PHRM246 Notes-Glucose Control & Diabetes PDF

BIOSYNTHESIS OF INSULIN Synthesis of Pre-proinsulin. Conversion of pre-proinsulin to proinsulin. Conversion of proinsulin to insulin.  Insulin is a peptide hormone synthesized as a precursor (pro-insulin) which undergoes proteolytic cleavage to form a dipeptide; the cleaved polypept...

BIOSYNTHESIS OF INSULIN Synthesis of Pre-proinsulin. Conversion of pre-proinsulin to proinsulin. Conversion of proinsulin to insulin.  Insulin is a peptide hormone synthesized as a precursor (pro-insulin) which undergoes proteolytic cleavage to form a dipeptide; the cleaved polypeptide remnant is termed protein C.  Both are secreted from the β-cell, normal individuals secrete both insulin and (but much less) pro-insulin.  Type 2 diabetics are found to secrete high levels of pro-insulin (pro-insulin is inactive); measuring the level of C-protein is a more accurate estimation of normal insulin secretion in type 2 diabetes.  GENETICS OF INSULIN SYNTHESIS The proinsulin precursor of insulin is encoded by the INS gene  In the post-absorptive period of a normal individual, low basal levels of circulating insulin are maintained through constant β-cell secretion. This suppresses lipolysis, proteolysis and glycogenolysis.  After ingesting a meal a burst of insulin secretion occurs in response to elevated glucose and amino acid levels. When glucose levels return to basal levels, insulin secretion returns to its basal level.  Insulin secretion is regulated by glucose levels, certain amino acids, hormones and autonomic mediators.  Secretion is most commonly elicited by elevated glucose levels;.  The influx of Ca2+ results in a pulsatile secretion of insulin; continued Ca2+ influx results in activation of transcription factors for insulin.  Oral glucose elicits more insulin secretion than native glucose; oral administration elicits gut hormones which augment the insulin response.  Insulin is normally catabolized by insulinase produced by the kidney. Pancreatic Islet Cells and their Secretory Products Cell Types Approximate Percent Secretory Products of Islet Mass Alpha (A) cell 20 % Glucagon, proglucagon Beta (B) cell 75 % Insulin, C-peptide, proinsulin, amylin Delta (D) cell 3–5 % Somatostatin G cell 1% Gastrin F cell (PP cell)1 1% Pancreatic polypeptide (PP)  Insulin binds to specific high affinity membrane receptors with tyrosine kinase activity  Phosphorylation cascade results in translocation of GLUT-4 (and some Glut-1) transport proteins into the plasma membrane.  It induces the transcription of several genes resulting in increased glucose catabolism & inhibits the transcription of genes involved in gluconeogenesis  Insulin promotes the uptake of K+ into cells.  Synthesis & release of insulin is modulated by: 1. Glucose (most important), AAs, FAs & ketone bodies stimulate release 2. Glucagon & somatostation inhibit releases 3. α-Adrenergic stimulation inhibits release (most important) 4. β-Adrenergic stimulation promotes release 5. Elevated intracellular Ca2+ promotes release.  CATABOLISM OF INSULIN Half life: 3-5 minutes Major organs of degradation Liver Kidney Placenta 50% of insulin removed in a single pass through liver MECHANISM: Insulin-specific protease. Glutathione insulin transhydrogenase (Insulinase)  Non-diabetic Insulin and Glucose Profiles Breakfast Lunch Supper 75 Insulin Insulin 50 (µU/mL) 25 0 Basal insulin 9.0 Glucose 6.0 Glucose (mmo/L) 3.0 Basal glucose 0 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 a.m. p.m. Time of Day Normally, your blood glucose levels increase slightly after you eat. This increase causes your pancreas to release insulin so that your blood glucose levels do not get too high  Normal insulin metabolism  Insulin after a meal: Stimulates storage of glucose as glycogen Inhibits gluconeogenesis Enhances fat deposition in adipose tissue Increases protein synthesis BIOLOGICAL EFFECTS OF INSULIN Regulation of Insulin Secretion INSULIN-MEDIATED GLUCOSE UP-TAKE Effect on carbohydrate metabolism  Glucose uptake oSkeletal muscles oCardiac muscles oAdipose tissue oMammary glands  Effect on carbohydrate metabolism (contd) Insulin independent tissues: o Brain o RBC o Testis o Kidney o Retina o Intestinal mucosal cells  CARBOHYDRATE METABOLISM Metabolism Net Effect Effect on important enzyme Glycolysis Increased Glucokinase Phosphofructokinase