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Biomedical subjects

P R Bouman

Publications and source records attributed to P R Bouman.

At least 19 recordsLinked to original sources
PubMed1980

Effects of calcium manipulation and glucose stimulation on a histochemically detectable mobile calcium fraction in isolated rat pancreatic islets.

Pancreatic B-cell calcium as histochemically detectable with glyoxal bis (2-hydroxyanil) = GBHA was studied in isolated islets of fed rats. GBHA has previously been shown by us to detect an ionized or readily ionizable Ca-fraction (GBHA-Ca). In the presence of Ca++ (2.5 mM), high glucose (15 mM) induced a rapid decrease (30%) of islet GBHA-Ca followed by a rise between 30 and 60 min to levels above the initial value. At low glucose (0 or 2.5 mM) GBHA-Ca showed a slight and gradual decline under these conditions. Omission of Ca++ at low glucose rapidly decreased (30%) islet GBHA-Ca. This decrease was markedly inhibited by high glucose, although glucose did not induce insulin secretion under these conditions. Preincubation in the absence of Ca++ (15 min) depleted islet GBHA-Ca, but partial restoration occurred during subsequent incubation with Ca++ at low glucose. By contrast, high glucose completely restored GBHA-Ca within 5 min, followed by a decline and a subsequent rise. Reintroduction of Ca++ also rapidly restored the glucose-induced insulin secretion. These results indicate that islet GBHA-Ca represents a mobile Ca-fraction which is dependent on extracellular Ca++ and which responds very rapidly to glucose stimulation. It is suggested that changes of GBHA-Ca in the B-cells may reflect changes in the Ca pool involved in the insulin secretory mechanism.

Aminophenols↗
PubMed1979

Evaluation of the glyoxal-bis-(2-hydroxyanil)-method for staining of calcium in model gelatin films and pancreatic islets.

The nature of tissue calcium, detectable with glyoxal-bis-(2-hydroxyanil), (GBHA), was investigated using gelatin films as model. The results indicate that in the films the procedure detects only the calcium fraction which was ionized in the original gelatin solution. The GBHA staining intensity (absorbance) appeared to be linear with the amount of ionized calcium in the range from 0 to 2 micrograms/cm2. The method allows detection of amounts of ionized calcium as low as 0.15 micrograms/cm2 or 0.0015 pg/mu2. For the measurement of calcium in pancreatic tissue of fed rats, the tissue was subjected to freeze-substitution at -80 degree C in acetone containing 1% oxalic acid. Adjacent sections were stained with either GBHA or aldehyde-fuchsin (AF). Exocrine tissue hardly stained with GBHA whereas islet tissue stained intensely. For GBHA as well as for AF a variation in staining intensity (visual evaluation) between islets was observed. Islet GBHA- and AF-staining intensities did not correlate. The AF-staining intensity but not the GBHA-staining intensity decreased with increasing islet diameter. Also in pancreatic islet tissue the GBHA method appears to be very sensitive and reproducible and small differences in islet GBHA-staining intensity can be detected. The results indicate that between islets differences in ionized calcium content exist. These differences do not correlate with the degree of B-cell granulation.

Animals↗
PubMed1979

Insulin secretion and cyclic adenosine 3', 5'-monophosphate levels in pancreatic islets of fed and fasted rats. Time course and dose kinetics during glucose stimulation.

Incubation of pancreatic islets of fed rats at glucose 10 and 15 mM induced a rapid rise of the islet cyclic adenosine 3',5'-monophosphate (cAMP) content. Maximum levels were attained at 15 min and lasted until 30 min, after which cAMP declined again. Insulin secretion increased most rapidly from 15 min onward, i.e. after the rapid rise of cAMP. Islet cAMP at either 15 or 30 min showed its major concentration-dependent increase between glucose 7.5 and 10 mM. Glucose 15 mM did not further enhance the cAMP response, although this concentration increased insulin secretion more than two-fold over values observed at glucose 10 mM. Thus, the glucose dose-response relations for cAMP levels and insulin secretion appear to be different, indicating that factors other than cAMP alone determine the secretory response to glucose. Fasting for 24 and 72 h progressively inhibited glucose-induced insulin secretion. At glucose 15 mM the secretory inhibition disappeared after 30-45 min, but at glucose 10 mM it persisted for at least 90 min. Increasing periods of fasting also progressively delayed and inhibited the cAMP response to glucose, most strongly at glucose 10 mM. Fasting for 24 h shifted the glucose dose-response curves for cAMP and insulin secretion to the right, but the maximum responses at glucose 37.5 mM were not significantly inhibited. The secretory inhibition appeared to be linearly related with the cAMP content in two different ways: (a) At fixed concentrations of glucose, the increasing of the cAMP response (at 15 min) as induced by 24 and 72 h of fasting correlated with the secretory inhibition over the initial 30 min. (b) At one fixed period of fasting (24 h), the variable percent inhibition of the cAMP response to graded concentrations of glucose (5-37.5 mM) correlated with the percent secretory inhibition at these concentrations. These correlations were no longer apparent after 30 min of incubation. The results support the view that inhibition of the adenylate cyclase-cAMP system is a major determinant factor in fasting-induced impairment of insulin secretion during the initial 30 min of glucose stimulation.

