Islet cell culture in defined serum-free medium

A serum-free, hormone- and factor-supplemented, defined medium was developed which maintains functional activity of primary cultures of adult islet cells and continuous islet cell lines. Medium supplements examined included proteose peptone (PP), transferrin (TrFe), insulin-like growth factor-I (IGF-I), an insulinotropic fragment of human GH [hGH-(6-13)], ethanolamine (EA), phosphoethanolamine (PEA), and human serum albumin (HSA). Glucose-stimulated insulin secretion from islet monolayers was determined after culture in serum-free supplemented medium by either 2- to 3-h static incubations or in a superfusion system with either low (2.8-8.3 mM) or stimulatory (16.7-19.4 mM) glucose concentrations. Glucose-induced secretion was not sustained after 3-4 days of culture in medium supplemented with PP (0.5 mg/ml) and TrFe (10 micrograms/ml) alone. Addition of T3 did not restore glucose-induced secretion, although a combination of T3 and IGF-I or of T3, IGF-I, and PRL (10(-10)-10(-9) M) maintained glucose-induced insulin secretion for 1 month. No beneficial effects were noted with hGH-(6-13). The beta-cell lines HIT-T15 and RINr 1046-38 were used to screen for a potential replacement for PP, the undefined component of the serum-free medium. A combination of HSA (1 mg/ml), EA (50 microM), and PEA (50 microM) provided a replacement for PP. In fact, insulin secretion from HIT-T15 cells was significantly better after culture in medium supplemented with HSA, EA, PEA, TrFe, T3, IGF-I, and PRL than in medium with PP, TrFe, T3, IGF-I, and PRL. HSA (1 mg/ml), EA (50 microM), and PEA (50 microM) in combination with TrFe (10 micrograms/ml), T3 (0.1 nM), IGF-I (0.65 nM), and PRL (1 nM) were used in studies with primary islet monolayers. After 3 weeks of culture islet monolayers were superfused, and the biphasic glucose-induced insulin secretion of cells maintained in defined medium was indistinguishable from the insulin secretion of cells maintained in medium with 5% fetal bovine serum. These studies indicate that adult rat beta-cells retain biphasic glucose-induced insulin secretion after extended culture in defined serum-free medium. The defined medium was also useful for cultures of RINr 1046-38 and HIT-T15 cells and should provide a basis for formulating media for islet cells from higher mammals, including man.     

Studies in the diabetic mutant mouse: III. Physiological factors associated with alterations in beta cell proliferation

Summary Beta cell replication was studied in normal (C 57 BL/Ks) and diabetic mutant (C 57 BL/Ks-db/db) mice following thymidine-³H administration. The specific activity of DNA of isolated islets (DPM/g islet DNA) was used as an index of proliferative activity and correlated with labeling determined by radioautography. Although thymidine-³H incorporation in islets of prehyperglycemic 5 to 6 week old mutants was limited, it was significantly greater than that in normal mice. With the elevation of blood glucose values, incorporation rose sharply, reaching a maximum level above 130 mg glucose/100 ml blood. Sustained, severe hyperglycemia subsequently correlated with a decline in islet DNA synthesis. Food restriction early in the syndrome reduced hyperglycemia and resulted in low incorporation of label. Animals refed ad lib for periods of 1, 2, or 3 weeks showed significant increases in labeling, with maximal values after 1 week of refeeding. Electron microscopic radioautographs of the islets revealed labeled beta cells but no labeled alpha cells, suggesting that proliferative activity is predominantly restricted to the beta cell population.USPHS Research Career Development Awardee, Grant K4-AM-7394.     

Studies in the diabetic mutant mouse: IV. DBM,a modified diabetic mutant produced by outcrossing of the original strain

Summary Body weight, blood glucose, serum insulin and islet morphology were studied in DBM mice, modified diabetic mutants produced by crossing mice from the original black diabetic strain (C 57 BL/Ks-db) with normal misty colored mice (C 57 BL/6J-m). DBM mutants appeared to live longer than most mice from the original strain. Only 1 of 6 animals, 7 months of age or older, showed the fall in body weight observed in the majority of the original mutants during the terminal stage of the disease. Blood glucose levels in both types of mutants were similar, generally reaching levels of 400 to 500 mg glucose/100 ml blood. The mean insulin level in older (18 weeks or greater) DBM mutants was significantly greater than in the original mutants. These differences could be explained by the failure of DBM mutants to develop the marked decrease in numbers of beta cells seen in older mutants from the original strain.U.S.P.H.S. Research Career Development Awardee, Grant 1 K4-AM-7394.     

