Normal SD Rats Research Articles

Inhibitory effect of nitric oxide on the metabolism of halogenated volatile anesthetics by cytochrome P-450.

This study was undertaken to examine the effect of nitric oxide (NO) on the metabolism of halogenated volatile anesthetics (HVA) by cytochrome P-450 (CYP) under both aerobic and anaerobic conditions using rat hepatic microsomes. A microsomal fraction was prepared by centrifugation from normal and phenobarbital-treated male SD rats. The anaerobic metabolism of HVA by CYP was followed by measuring the formation of a halothane CYP complex spectrophotometrically. Aerobic CYP activity was determined using either the defluorination of sevoflurane or the demethylation of aminopyrine. The formation of the halothane-CYP complex was dose-dependently inhibited by NO. NO also decreased CYP defluorination of halothane in a dose-dependent manner. In phenobarbital-induced microsomes, the inhibition rates of both complex formation and the defluorination of halothane were the same as those seen in normal microsomes. Although the defluorination of sevoflurane and the demethylation of aminopyrine were inhibited by NO aerobically, the inhibition was much less than that of the metabolism of halothane under anaerobic conditions. These results suggest that NO binds the heme of CYP and inhibits the metabolism of HVA, with the effect lasting for a prolonged period of time. Furthermore, the balance between NO and O(2) is important for NO to inhibit CYP.

A study of portal vein embolization with absolute ethanol injection in cirrhotic rats.

AIM:To investigate the effects of portal vein embolization (PVE) with absolute ethanol injection on the cirrhotic livers.METHODS:Absolute ethanol was injected intraportally into normal and cirrhotic SD rats and the changes of the animals in anatomy, pathology, liver function as well as portal hemodynamics were observed.RESULTS:At a dose of 0.05mL/100g of ethanol, the survival rate was 100% in normal rats compared with 40.9% in cirrhotic rats. PVE in the cirrhotic rats with 0.03mL/100g of ethanol, caused significant hypertrophy in non-embolized lobes, mild or moderate damage to the hepatic parenchyma, slight and transient alterations in liver function, portal pressure and portal flow.CONCLUSION:PVE with absolute ethanol injection in the setting of liver cirrhosis could be safe at an appropriate dose, and precautions aimed at preserving liver function were preferable.

Interstitial muscle insulin and glucose levels in normal and insulin-resistant Zucker rats.

To study interstitial insulin and glucose concentrations, microdialysis was performed in the medial femoral muscles in normal SD rats as well as in insulin-resistant obese Zucker rats during a euglycemic insulin clamp. [14C]inulin was given (0.1 mCi/rat) as a constant subcutaneous infusion 24 h before the insulin clamp. Insulin infusion rates were 5-8 mU x kg(-1) x min(-1) (low rate) for 140 min and 10-20 mU x kg(-1) x min(-1) (high rate) for another 100 min. The relationship between insulin and [14C]inulin dialysate recoveries was evaluated in vivo and in vitro in plasma to calculate interstitial insulin concentration. Relative microdialysis recovery of interstitial insulin in vivo was 3.0 +/- 0.3% (mean +/- SE, n = 68). In normal SD rats, plasma and interstitial insulin concentrations were identical when plasma insulin was < or =250 mU/ml, whereas interstitial insulin was lower when plasma insulin was > or =350 mU/ml. Half-maximal glucose infusion rate was achieved in the presence of plasma and interstitial insulin concentrations of approximately 140 mU/ml, whereas maximal glucose disposal was seen at interstitial insulin concentrations of approximately 325 mU/ml, corresponding to approximately 500 mU/ml in plasma. In electrically stimulated and contracting (1 Hz) normal muscle with markedly increased blood flow, the dialysate insulin concentration was significantly higher at high rates, but not at low rates, of insulin infusion. In insulin-resistant obese Zucker rats, the interstitial insulin concentration was similar to that in plasma, even at pharmacological concentrations. The glucose infusion rate was significantly lower in the obese Zucker rats at both insulin infusion rates than in the lean animals. The glucose content in dialysates from skeletal muscle was equal in both obese and lean rats during the low insulin infusion rate. During the high insulin infusion rate, dialysate glucose concentrations decreased significantly in both groups but were significantly higher in the obese Zucker rats. The data suggest that transport of insulin and glucose diffusion across the capillary wall are rate limiting for insulin as well as for glucose metabolism in muscle in normal rats. This does not appear to be the case in the insulin-resistant obese Zucker rats, where the reduced insulin responsiveness in muscle is due to muscular cellular defects rather than an inhibited transcapillary delivery of insulin.

