Robert L. Russell

Stimulation of serum lecithin-cholesterol acyltransferase activity by phenobarbital in the rat.

Abstract The activity of serum lecithin-cholesterol acyltransferase was increased on administration of phenobarbital to the rat. This effect was dependent on dose and elapsed time after administration of the drug. Phenobarbital did not stimulate lecithin-cholesterol acyltransferase activity when added to serum from normal animals in vitro. Presumably, phenobarbital increased serum lecithin-cholesterol acyltransferase activity by induction of the microsomal enzyme and subsequent secretion by the liver.

Depressant Agent from Walnut Hulls

Crushed unripe walnut hulls (Juglans nigra), when extracted with ether, yield an extract which sedates or at least depresses the movements of Daphnia magna, leopard frogs, perch, catfish, goldfish, mice, rats, and rabbits. One purified depressant compound, 5-hydroxy-1,4-naphthoquinone (juglone), has been isolated and tested on most of these species.

Enzymatic aspects of the reduction of microsomal glycerolipid biosynthesis after perfusion of the liver with dibutyryl adenosine-3′,5′-monophosphate

Abstract Livers from fed male rats were perfused in a nonrecycling system for 60 min with a medium containing 100 mg/dl glucose, 3 g/dl bovine serum albumin, and ~0.5 m m oleic acid, with or without 20 μ m dibutyryl cyclic adenosine-3′,5′-monophosphate (Bt2cAMP). At the termination of the experiment, microsomes were isolated from these livers. In agreement with data reported previously, Bt2cAMP decreased output of triacylglycerol, but stimulated ketogenesis and output of glucose; uptake of free fatty acid was unaffected by the nucleotide. Perfusion with Bt2AMP decreased the biosynthesis of triacylglycerol, diacylglycerol, and phosphatidate from sn-[U-14C]glycerol-3-phosphate by microsomes isolated from these livers. Perfusion with Bt2cAMP also decreased incorporation of sn-glycerol-3-phosphate into phosphatidate by microsomes isolated from the livers, when the microsomes were incubated with NaF to inhibit phosphatidate phosphohydrolase, and when fatty acid, coenzyme A and ATP were replaced by the acyl coenzyme A derivative; the formation of phosphatidate under these conditions was used as an estimate of the activity of sn-glycerol-3-phosphate acyltransferase (EC 2.3.1.15). However, the activities of microsomal phosphatidate phosphohydrolase (EC 3.1.3.4) and diacylglycerol acyltransferase (EC 2.3.1.20), measured with microsomal bound substrate, were increased by Bt2cAMP. These data have been interpreted to mean that Bt2cAMP inhibits hepatic microsomal synthesis of triacylglycerol at a step prior to the formation of phosphatidate, presumably at the glycerophosphate acyltransferase (EC 2.3.1.15) step(s).

Reciprocal relationship between uptake of Ca++ and biosynthesis of glycerolipids from sn-glycerol-3-phosphate by rat liver microsomes

Abstract The relationship between uptake of Ca ++ and incorporation of sn-[ 14 C]-glycerol-3-phosphate into phosphatidate, diglyceride, and triglyceride was evaluated in microsomes isolated from livers of normal fed male rats. Uptake of Ca ++ was dependent on concentration of Ca ++ (0.1 – 2.5 mM), and accompanied by a decrease in the rate of glycerolipid synthesis. The quantity of Ca ++ ion taken up at 20 μM CaCl 2 in the presence of ATP was equivalent to that observed with 2.5 mM CaCl 2 in the absence of ATP. The ATP dependent uptake of Ca ++ , like the passive uptake at higher concentrations of Ca ++ , was correlated with inhibition of incorporation of sn-glycerol-3-phosphate into phosphatidate. Accumulation of Ca ++ in hepatic microsomes, therefore, appears to result in a calcium-dependent decrease in biosynthesis of phosphatidate and other glycerolipids.

A possible role of calcium in the action of glucagon, cAMP and dibutyryl cAMP on the metabolism of free fatty acids by rat hepatocytes.

Summary The effects of calcium (Ca ++ ) on the actions of glucagon, cAMP and dibutyryl cAMP on triacylglycerol synthesis, ketogenesis and output of glucose were studied using isolated hepatocytes. Glucagon, cAMP and Bt 2 cAMP decreased the incorporation of [1- 14 C]oleate into triacylglycerol and increased synthesis of ketone bodies and output of glucose. Basal rates of triacylglycerol synthesis, ketogenesis, and output of glucose, and the responses to glucagon and the cyclic nucleotides were diminished by depletion of calcium. Triacylglycerol synthesis was restored toward control values by treatment with calcium. Ionophore A 23187, mimicked the effects of glucagon on triacylglycerol biosynthesis provided calcium was present in the medium. Uptake of [1- 14 c]oleate was impaired when the hepatocytes were depleted of calcium. These observations suggest that calcium plays an important role in hepatic triacylglycerol synthesis and in ketogenesis and on the actions of glucagon and adenylic cyclic nucleotides on these metabolic pathways.