Pyruvate kinase Glycogenesis Increased Glycogen synthatase HMP shunt Increased Glucose 6-phosphate dehydrogenase Gluconeogenisis Decreased Pyruvate carboxylase Phosphoenol Pyruvate carboxylakinase Glucose 6-phosphatase Glycogenolysis Decreased Glycogen phosphorylase  Lipid Metabolism Metabolism Net effect Effect on important enzymes Lipogenesis Increased de novo FA Synthesis Increased Acetyl CoA carboxylase Availability of NADPH Adipose tissue Increased Provide α-glycerol-3-PO4 Lipoprotein lipase Lipolysis Decreased Hormone sensitive lipase Ketogenesis Decreased HMG CoA synthetase Lipoprotein Increased Utilization of VLDL & LDL  Protein Metabolism Metabolism Net Effect Effect on important enzymes Protein Increased RNA polymerase synthesis Amino acids up take Protein Decreased Transaminases degradation Deaminases CELL GROWTH & DEVELOPMENT Promotes cell growth and development Mediated by o Epidermal growth factors o Platelet derived growth factor o Prostaglandins ADVERSE EFFECTS OF INSULIN Hypoglycemia Lipoatrophy Lipohypertrophy Obesity Insulin allergy Insulin antibodies Insulin induced edema CLINICAL CORRELATIONS  Symptoms of Diabetes Frequent urination Thirst Hunger Weight loss (despite thirst, hunger) Fatigue Vision impairment LEPRECHAUNISM  INSULINOMA HYPERINSULINISM  Islet cell tumors, producing such symptoms, are called insulinomas  Insulin shock High level of insulin. Fall in blood glucose level. CNS depression. 50-70 mg/dl CNS excitability 20-50 mg/dl CONVULSION & COMA < 20 mg/dl COMA HYPOGLYCAEMIA IN FOETUS OF DIABETIC MOTHER Maternal blood glucose level. Transferred through placenta. Fetal blood glucose level. o β-cells of foetus secrete insulin. o Saturation of placenta 30 mmol/L o Hypoglycaemia Glucose Homeostasis  Introduction Glucose is the carbohydrate currency of the body. An adult human body contains about 18g free glucose. This amount is just sufficient to meet the basal energy requirements of the body for one hour. The liver has about 100g stored glycogen. Besides this it is capable of producing 125- 150 mg of glucose/min or 180-220g/24hrs.  Normal blood sugar level varies from 80- 120 mg per 100 ml (fasting) & 100-120 mg per 100 ml (after meal). Plasma concentration of glucose is slightly higher (about 15%) than blood glucose. The glucose concentration of 180 mg/dl (plasma or blood) corresponds to 10mmol/l.  Large quantities of sugar are constantly entering the blood stream (absorption, gluconeogenesis, glycogenolysis) & are constantly being removed from it (glycogenesis, oxidation of sugar, lipid synthesis). In spite of those opposing forces, blood sugar level remains fairly constant within this limited range. This indicates that there must be a strong machinery for blood sugar regulation in the body.  Regulation of blood glucose level The mechanism involves the following factors: ALIMENTARY MECHANISM: Assimilation limits of glucose o 200g glucose given by mouth; no sugar found in the urine. o 300-500g given- large amount of water is osmotically- drawn in & stomach becomes distended. o >500g given at a time, subject develops nausea & the glucose is vomited out.  Digestion of starch: slow & long process. Necessarily absorption becomes slow. So that sharp rise of blood sugar is prevented. Rate of absorption: maximum limit of absorption of glucose is about 1.84 g per kg per hour. What ever be the amount of sugar given, the rate of absorption does not go beyond it, hence blood sugar cannot have a sharp rise. ROLE OF LIVER : Liver stores sugar as glycogen, when blood sugar rises & thus rise of blood sugar is checked. Liver mobilizes glycogen stores, when blood sugar level falls & speeds the rate of gluconeogenesis & thus restores the level to normal. ROLE OF MUSCLES: Muscles stores glucose from blood stream & stores it as glycogen, thus tending to reduce blood sugar. In hypoglycemia or after severe muscular exercise, lactic acid is mobilized from the muscles, converted first to glycogen then to glucose in the liver & discharged into blood stream, raising the blood sugar level. ROLE OF ENDOCRINES (endocrines are chief regulators of blood sugar level) Insulin : strongest blood sugar reducing factor; lowers blood sugar in three ways: oIncreases glycogenesis oPromotes glucose uptake in muscles & adipose tissues. oPrevents gluconeogenesis  ROLE OF ENDOCRINES… Anterior pituitary : These hormones increases blood sugar levels oGrowth hormone: Decreases peripheral utilizations of glucose & increases blood sugar levels. oACTH: Through adrenal cortex increases blood sugar. oTSH: Through thyroid increases blood sugar.  