氧自由基在高氧所致离体血管内皮细胞损伤中的作用

本实验研究了离体兔主动脉血管内皮细胞在常压高氧(100%O_2)条件下(0～72h)细胞形态、三磷酸腺苷(ATP)、黄嘌呤氧化酶(XO)活性、丙二醛(MDA)含量及谷胱甘肽过氧化物酶(GSH-px)活性的改变。我们的实验发现内皮细胞形态改变(细胞肿胀、畸形、脱落)呈时间依赖性;ATP含量经短暂的升高后(24h)持续降低(48～72h);高氧作用24～48h内皮细胞XO活性、MDA含量持续升高,72h XO活性、MDA含量开始降低,但仍高于对照组;GSH-px活性在48h内无明显改变,72h其活性升高。上述结果表明高氧确能引起内皮细胞损伤,氧自由基在其损伤过程中有重要作用。     

Reversible mitochondrial swelling in cultured rat hepatocytes exposed to 1,2-dimethylhydrazine

The early structural changes of F344 rat hepatocytes exposed to the hepatocarcinogen 1,2-dimethylhydrazine (DMH) were characterized in short-term monolayer cultures. Continuous exposure of monolayers to DMH (2-16 mM) caused cytoplasmic vacuoles visible by phase-contrast microscopy in all hepatocytes within 6 hr of exposure. These changes preceded maximal release of lactate dehydrogenase (LDH) which occurred after 48 hr of continuous exposure to cytocidal concentrations of DMH (8-16 mM). Ultrastructurally, hepatocytes exposed to DMH (4 mM, 6 hr) showed a twofold increase in mitochondrial diameter from 340 +/- 70 nm in control hepatocytes to 800 +/- 140 nm in DMH-exposed cells. Hepatocyte monolayers exposed to DMH (4 mM, 6 hr) with subsequent removal of DMH attained normal phase-contrast appearance within 6 hr. Ultrastructural studies showed no significant differences when compared with control hepatocytes and mitochondrial diameters (330 +/- 70 nm) were comparable with control hepatocytes. Pretreatment of hepatocytes with depletors of cellular reduced glutathione concentration, including 1,3-bis(2-chloroethyl)-1-nitrosourea (40 microM) and diethyl maleate (160 microM), did not potentiate hepatocellular vacuolation nor release of LDH from hepatocytes exposed to DMH (0-16 mM, 48 hr). These studies demonstrate a distinctive form of reversible high-amplitude mitochondrial swelling that can be monitored by phase-contrast microscopy of cultured hepatocytes in monolayers. Since DMH-induced mitochondrial swelling and its progression to irreversible injury are not potentiated by depletors of reduced thiols, this response appears distinct from prelethal mitochondrial swelling in hepatocytes subjected to oxyradical-mediated mechanisms of injury.     

Bronchial hyperresponsiveness and cellular infiltration in the lung of guinea-pigs sensitized and challenged by aerosol

We have studied the development of airway hyperresponsiveness and the pulmonary cell infiltration in a guinea-pig model in which both initial sensitization and subsequent exposure to the antigen were performed by aerosol. Enhanced bronchopulmonary response to aerosol administration of acetylcholine (ACh) and 5-hydroxytryptamine (5-HT) was observed 3-4 hr and 18-24 hr after antigen exposure of sensitized animals. In contrast, when ACh and 5-HT were administered intravenously 3-4 hr after the challenge, no significant alteration of the dose-response curves was observed. However, 18-24 hr after antigen challenge, a marked leftward shift of the dose-response curve was observed on intravenous injection of ACh or 5-HT. The increased bronchial reactivity to aerosolized ACh in sensitized and challenged guinea-pigs reached a maximum by days 2-4, was still significantly increased at day 5 and returned to the basal value by day 8. No further alteration of the dose-related bronchopulmonary response to aerosol or intravenous administration of ACh was recorded 24 hr after a second antigen challenge, performed 8 days after the initial one. The analysis of bronchoalveolar lavage fluids showed a significant increase in the number of polymorphonuclear neutrophils 3-4 hr after the exposure of sensitized animals to the antigen, which was also associated with a significant eosinophilia at 18-24 hr. Histological examination of lung specimens obtained from animals 3-4 hr following challenge demonstrated eosinophil infiltration in the peribronchial regions and bronchial walls, as well as within the epithelium. Furthermore, as compared to time 3-4 hr, less eosinophils in the peribronchial area and submucosa were counted 24 hr after antigen challenge. However, a role of eosinophil-derived products in the development of bronchial hyperresponsivenss in this experimental model remains to be established.     

