Insulin is a hormone produced by the beta cells of the pancreas. Insulin delivered into the body through a syringe, insulin pen, or other delivery method is known as exogenous insulin. The role of exogenous insulin in treating diabetes mellitus was first discovered, and the substance refined, in 1921 at the University of Toronto by Sir Frederick Banting , and colleagues Best, Collip, and Mcleod. Commercial production began in 1923 at the newly formed Nordisk Insulin Labs (now Novo Nordisk) in Denmark, and at Eli Lilly and Co. in the USA.
How it worksEdit
Insulin is necessary to enable the body to perform normally. It controls the rate at which the body's cells can take in fuel (glucose). Without the insulin system, the body would burn fuel whenever it was available, instead of when it was most needed.With the insulin system working, insulin allows cells to use glucose found in the bloodstream, keeping them fed and preventing hyperglycemia. In the cells themselves, insulin aids in the anabolic (a positive, building or maintaining process) processes of turning glycogen stored in the liver and in muscles, into energy, and helps transform fatty acids and protein into forms both useful and necessary to the body.
In diabetes, insulin is not produced in adequate quantities, or some of the insulin is not accepted by the receptors. While there is plenty of glucose within the system, the body's cells cannot accept it, and suffer what's called intracellular hypoglycemia. The hyperglycemia seen in blood glucose readings represents the glucose present in the body, which, without enough insulin, is unable to use it properly--it's called extracellular hyperglycemia.
In those without diabetes, the healthy pancreas secretes insulin in pulses or spurts. Basal insulin secretion is a series of small pulses or spurts at a given rate day and night; these insulin pulses or spurts are to take care of the body's basic needs. When someone without diabetes eats a meal, the pancreas goes into higher gear, producing larger quantities of Post-prandial insulin to handle the additional glucose created by the food.
It is this pattern that diabetics try to mimic as closely as possible; with Basal insulin injections for the body's needs without considering food and Bolus insulin injections to cover meals replacing the Basal and Postprandial insulin their bodies no longer produce or do not produce in sufficient quantity.
Insulin, then, in 10 words or less, is the hormone that lowers blood glucose and feeds the body. And if you read no further, it would appear that as long as one has some insulin, either endogenous or exogenous, this is simple and everything will be fine.
Kinetics & dynamicsEdit
When reading various medical literature about insulin and its actions, one often sees the terms kinetics and dynamics used. Knowing what each means in terms of blood glucose can help you understand where it applies to you or your pet.
Insulin Kinetics refers to the time when an insulin can be measured in the bloodstream. It's important to understand that even though it's "officially" made its way there, the insulin has not yet done so in sufficient quantity to effectively begin to lower blood glucose.
Insulin Dynamics is the point where it has an effect on blood glucose levels.
The dotted line shows insulin entering the bloodstream (kinetics).
The bold line (dynamics) illustrates the insulin at the point where
blood glucose is lowered by it.
A good illustration of kinetics and dynamics is having a headache and taking an aspirin for it. You will get relief after the aspirin's level in your system has reached the dynamic stage. While it is in the kinetic one, you are still waiting for headache relief.
Complements to insulinEdit
There are other hormones present and also necessary to the body, which do the exact opposite of insulin--raising blood glucose levels. Cortisol,growth hormone, adrenalin AKA epinephrine, glucagon, progesterone and thyroid hormone are considered counterregulatory hormones as far as diabetes and blood glucose levels are concerned.
They need just as much consideration as insulin, because changes in their bloodstream levels, can mean a possible interference with insulin, or a need for more of it. These changes can occur normally within the body to supply extra fuel when needed, or as symptoms of a disease state (Acromegaly=too much growth hormone, Cushing's Disease=too much cortisol/cortisone, Hyperthyroidism=too much thyroid hormone, Hypothyroidism=too little thyroid hormone, Addison's disease=too little cortisol/cortisone ), or as a result of other medications, such as steroids.
The counter-regulatory hormones such as adrenalin/epinephrine, glucagon and cortisol/cortisone are released to provide extra energy to the body in various circumstances, or if the body believes it's threatened with hypoglycemia. In some cases this is part of the body's "self-defense" mechanism to counter the effects of too much insulin.
So there's more than just insulin one needs to think about. It's vital to life whether enough is produced by the body or whether it's injected. The other hormones are also vital to the body and being able to understand how the various hormones react or interact with each other is very helpful in understanding and successfully controlling diabetes.
The strength of an insulin is measured in International Units (IUs) of insulin per millilitre (ml). The two most common strengths used in pets are U40 (40 units insulin per ml) and U100 (100 units insulin per ml). U100 insulins are developed primarily for use in humans, although they are commonly used in pets. U40 insulins were commonly available in the US until the 1980's, along with the now-standard U100 strength. They are still available in some countries, but have been phased out in many, in favor of U100. For many years, insulin was produced in varying strengths
U40 insulins are able to be drawn and dispensed in smaller doses (less than 5 units) with much greater accuracy than their U100 counterparts. This makes them advantageous for use in treating both children and pets, who both have smaller bodies and smaller insulin requirements than adult humans.