Inferior colliculus neuronal membrane and synaptic properties in genetically epilepsy-prone rats

Previous studies using single-unit recording techniques have shown that the inferior colliculus is critical for audiogenic seizure initiation in genetically epilepsy-prone rats (GEPR). In order to investigate cellular abnormalities that may be important in causing audiogenic seizure susceptibility, intracellular recording were made from neurons of inferior colliculus dorsal cortex (ICd) in a GEPR variety that exhibits severe audiogenic seizures (GEPR-9). GEPR neuronal membrane and synaptic properties were compared to those of normal Sprague-Dawley rats (SD), the strain from which GEPR were derived. We found six electrophysiological differences between GEPR and normal SD ICd neurons, all of which could promote seizures in GEPR. (1) Input resistances was higher in GEPR than in normal ICd neurons. (2) Threshold for repetitive action potential firing was closer to resting membrane potential in GEPR ICd neurons. (3) GEPR neurons showed faster repetitive spike firing than normal SD neurons. (4) Anode break spikes occured at the offset of a hyperpolarizing pulse more often in GEPR than in normal SD neurons. (5) Stimulation of the commissure of the inferior colliculus caused synaptic paired pulse inhibition in normal ICd neurons, but paired pulse facilitation was always observed in GEPR neurons. (6) In GEPR, a large epileptiform depolarizing event could be elicited by strong electrical stimulation of the commissure of the inferior colliculus. In normal SD rats, similar epileptiform activity was seen only after application of bicuculline or NMDA. Our results suggest that both abnormal neuronal membrane properties and altered synaptic transmission are likely to contribute to seizure predisposition and audiogenic seizure initiation in GEPR.

Functional integrity of hepatocyte canalicular membrane transport of taurocholate and bilirubin diglucuronide in eisai hyperbilirubinuria rats

Eisai hyperbilirubinuria rats (EHBR) are characterized by conjugated hyperbilirubinemia, and impaired or defective excretion of bilirubin, reduced glutathione and other organic anions from hepatocytes. Hepatocyte canalicular membrane vesicles (CMV) from EHBR and normal SD rats were studied with regard to taurocholate (TC) transport driven by ATP or a membrane potential and bicarbonate-stimulated bilirubin diglucuronide (BDG) transport. ATP-dependent uptake or association of BDG with CMV was also studied in both strains of rats. No significant differences in the uptake of TC and BDG by CMV were observed. This indicates the functional integrity of the canalicular transporters for both organic anions in EHBR. Biliary excretion of taurolithocholic acid sulfate (TLCS) is defective in EHBR. However, TLCS inhibited ATP-dependent TC uptake by SD rat CMV competitively, which may be against the hypothesis that a common organic anion carrier is defective in canalicular membranes of jaundiced rats.

The micronucleus assay using peripheral blood reticulocytes from mitomycin C- and cyclophosphamide-treated rats

It used to be believed that the use of rat peripheral blood for the micronucleus assay would be difficult because micronucleated erythrocytes are captured and destroyed by the spleen quickly. We have applied an acridine orange (AO) supravital staining method to rat peripheral blood using AO-coated glass slides. Normal and splenectomized SD rats were treated once with mitomycin C (i.p.) or cyclophosphamide (p.o.), and 5 μl of blood was collected at intervals from the tail vein between 0 and 72 h after treatment. For comparison, bone marrow cells were smeared conventionally 30 h after treatment. Although the frequencies of spontaneous and chemically induced micronucleated reticulocytes (MNRETs) from normal rats were lower on average in the highest dose group than those of splenectomized rats, the incidence of micronuclei among type I and II reticulocytes in normal rats at 48 h was almost identical to the incidence of RNA-containing erythrocytes with micronucleus in bone marrow. Thus, we suggest that rat peripheral reticulocytes can be used as target cells for the micronucleus assay.

Proteinuria, not altered albumin metabolism, affects hyperlipidemia in the nephrotic rat.