Differing role of dendritic cells and macrophages in the induction of delayed-type hypersensitivity responses to PPD.

In order to study the antigen-presenting cell (APC) requirements for the priming of delayed-type hypersensitivity (DTH), murine spleen cells were fractionated on bovine serum albumin gradients, pulsed in vitro with tuberculin, and then injected subcutaneously into normal mice. The other footpad was challenged with tuberculin between 24 hr and 7 days later and swelling was measured 2 hr and 18-24 hr after challenge. Optimum priming for 2-hr and 24-hr responses at 7 days was achieved by an injection of 5 X 10(5) tuberculin-pulsed intermediate-density Fc + ve cells. Time-course studies revealed that the 2-hr component could be elicited as early as 24 hr after injection of pulsed APC, while the 24-hr component became significant at 3 days. Elimination of T cells or B cells did not affect the response. Injection of pulsed APC into allogeneic mice primed the 2-hr but not the 24-hr component. Neither pulsed high-density cells (mostly T cells) nor pulsed dendritic cells (DC) primed mice for these responses. Failure to elicit DTH after injection of tuberculin-pulsed DC was due to their failure to prime the 2-hr component, which other authors have shown to be a prerequisite for the appearance of the later components. That DC did prime the MHC-restricted 24-hr component was demonstrated by protocols involving the use of both macrophages and DC as APC.     

Time course of contact hypersensitivity to DNFB and histologic findings in mice

This experiment pursued the time course of contact hypersensitivity to 2,4-dinitro-1-fluorobenzene (DNFB) and histologic changes of the cutaneous reaction in mice. The contact hypersensitivity reached a maximum 4 days after sensitization (96.9 +/- 6.7% vs. 22.7 +/- 1.3% in control) and persisted for 3 weeks. The cutaneous hypersensitivity reaction showed peak reactivity at 24 hr after challenge (96.2 +/- 4.7% vs. 11.5 +/- 1.7% in control), and persisted up to 96 hr (13.2 +/- 2.1%). Prime histologic changes observed in this experiment were the exocytosis of lymphoid cells and epidermal thickening which appeared at 20 hr after challenge. Edema, vasodilatation and increased mast cells were observed within the dermis at 4-8 hr. However, edema and vasodilatation disappeared gradually, but numbers of mast cell increased up to 96 hr. The dermal infiltrates were maximum at the 28-72 hr after challenge.     

Rubratoxin B mycotoxicosis in the Syrian hamster: ultrastructural alterations

Rubratoxin B was given to Syrian hamsters as a single intraperitoneal dose of 0.4 mg/kg. Hamsters were killed at 1, 2, 4, and 6 hr after dosing, and the kidneys and liver were fixed by intravascular perfusion. Renal ultrastructural alterations were evident at 1 hr after treatment and were limited to the straight portion of the proximal tubule. The most prominent alterations were brush border disruption, dilation of smooth endoplasmic reticulum, mitochondrial swelling, cytoplasmic rarefaction, myelin figure formation, and swelling of basal interdigitating processes. Renal alterations were suggestive of damage to membrane structure and/or transport functions and interference with cellular bioenergetics. Hepatic alterations were not seen in the rubratoxin B-treated hamsters of this study.     

The pharmacokinetics and antihistaminic effects of brompheniramine

We studied the pharmacokinetics and antihistaminic effect of brompheniramine in seven normal adults. The mean peak serum brompheniramine concentration of 11.6 +/- 3.0 ng/ml occurred at a mean time of 3.1 +/- 1.1 hr. The mean serum half-life value was 24.9 +/- 9.3 hr, the mean clearance rate was 6.0 +/- 2.3 ml/min/kg, and the mean volume of distribution was 11.7 +/- 3.1 L/kg. The mean wheal size was significantly suppressed (p less than or equal to 0.1) at 3, 6, and 9 hr after the brompheniramine dose when mean concentrations ranged from 10.2 +/- 2.9 to 7.0 +/- 2.2 ng/ml. Significant suppression (p less than or equal to 0.05) of mean flare size was found from 3 to 48 hr after the brompheniramine dose, when mean concentrations ranged from 10.2 +/- 2.9 to 2.5 +/- 0.6 nl/ml. The mean pruritus score was significantly suppressed at 9 and 12 hr (p less than or equal to 0.1) and at 24 hr (p less than or equal to 0.05). Brompheniramine had a long half-life and large volume of distribution in normal adults. It also had a prolonged antihistaminic effect in the skin as evidenced by suppression of the wheal and flare response to histamine and by suppression of pruritus.     