U40 insulin has its advantages for more than children and pets.
Less strength=speedEditThe hexamers of insulin tend to associate with each other (stay together); they cannot be readily absorbed while they remain this way. Diluting insulin into U40 strength forces them into dissociating (staying apart from each other, and becoming dimers and monomers), which means they are absorbed better and more rapidly. An easy way to visualize this might be to think of a whole pie, slicing it into 6 pieces, then putting each piece on a separate plate. The pie can't be eaten until it's cut and everyone has a piece on his or her plate.
A normally working pancreas secretes insulin in monomer form, so there's no formation of hexamers by self-association and nothing to break down; the monomer insulin is ready to work.
This study compares the absorption rate of U100 and U40 insulins.. The findings show U100 insulin to be significantly slower acting than U40 because it has a slower absorption rate. (Note the same study is available through a URL from Diabetes Care--a publication of the American Diabetes Association.) From 30-40 minutes after injection, U40 insulin produces a 20% higher insulin level in the body than the identical amount of U100 insulin injected at the same time. U40 insulin often has a faster onset then does U100 insulin
U40 insulin was also the subject of another 1998 study. This one compared it to both U100 insulin and the rapid-acting analog insulin Lispro (The only one marketed at the time.) Insulin lispro, known as Humalog, was found to be only slightly more rapidly absorbed than U40 non-analog insulin. The rapid-acting analog insulins such as Humalog, Novolog, NovoRapid and Apidra have amino acid sequences which are altered to prevent the insulin hexamers from remaining together in self-association. Diluting insulin from U100 strength also prevents this self-association.
The fact that U40 insulin has a similar pharmacokinetic profile to analog insulin, has not been lost on the German Institute for Health Care Quality (government department). They proposed a cost-cutting move which would stop prescription coverage of the rapid-acting analogs for all newly-diagnosed Type 2 diabetics in Germany. The decision was reached July 17, 2006; rapid-acting analog insulins are no longer covered unless they are price-equivalent to non-analog insulins or if the patient can medically demonstrate intolerance.
It is also possible to delay the absorption of an insulin by increasing its strength. U500 insulin, which is five times more concentrated than U100, has been available through both Lilly and Novo Nordisk (Note: Their similar product is U400 strength insulin) by special order for many years. The insulin's main use is for people with extreme Insulin resistance, and is commercially available only in R/Neutral type.
Since there are no additives such as suspensions to alter R/Neutral insulin's action, the strength of the insulin formula hinders its breakdown into dimers and monomers, thus making it much slower-absorbed than U100 and lesser strength insulins.
In cases of severe insulin resistance, using a much higher concentration of insulin appears to "negate" the effects of immune-related Insulin resistance.
The studies at the link below shows that there was no difference regarding antibodies when these patients were transferred from Iletin II NPH at U100 strength to a form of Iletin II R at U500 strength. However, the stronger insulin reduced their insulin needs from 33-75%.
Types by length of actionEdit
Insulins are categorized first by length of action, then by origin and by suspension. The four durations are:
Insulin types: length of action
|Rapid onset-fast-acting (analog) insulin|
The usual times for onset, peak, and duration are found with the information for the insulin itself, but they also depend on the species, the suspension, and the individual. In particular, a given insulin that lasts, say, 20 hours in humans or dogs is more likely to last 10 hours in cats due to cats' faster metabolism. So the times found here are average for humans and dogs, but will last less time in cats. This insulin chart is a bit dated, but seems to be a good guide to onset, maximum effect (peak) and duration. Looking at NPH for both dogs and cats gives example of cats' faster metabolism; its expected duration for cats is half that for dogs.
Types by originEdit
Insulins differ by species. Most commonly available types are:
|r-DNA human insulin|
Genetically-engineered (GE) human insulin
Genetically-modified (GM) human insulin
|porcine (pork) insulin|
|bovine (cow) insulin|
|human analog insulins|
Porcine insulin is identical to canine. Bovine insulin is similar to feline, differing by only a single amino acid in position 18. (Mnemonic device: piG = doG, Cow = Cat). Both differ in up to four amino acids (positions 8, 10, 18, 30) from natural human insulin. Porcine (pig) and bovine (cow) insulins can be combined to produce a "blended" insulin (such as Iletin I (beef/pork) and PZI Vet). Genetically-engineered artificial insulins with different amino acid composition such as Lantus, Levemir, Humalog, Novolog, and Apidra, are known as analog insulins.
|Amino Acid Sequence of Insulin Preparations|
|Amino Acid Substitutions|
Types by suspensionEdit
Insulin types: suspension
Clear soluble insulins have no suspension.
