This document only includes an excerpt of the corresponding thesis or dissertation. To request a digital scan of the full text, please contact the Ruth Lilly Medical Library's Interlibrary Loan Department (rlmlill@iu.edu). / This investigation was initiated to test the hypothesis that streptozotocin (STZ) and N-methylnitrosourea (MNU) damage B-cells of islet of Langerhans by depleting islets pyridine nucleotide content. Islets of Langerhans isolated by the collagenase method from nonnal rats were exposed to STZ rmder various experimental conditions and islets pyridine nucleotide content was temporally correlated with cytotoxicity. Metabolic and insulin secretory function of islets of Langerhans were used as indices of B-cell toxicity. The nitrosoureas (STZ and MNU) exerted time-, dose-, and temperature-dependent suppression of glucose-stimulated insulin secretion. Identical studies indicated that rmlike the nitrosoureas, alloxan was B-cytotoxic at 0°c even in the presence of 16.7 mM glucose. Whereas 2 mM alloxan elicited transient but consistent release of insulin by islets perifused in low glucose (1.7 mM) at 37°c, there was no release of insulin by islets perifused with 5 mM STZ, The effect of 5 mM STZ or of 10 mM MNU can be completely inhibited by the simultaneous presence of nicotinamide, isonicotinamide, picolinamide and other primary amides (e.g. pyrazinamide and benzamide) at concentration of 20 mM. Glucose (16.7 mM), pyridine nucleotides (10 mM) and acid derivative of amides (e.g. nicotinic acid; 20 mM) were ineffective. 2-Deoxyglucose (20 mM) or 3-0-methylglucose (20 mM) offered partial protection. After exposure of islets to STZ (5 mM) or MNU (10 mM), complete reversal of the effect was obtained with nicotinamide (20 mM) or its isomers, with time of exposure not exceeding 30 minutes. Beyond 30 minutes, the reversibility was partial or absent, except in the presence of 0.5 mM phenazine methosulfate (PMS) which induced release of insulin in both normal and nitrosoureas pre-treated islets. Insulin releasing action of PMS was dose-, time- and temperature-related; occurred even in the absence of glucose; was inhihitcd hy epinephrine (10 mM, hut not by mannoheptulose (20 mM); and was not potentiatcd by cyclic AMP (5 mM) or theophylline (10 mM). In the perifusion system, the patterns of response induced by PMS (0,5 mM) was spike-like release reaching a maximum in 5 minutes and declining rapidly to half-maximal value in 10 minutes. Normal islets pre-exposed to PMS was refractory to subsequent glucose (16.7 mM) stimulation. Islets pre-treated with STZ (1-5 mM) metaholized less 14c-glucose than control islets. The order of inhibition hy STZ of 14c-glucose metabolism by islet was: l-14C->U- 14C->6-14C-glucose. PMS (0.5 mM) augmented the metabolism of U-14C- and 1-14C glucose by STZ pre-treated islets. However, the metabolism of 6-14C-glucose was unelevated by PMS. The level of NADP+ + NADPII but not the level of NAD, decreased after two minutes exposure of islets to STZ. At thirty minutes, however, the levels of NAD,6-phosphogluconate and NADP+ + NADPII were decreased. The depletion paralleled suppression of insulin secretion. The level of NADP+ + NADPH in islets was decreased more than the level of NAD. Whereas PMS (0.5 mM) elevated the level of NADP+ + NADPH, the level of NAD was not augmented. Islets isolated from rats 3 or more hours after pre-injection with STZ (65 mg/kg) or 6-aminonicotinamide (40 mg/kg) failed to secrete insulin in response to glucose stimulation. However, insulin secretion by such islets was elevated in the presence of PMS (0.5 mM). Whereas PMS induced insulin secretion was much reduced 48 hours after preinjection of rats with STZ, the secretory activity in islets of rats 48 hours after 6-aminonicotinamide injection was slightly decreased. Pyridine nucleotides augmented secretion only in islets of 6-aminonicotinamide pre-injected rats. It is concluded that the immediate response of islets to nitrosoureas in vitro differs from islets response to alloxan. The actions of STZ and MNU are qualitatively similar. The B-cytotoxic effect of nitrosoureas is exerted directly or indirectly on the metabolic and energy coupling functions of pyridine coenzymes. Such an effect could be reversed by supplying the islets with reactive proton donors as substitutes for pyridine nucleotides.
| Identifer | oai:union.ndltd.org:IUPUI/oai:scholarworks.iupui.edu:1805/32811 |
| Date | January 1977 |
| Creators | Akpan, Jones Okon |
| Source Sets | Indiana University-Purdue University Indianapolis |
| Language | en_US |
| Detected Language | English |
| Type | Dissertation |
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