Purified native and recombinant human alpha lymphotoxin [tumor necrosis factor (TNF)-beta] induces inflammatory reactions in normal skin

These studies report findings that demonstrate that human alpha lymphotoxin (LT) induces local, visible, and microscopic inflammatory reactions in normal skin. Skin sites in rabbits, when inoculated with a single injection of native or recombinant human alpha lymphotoxin, demonstrated erythema, swelling, and warmth within 5 hr. Erythema peaked between 24 and 48 hr and resolved by 72 hr. Histologic studies of skin sites injected with native LT revealed polymorphonuclear neutrophil (PMN) infiltration and edema beginning as early as 3 hr posttreatment. Individual skin sites that received three daily injections of native LT exhibited persistent erythema and swelling. Palpable induration was evident 24 hr after the second injection in the series. Histologic examination revealed the presence of many PMNs with associated focal dermal destruction, in the form of microabscesses, and scattered mononuclear cells. In contrast, control materials and recombinant human tumor necrosis factor (TNF-alpha) did not induce visible skin reactions in the rabbit. Several additional controls excluded endotoxin as being the agent responsible for the inflammatory skin reactions observed. The ability of LT to induce inflammation may have a role in its antitumor activity and it may be an important endogenous mediator in other immunologic reactions.     

The influence of electrolytes on the volume of non-metabolizing renal cortical cells

1. The metabolism of rat renal cortex slices was inhibited by iodoacetate and anoxia, and swelling was prevented by the presence in the medium of 7.2 g polyethylene glycol 6000/100 ml. (referred to as PEG medium).2. Slices were incubated for up to 12 hr in PEG medium, and in PEG media containing 440 m-osmole/kg H(2)O of an electrolyte (LiCl, NaCl, KCl or RbCl), or a non-electrolyte (glucose).3. It was concluded that the slices in all media were at equilibrium with the medium after incubation for 8 hr.4. Slices in the medium containing glucose reached the same equilibrium water content as those in the PEG medium, but slices in all the electrolyte media had significantly lower equilibrium water contents, although these did not differ significantly from each other.5. It is suggested that the results demonstrate a non-specific effect of electrolytes on the swelling of non-metabolizing cells.     

The kinetics of chlorite and chlorate in rats

Chlorine dioxide (ClO2) is under consideration as an alternative to chlorination as a disinfectant for public water supplies. The primary products resulting from ClO2 disinfection of surface waters are chlorite (ClO2-) and chlorates (ClO3-). The kinetics of 36ClO2- and 36ClO3- was studied in rats. Radioactivity was rapidly absorbed from the gastrointestinal tract following the administration of (0.17 microCi) 36ClO2- or (0.85 microCi) 36ClO3- orally; and 36Cl in plasma reached a peak at 2 hr and 1 hr, respectively. After 72 hr, radioactivity was highest in whole blood, followed by packed cells, plasma, stomach, testes, skin, lung, kidney, duodenum, carcass, spleen, ileum, brain, bone marrow and liver in 36ClO2- treatment. 36Cl excretion was greatest at 24 hr after the administration of 36ClO3-, but in the 36ClO2-, the excretion most likely represented saturation of the biotransformation and excretion pathways. About 40% of the total initial dose was excreted at 72 hr in the urine and feces in both treatments. No 36Cl was detected in expired air throughout the 72 hr studied.     

Effects of cholera toxin on human colon carcinoma cell lines.

