INCREASED PLASMA-LEVELS OF ISLET AMYLOID POLYPEPTIDE IN PATIENTS WITHPRIMARY HYPERPARATHYROIDISM

Amylin, also named islet amyloid polypeptide (IAPP), is a protein that is processed and released from pancreatic beta-cells in parallel with insulin. Islet amyloid polypeptide is currently studied with regard t o a role for insulin resistance in non-insulin-dependent diabetes. To elucidate a possible function of IAPP for impaired glucose tolerance i n primary hyperparathyroidism (pHPT), we studied plasma IAPP levels du ring an oral glucose tolerance test (OGTT) in seven pHPT patients befo re and 8 weeks after surgery and in six healthy subjects. The B-glucos e level of the patient groups was 4.34 +/- 0.12 mmol/l before and 3.97 +/- 0.16 mmol/l after surgery (NS), while the serum level of insulin was significantly higher before (16.9 +/- 2.8 mlU/l) than after (8.9 /- 1.9 mlU/l) the operation (p < 0.05), indicating a moderately increa sed insulin resistance in pHPT. The basal plasma levels of IAPP were s ignificantly higher in pHPT patients before than 8 weeks after surgery (9.71 +/- 1.05 and 4.30 +/- 0.82 pmol/l, respectively; p < 0.01). Whe n compared to the plasma IAPP level of the controls at 1.80 +/- 0.38 p mol/l, pHPT patients had higher IAPP values both before (p < 0.01) and at 8 weeks after (p < 0.05) operation. There was a significant correl ation between the serum levels of insulin and plasma levels of IAPP in pHPT patients before (r = 0.87, p < 0.01) as wells as 8 weeks after s urgery (r = 0.69, p < 0.05). The area under the curve for IAPP during OGTT in pHPT patients was 1872.4 +/- 187.7 pmol . min/l, which is sign ificantly higher than after surgery (1010.8 +/- 93.7 pmol . min/l) (p < 0.05) and compared to the area for the controls at 840.3 +/- 49.9 pm ol . min/l (p < 0.01), In conclusion, pHPT is associated with an incre ased plasma level of IAPP, correlated to the serum insulin level, but persistently higher than in controls also 8 weeks after surgery. Possi bly, increased IAPP levels can have a role for impaired glucose tolera nce in pHPT. The hyperparathyroid state might have a specific role for the release of this peptide, otherwise closely connected to insulin s ecretion.