Animals↗
PubMed1978

Plasma insulin patterns in the unanesthetized rat during intracardial infusion and spontaneous ingestion of graded loads of glucose.

Rats were provided with double permanent heart catheters, allowing simultaneous infusion and rapid blood sampling in the freely moving animals. Intracardial glucose infusion (75, 150, and 300 mg) over 15-min periods induced biphasic plasma insulin responses, their onset and magnitude being correlated with the blood glucose increments. The insulin-ogenic index decreased at increasing infused loads. After spontaneous oral ingestion of 75, 150, 300, and 750 mg glucose over 2 min or less, plasma insulin increased rapidly during the initial 4 to 8 min. At the highest leads this was followed by a gradual further increase until 15 min. The rapid insulin response increased with the ingested load. About half of this response had occurred already at 2 min, i.e., prior to the first rise of blood glucose at 3 min. Maximum blood glucose levels (125-135 mg/dl) occurred between 8 and 15 min and did not correlate with the ingested loads. The insulinogenic index increased at higher oral loads. It is suggested that the plasma insulin response to glucose ingestion results from successive and cumulative operation of anticipatory nervously triggered insulin secretion, anticipatory loaded-dependent potentiation of secretory stimulation by rising blood glucose, and further adjustment of the secretion rate until blood glucose declines. The possible mechanisms are discussed.

Administration, Oral↗
PubMed1976

Effect of fasting on the incorporation of [3H]-L-phenylalanine into proinsulin-insulin and total protein in isolated rat pancreatic islets.

Pancreatic islets of fed, 24 hr and 72 hr fasted rats were incubated with [3H]-L-phenylalanine at verious concentrations of glucose. Total islet protein was isolated by TCA-precipitation, proinsulin-insulin by polyacrylamide gel electrophoresis. The incorporation of label was expressed per mug dry islet weight. Fasting for 24 hr reduced the incorporation of label into (pro)insulin at glucose 3 mg/ml, but not at glucose 1 mg/ml. After 72 hr of fasting the incorporation into (pro)insulin was decreased both at glucose 1 and 3 mg/ml and the slope of the dose-response curve for glucose stimulation was reduced by 31%. In contrast, fasting caused the incorporation into total islet protein to increase. A similar tendency was observed in an unidentified protein fraction, which failed to migrate from the spacer gel on disc electrophoresis. Fasting did not affect the islet DNA content per mug dry weight. These results suggest that fasting reduces the rate of insulin biosynthesis by decreasing the glucose sensitivity of this process. Fasting may stimulate, however, the biosynthesis of an unidentified islet protein component.

Animals↗
PubMed1975

Quantitative analysis of pancreatic islet development and insulin storage in the foetal and newborn rat.

Pancreatic islet development and insulin storage were studied in foetal rats during the last 4 days of gestation (day 19 to 22 post-coitum (p.c.)) and in 1 and 5 days old neonatal rats. Adult female virgin rats were also studied. The percentage of granulated B-cells per islet, the degree of B-cell granulation and the islet insulin concentration rose from low levels on day 19 to adult levels on day 22 and remained stable after birth. This indicates that the qualitative maturation of the pancreatic islets as insulin producing units is completed on the last day of gestation. The percentage of islet tissue slowly rose from 0.7% at day 19 to 1.5% on day 22. A further and much more rapid rise occurred during the first day of birth. At the 5th postnatal day the islets comprised 3.6% of the pancreas versus 1.1% in adult rats. Likewise, the neonatal pancreatic insulin concentration was about 3 times higher than in the adult pancreas. The foetal pancreas as a whole showed rapid exponential growth between day 18 and 21 p.c., but a sudden decline in growth rate occurred from day 21 onward. The total mass of islet tissue, on the other hand, continued to expand at its high initial rate up to the first day after birth, whereafter this high rate also declined. The high concentration of insulin in the neonatal rat pancreas therefore appears to be due to differential growth rates of the endocrine and exocrine tissue during the last day of pregnancy and the first day after birth.

Age Factors↗