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Biomedical subjects

R J Cenedella

Publications and source records attributed to R J Cenedella.

At least 73 records · Page 4Linked to original sources
PubMed1982

Studies on the mechanism of the epileptiform activity induced by U18666A. II. Concentration, half-life and distribution of radiolabeled U18666A in the brain.

The concentration, half-life, and distribution in brain of U18666A, a drug that can drastically alter cerebral lipids and induce a chronic epileptiform state, was determined following both acute and chronic drug administration. U18666A specifically labeled with tritium was prepared by custom synthesis. Brain levels of 1 x 10(-6)M and higher were reached soon after giving an acute 10-mg/kg dose (i.p. or s.c.) of U18666A containing 7-3H-U18666A of known specific activity. A steady state concentration of 1 to 2 x 10(-6)M was reached with chronic injection of 10 mg/kg every 4th day, a treatment schedule that results in altered brain lipids and induction of epilepsy if begun soon after birth. The disappearance of U18666A from both brain and serum was described by two similar biexponential processes, a brief rapid clearance (t1/2 = 10 h) and a sustained and much slower one (t1/2 = 65 h). Brain levels of the drug were about 10 times higher than serum at all times examined. Few differences were seen in the regional distribution of radiolabeled drug in brain as determined by both direct analysis and by autoradiographic examination; but the drug did concentrate in lipid-rich subcellular fractions. For example, the synaptosome and myelin fractions each contained about 25-35% of both the total 3H-labeled drug and total lipid in whole brain. The lipid composition of these fractions was drastically altered in treated animals. In conclusion, the chronic epileptiform state induced by U18666A does not appear to involve localization of the drug in a specific brain region or particular cell type. Rather, the condition could involve localization of the drug in lipid-rich membranes and marked changes in the composition of these membranes.

Androstenes↗
PubMed1982

Sterol synthesis by the ocular lens of the rat during postnatal development.

Great amounts of plasma membranes are formed during early postnatal development of the ocular lens as lens epithelial cells differentiate into fiber cells. Little information is available on the source of the lipids, and particularly cholesterol, required for formation of these plasma membranes. The present study measured the capacity of the lens of the rat to synthesize cholesterol during this dynamic period of growth. Incorporation by lens of (3)H(2)O into total fatty acids was also examined. Absolute rates of cholesterol synthesis per whole lens were estimated in vitro from incorporation of (3)H from (3)H(2)O into digitonide precipitable sterols (DPS) by intact lenses of 6- to 30-day old rats. Rates of cholesterol synthesis were calculated which were adequate to furnish from either 50-100% or 20-40% of the cholesterol required by the lens for growth, depending upon the animal's age and upon whether one considered NADPH to be generated by the pentose phosphate pathway or by oxidative enzymatic processes (NADPH from the pentose pathway is not labeled from (3)H(2)O). Generation of the NADPH necessary for cholesterol synthesis principally by the pentose pathway would support the higher percent contribution of synthesis to the total growth requirement. The pentose pathway was clearly active in the young rat lens, since between 7.5 to 9.0 times more [1-(14)C]glucose than [6-(14)C]glucose was oxidized in vitro to (14)CO(2) by 6- and 22-day old lenses. Incorporation of (3)H(2)O into DPS decreases sharply after 2 weeks of age in spite of a constant rate of cholesterol accumulation by the lens. These results indicate that the ocular lens of the rat can furnish most if not all of its cholesterol requirements by synthesis de novo during the first 2 weeks of life, and imply a contribution from another source at older ages. Whether lipoproteins can supply cholesterol to the lens is still unclear, although neither HDL nor LDL altered the incorporation in vitro of [U-(14)C]glucose into DPS by lens.-Cenedella, R. J. Sterol synthesis by the ocular lens of the rat during postnatal development.

Animals↗
PubMed1981

Studies on the source of urinary cholesterol in the normal human male.