Magnetic Resonance Imaging of the Brain in Alcoholics: Cerebral Atrophy, Lifetime Alcohol Consumption, and Cognitive Deficits

Magnetic resonance imaging of the brain in 69 detoxified alcoholics revealed that relaxation time (T1) in whole brain and in grey matter and parietal white matter was greater than in age-matched controls. In 48 patients, data on cognitive function and lifetime alcohol consumption were available. With age-controlled, lifetime consumption, and impairment on performance in the cognitive test (a Category Sorting Test) correlated positively with T1 whole brain and in selected regions. Impairment in the cognitive test correlated with increased T1 in whole brain and white matter independently of cerebral atrophy. Alcohol consumption patterns in the following 6 months were unrelated to changes in T1. The excess water implied by the elevated T1 values may be intra- or extracellular. It is uncertain whether or not T1 elevation in alcoholics is a marker of neuronal damage. T1 elevation appears to be a marker of one type of alcohol-related cognitive impairment.     

The effect of nifedipine on cardiopulmonary responses during exercise in normal subjects

We investigated the effects of a single dose of nifedipine (10 mg orally) on exercise performance during progressive incremental cycle ergometry in nine sedentary normal subjects in a double-blind, placebo-controlled crossover study. Maximum work load after nifedipine (213 +/- 42 watts; mean +/- SD) was less than after placebo (222 +/- 41 watts; p less than 0.05). Maximum oxygen consumption was unchanged. In addition, the drug decreased lactate threshold from 19.7 +/- 4.9 ml O2/min/kg to 15.5 +/- 5.5 ml O2/min/kg (p less than 0.02); gas exchange anaerobic threshold was unaffected. There were higher plasma lactate concentrations at low and intermediate exercise intensities after nifedipine compared with placebo (p less than 0.05). Systolic blood pressure was lower at high work loads (p less than 0.05) and heart rate was higher at low work loads (p less than 0.05) after nifedipine. We conclude that the short-term administration of nifedipine limits peak performance and increases plasma concentration of lactic acid in normal subjects. One or more of the following mechanisms may account for these observations: nifedipine decreases blood flow to skeletal muscle by diverting blood to nonexercising tissues; nifedipine increases catecholamine levels, thereby augmenting lactic acid production; and nifedipine decreases skeletal muscular contractility by selectively impairing fatigue-resistant fibers.     

Pentoxifylline relaxes isolated pulmonary arteries after preconstriction with norepinephrine

Pentoxifylline (PTX) is a methylxanthine derivative which improves systemic microvascular flow and tissue oxygen delivery, presumably through actions on platelet aggregation and erythrocyte deformability. Although PTX also improves pulmonary vascular flow, recent evidence suggests that part of this improvement may be due to pulmonary vasodilation. To evaluate these effects we studied isolated rabbit lobar pulmonary artery (PA) ring segments to determine if PTX had direct effects on PA tissues and whether these effects could be modulated pharmacologically or by endothelial disruption. PTX had no effect on PA at resting tension. However, if the PA tension was actively increased by norepinephrine (5 microM), subsequent PTX application caused concentration-dependent PA relaxation. Relaxation occurred promptly and was maximal within 45-60 s. The threshold PTX concentration necessary for relaxation was 1 microM. PTX-induced relaxation was not affected by pretreatment with the cyclo-oxygenase inhibitor indomethacin (1 microM). Endothelial disruption by gentle rubbing of the intimal PA surface abolished relaxation of preconstricted PA by acetylcholine, but had no effect on relaxation by PTX. Although PA at resting tension displayed no response to PTX, PA constriction by norepinephrine in the presence of PTX concentrations greater than 10 microM was significantly decreased. These data indicate that PTX has direct actions on isolated rabbit PA which are not blocked by indomethacin nor require the presence of intact endothelium. Furthermore, PTX can suppress norepinephrine-induced constriction of isolated PA.