Abstract
It is clear that insulin is released by glucose infusion. This fact has been reported mainly on the basis of histological change of beta cells granulation after glucose infusion.
The present author measured the blood sugar, the extractable pancreatic insulin and also histologically studied degranulation of beta cells, insulin in the Langerhans' islets with immunofluorecein technics at 10, 30, 60, 120, 180, 360 minutes respectively after infusion of glucose solution injected peritoneally into rats.
The results were as follows.
1) The decrease of beta cells granulation from the presumptive standard in 19 (34 %) of 56 islets in the pancreas was found even before glucose infusion. The maximum of beta degranulation was shown at 60 minutes after infusion, when the blood sugar level was lower than that of 10 minutes level. Though blood sugar was on the average level of 97 mg/dl at 180 minutes after glucose infusion, beta cells granulation still decreased. Thus an intimate relationship between the blood sugar level and the decrease of beta granulation could not be found. And it was recognized that beta cells degranulation was changeable under various physiological conditions. However, the increase of beta degranulation generally paralled the decrease of insulin content of Langerhans' islets.
2) Immunological insulin in the Langerhans' islets was demonstrated by the immunofluorecein technic using labelled anti-insulin serum. Especially, the illumination was strong on the peripheral portions of the beta cell cytoplasm near the cell membrane and the islet sinusoids. This phenomenon was thought to be caused by the reaction of the dissolved and secreted insulin in the Langerhans' islets with the antiserum. On the other hand, the acid-ethanol extractable insulin of the pancreas was considered to be the whole insulin in the pancreas. Concerned the relationship between the illumination in the Langerhans' islets and the extractable pancreatic insulin content, despite the latter showed remarkable variations with the times following glucose infusion, the former changed little till 120 minutes after glucose infusion. After 180 and 360 minutes, intensity of fluorecein staining was decreased.
3) The blood insulin levels had three peaks after glucose infusion. The first peak showed the average value of 107 μ/ml at 10 minutes after glucose infusion, this was 3 times as large as that before glucose infusion. It was suggested that the first peak showed the reactive insulin secretion from pancreas to stimulation of glucose infusion. The second peak at 60 minutes after glucose infusion, was thought to be the additional secretion of insulin following hyperglycemia. Though blood sugar was on normal level at the third peak at 180 minutes blood insulin showed to be on high level. These variations of blood insulin levels were thought to be a kind of homeostasis in biological organisms.
4) The inverse correlation was shown between extractable pancreatic insulin contents and blood insulin levels. The extractable pancreatic insulin content decreased remarkably at 10 minutes and showed a slight increase at 30 minutes. Therefore, taking the blood insulin levels into the consideration, it may be said that new insulin synthesis as well as its release were already accelerated in the pancreas.
At 120 minutes, the extractable pancreatic insulin content was 0.43 u/g, and almost equivalent to that before glucose infusion, but at 180 and 360 minutes, it was again decreased.
