Wilford Saul

Enhanced hepatotoxicity of carbon tetrachloride, thioacetamide, and dimethylnitrosamine by pretreatment of rats with ethanol and some comparisons with potentiation by isopropanol

Abstract Elevated plasma glutamic-pyruvic transaminase (GPT) activity induced by carbon tetrachloride (CCl 4 ), thioacetamide, or dimethylnitrosamine in male rats was increased by pretreatment with four doses (each 5 ml/kg) of ethanol orally 48, 42, 24, and 18 hr before the hepatotoxic agent. The potentiated hepatotoxicity of CCl 4 was confirmed by histologic evaluation. During the pretreatment, blood ethanol concentrations fluctuated between 0 and 300 mg/100 ml, but were less than 5 mg/100 ml when a hepatotoxic agent was injected ip. Pretreatment with ethanol did not affect the hepatic concentrations of CCl 4 or its metabolite, chloroform (CHCl 3 ), at 1 hr after administration of CCl 4 . The CCl 4 -induced diene conjugation tended to increase after ethanol pretreatment and was significantly potentiated by pretreatment with isopropanol or pyrazole and a single dose of ethanol. In rats pretreated with ethanol, covalent binding of 14 CCl 4 to liver protein and lipid in vivo was significantly greater at 6 and 24 hr, but not during the first 3 hr, than in control rats. The in vitro binding of 14 CCl 4 , 14 CHCl 3 , and 14 CBrCl 3 to hepatic microsomal protein was increased by ethanol pretreatment. Ethanol pretreatment also doubled the in vitro rate of demethylation of dimethyl-nitrosamine by liver microsomes, but did not affect the amount of microsomal protein and cytochrome P-450, NADPH c reductase activity nor the rate of N-demethylation of ethylmorphine. The similarities in microsomal effects of pretreatment with isopropanol and pretreatment with four doses of ethanol suggest that similar mechanisms are involved in their potentiation of CCl 4 -induced hepatotoxicity. The potentiation by pretreatment with ethanol, but not with isopropanol, of the hepatotoxicity of thioacetamide and dimethylnitrosamine suggests that ethanol pretreatment also activates some additional mechanisms.

Nature of the protection against carbon tetrachloride-induced hepatotoxicity produced by pretreatment with dibenamine [N-(2-chloroethyl) dibenzylamine]

Abstract In this paper, we assess various plausible mechanisms by which pretreatment with Dibenamine [ N -(2-chloroethyl) dibenzylamine] hydrochloride (25 mg/kg, s.c., 48 and 24 hr before the administration of CCl 4 ) protects rats against the hepatotoxic effects of CCl 4 . Dibenamine pretreatment did not affect significantly the absorption of CCl 4 after i.p. administration or the elimination of CCl 4 from various tissues, as evident from unchanged tissue levels. Dibenamine pretreatment decreased the accumulation of the metabolite CHCl 3 in liver, the isopropanol-potentiated covalent binding of a small dose of 14 CCl 4 (0.1 ml/kg) and the covalent binding of a necrosis-producing dose of 14 CCl 4 (1.0 ml/kg) to proteins and lipids in liver, and the diene conjugation of liver microsomal lipids induced by CCl 4 . These findings suggest that Dibenamine pretreatment impairs the microsomal enzymes which catalyze the formation of free radical derivatives of CCl 4 . Dibenamine protection is not correlated with its concentration in liver or with the covalent binding of Dibenamine derivatives to liver microsomal protein.

Carrageenan-stimulated release of arachidonic acid and of lactate dehydrogenase from rat pleural cells

Cells isolated from the rat pleural cavity consist mainly of macrophages, mast cells, eosinophils, and lymphocytes. Isolated pleural cells labeled with [14C]arachidonic acid released appreciable amounts (approximately 12%) of radiolabel upon exposure to pharmacological concentrations of carrageenan (1-100 micrograms/ml). The release of radiolabel was decreased by an inhibitor of phospholipase A2 (p-bromophenacyl bromide) but not by an inhibitor of arachidonate cyclooxygenase (indomethacin). The released products were arachidonic acid and, to a much lesser extent, prostaglandin E2 and leukotriene C4. The release of radiolabel was associated with release of cytosolic lactate dehydrogenase over the same range of carrageenan concentrations. Time-course studies indicated that release of radiolabel preceded that of lactate dehydrogenase. Since p-bromophenacyl bromide blocked stimulated release of radiolabel but did not prevent release of lactate dehydrogenase, it is unlikely that increase in arachidonate causes carrageenan-induced cell damage. Nevertheless, the question of whether the activation of phospholipase A2 in the pleural cells, most probably the macrophages, was sufficient to initiate the carrageenan-induced inflammatory response requires further study. Cytotoxicity which was apparent with as little as 5 micrograms/ml of carrageenan, may have been a significant consequence of carrageenan action.

Reduced body clearance as the major mechanism of the potentiation by β2-adrenergic agonists of paraquat lethality in rats

Reduced Body Clearance as the Major Mechanism of the Potentiation by β 2 -Adrenergic Agonists of Paraquat Lethality in Rats. Maling, H. M., Saul, W., Williams, M. A., Brown, E. A. B., and Gillette, J. R. (1978). Toxicol. Appl. Pharmacol. 43 , 57–72. In rats, the potentiation of paraquat toxicity by l -isoproterenol and by preferential β 2 -adrenergic agonists (salbutamol, carbuterol, and fenoterol) was blocked by pretreatment with dl -propranolol. l -Propranclol and dl -propranolol were equally effective and d -propranolol was relatively ineffective. l -Isoproterenol and the β 2 -agonists did not increase paraquat uptake by rat lung slices in vitro . Isoproterenol treatment in vivo decreased urinary excretion of paraquat during the first 2 hr and enhanced paraquat concentrations in tissues. These increased tissue concentrations were correlated with reduced body clearances of paraquat in isoproterenol-treated rats. Isoproterenol treatment also decreased the body clearance of N -methyl nicotinamide (NMN) and p -aminohippuric acid (PAH). Since the body clearance of both acidic (PAH) and basic (NMN and paraquat) substances was decreased, it appears possible that isoproterenol caused these effects by decreasing the effective renal blood flow.

