lixisenatid
- Liraglutid
- Albiglutid, dulaglutid
- Inhibitors of dipeptidyl peptidase 4 (DPP4)
- sitagliptin, vildagliptin, saxagliptin, alogliptin, linagliptin
- DM2
GLP-1 and GLP-2 show incretin effect preparing insulin secretion in dependence on glucose presence in GIT lumen
Glucagon - secretion and its regulation
Caz+ Na1 Ca2*
Glucagon secretion requires depolarizing cascade which ends with Caz+ influx and glucagon secretion
Physiological effects of glucagon
Target enzyme	Metabolic response
(+) Glu-6-phosphatase expression	Glu entering circulation
(-) glucokinases	Lower rate of Glu entering glycolytic cascade
(+) phosphorylation (activation) of glycogen Phosphorylase	Stimulation of glycogenolysis
Inhibition of glycogen synthase	Inhibition of glycogen synthesis
Inactivation of phosphofructokinase 2, activation of fructose-6-phosphatase	Inhibition of glycolysis, stimulation of gluconeogenesis
Inhibition of pyruvate kinase	Inhibition of glycolysis
\l Insulirvglucagon
Other effects
Stimulation of phosphorylation (activation) of hormone-sensitive lipase and lipolysis - substrates for gluconeogenesis and antibody production
FFA as a source of energy mainly for skeletal muscles
arget organ for glucagon effect is liver, where it stimulates gluconeogenesis and glycogenolysis, thus increasing glycemia.
ntegration of system insulin - glucagon
Orbital prefrontal cortex
I
I I
I
r
J Glucose
Physiology
Medial prefrontal cortex
]
Pancreatic islets
p-cells —► 1 Insulin i
u-cells —► t Glucagon
t	A-	Hippocampus
Dorsal midline thalamus		Brain stem
±		Amygdala
Hypothalamus	\	
Ť Sympathoadrenal activity +
i Insulin + t Glucagon
y
J
Somatostatin
Characteristics
Peptide hormone (14 AA) Secretion stimulated by:
- food rich in lipids (FFA)
- food rich in saccharides (Glu)
- food rich in proteins (AA - Leu, Arg)
Functions
- Paracrine effect - (-) insulin, glucagon, PP
- Inhibition of practically all exocrine and endocri GIT functions
- Inhibition of motility
Clinical relevance
- Somatostatin analogues and insulin/glucagon producing tumors
Insulin
Role of paracrine cholinergic signaling in somatostatin secretion - paracrine effect of acetylcholine stimulates insulin secretion, but also secretion of somatostatin.
Pancreatic polypeptide - PP
Characteristics
- Peptide hormone (36 AA)
- Secretion stimulated by:
- Food (proteins), distention of stomach
- Exercise
- Direct vagal stimulation
- Insulin-induced hypoglycemia
- Secretion inhibited by:
- Hyperglycemia
- Bombesin, somatostatin
- Receptors:
- Stomach, small intestine, colon, pankreas, prostate, enteric NS, CNS
Functions
- Inhibition of pancreatic exocrine secretion
- Inhibition of gallbladder contraction Modulation of stomach secretion Modulation of stomach motility Regulation of food intake?
PVN
Activity of hepatic vagal nerve
energy expenditure T
pancreatic exocrine secretion ]
Ghrelin
gastric emptying 1
Pancreatic polypeptide stimulates energy consumption thrc sympathetic stimulation of brown adipose tissue. It also modulates secretion of CCK and inhibits ghrelin secretion.
Amylin
Characteristics
- Peptide hormone (37 AA)
- ß cells, stomach, proximal small intestine
- Posttranslational modification (amidation)
- Secretion together with insulin and C-peptide
- Increase after application of:
- p.o. and p.e. glucose
Function
- Slowing of emptying of stomach on vagal basis
- Inhibition of glucagon secretion (postprandial)
- Muscles
- Inhibition of glycogen synthesis Stimulation of glycogenosis, glycolysis and lactate production
food 0 intake ,tr'
Clinical relevance
- Increased plasmatic concentration during obesity, gastric diabetes and DM2
- Analogue of amylin DM1 and DM2 therapy (pramlintid) -amylin-deficient states
glucagon 0 release
pancreas
amyl
* Adiposity
* Nociception
* Maternal behaviors
• Neurogenesis
• Anxiolytic/antidepressant
• Bone homeostasis