Pharmacological aspects of juglone

Abstract Juglone (5-hydroxy, 1-4 naphthoquinone), isolated from Juglans nigra (Black Walnut) in pure crystalline form has been investigated pharmacologically. These studies indicate that juglone is a depressant agent to unanesthetized fish, mice, rats and rabbits. It dilates the ear vessels of the intact rabbit and coronary arteries of the isolated rabbit heart. In spite of this dilatation juglone has no effect on the blood pressure and heart rate in the dog. It depresses the activity of isolated smooth muscle of rat intestine and uterus.

Effect of Triton WR-1339 on lecithin-cholesterol acyltransferase in the rat.

Abstract The effect of Triton WR-1339 on activity of lecithin-cholesterol acyltransferase was measured in rat serum following addition of Triton to the serum in vitro or after intravenous injection of the detergent. The inhibitory effect of Triton WR-1339 on activity of lecithin-cholesterol acyltransferase when the detergent was added in vitro was dose dependent and appeared to result from a direct action on the enzyme rather than from a physical modification of the substrate by the detergent. The serum half-life ( T 1 2 ) of Triton WR-1339 injected intravenously in the rat was 23.1 ± 1.0 h. The inhibitory effect of Triton on serum LCAT activity when the detergent was given intravenously was also dose dependent and was reversed when the serum concentration of Triton decreased; under specific conditions, LCAT activity reached values higher than control. This behavior after treatment of the animal may be explained by increased concentration of the enzyme in the plasma, by stimulation of LCAT activity by the very low density lipoprotein or metabolites accumulating in the plasma of rats treated with Triton WR-1339, or by a combination of these factors.

Possible relationship of the hepatic microsomal ATP-dependent calcium pump to sex differences in triacylglycerol synthesis☆

Abstract Microsomes were isolated from livers of fed male and female rats and the rates of incorporation of sn-[14C]-glycerol-3-phosphate into phosphatidate, diacylglycerol and triacylglycerol by the microsomes were measured. Simultaneously, microsomal ATP-dependent uptake of calcium was evaluated and correlated with synthesis of phosphatidate from sn-glycerol-3-phosphate. The rate of glycerolipid synthesis by hepatic microsomes from female rats was greater than that of microsomes from male rats. By contrast, the active accumulation of calcium and subsequent inhibition of synthesis of phosphatidate from glycerol-3-phosphate was lower in microsomes from livers of female rats than from male animals. This reciprocal relationship between uptake of calcium and incorporation of sn-glycerol-3-phosphate into phosphatidate as reported earlier (Biochem. Biophys. Res. Commun. 78 , 1053–1059 (1977)) may, in part, be responsible for the differences in the rates of hepatic triacylglycerol synthesis between livers from male and female rats.

Hepatic secretion and turnover of serum phosphatidylcholine-cholesterol acyltransferase in male and female rats

The activity of serum phosphatidylcholine-cholesterol acyltransferase (LCAT), output of the enzyme by the perfused rat liver, and the effect of pretreatment with colchicine on LCAT were studied in male and female rats. It was observed that: 1. Serum LCAT activity in the female exceeded that of the male in fasted animals, whereas in fed animals, LCAT activity was higher in the male than the female. With both sexes, however, serum LCAT activity in fed animals was greater than that in fasted animals. Data are presented which suggest that the observed sex differences were due to concentration and/or composition of the substrate rather than to differences in the serum concentration of the enzyme. 2. The release of LCAT by perfused livers from fasted female rats exceeded that of the male animals. The output of LCAT was inhibited by pretreatment (male) with colchicine, which suggests that hepatic secretion of LCAT is dependent on vesicular transport. 3. The decay of serum LCAT activity in vivo following injection of colchicine was more rapid in fasted female rats than in male animals. These observations lead us to postulate that the turnover rate of LCAT is higher in female rats than in male animals.

A comparison of progesterone and epinephrine inhibition on the myometrium of the rat.

Abstract This study was executed to gain insight into the possibility of a relationship between the smooth muscle depressing effects of epinephrine and of progesterone. The first part of the investigation considered the possibility that an adrenergic blocking agent, dichloroisoproterenol, may affect the ability of progesterone to exert its inhibitory effects on smooth muscle as the blocking agent does with epinephrine. The second was a comparative study on the oxygen-stimulating effects of epinephrine and progesterone. The rationale behind this last experiment was derived from observations of Bueding and Bulbring ∗ which have led them to the conclusion that the epinephrineinduced relaxation of smooth muscle is mediated through an increase in oxidative metabolism. Epinephrine (1.04 mg/ml) caused inhibition of the spontaneous contractions of rat uterine strips when bathed in Krebs original Ringer phosphate buffered solution. Progesterone, at a concentration of 20 mg/ml, also caused inhibition of spontaneous activity of the rat uterus under the same conditions. Dichloroisoproterenol, at 1 mg/ml, inhibited the depressing effect of epinephrine at the previously mentioned dose, but had no effect on the depressing effect of progesterone. Epinephrine caused an increase in the rate of oxygen consumption of the rat uterus at 5, 15, and sometimes 30 min, after which the rate diminished as the effect wore off. Progesterone caused a significant depression of oxygen consumption of the uterus over the entire hour measured, and especially during the last 15-min period. The conclusion was drawn from these results that epinephrine and progesterone depress smooth muscle activity via independent mechanisms.