Determination of rat brain buffering in vivo by 31P-NMR

Buffering capacity of most tissues is composed of both rapid and slow phases, the latter presumably due to active acid extrusion. To examine the time course of brain buffering the brain pH of Sprague-Dawley rats was measured using 31P-nuclear magnetic resonance. The effect on brain pH of 30- or 58-min exposures to 20% CO2 followed by 30- or 38-min recovery periods, respectively, was studied. Brain pH reached its lowest value after a 15-min exposure to elevated CO2, thereafter slowly and steadily increasing. During recovery brain pH rose rapidly in the first 5 min exceeding control brain pH by 0.08 pH units. Brain pH fell during the next 30 min despite increases in blood pH and decreases in blood CO2 tension. Calculated intrinsic brain buffering rose steadily threefold during the last 40 min of CO2 exposure and during the final 30 min of recovery. These data show that in rat brain there is a temporally late buffering process, most likely active acid extrusion, requiring greater than 30 min for full activation and at least 30 min for discontinuation.     

Human immunodeficiency virus neutralizing antibodies recognize several conserved domains on the envelope glycoproteins.

Serum neutralizing antibodies against the human immunodeficiency virus were frequently detected in infected individuals, and low or absent serum neutralizing titers correlated with poor prognosis. Multiple diverse human immunodeficiency virus isolates were found to exhibit similar susceptibility to neutralization by a panel of human seropositive sera, suggesting that neutralizing antibodies are largely directed against conserved viral domains. Furthermore, utilizing antisera raised against a library of synthetic env peptides, four regions which are important in the neutralization process have been identified within both human immunodeficiency virus envelope glycoproteins (gp41 and gp120). Three of these are in conserved domains and should be considered for inclusion in a candidate vaccine.     

The pancreatic glucagon and C-peptide secretion during hyperinsulinemia in euglycemic glucose clamp with or without somatostatin infusion in normal man

6 normal subjects received two times of 2 hr euglycemic glucose clamp studies (insulin infusion rate 40 mU/M2/min) one with and the other without somatostatin (SRIF) infusion (500 microgram/hr). Serum C-peptide and glucagon levels were measured during clamp to study the sensitivity of pancreatic alpha and beta cells to the suppressive effects of exogenous hyperinsulinemia during normoglycemia in normal subjects and to find whether SRIF had any modulative effects on endocrine pancreas secretion at the status of hyperinsulinemia. The results showed that in normal man the degree of suppression of pancreatic glucagon secretion by hyperinsulinemia (approximately 100 uU/ml) during euglycemic glucose clamp without SRIF infusion was less than that of C-peptide with mean value of 62 +/- 4% of basal glucagon remained at the end of clamp study; while only about 30 +/- 2% of basal C-peptide concentrations remained. But during SRIF infused glucose clamp studies (SRIF was infused from 60 to 120 min), 32 +/- 2% of mean basal C-peptide concentrations and 38 +/- 6% of mean basal glucagon concentrations left at the end of 2 hr clamp studies when serum insulin level was about 100 uU/ml. For the glucose infusion rate (M value), it was significantly greater in our normal subjects in response to insulin + SRIF as compared to insulin alone (12.0 + 0.9 vs 8.8 +/- 1.4; P less than 0.01). We concluded: during hyperinsulinemia (100 uU/ml), the sensitivity of pancreatic alpha cells to insulin seems less than that of beta cells in normal man at normoglycemia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of growth phase on phospholipid biosynthesis in Saccharomyces cerevisiae.