Reduction by pretreatment with dibenamine of hepatotoxicity induced by carbon tetrachloride, thioacetamide or dimethylnitrosamine

Abstract Pretreatment with dibenamine (25 mg/kg sc 48 and 24 hr before the administration of a hepatotoxic agent) protected rats against the hepatotoxicity of CCl4, thioacetamide, or dimethylnitrosamine, but not against allyl alcohol or bromobenzene. Protection was evident from reduced activity of plasma glutamic-pyruvic transaminase and reduced liver necrosis as demonstrated by histologic evaluations. In rats pretreated with dibenamine, LD50 values for CCl4 and thioacetamide were elevated and liver triglycerides after CCl4 and dimethylnitrosamine were reduced. Dibenamine protection against hepatotoxicity did not correlate with alpha-adrenergic receptor blockade. Similar pretreatment with 3 other alpha-adrenergic blocking agents, tolazoline, phenoxybenzamine, and EEDQ (N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline), failed to protect rats against CCl4-induced hepatotoxicity.

Tetraethylammonium as a Probe for Estimating Renal Plasma Flow in Unanesthetized Rats

Summary Mean total body clearances were measured in unanesthetized rats as Dose iv/AUC in which AUC is the area under the plasma radioactivity disappearance curve for [14C]labeled inulin, PAH, and TEA and also for [3H]inulin. The clearance of inulin radioactivity, either 14C or 3H, was a satisfactory estimate of glomerular filtration rate. The clearance of [14C] radioactivity from labeled TEA was a reliable estimate of renal plasma flow. The renal filtration fraction, which was calculated as the ratio of inulin and TEA clearances, varied from 0.15 to 0.30, with a mean value of 0.21 in the 20 rats in which both clearances were measured simultaneously. Renal plasma flow and glomerular filtration rate can therefore be estimated in the same unanesthetized rat by the clearances of TEA and inulin, calculated as Dose iv/AUC from the disappearance curves of 14C and 3H plasma radioactivity after a single iv injection containing both [14C]TEA and [3H]methoxyinulin.

Mechanisms in the potentiation and inhibition of pharmacological actions of hexobarbital and zoxazolamine by glycofurol

Abstract When used as a solvent, glycofurol increased the sleeping and paralysis times of hexobarbital and zoxazolamine. These effects were correlated with increases in rates of absorption, decreases in volumes of distribution, decreases in average total body clearances and with in vitro inhibition of hepatic microsomal metabolism. In contrast, when glycofurol was administered in repeated doses (1 ml/kg, i.p., twice a day for 4 days), it decreased the sleeping and paralysis times of hexobarbital and zoxazolamine, probably as the result of their increased hepatic metabolism. Repeated doses of glycofurol also increased significantly cytochrome P-450, cytochrome b 5 , NADPH cytochrome c reductase, and activities of ethylmorphine N -demethylase and benzopyrene hydroxylase, in liver microsomes.

A New Principle for Estimating Hepatic Blood Flow Rates

A new principle for estimating hepatic blood flow rates is demonstrated in steady-state experiments in rats in which p-aminohippurate, labeled with either 14C or 3H, was infused into the portal vein, with simultaneous infusion into the tail vein of the same compound labeled with the other isotope. Hepatic blood flow and hepatic extraction ratios were calculated from measurements of urinary and biliary excretion rates and blood concentrations of each isotope. The principle may be used to calculate hepatic blood flow from measurements of urinary excretion and systemic blood concentrations of drug and metabolite after intravenous injections of radiolabeled drug and precursor.

Evaluation of the Effects of Cephaloridine on Urate Excretion in the Rat

In female Sprague-Dawley rats, the renal clearance of cephaloridine decreased as the plasma concentration of the drug declined from above 10 micrograms/ml to below about 3 micrograms/ml, thus suggesting a saturable tubular reabsorption of cephaloridine similar to that shown previously in man. The effects of cephaloridine (250 mg/kg i.v.) were compared with those shown by a group of rats receiving saline and another group of rats receiving probenecid (250 mg/kg i.v.). Probenecid caused a sustained increase in the urate excretion rate. By contrast, cephaloridine produced a relatively small and transient increase in urate excretion, which may have been caused by its diuretic effect. Thus, it is unlikely that the reabsorption mechanism of urate is the principle mechanism by which cephaloridine is reabsorbed.

Jumping Activity Induced by Sodium 5-(l,3-Dymethylbutyl)-5-Ethyl Barbiturate II. The Effects of Age Difference

Summary In small doses (12.5–20.0 mg/kg ip), DMBEB produced greater jumping activity in 1-month- than in 9-month-old mice, both in the rates of jumping as well as in number of jumping mice. There were no appreciable differences between young and old mice with large doses (22.5–25.0 mg/kg). The brain levels of DMBEB were similar in young and old mice. Jumping was markedly reduced in old and young mice by the beta-adrenergic blocking agent, propranolol, and the ganglionic blocking agent, chlorisondamine. Both propranolol and chlorisondamine prevented convulsions and death from a large dose of DMBEB (22.5 mg/kg). The authors thank Mr. Morton Raff and Mr. William Blackwelder, Biometrics Research Branch of the National Heart and Lung Institute, for the statistical analyses of the data reported in this paper.