The suspension (liquid the insulin is suspended in) is the key to its activity over time. Typical suspensions are Isophane (NPH, Mixed), Zinc (Lente, semilente, Ultralente) and Protamine Zinc (PZI). In general, all insulins with the same suspension will have a similar time activity profile and behave similarly. In non-analog insulins, it is the suspension that makes intermediate and long-acting types work longer than R/neutral.
Manufactured insulin diluents contain both suspension and preservative additives which are also present in the insulin(s) they are made to dilute. Using the wrong diluent for an insulin may alter its activity profile, causing the insulin to work to rapidly or too slowly. This is one reason why insulins should be diluted only with the correct approved diluent for that insulin.
Guidance on useEdit
Note that any insulin, given in overdose, can lead to hypoglycemia and coma or death.
Before each use, take a moment to inspect the insulin prior to drawing it into the syringe; clear insulins should appear not discolored and clear; suspended insulins should be uniform in their cloudiness.
Do not use the insulin if:
If you made a mistake and forgot to put the insulin back into the refrigerator, even for several hours, there should be no problem. Many keep their insulin (see instructions for your brand) at room temperature all the time. When comparing it to insulin which is in the fridge except when used, it may be more likely to have slight potency loss. If the insulin was exposed to heat or direct light for a while when it was out of the refrigerator, or shaken vigorously or dropped a long way, the best thing to do would be to start with a new vial.
- Absorption Kinetics of Regular, Isophane & Protamine Zinc Insulin in Normal Cats-Domestic Animal Endocrinology-1990
- Comparison of 2 Ultralente Insulin Preparations (Human & Beef/Pork) With Protamine Zinc Insulin (Beef/Pork) in Clinically Normal Cats--American Journal of Veterinary Research-1994
- Insulin Therapy in Cats with Diabetes Mellitus-Journal of the American Veterinary Association (JAVMA)-1983
Some Time Activity information re: NPH/isophane & PZI insulins.
- Diabetes control in Siberian Husky Case details about using R/neutral and/or mixed insulins in dogs.
- More details on insulin types for animal use
- More general insulin information :Good illustrations and charts for seeing where bovine and porcine insulins differ from human insulin and how analog insulins Lantus (insulin glargine), Novolog (insulin aspart), and Humalog (insulin lispro) have been altered to produce their respective effects. Some absorption discussion related to humans, some of which is relevant to animals, as absorption is an important factor in how the insulin is used for all with diabetes. Time activity profiles for everything except Levemir and any PZI. Aspart/Lispro chart would be applicable for the new Aventis Apidra, as it is also a rapid-acting insulin designed for bolus in humans.
- The History of Insulin
- The Discovery of Insulin
- The Discovery and EarlyDevelopment of Insulin--University of Toronto
- All About Insulin In Depth
- Time Activity Profile Tables for human approved insulins sold outside of North America
- A chart of the variations in amino acid sequence on the A and B chains of different species.
- Dr. Ragnar Hanas is a Swedish pediatrician whose book about Insulin-Dependent Diabetes is clearly written and easy to understand. Unlike many doctors, you feel she's talking with you and not down to you. Even though it was written in 1999 and insulins Lantus and Levemir were not yet marketed, the explanations are classic. She intended it for explaining human diabetes, but there is much we can gain from it too. The link is to a chapter she graciously donated to Children With Diabetes.
