Biomedical subjects
Publications and source records attributed to H J Hahn.
Using immunofluorescence technique a positive reaction to insulin antiserum could be revealed in different parts of the CNS of Wistar rats and sand rats.
The hypothalamic and extrahypothalamic distribution of somatostatin-like immunoreactivity (SLI) was investigated in fed adult sand rats (Psammomys obesus) of both sexes using the immunofluorescence technique. Blood glucose and insulin concentrations were determined in these animals prior to decapitation. In a blind study, the amount of immunofluorescence of certain CNS areas and the glucose: Insulin ratio were compared and found to be connected: High amounts of SLI were detected in the dorsal hippocampus, in some hypothalamic nuclei and the median eminence of rats displaying low glucose levels. Sand rats with high blood glucose values did not show SLI in the hippocampal formation and the immunofluorescence of the circumventricular (hypothalamic) regions and the Eminentia mediana was drastically reduced. A possible correlation of SLI with insulin concentrations in the blood could not be revealed. The data obtained are discussed as a possible expression of a CNS influence on glucoregulation in this species.
Islets of Langerhans were investigated with the indirect immunofluorescence technique for somatostatin. Fluorescence was observed in cells which are by number and localization typical "D-cells". somatostatin-like immunoreactivity was also present in few cells of the exocrine part of pancreas.
The influence of glucose on the beta-cell handling of Ca2+ was studied in pancreatic islets isolated from ob/ob mice. Glucose had both stimulatory and inhibitory effects on the washout of radioactivity from islets preloaded with 45Ca. Although the phenomenon of stimulation may be essentially associated with an increased turnover of 45Ca incorporated in response to glucose, the inhibitory effect might merely reflect a lowering of Ca2+ in the cytoplasm following from its accumulation into secretory granules and mitochondria. It is suggested that the Ca2+ uptake by the granules is mediated by an ATP-dependent proton gradient and that these organelles serve as a regulator of the cytoplasmic Ca2+ involved in stimulus-secretion coupling. Alterations in the beta-cell handling of Ca2+ may not only explain the role of glucose as an initiator of insulin release, but also the potentiation by cAMP of the action of glucose. The latter effect can tentatively be ascribed to an increase of cytoplasmic Ca2+ following cAMP-induced inhibition of the net Ca2+ uptake by mitochondria.
Goldthioglucose enhanced independently of glucose but related to dose the insulin secretion of pancreatic rat islets in vitro. The stimulatory action is additive to that of glucose, is not inhibited by mannoheptulose and not connected with an altered glucose-utilization. The gold thioglucose-induced insulin secretion is diminished in the presence of epinephrine and Mg++, respectively, and characterized by a uniphasic response peaking at 15 min. In the absence of glucose goldthioglucose did not modify the pancreatic glucagon secretion.
The dynamics of insulin release from spiny mouse perifused pancreatic islets was investigated. In agreement with earlier studies we found no initial (0-10 min) insulin secretion in response to glucose in islets prepared from mice up to 35 weeks of age. The islets of animals older than 40 weeks, however, were characterized by greater insulin content, and a restored typical biphasic insulin secretion profile. The results suggest that immediate glucose response is modified by environmental or other factors related to age.
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A subpopulation (n = 27) of normoglycaemic Sand rats was characterized as carbohydrate-intolerant by intraperitoneal glucose loading. Five of these animals did not show any rise in peripheral insulin concentrations when injected with glucose. However, when isolated by collagenase digestion their islets still exhibited a significant enhancement of insulin secretion in response to glucose, glyceraldehyde, mannose and theophylline. The in vitro secretory responses were comparable to those of islets from carbohydrate-tolerant Sand rats. The results underline the importance of the natural environment for the B-cell response in vivo.
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Glucose stimulates the uptake of 45Ca into beta-cell-rich pancreatic islets isolated from ob/ob-mice. The distribution of the incorporated radioactivity was analysed by labelling the organelles with 45Ca in their cellular environment. The radioactive content of the organelles was measured after homogenization and fractionation of the islets under conditions preventing 45Ca redistribution. The 45Ca taken up in response to glucose appeared essentially in the secretory granule fraction and in that enriched in mitochondria. Modification of the 45Ca loading procedure, involving reduction of the oxygen tension and incubation volume, resulted in the disappearance of the glucose effect on the mitochondrial fraction whereas part of the stimulatory effect on the secretory granules persisted. Buffering of calcium by the secretory granules and mitochondria may be important for regulating the cytoplasmic Ca2+ involved in stimulus-secretion coupling.
Somatostatin-like immunoreactivity (SLI) was demonstrated in neurons of the dorsal hippocampus of the sand rat by means of the immunofluorescence technique.
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The effect of sulphydryl reagents on glucagon secretion of isolated Wistar rats islets was studied. Chloromercuribenzene-p-sulphonic acid (CMBS) is a strong stimulator of glucagon secretion, whereas 5,5'-dithiobis (2-nitrobenzoic acid) (DTNB) markedly inhibited the hormone release. The effect of CMBS could not be suppressed by 20 mM glucose, but in the presence of 1 mM 4-acetamido-4'-isothiocyano-stilbene-2,2'-disulphonic acid (SITS), and is independent of the glucagon content of islets. The results let us assume that sulphydryl-groups of pancreatic A-cells are involved in the regulation of glucagon secretion.