It has been established previously that nephrotic hyperlipidemia is characterized by both an increase in lipid synthesis and a defect in removal of lipoproteins. The relationship between these defects and altered albumin metabolism is uncertain. One hypothesis is that hepatic lipogenesis increases in parallel with albumin synthesis. To test this hypothesis, albumin synthesis was increased in nephrotic rats fed an 8.5% protein diet (LPN) by increasing dietary protein to 40% (HPN). Proteinuria was modulated in half of the rats fed 40% protein by enalapril (HPE). Albumin synthesis was the same in both HPN and HPE, but proteinuria was reduced in HPE compared to HPN, and so were serum cholesterol and triglycerides (TG). To examine the effect of serum albumin on lipid clearance in the absence of proteinuria, plasma clearance of chylomicrons (CM) and VLDL was measured in Nagase analbuminemic rats (NAR) and found to be no different than in normal SD rats. When proteinuria was induced in NAR and in SD rats, a severe and identical defect in both CM and VLDL clearance was acquired in both groups and blood lipid levels were increased to a similar degree in both groups. Neither hyperlipidemia nor defective removal of lipoproteins from the circulation are linked to albumin synthesis or serum albumin concentration but result, at least in part, from proteinuria. Postheparin lipoprotein lipase (LPL) activity was reduced slightly in nephrotic animals compared to nonnephrotic controls, but the most striking finding was a highly significant decrease in postheraprin LPL activity in normal NAR compared to SD rats (P less than 0.001), suggesting that reduced LPL activity is not responsible for reduced clearance of CM and VLDL in nephrotic rats.

ラット胸腔細胞でのＰＭＡ刺激によるＰＡＦ産生機構の検討

We have previously demonstrated the involvement of platelet-activating factor (PAF), which was newly generated by resident mononuclear cells with PMA-stimulation, in the rat pleurisy induced by phorbol myristate acetate (PMA) .In the present study, we examined the mechanism of PAF production by mononuclear cells stimulated with PMA. Mononuclear cells from normal SD rats were incubated with PMA (1μM) at 37°C in the presence or absence of inhibitors. After a certain time of incubation, medium and cell fraction were extracted separately as previously reported. Mononuclear cells mainly produced C16-PAF, and the content in cell fraction peaked at 30 min as about 10 ng/107 cells. While PAF released in the medium was about 4 ng/107 cells at 30 to 60 min. Acetyltransferase activity in the cells stimulated by PMA increased at 10 min. Addition of p-BPB into the medium completely suppressed PMA-stimulated PAF production by mononuclear cells. While indomethacin and AA-861 did not affect the production. W-7, calmodulin inhibitor, and diltiazem, Ca2+ channel blocker, did not show significant reduction of PAF production. In contrast, staurosporine, c-kinase inhibitor, significantly reduced not only PAF production but also increased acetyltransferase activity.Therefore it seems likely that PMA-induced PAF production links with c-kinase system.

High incidence of renal tumors induced by N-dimethylnitrosamine in analbuminemic rats.

Analbuminemic rats were found to be highly susceptible to induction of renal tumors. Thirty-nine weeks after N-dimethylnitrosamine administration, the incidence of renal tumors and average weight of kidneys (including tumors) were 76.0% and 10.8 +/- 4.1 g in male analbuminemic rats, respectively, whereas they were 37.1% and 3.5 +/- 0.1 g, respectively, in normal male SD rats.

GABA in peripheral tissues: Presence and actions in endocrine pancreatic function

Of 9 male Sprague-Dawley rat organs examined, GABA was present at highest levels in the pancreas, thymus, and adrenal (34–40 pmol/mg wet weight) and lowest in heart and testis (6–10). Intermediate levels were present in stomach, liver, spleen and lung. Streptozotocin, a B cytotoxic agent, lowered pancreas GABA levels to 1/3 control values without significantly affecting that of the other organs or plasma levels. Collagenase isolated rat islets contained 190 ± 25 (SE) whereas hand isolated catfish Brockmann bodies contained 121 ± 16 (SD) pmol GABA/mg wet weight. Rabbit pancreas contained 14 ± 4 and 3 ± 1 pmol/mg in the tail and body, respectively. In cannulated rats, injection of GABA increased plasma glucose with and without AOAA. In 15 normal SD rats, plasma glucose correlated with plasma GABA in a positive manner ( r + 0.644), though in 6 human diabetics (treated) this correlation was of a negative nature and of low order ( r = − 0.339). Incubation of rabbit pancreas pieces in vitro (method of Coore and Randle) indicated GABA may facilitate insulin release and inhibit glucagon release. Additionally, GABA was released in response to high glucose concentration, and pieces of pancreas incubated in 10 −3 M GABA for 30 min evidenced significant uptake of GABA whereas those in 10 −5 or 10 −7 did not. Though the variation in these later data is large, further experiments using more refined techniques are warranted. (Supported in part by H. D. Foundation and USPHS Grant MH-28243.)