Posterior pituitary: large dose of vasopressin & oxytocin increases the blood sugar levels temporarily. Adrenal cortex: Glucocorticoid work in following ways; o Decreases peripheral utilization of glucose due to retardation of phosphorylation. o Increases gluconeogenesis in the liver due to retarded amino acids incorporation into protein, thus making more glucogenic material available. o Administration of glucocorticoids produces temporarily diabetes in a number of animal species. o Partially pancreatectomised animals may be made permanently diabetic by administration of cortisol or cortisone.  Epinephrine & Norepineprine: Raises blood sugar levels o By stimulating glycogenolysis from liver. o Converting muscle glycogen into lactic acid, increases blood sugar level. o Also increases BMR by 20%, & increases the oxidation of glucose in the tissues. Thyroid : effects are exhibited by thyroxine o Increase in the peripheral utilization & combustion of glucose in the tissues. o Stimulation of glycogenolysis & gluconeogenesis Glucagon: Increases blood sugar due to glycogenolysis in liver & gluconeogenesis. ROLE OF NERVOUS SYSTEM: Hypothalamic lesions causes disturbances of carbohydrate metabolism , namely hypoglycemia, increased sensitivity to insulin. Autonomic nervous system takes a great part in blood glucose regulation by following ways o Stimulation of the right vagus reduces blood sugar level by increasing insulin secretion. o Stimulation of the sympathetic nerves increases blood sugar level by mobilizing liver glycogen & by stimulating epinephrine secretion. ROLE OF BLOOD SUGAR : Blood sugar regulates its own level. Hyperglycemia stimulates insulin secretion directly acting on the beta cells, & stimulating the right vagus It also increases the rate of oxidation of sugar in the tissue independent of hormones Depresses the secretion of the growth hormone. In this way, the raised blood sugar is brought down to normal. On the other hand, hypoglycemia depresses insulin secretion by opposite effects. ROLE OF TISSUES, TISSUE FLUID & SKIN : The tissues fluid, having nearly the same glucose content as plasma, can store a large amount of glucose. Any rise or fall of blood sugar is at once compensated by appropriate exchange with tissue fluid. The skin & subcutaneous tissue can store a large amount of glucose temporarily. The tissues in general use up sugar in a number of ways- such as, conversion into lipids, synthesis of other substances, oxidation of glucose. ROLE OF KIDNEYS: Kidneys act as the last outposts. Glucose is continuously filtered by the glomeruli, reabsorbed & returned to the blood. When blood sugar goes above the renal threshold(180 mg per 100 ml), it leaks out through the kidneys. This value is referred to as renal threshold for glucose. The maximum ability of the renal tubules to reabsorb glucose per minute is known as tubular maximum for glucose. The value is 350 mg/min.  Hypoglycemia Is a condition in which blood sugar level is below the normal level i.e., below 80 mg per 100ml. In diabetic subjects whose tissues are accustomed to high blood sugar, hypoglycemia symptoms may start at a blood sugar level much above normal.  Hypoglycemic symptoms depends on three factors: o The actual blood sugar level o The rapidity of blood sugar reduction o The previous blood sugar level.  Since nerve cells have very little stored food & use sugar mostly as a sole source of energy, hypoglycemia affects the nerve cells first. Thus, the earliest manifestation will be nervous in origin & they are: o A feeling of fatigue, weakness & hunger. o Extreme anxiety & irritability o Abnormal behavior as in alcohol poisoning. o Tremors develop & fine movements are not possible. o Vasomotor disturbances, such as flushing or pallor, perspiration & chilliness. o Lastly there may be delirium, diabetic coma, convulsion & loss of deep reflexes. Hypoglycemia symptoms are relieved by administration of glucose.  Compensatory reactions of hypoglycemia: o Stimulates hypothalamus which then promotes the ACTH secretion & other hormones which then oppose the actions of insulin & restore the blood sugar level to normal. o Hypoglycemia also stimulates the secretion of epinephrine which stimulates glycogenolysis & raises the blood sugar level.  