[en] The four monoiodinated insulin derivates were prepared by a modification of the lactoperoxidase method. The iodinated insulin mixture was then separated by reserved-phase high-performance liquid chromatography and the identity of iodinated products was assessed by sequential oxidative sulphytolysis and enzymatic proteolysis. A total separation of the A14, A19, B16 and B26 monoiodinated insulins from one another and from unreacted insulin was accomplished. Thus, the reported procedure represents a rapid, selective and generally applicable method for purifying insulin derivates selectively labelled in one of the four tyroisine residues

[en] We studied total cell-associated A14-[¹²⁵I]insulin radioactivity (including surface-bound and internalized radioactivity), insulin internalization, and its intracellular degradation at 37 C in monocytes from nonobese type II untreated diabetic patients (n = 9) and normal subjects (n = 7). Total cell-associated radioactivity was decreased in diabetic patients [2.65 +/- 1.21% (+/- SD) vs. 4.47 +/- 1.04% of total radioactivity. Insulin internalization was also reduced in diabetic patients (34.0 +/- 6.8% vs. 59.0 +/- 11.3% of cell-associated radioactivity. Using high performance liquid chromatography six intracellular forms of radioactivity derived from A14-[¹²⁵I] insulin were identified; 10-20% of intracellular radioactivity had approximately 300,000 mol wt and was identified as radioactivity bound to the insulin receptor, and the remaining intracellular radioactivity included intact A14-[¹²⁵I]insulin, [¹²⁵I]iodide, or [¹²⁵I]tyrosine, and three intermediate compounds. A progressive reduction of intact insulin and a corresponding increase in iodine were found when the incubation time was prolonged. Intracellular insulin degradation was reduced in monocytes from diabetic patients; intracellular intact insulin was 65.6 +/- 18.1% vs. 37.4 +/- 18.0% of intracellular radioactivity after 2 min and 23.6 +/- 22.3% vs. 3.9 +/- 2.3% after 60 min in diabetic patients vs. normal subjects, respectively. In conclusion, 1) human monocytes internalize and degrade insulin in the intracellular compartment in a stepwise time-dependent manner; and 2) in monocytes from type II diabetic patients total cell-associated radioactivity, insulin internalization, and insulin degradation are significantly reduced. These defects may be related to the cellular insulin resistance present in these patients

No abstract available

[en] In kinetic studies, the peripheral injection of the tracer brings about a systematic error which equally affects MCR and secretion rate, this latter being the product of the clearance by the plasma concentration of the native hormone. Such an error is due to the first-passage hepatic extraction. From our experiments, in dog this extraction is about 20%. Several studies, conducted by the isolated organ perfusion technique, report a first-passage hepatic extraction ranging from 60 to 40% for cold insulin, and from 40 to 3% for labelled insulin. These differences can be accounted for by different experimental conditions, the quality of the tracer and the system of detecting the radioactive hormone in plasma. (orig.)