RESEARCH DESIGN AND METHODS

Institutional review board approval and informed consent were obtained before the study began. Nineteen subjects between 7–42 and 1–24 months postdiagnosis of type 1 diabetes came to the Clinical Research Center after an overnight fast. Morning insulin was withheld. Subjects on insulin pumps continued their basal rate until the start of the test. Tests were not performed if fasting glucose was≤ 4.0 or≥ 11 mmol/l. Subjects underwent paired MMTT (baseline samples, oral Boost [6 mg/kg to maximum of 360 ml], samples at 30, 60, 90, and 120 min) and arginine testing (baseline samples, intravenous arginine [0.07 mg/kg to maximum of 5 g], samples at 2, 3, 5, 7, and 10 min) on separate days within 4 weeks of each other.

RESULTS

There was no difference in basal C-peptide (1.0±0.3 nmol/l for MMTT and 1.1±0.3 nmol/l for arginine [mean±SE]) or glucose (7.3±0.6 mmol/l for MMTT and 7.7±0.4 mmol/l for arginine) values. Likewise, there was no difference in mean or peak C-peptide values between MMTT and arginine-stimulated tests. There was a strong relationship between C-peptide values obtained from MMTT and arginine-stimulated tests whether assessed by mean (r= 0.96), peak (r= 0.95), or area under the curve (r= 0.95) calculations. In addition, a strong relationship between basal and stimulated C-peptide values was observed for both MMTT and arginine.