Hyperglycemia blood sugar increases above the normal level, i.e., above 120mg per 100 ml. blood sugar level exceeds the renal threshold (180 mg per 100 ml), sugar appears in the urine. Persistent hyperglycemia occurs when there is diminished utilization of glucose, & discharge of excess sugar from the liver. Hyperfunction of some of the endocrine glands causes hyperglycemia. Lack or diminished secretion of insulin is the main factor which produces hyperglycemia & glycosuria as in diabetes melletus.  Glycosuria blood glucose level exceeds 180 mg glucose per 100 ml blood above the normal blood glucose level. The renal tubular cells are not able to reabsorb all the glucose, some glucose reaches the urinary bladder & glycosuria results.  Hypoglycemic drugs ; Sulfonylureas (acetohexamide, tolbutamide & gibenclamide) & Biguanides. These drugs promote the secretion of endogenous insulin & reduces blood glucose levels. Insulin : 2 types of insulin preparation are commercially available a. short acting b. long acting DIABETES  What is diabetes?  Diabetes mellitus (DM) is a group of diseases characterized by high levels of blood glucose resulting from defects in insulin production, insulin action, or both.  The term diabetes mellitus describes a metabolic disorder of multiple aetiology characterized by chronic hyperglycaemia with disturbances of carbohydrate, fat and protein metabolism resulting from defects in insulin secretion, insulin action, or both.  The effects of diabetes mellitus include long–term damage, dysfunction and failure of various organs.  Diabetes mellitus The term diabetes means that a large volume of urine is passed. The term mellitus means (sweet) dates from the time when the urine was tested by tasting. It is a disorder of metabolism characterized by high blood sugar level & excretion of sugar in urine.  Diabetes mellitus may present with characteristic symptoms such as thirst, polyuria, blurring of vision, and weight loss.  In its most severe forms, ketoacidosis or a non–ketotic hyper-osmolar state may develop and lead to stupor, coma and, in absence of effective treatment, death.  Often symptoms are not severe, or may be absent, and consequently hyperglycaemia sufficient to cause pathological and functional changes may be present for a long time before the diagnosis is made.  Principal abnormalities of DM are, oAn increased liberation of glucose in circulation from liver oReduced entrance of glucose in peripheral tissues. Hyperglycemia, glycosuria, ketosis, acidosis, diabetic coma, polyuria, weight loss in spite of polyphagia & polydipsia are the abnormal characteristics of diabetes. Major metabolic changes in diabetes Hyperglycemia Ketoacidosis Hyper-triglyceridemia Long term effects of diabetes Atherosclerosis Retinopathy Nephropathy Neuropathy  Diabetes Long-term Effects  The long–term effects of diabetes mellitus include progressive development of the specific complications of retinopathy with potential blindness, nephropathy that may lead to renal failure, and/or neuropathy with risk of foot ulcers, amputation, Charcot joints, and features of autonomic dysfunction, including sexual dysfunction.  People with diabetes are at increased risk of cardiovascular, peripheral vascular and cerebrovascular disease.  Burden of Diabetes  The development of diabetes is projected to reach pandemic proportions over the next 10-20 years.  International Diabetes Federation (IDF) data indicate that by the year 2025, the number of people affected will reach 333 million – 90% of these people will have Type 2 diabetes.  In most Western societies, the overall prevalence has reached 4- 6%, and is as high as 10-12% among 60-70-year-old people.  The annual health costs caused by diabetes and its complications account for around 6-12% of all health-care expenditure.  Types of Diabetes Type 1 Diabetes Mellitus Type 2 Diabetes Mellitus Gestational Diabetes Other types: LADA (latent auto-immune disease in adults) MODY (maturity-onset diabetes of youth) Secondary Diabetes Mellitus  Type 1 diabetes Was previously called insulin-dependent diabetes mellitus (IDDM) or juvenile-onset diabetes. Type 1 diabetes develops when the body’s immune system destroys pancreatic beta cells, the only cells in the body that make the hormone insulin that regulates blood glucose. This form of diabetes usually strikes children and young adults, although disease onset can occur at any age.  