The effect of growth phase on the membrane-associated phospholipid biosynthetic enzymes CDP-diacylglycerol synthase, phosphatidylserine synthase, phosphatidylinositol synthase, and the phospholipid N-methyltransferases in wild-type Saccharomyces cerevisiae was examined. Maximum activities were found in the exponential phase of cells grown in complete synthetic medium. As cells entered the stationary phase of growth, the activities of the CDP-diacylglycerol synthase, phosphatidylserine synthase, and the phospholipid N-methyltransferases decreased 2.5- to 5-fold. The subunit levels of phosphatidylserine synthase and the cytoplasmic-associated enzyme inositol-1-phosphate synthase were not significantly affected by the growth phase. When grown in medium supplemented with inositol-choline, cells in the exponential phase of growth had reduced CDP-diacylglycerol synthase, phosphatidylserine synthase, and phospholipid N-methyltransferase activities, with repressed subunit levels of phosphatidylserine synthase and inositol-1-phosphate synthase compared with cells grown without inositol-choline. Enzyme activity levels remained reduced in the stationary phase of growth of cells supplemented with inositol-choline. The phosphatidylserine synthase and inositol-1-phosphate synthase subunit levels, however, were depressed. Phosphatidylinositol synthase (activity and subunit) was not affected by growth in medium supplemented with or without inositol-choline or the growth phase of the culture. The phospholipid composition of cells in the exponential and stationary phase of growth was also examined. The phosphatidylinositol to phosphatidylserine ratio doubled in stationary-phase cells. The phosphatidylcholine to phosphatidylethanolamine ratio was not significantly affected by the growth phase of cells.     

Absence of heat shock protein synthesis in isolated mitochondria and plastids from maize

Examination of the proteins synthesized by isolated mitochondria, chloroplasts, or proplastids from maize tissues showed that a heat treatment at 40 degrees C does not induce or enhance the synthesis of any protein when compared to preparations treated at the control temperature of 28 degrees C. These observations are consistent with the results obtained by labeling proteins in vivo under sterile conditions. In vivo labeling in the presence of cycloheximide during heat shock showed no heat shock protein synthesis. Labeling in the presence of chloramphenicol during heat shock showed a similar heat shock protein pattern as in the absence of the inhibitor. It is concluded that maize organelles do not synthesize heat shock proteins and that, if present, they may be due to bacterial contamination.     

Hepatic metabolism and secretion of a cholesterol-enriched lipoprotein fraction

A potentially important source of cholesterol secreted in bile is cholesterol-rich lipoproteins. However, the fate of the cholesterol carried in these lipoproteins after hepatic uptake has not been investigated. We harvested an apoE- and cholesterol-rich lipoprotein fraction (d 1.02-1.06 g/ml) from hypercholesterolemic rats and examined the acute effects of these lipoproteins on hepatic cholesterol metabolism, very low density lipoprotein (VLDL) secretion, and biliary lipid secretion. Administration of a lipoprotein bolus (20 mg of cholesterol) to rats resulted in a significant decrease in 3-hydroxy-3-methylglutaryl coenzyme A reductase activity and a significant increase in acyl-coenzyme A:cholesterol acyltransferase activity over controls at 1 hr. Hepatic cholesteryl ester content increased 400% with no change in hepatic free cholesterol content or biliary cholesterol secretion. These cholesterol-rich lipoproteins delivered in the isolated perfused liver effected a fivefold increase in hepatic VLDL secretion with no change in composition. Therefore, cholesterol-rich lipoproteins do not acutely alter biliary cholesterol secretion. Rather, the majority of the cholesterol delivered to the liver in these lipoproteins is either esterified and stored as cholesteryl ester or resecreted as free and esterified cholesterol in hepatic VLDL.     

Phosphatidylinositol Phosphodiesterase (Phospholipase C) Activity in the Pineal Gland: Characterization and Photoneural Regulation

Phosphatidylinositol phosphodiesterase (PL-C) appears to be a key element in the adrenergic regulation of pineal cyclic AMP levels. In the present study, the rat pineal enzyme was characterized using exogenous [3H]phosphatidylinositol (0.5 mM) as substrate. Half the enzyme activity was found in the cytosolic fraction, but the highest specific concentration was associated with the membrane fraction. Two pH optima (5.5 and 7.5) of enzyme activity were observed for the membrane fraction but only one in the cytosol fraction (pH 5.5). Enzyme activity in both fractions was Ca2+ dependent. In the case of the membrane protein in pH 7.5, the enzyme activity was sensitive to changes in Ca2+ in the 10-100 nM range. Addition of an equimolar concentration of phosphatidylinositol 4-phosphate nearly completely inhibited the hydrolysis of [3H]phosphatidylinositol; other phospholipids (1.0 mM) were less potent. This may reflect our present finding that [3H]phosphatidylinositol 4-phosphate is a better substrate than [3H]phosphatidylinositol for the enzyme. Stimulus deprivation (2 weeks of constant light or superior cervical ganglionectomy) reduced the cytosolic activity by 30% and had no effect on the membrane-associated enzyme.