Analysis of insulin secretion based on changes in plasma insulin and C-peptide in man.

Abstract

In order to clarify the mechanism of insulin secretion, responses of insulin (IRI) and C-peptide (CPR) in plasma to various stimuli were investigated in normal subjects and patients with diabetes mellitus, liver cirrhosis, chronic nephritis or insulinoma. The response of plasma IRI and CPR to oral glucose load was less marked in the mild and moderate diabetes groups than in the normal controls. Neither IRI nor CPR in the severe diabetes group responded to oral glucose. The patients with liver cirrhosis revealed an exaggerated and delayed response of IRI and CPR, and a lowered CPR/IRI ratio, indicating a remarkable response of IRI to glucose. In contrast, the patients with chronic nephritis showed a prominent rise of CPR alone. In the insulinoma patients, both plasma IRI and CPR increased after glucose load. In the response to glucose, there was approximately 30-min lag time between the peaks of IRI and CPR in the normal controls and the patients with various diseases. Following arginine infusion, plasma IRI and CPR increased in the normal subjects and the patients with moderate diabetes. In the normal subjects, plasma IRI reached a peak at 6 min and 3 min in response to tolbutamide and glucagon, respectively, which elicit an abrupt and sharp rise of insulin from B-cells. However, diabetic patients showed a minimal change in plasma IRI and CPR, whereas there was an exaggerated response of plasma IRI and CPR in insulinoma patients. In analysis of responses of plasma IRI and CPR to tolbutamide or glucagon, there was a lag time longer than 10 min in the normal subjects.The present study confirms the concurrent release of C-peptide from the B-cells in the secretion of insulin. In addition, it was suggested that insulin and C-peptide are mainly handled in the liver and the kidney, respectively.Furthermore, a longer lag time between the peaks of IRI and CPR in response to tolbutamide or glucagon did not necessarily indicate a simultaneous release of insulin and C-peptide from the B-cell, but a delayed release of the latter.glucose tolerance test; arginine; tolbutamide; glucagon The development of the immunoassay for insulin has made the measurement of a minute amount of insulin in plasma possible and has given much information concerning B-cell function of the pancreas. In 1967, Steiner and his co-workers discovered proinsulin from insulinoma tissues as well as from the normal rat

A new C‐peptide correction model used to assess bioavailability of regular human insulin

“…Converting the estimate for β from µ U/ng to a molar dimensionless ratio (M/M) β is ≈0.08. The inverse of 0.08 is the molar ratio of C‐Peptide to insulin (≈12.5) and is consistent with previously reported values of fasting and post‐prandial circulating C‐Peptide to insulin ratios 6, 7.…”

A Case of Secretin-responsive Insulinoma with Low Serum C-peptide Levels

“…In conclusion, this case report emphasizes some unusual features of an insulinoma, including a positive [18] 14.7 8 Kajinuma et al [19] 12.1 20 Okada et al [20] 11.2 136 Our case (after surgery) 17.6 1 Insulinoma Smythe et al [21] 20.0 1 Katabami et al [22] 7.2 4 Gin et al [23] 6.3 8 Sakai et al [18] 6.1 1 Scarlett et al [24] 5.9 1 Saudek [25] 5.6 1 Gerbitz and Spelsberg [26] 5.0 5 Lebowitz and Blumenthal [27] 4.9 3 Kondo et al [28] 4.2 3 Service [29] 3.6 1 Ciavarella et al [30] 2.9 1 Turner and Heding [31] 2.0 2 Our case (before surgery) 2.0 1 insulin response to secretin and decreased C-peptide levels, of which clinicians should be aware. The diagnosis of insulinoma should not depend on some particular endocrinological tests and should be made comprehensively.…”

“…Service et al reported that insulinoma patients had C-peptide values at the end of the 72 h fasts greater than or equal to 0.20 nmol/mL (0.60 ng/mL); however, our case does not fulfill that criterion even before conducting the prolonged fasting test [12]. According to the data from the literature, the molar ratio of serum C-peptide to insulin is, in general, decreased in patients with insulinoma than normal subjects, while in our case the ratios were much lower (Table 2) [18][19][20][21][22][23][24][25][26][27][28][29][30][31].…”