Type 1 diabetes may account for 5% to 10% of all diagnosed cases of diabetes. Risk factors for type 1 diabetes may include autoimmune, genetic, and environmental factors. Most often occurs in people under 30 years of age Peak onset between ages 11 and 13  Type 1 Diabetes Mellitus Etiology and Pathophysiology Progressive destruction of pancreatic  cells Autoantibodies cause a reduction of 80% to 90% of normal  cell function before manifestations occur Causes: Genetic predisposition Related to human leukocyte antigens (HLAs) Exposure to a virus Manifestations develop when the pancreas can no longer produce insulin Rapid onset of symptoms Present at ER with ketoacidosis  Type 1 Diabetes Mellitus Onset of Disease Weight loss Polydipsia Polyuria Polyphagia Diabetic ketoacidosis (DKA)  Occurs in the absence of exogenous insulin  Life-threatening condition  Results in metabolic acidosis  Type 2 diabetes  previously called non-insulin-dependent diabetes mellitus (NIDDM) or adult-onset diabetes.  account for about 90% to 95% of all diagnosed cases of diabetes.  begins as insulin resistance, a disorder in which the cells do not use insulin properly. As the need for insulin rises, the pancreas gradually loses its ability to produce insulin.  associated with older age, obesity, family history of diabetes, history of gestational diabetes, impaired glucose metabolism, physical inactivity, and race/ethnicity. is increasingly being diagnosed in children and adolescents. Accounts for 90% of patients with diabetes Usually occurs in people over 40 years of age 80-90% of patients are overweight  Type 2 Diabetes Mellitus Etiology and Pathophysiology Pancreas continues to produce some endogenous insulin Insulin produced is either insufficient or poorly utilized by the tissues Insulin resistance  Body tissues do not respond to insulin  Results in hyperglycemia  Impaired glucose tolerance (IGT) Occurs when the alteration in  cell function is mild Blood glucose levels are higher than normal but not high enough for a diagnosis of diabetes  Inappropriate glucose production by the liver  Not considered a primary factor in the development of type 2 diabetes Insulin resistance syndrome (syndrome X)  Cluster of abnormalities that act synergistically to  the risk of cardiovascular disease  Type 2 Diabetes Mellitus Onset of Disease Gradual onset Person may go many years with undetected hyperglycemia Marked hyperglycemia (500 to 1000 mg/dl)  Natural History of Type 2 Diabetes Normal Prediabetes Type 2 diabetes Insulin Increasing insulin resistance resistance Insulin Hyperinsulinemia, secretion then islet cell failure After meal Abnormal glucose glucose tolerance Fasting High sugar levels glucose Adapted from International Diabetes Center (IDC), Minneapolis, Minnesota. Pre-diabetes Impaired glucose tolerance and impaired fasting glucose  Prediabetes is a term used to distinguish people who are at increased risk of developing diabetes. Associated with impaired fasting glucose (IFG) or impaired glucose tolerance (IGT). Some people may have both IFG and IGT.  IFG - fasting blood sugar level is elevated (100 to 125 milligrams per decilitre or mg/dL) after an overnight fast but is not high enough to be classified as diabetes.  IGT - blood sugar level is elevated (140 to 199 mg/dL after a 2- hour oral glucose tolerance test), but is not high enough to be classified as diabetes.  Prediabetes… Progression to diabetes is not inevitable. Studies suggest that weight loss and increased physical activity among people with prediabetes prevent or delay diabetes and may return blood glucose levels to normal. People with prediabetes are already at increased risk for other adverse health outcomes such as heart disease and stroke.  Gestational diabetes  A form of glucose intolerance that is diagnosed in some women during pregnancy.  It is also more common among obese women and women with a family history of diabetes.  During pregnancy, gestational diabetes requires treatment to normalize maternal blood glucose levels to avoid complications in the infant.  After pregnancy, 5% to 10% of women with gestational diabetes are found to have type 2 diabetes.  