The aim of the present study was to obtain information on the source of urinary cholesterol in normal men of various age groups (22-25, 37-42, greater than 63 yrs). Aliquots of 24-hr urine samples were fractionated by ultracentrifugation. Between 10-20% of the total cholesterol in urine (measured by gas-liquid chromatography) separately sedimented after 2 x 10(4) g-min and after 4 x 10(5) g-min of centrifugation. However, an average of more than 50% of the total sedimented after 6 x 10(6) g-min and only 10-20% of total cholesterol remained in this supernatant. These results indicate that most of the cholesterol in urine of normal males is a component of a light particulate fraction. Little difference was seen in the distribution of urinary cholesterol among the various age groups examined The 4 x 10(5) g-min supernatant from 24-hour total urine samples was recentrifuged at 10(5) g for 60 min. The resulting pellet (100 P) was assayed for protein, total cholesterol and phospholipid. The cholesterol was 12-14% esterified. A molar ratio of total cholesterol to phospholipid of 1 to 0.8 was calculated. Assay of the 100 P fraction for marker enzymes showed an activity pattern characteristic for plasma membranes. Fractionation of the 100 P proteins by electrophoresis and separation of the 100 P phospholipids by thin-layer chromatography revealed patterns clearly different from those of human red cell plasma membrane. Electron micrographs of the 100 P fraction revealed an appearance similar to that of deteriorated membranes. The results suggest that most of the cholesterol in urine of the adult human male is present as a component of membranes derived from endogenous cells of the urogenital system.

Adult↗
PubMed1978

Induction of chronic epileptiform activity in the rat by an inhibitor of cholesterol synthesis, U18666A.

Earlier work in our and other laboratories suggest that alteration of brain lipids, primarily sterols, could be a precondition for the development of epileptiform activity. The present study further tests this hypothesis by attempting to produce chronic epileptiform activity in the rat by a drug which impairs biosynthesis of cerebral cholesterol. Starting one day after birth, weekly injection of the rat with U18666A, 3-beta(2-diethylaminoethoxy)androst-5-en-17-one hydrochloride (10 mg/kg, s.c.), produced a reduced seizure threshold to flurothyl ether and a recurrent, spontaneous seizure state by the sixth and tenth weeks of life, respectively. These conditions were not seen if treatment was delayed until rats were about 4 weeks old. The seizure pattern, as seen by continuous ECoG and EMG recordings, consisted of a 3--5 sec burst of high voltage spiking and corresponding increases in muscle activity. However, major motor seizures were not produced. The total episode lasted 10--15 sec. Seizure frequency ranged from 5 to 21 per day. U18666A decreases cholesterolsynthesis, presumably by inhibiting enzymatic reduction of desmosterol to cholesterol. After the first two weeks of treatment, cerebral cortical cholesterol levels decreased to about 50% of control cortical levels. However, the concentration of cerebral total sterols did not change because desmosterol levels reciprocally increased. In spite of continued drug dosage, cholesterol and desmosterol levels of treated rats approached those of controls by 8 weeks of age. These observations, plus finding that a seizure-prone state did not develop in rats when the onset of drug treatment was postponed until about 4 weeks of age, suggest that alterations of brain sterols early in development of the mammalian brain can result in development of a chronic, epileptiform condition later in life.

Age Factors↗
PubMed1978

Cerebral cortical cholesterol changes in cobalt-induced epilepsy.

The present study was designed to elucidate cerebral cortical cholesterol changes observed earlier in cobalt-induced epilepsy in the rat. This model is produced by insertion of cobalt metal rods into the cerebral cortex. Seven days after implantations of cobalt (or other metals), measurements of cerebral cortical lipid concentrations were made in the direct area of metal implantation (lesion area) and in the nonnecrotic tissue immediately adjacent to the lesion site (adjacent area). The cortical concentration of free cholesterol decreased and the concentrations of cholesterol esters (CE) greatly increased in the adjacent area of rats implanted with epileptogenic metals (cobalt and nickel) but not in those implanted with nonepileptogenic metals (copper and stainless steel). Differences in the fatty acid compositions of CE from plasma and those from cobalt-lesioned cortex indicated that the accumulated CE originated in the brain rather than from the plasma CE pool. A time course study revealed that changes in the cortical concentrations of free and esterified cholesterol precedes the first appearance of epileptiform activity as measured by electrocorticography. The reduction of free cholesterol levels most likely reflects increased cholesterol metabolism in the cobalt-lesioned cortex. A major portion of this free cholesterol appears to be converted to CE, but not to bile acid or neutral sterol (potential products of cholesterol metabolism). The concentration of free fatty acids, the other substrate of CE formation, was decreased in the lesion site. The increased metabolism of cholesterol could not be explained by changes in the activities of CE synthetase and hydrolase(s). Since cholesterol in the brain is found almost exclusively in membranes, it is likely that these sterol changes reflect membrane alterations or disintegration. However, the exact relationship of these changes to the epileptogenic effect of cobalt remains unclear.

