Insulin Secretion in Patients with Hyperthyroidism: in Relation to Abnormalities in Carbohydrate Metabolism

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Abstract
Oral glucose tolerance tests (OGTT) were performed on 108 patients with hyperthyroidism who were suspected, from their clinical records, of having abnormalities in carbohydrate metabolism. Of these, i.v. glucose tolerance tests (IVGTT) were performed on 24 patients and i.v. tolbutamide tests (IVTT) on 34. Five control subjects were included in the study. In OGTT, an oxyhyperglycemic pattern (OH) was observed in 31 patients, a borderline pattern in 13, and a diabetic [D] pattern with FBS [fasting blood sugar] < 120 mg/dl (Da) in 31; 120-139 mg/dl (Db) in 11; and, .gtoreq. 140 mg/dl (Dc) in 22. Insulin secretory response (ISR) during OGTT increased in the OH group, slightly increased in the Da group, and decreased in the Db and Dc groups, compared with the control group. The insulinogenic index (.DELTA.IRI[immunoreactive insulin]/.DELTA.BS [blood sugar] .cntdot. 30'' [min after oral glucose load]) during OGTT was higher in the OH group but was significantly lower in the Da, Db, Dc groups than in the control group. K-value and insulinogenic index (.DELTA.IRI/.DELTA.BS .cntdot. 3'') during IVGTT were 2.3 .+-. 0.45 and 0.10 .+-. 0.07 (mean .+-. SD, n = 5) in the control group, 2.81 .+-. 1.66 and 0.56 .+-. 0.25 (n = 6) in the OH group, 1.51 .+-. 0.29 and 0.25 .+-. 0.15 (n = 9) in the Da group, 0.88 .+-. 0.32 and 0.04 .+-. 0.03 (n = 5) in the Db group, and 0.75 .+-. 0.11 and 0.00 .+-. 0.11 (n = 4) in the Dc group. While ISR significantly increased in the OH and Da groups during IVTT, the fall of the blood glucose level after tolbutamide administration was similar or suppressed, compared with the control group. Although ISR decreased after the patients had been made euthyroid, there was an increase in glucose disappearance in almost all of the patients. Patients who have an ISR capacity in accordance with that required in a hyperthyroid state may be included in the OH group and patients who do not have it, although they have a significant insulin secretory capacity in an euthyroid state, may be included in the Da group; ISR may decrease in most hyperthyroid patients with FBS .gtoreq. 120 mg/dl; there may be peripheral insulin resistance in hyperthyroidism.

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