[Amylin as an additional possible pathogenic factor in NIDDM and the insulin resistance syndrome]

The syndrome of insulin resistance comprises the following H-phenomena: 1. Hyperinsulinism compensating the inborn postreceptor insulin resistance, 2. Hyperglycaemia-non-insulin-dependent diabetes mellitus, 3. Hyperlipoproteinaemia with android obesity, 4. Hypertension, 5. Hirsutism with the syndrome of polycystic ovaries as a manifestation of a hyperandrogenic situation in the female organism. Molecular syndromes of this syndrome of insulin resistance are obscure. They are the subject of intensive studies because H-phenomena are an aggregation of the main risk factors of atherogenesis. Recently attention is focused also on amylin--a 37 amino acid peptide with a 50% homologous amino acid sequence with a calcitonin-gene--related peptide (CGRP), which is the product of a gene made up of three introns on the 12th chromosome. Amylin acts in the beta-cells of the pancreas as a co-secretion of insulin. If in excess, it is deposited in the form of an amyloid in the beta-cells. In the early stage of NIDDM it alters the physiological response of the beta-cell to glycaemic stimuli and food, in later stages of the disease, after accumulation, it causes apoptosis of the beta-cell and reduces thus the secretory capacity of the Langerhans islets. It is excreted in the urine and thus, if the glomerular filtration is reduced, it cumulates in the blood stream and thus enhances insulin resistance already in the early stages of chronic renal insufficiency, or in diabetic nephropathy. In type II diabetes similarly as insulin levels also amylin levels are elevated, while in type I diabetes with early autoimmune destruction of the beta-cells the insulin and amylin levels are reduced or even zero. Amylin reduces in the muscle, probably by inhibition of glycogen synthase, the insulin stimulated non-oxidative utilization of glucose into muscle glycogen and conversely by stimulation of phosphorylase it stimulates glycogenolysis and thus also lactate production and gluconeogenesis in the liver which all are anti-insulin effects which intensify the insulin resistance of the main target tissues. Amylin, similarly as CGRP or calcitonin, reduces Ca blood levels and has a vasodilatating effect; it reduces the BP but in different minimal and maximal doses and by a different mechanism and via special receptors because the link of amylin to calcitonin receptors is 100 times lower and does not produce a rise of cAMP in the target cell. The effect on the enhancement of insulin resistance in muscle was proved also by direct measurements using an hyperinsulinaemic euglycaemic clamp. After prolongation of the clamp to more than two hours the effect on insulin resistance disappeared, although the hypocalcinaemic effect persisted. Amylin is able by its biological action to modify the secretion as well as the effectiveness of insulin to pathological values. These two characteristics are typical for impaired glucose tolerance in type II diabetes. Studies are under way to find out whether the effect of amylin is involved directly also in the pathogenesis of the other H-phenomena or only via accentuation of hyperinsulinism. In any case amylin is a new link the role of which in the pathogenesis of NIDDM and the syndrome of insulin resistance awaits evaluation. Due to its effect on gastric evacuation it participates also in the postprandial glycaemic control in particular in type I diabetes where it it begins to be used in therapy. Perhaps it will be possible to administer it in these patients along with insulin to improve diabetes compensation.