- Click Here To View Time Activity Profiles of Lilly Insulins in humans and dogs (cats are about 2x faster)(see also Cats' faster metabolism)
- Health Canada--Insulin Comparison Chart--All But Levemir & Apidra
- Health Canada--Intro to Diabetes and Insulin
- Insulin Synthesis & Secretion--CSU Veterinary School of Medicine
- NetDoctor.co.UK List of Insulins in the UK
- Type I Diabetes and Insulin Therapy Nursing Clinics of North Americs-Hirsch-Farkas-Hirsch 1993
- OSU Endocrinology Symposium 2006-Selecting an Insulin for Treatment of Diabetes Mellitus in Dogs & Cats-Nelson-Page 39
- Switching to Another Insulin: What & How-North American Veterinary Conference 2006
- ↑ Sir Frederick Banting
- ↑ Insulin-National Institutes of Health
- ↑ The Genetic Landscape of Diabetes
- ↑ Dorlands Medical Dictionary-Glycogen Description/Definition
- ↑ The Genetic Landscape of Diabetes-Drs. Dean & McIntyre
- ↑ Dorlands Medical Dictionary-Catabolic Definition
- ↑ Wikipedia-Lipolysis Description
- ↑ Dorlands Medical Dictionary-Glycogen Breakdown Explanation
- ↑ Intervet-Caninsulin UK-Diagram-Pathophysiology of Diabetes Mellitus-Insufficient Insulin--What Happens
- ↑ Postgraduate Medicine, White, et. al. 2003
- ↑ Intervet-Caninsulin UK-Diagram of Insulin's Effects on the Body
- ↑ Diabetesnet.com-Insulin Kinetics & Dynamics
- ↑ Elmhurst College-Carbohydrate Hormone Control
- ↑ Explanation of Progesterone's Functions-Veterinary Partner
- ↑ Counter-Regulatory Hormones
- ↑ Insulin by Connaught 10 units 5 c.c. vial-10 units per c.c. 1923
- ↑ Lilly Iletin--1922--20 units in 5 cc
- ↑ Iletin Vial and 2 Cartons-1923. Carton on Right is U20-U40 Carton is on Left
- ↑ Closer Look at Iletin 1923 Vial
- ↑ Accuracy of Dosing U40 Insulin Register Free to View
- ↑ Insulin Dependent Diabetes-Dr. Ragnar Hanas-1999 (Page 5)
- ↑ Comparison of U100 and U40 Insulins-PubMed
- ↑ Type 1 Diabetes Mellitus & Use of Flexible Insulin Regimens--Hirsch-American Family Physician-1999
- ↑ Chemistry and Pharmacology of Therapeutic Insulin Preparations, Abrams-Ogg, ACVIM 2007
- ↑ Absorption Comparison--U40 & U100 Insulins-PubMed
- ↑ Copy of Reference 9 in ADA's Diabetes Care Publication
- ↑ Insulin-Dependent Diabetes--Dr. Ragnar Hanas
- ↑ Comparison of U40, U100 and Rapid-Acting Insulin Lispro-PubMed
- ↑ Subcutaneous Absorption of Insulin in Insulin-Dependent Diabetic Patients. Influence of Species, Physico-chemical Properties of Insulin and Physiological Factors-PubMed-Danish Medical Bulletin 1991
- ↑ German Institute for Health Care Quality Study--English Translation
- ↑ Google Auto-Translated Decision of German Institute for Health Care Quality & Ecomony
- ↑ Resource Guide-2005-American Diabetes Association
- ↑ Use of U500 Insulin in Patients With Extreme Insulin Resistance-Diabetes Care-ADA-2005
- ↑ Diabetes Forecast-ADA,2006-Page 4
- ↑ Diabetes-World Mailing List Web Site-Questions About Insulin
- ↑ Five Fold Increase of Insulin Concentration Delays the Absorption of Human Insulin Injections in Pigs-Diabetes Research & Clinical Practice-2000
- ↑ Use of U500 R Insulin by Continuous Insulin Infusion (Insulin Pump)in Patients With Type 2 Diabetes & Severe Insulin Resistance Endocrine Practice-2006
- ↑ U500 Insulin in the Treatment of Antibody-Mediated Insulin Resistance-Annals of Internal Medicine-1981
- ↑ Enhanced Efficacy of U500 Insulin in the Treatment of Insulin Resistance Caused by Target Tissue Insensitivity-American Journal of Medicine-1984
- ↑ RxEd.org-Insulin Therapy
- ↑ Insulin Activity Profiles
- ↑ Time Activity Profiles Insulin Chart--Dogs and Cats-Newman Veterinary
- ↑ Feline Insulin Sequence-Science Direct
- ↑ Insulin Amino Acid Sequences-Petdiabetes.org
- ↑ Diabetes Forecast-ADA, 2006-Page 3
- ↑ BCP Veterinary Pharmacy-Bovine PZI Insulin
- ↑ Intervet-Caninsulin-Product Information
- ↑ Pharmacy Times-Guide to Insulin Preparations
- ↑ Lilly Discontinues Diluent for all Lente & Ultralente Insulins
- ↑ RxEd.org-Insulin Therapy-Stability & Storage
- ↑ Flocculation & Loss of Potency of Human NPH Insulin-Diabetes /Care-ADA-1988
- ↑ Flocculation of NPH Insulin-Revista Clinica Espanola-(English Translation)-1994
- ↑ Frosting Caused in NPH/Isophane Insulin By Heat/Cold-Journal-Diabetes.org-1998
- ↑ Dorlands Medical Dictionary-Definition of Flocculation
- ↑ ADA-Diabetes Forecast, 2006-Storage & Safety-Frosting of NPH, Lente, Ultralente Insulins-Page 5
- ↑ Diabetesnet.com-Humalog & Heat
- ↑ Injection Insulin-Transcript of American Diabetes Association Videotape-2003
- ↑ ADA-Diabetes Forecast, 2006-Storage & Safety-Particles or Clumps in NPH, Lente, Ultralente Insulins-Page 5
- ↑ FAQs.org-Travelling With Insulin
- ↑ Tips on Caring for Diabetic Pets-Diabetic-help.com