HUMAN ISLET AMYLOID POLYPEPTIDE AT PHARMACOLOGICAL LEVELS INHIBITS INSULIN AND PHORBOL ESTER-STIMULATED GLUCOSE-TRANSPORT IN INVITRO INCUBATED HUMAN MUSCLE STRIPS

Human islet amyloid polypeptide, at concentrations of 1-100 nmol/l, has been demonstrated to inhibit the insulin-stimulated increase in rat muscle glycogen content. However, at physiological concentrations (1-10 pmol/l) of islet amyloid polypeptide, no effects have been reported. We tested the effect of a wide range of concentrations of human islet amyloid polypeptide on insulin- and phorbol ester-stimulated 3-0-methylglucose transport in in vitro incubated human skeletal muscle. Muscle specimens from the quadriceps femoris muscle were obtained from 23 healthy subjects with the use of a newly-developed open muscle biopsy technique. Human islet amyloid polypeptide at a concentration of 100 nmol/l had no effect on basal glucose transport, but inhibited the stimulatory effect of a maximal insulin concentration (1000-mu-U/ml) by 69 % (p < 0.001). The presence of human islet amyloid polypeptide at 1, 10 and 100 nmol/l decreased the effect of 100-mu-U/ml of insulin on glucose transport by 61% (p < 0.05), 78% (p < 0.05) and 76% (p < 0.05), respectively. Similarly, human islet amyloid polypeptide at a concentration of 10 nmol/l inhibited phorbol ester-stimulated glucose transport by 100% (p < 0.05). The inhibitory effects of human islet amyloid polypeptide on glucose transport were present in the muscle strips despite no net changes in glycogen content. Human islet amyloid polypeptide at 10 and 100 pmol/l had no effect on the rate of insulin-stimulated glucose transport. In conclusion, pharmacological concentrations of human islet amyloid polypeptide inhibit insulin-as well as phorbol ester-stimulated glucose transport in human skeletal muscle, while physiological concentrations do not exert an inhibitory effect. Furthermore, these results suggest that the inhibitory effect of human islet amyloid polypeptide on glucose transport is located at a point distal to the insulin binding process.