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Diabetes 2 tyebes:
Diabetes mellitus type 1 : treated by insulin , because of ß cells don’t secrete enough insulin .
Type 2 : can be treated by oral tablets, insulin or both .
Insulin is hormone secreted from ß cells of pancreatic islets of Langerhans into blood.
It is a protein (MW 5800) consisting of two peptide chains linked by two disulfide bridges; the A chain has 21 and the B chain 30 amino acids

It cause blood –sugar lowering .by promoting its uptake inside specific organs like heart, adipose tissue and skeletal muscle or convert it to glycogen in liver (storing)
It increase protiensynthesis and lipogenises and inhibit release of free fatty acids and lipolysis.  
Side effects of insulin, is hypoglycemia, caused by over dose from insulin
Insulin preparations:
A-     From animals: Porcine insulin differs from human insulin merely by one B chain amino acid, bovine insulin by two amino acids in the A chain and one in the B chain.
Compared with human hormone, porcine insulin is barely antigenic and bovine insulin has a little higher antigenicity

B-human insulin
Biosynthetically, by substituting threonine for the C-terminal alanine in the B chain of porcine insulin;
Or
Gene technology involving insertion of the appropriate human DNA into E. coli bacteria.
Insulin is unsuitable for oral administration (destruction by gastrointestinal proteases) and thus needs to be given parentally. Usually, insulin preparations are injected subcutaneously.
The duration of action depends on the rate of absorption from the injection site.

Short-acting insulin is dispensed as a clear neutral solution known as regular insulin. In emergencies, such as hyperglycemic coma, it can be given intravenously (mostly by infusion because
i.v. injections have too brief an action; plasma t1/2 ~ 9 min). With the usual subcutaneous application, the effect is evident within 15 to 20 min, reaches a peak after approx. 3 h, and lasts for approx.6 h. Lispro insulin has a faster onset and slightly shorter duration of action.

Insulin suspensions. When the hormone is injected as a suspension of insulin-containing particles, its dissolution and release in subcutaneous tissue are retarded (rapid, intermediate, and
slow insulins). Suitable particles can be obtained by precipitation of apolar, poorly water-soluble complexes consisting of anionic insulin and cationic partners, e.g., the polycationic protein protamine or the compound aminoquinuride
(Surfen). In the presence of zinc and acetate ions, insulin crystallizes ,crystal size determines the rate of dissolution.
Intermediate insulin preparations (NPH or isophane, lente or zinc insulin) act for 18 to 26 h, slow preparations (protamine zinc insulin, ultralente or extended zinc insulin) for up to 36 h.
Combination preparations contain insulin mixtures in solution and in suspension (e.g., ultralente); the plasma concentration-time curve represents the sum of the two components.

Unwanted effects. Hypoglycemia:results from absolute or relative overdosage. Allergic reactions are rare—locally: redness at injection site, atrophy of adipose tissue (lipodystrophy);
systemically: urticaria, skin rash anaphylaxis. Insulin resistance can result from binding to inactivating antibodies.
A possible local lipohypertrophy can be avoided by alternating injection sites.