Women who have had gestational diabetes have a 20% to 50% chance of developing diabetes in the next 5-10 years.  Other types of DM Other specific types of diabetes result from specific genetic conditions (such as maturity- onset diabetes of youth), surgery, drugs, malnutrition, infections, and other illnesses. Such types of diabetes may account for 1% to 5% of all diagnosed cases of diabetes.  MODY  MODY is a monogenic form of diabetes with an autosomal dominant mode of inheritance: ◦ Mutations in any one of several transcription factors or in the enzyme glucokinase lead to insufficient insulin release from pancreatic ß-cells, causing MODY. ◦ Different subtypes of MODY are identified based on the mutated gene.  Originally, diagnosis of MODY was based on presence of non- ketotic hyperglycemia in adolescents or young adults in conjunction with a family history of diabetes.  However, genetic testing has shown that MODY can occur at any age and that a family history of diabetes is not always obvious.  LADA  Latent Autoimmune Diabetes in Adults (LADA) is a form of autoimmune (type 1 diabetes) which is diagnosed in individuals who are older than the usual age of onset of type 1 diabetes.  Alternate terms that have been used for "LADA" include Late-onset Autoimmune Diabetes of Adulthood, "Slow Onset Type 1" diabetes, and sometimes also "Type 1.5  Often, patients with LADA are mistakenly thought to have type 2 diabetes, based on their age at the time of diagnosis.  LADA… About 80% of adults apparently with recently diagnosed Type 2 diabetes but with GAD auto-antibodies (i.e. LADA) progress to insulin requirement within 6 years. The potential value of identifying this group at high risk of progression to insulin dependence includes: – the avoidance of using metformin treatment – the early introduction of insulin therapy  Secondary DM Secondary causes of Diabetes mellitus include: Acromegaly, Cushing syndrome, Thyrotoxicosis, Pheochromocytoma Chronic pancreatitis, Cancer Drug induced hyperglycemia:  Drug induced hyperglycemia: Atypical Antipsychotics - Alter receptor binding characteristics, leading to increased insulin resistance. Beta-blockers - Inhibit insulin secretion. Calcium Channel Blockers - Inhibits secretion of insulin by interfering with cytosolic calcium release. Corticosteroids - Cause peripheral insulin resistance and gluconeogensis. Fluoro-quinolones - Inhibits insulin secretion by blocking ATP sensitive potassium channels. Naicin - They cause increased insulin resistance due to increased free fatty acid mobilization. Phenothiazines - Inhibit insulin secretion. Protease Inhibitors - Inhibit the conversion of proinsulin to insulin. Thiazide Diuretics - Inhibit insulin secretion due to hypokalemia. They also cause increased insulin resistance due to increased free fatty acid mobilization.  Diabetes Mellitus Diagnostic Studies Fasting plasma glucose level 126 mg/dl Random plasma glucose measurement 200 mg/dl plus symptoms Two-hour OGTT level 200 mg/dl using a glucose load of 75 g  Impaired glucose tolerance (IGT)  Fasting blood glucose level 110 mg/dl but less than 126 mg/dl Hemoglobin A1C test:  Measures blood levels over 2-3 months  High levels of glucose will attach to hemoglobin  Helps to ensure that the patient’s gluco-meter is accurate.  Glycosylated Hemoglobin: HbAlc Blood test that measures the amount of glucose that has been incorporated into the hemoglobin protein of the red blood cell (RBC). Reflects the lifespan of a RBC, so test will reveal the effectiveness of diabetes therapy for the preceding 8-12 weeks. HbA1c levels remain more stable than sugar levels. Not affected by short-term fluctuations in sugar Normal is 4-6% Evaluated periodically (1-2 per year if well controlled, more frequently if not)  Diabetes Mellitus Acute Complications Diabetic ketoacidosis (DKK) Hyperosmolar hyperglycemic nonketotic syndrome (HHNS) Hypoglycemia  Diabetes Ketoacidosis (DKA) Life-threatening illness in type 1 Hyperglycemia, dehydration, coma Excess glucose leads to dehydration, sodium and potassium loss Burning of fat leads to ketosis Kidneys unable to excrete ketones, leads to ketoacidosis  DKA… Diabetic ketoacidosis tends to occur in individuals younger than 19 years, but it may occur in patients with diabetes at any age. Criteria – Hyperglycemia: blood glucose >11mmol/L(200mg/dL) – Venous pH