Acyltransferases↗
PubMed1976

Halofenate and clofibrate: mechanism of hypotriglyceridemic action in the rat.

Rats fed a fat-free diet containing no drug, 0.02% or 0.10% halofenate, or 0.25% clofibrate for 14 days were injected intravenously with equivalent amounts of either [2-3H]glycerol or [1(3)-3H]glycerol. Blood samples were collected at times up to 150 min after injection and serum triglycerides were isolated and assayed for radioactivity. Kinetic analysis of the serum appearance and clearance curves of 3H-labeled triglyceride permits estimation of serum total 3H-labeled triglyceride formation and triglyceride fractional turnover rates. The total amounts of 3H-labeled triglyceride formed from [2-3H] or from [1(3)-3H] glycerol in control-fed animals were very similar. Over 95% of the serum 3H-labeled triglyceride formed from either substrate circulated in a rapidly turning-over triglyceride pool (t1/2 = 8 min). Treatment with 0.10% halofenate or 0.25% clofibrate decreased labeling of serum triglycerides by 75-80% without increasing serum 3H-labeled triglyceride fractional turnover rates. Furthermore, both drugs decreased incorporation in vivo of 14C from [U-14C]glycerol into hepatic but not intestinal triglycerides without significantly decreasing incorporation of 14C into total phospholipids of either tissue. From these observations we suggest that, in the intact normal rat, sustained reduction of serum triglyceride levels produced by treatment with halofenate or clofibrate is due to inhibition of hepatic triglyceride formation.

Animals↗
PubMed1975

Brain free fatty levels in rats sacrificed by decapitation versus focused microwave irradiation.

Values are presented for whole brain free fatty acid levels of rats sacrificed by decapitation vs focused microwave irradiation. Free fatty acids were quantitated by specific colorimetric analysis. Within ca. 1 min of sacrifice by either decapitation or microwave, rat whole brain free fatty acid concentrations ranged from ca. 80-100 mug/g fresh tissue. If the brain remained in the head for a total of 5 min after decapitation, free fatty acid levels increased by over 100%. The free fatty acids at this time were enriched with arachidonic acid. The increase in free fatty acid levels following decapitation was completely absent in rats sacrificed by the microwave irradiation. This microwave technique could be a valuable tool in determining free fatty acid and other heat stable compounds in brain tissue.

Animals↗
PubMed1975

Clofibrate pharmacokinetics: effect of elevation of plasma-free fatty acids.

The pharmacokinetics of rho-chlorophenoxyisobutyrate (CPIB), the active metabolite of clofibrate were determined following intravenous administration in the rat. Serum CPIB concentrations were measured using an new TLC-GLC method. The results agree favourably with pharmacokinetics in human subjects after oral administration of clofibrate. Both clofibrate and free fatty acids (FFA) are extensively bound to circulating plasma proteins. When plasma FFA were elevated to about 2,000 muEq/1, the CPIB elimination half-life decreased form 19.3 h in controls to 7.3 h. Thus, elevation of FFA appears to significantly alter the pharmacokinetics of a highly bound drug.

Animals↗
PubMed1975

Alteration of drug pharmacodynamics by hyperlipidemia.

Circulating lipid levels, when elevated, can alter the pharmacodynamics of lipophilic drugs presumably by acting as an additional storage depot for such drugs. Prostaglandin E1 (PGE1) and phenylephrine produced less effect on the blood pressure of atherosclerotic-hyperlipidemic rabbits than of control rabbits. This difference was apparently not due to alterations in vascular smooth muscle since aortic strips from the normal and severely atherosclerotic rabbit responded identically to the contractile effects of these drugs. Further, hyperlipidemic rats which had not yet become atherosclerotic were less responsive to the convulsant effects of fluorthyl, a highly lipophilic drug. In the presence of emulsified fat the contractile response of the rat ileum in vitro to PGE1 and acetylcholine was greatly reduced. The inhibition was reversed when fat was removed from the bathing solution. The response to PGE1, which is more lipid-soluble than acetylcholine, was more sensitive to inhibition by the presence of lipid. Finally, the pharmacokinetics of intravenously administered sulfamerazine, a lipophilic drug, appeared to be altered in the hyperlipidemic rabbit.

Animals↗