This study reports on changes in morphology and membrane transport in 5 human colon carcinoma cell lines treated with cholera toxin (CT). Three of the cell lines that grew as monolayers (LIM 1215, LIM 1899, LIM 2099) and 1 that grew as floating clumps (LIM 2408) did not show morphological changes after CT treatment. However, cell line LIM 1863 that grows as floating "crypt-like" organoids showed rapid and distinctive changes in morphology and membrane transport after CT treatment. At 1 and 6 hrs after CT treatment, light and transmission electron microscopy revealed rapid dilatation of the central lumen of organoids and the appearance of 2 populations of apical vesicular inclusions. The first population was unusual in being non-membrane bound and limited by fuzzy filamentous material. The second population was membrane bound. Scanning electron microscopy at 1-6 hr after CT treatment showed swelling and loss of surface microvilli on some, but not all, cells. At 24 hr after CT treatment the majority of organoids showed evidence of fluid accumulation and small apical vesicles coalesced to form large single vacuoles that obliterated normal cell morphology. By 48 hr, continued swelling produced extreme attenuation of the plasma membrane with cells taking on an "endothelial cell-like" appearance. The response to CT was dose-dependent. Uptake studies using 86Rubidium and blocking studies using ouabain and amiloride indicated that CT is acting on the Na+/K+ ATPase membrane pump to cause the increased fluid uptake by LIM 1863 cells. This study is the first to report specific morphological changes in intestine-derived cells in response to CT.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of the platelet activating factor antagonists BN 52021 and BN 50730 on antigen-induced bronchial hyperresponsiveness and eosinophil infiltration in lung from sensitized guinea-pigs

The involvement of platelet activating factor (PAF) in antigen-induced bronchial hyperresponsiveness was investigated by the use of the PAF antagonists BN 52021 and BN 50730, in a guinea-pig model where sensitization and challenge were performed by aerosol. Male Hartley guinea-pigs were sensitized by two aerosol exposures at 48 hr intervals to a 0.9% NaCl solution (saline) containing 2 mg/ml ovalbumin for 30 min. Fifteen to 20 days later, guinea-pigs were challenged by exposure to five successive aerosols of increasing concentrations of ovalbumin (OA) or respectively, 10 microg/ml, 100 microg/ml, 1 mg/ml, 5 mg/ml and 10 mg/ml for 15 min each, or saline alone. Three to four hr and 18-24 hr after the aerosol challenge the guinea-pigs were prepared for recording of bronchopulmonary response and aerosol administrations were then generated with an ultrasonic nebulizer. The bronchopulmonary responses induced by successive 1-min aerosol bursts of acetylcholine (ACh) was assessed. As compared with saline-challenged guinea-pigs, an enhanced bronchopulmonary response to aerosol administration of cumulative doses of ACh was observed, 3-4 hr and 18-24 hr post-ovalbumin challenge. When the sensitized guinea-pigs were pretreated 1 hr before ovalbumin exposure with BN 52021 or BN 50730 (25 mg/kg, per os), a significant inhibition of the increase in the bronchopulmonary response to ACh was observed, both at 3-4 hr and 18-24 hr. Furthermore, when guinea-pigs were treated 3-4 hr after the ovalbumin exposure with BN 52021 or BN 50730, a significant inhibition of the hyperresponsiveness to ACh was recorded at 18-24 hr. A marked accumulation of eosinophils in the peribronchial regions was observed on histological preparations of lung specimens collected 4 hr or 24 hr after ovalbumin exposure. Pretreatment of the guinea-pigs by BN 50730 or BN 52021 did not modify the eosinophil accumulation in the peribronchial area. No significant difference in the number of eosinophils collected in the bronchoalveolar lavage fluid is observed, 24 hr post-ovalbumin challenge, under the pretreatment with BN 52021 or BN 50730. Pretreatment of guinea-pigs by BN 50730 or BN 52021 significantly reduced the PAF-induced (100 microg/ml) increase in eosinophil number in the peribronchial area. By contrast, they did not inhibit the eosinophilia induced by aerosol administration of LTB4 (5 microg/ml). These results suggest that the bronchial hyperresponsiveness observed in this study is associated with eosinophil accumulation in the lung. The potent inhibition of the bronchial hyperresponsiveness by the two unrelated antagonists of PAF suggests that the lipid mediator is involved in its triggering and duration, but not in the eosinophil infiltration.     

Mitochondrial membrane potential change induced by Hoechst 33342 in myelogenous leukemia cell line HL-60

Abstract. Hoechst 33342's effects on apoptosis and mitochondrial membrane potential (delta psi) were investigated in a myelogenous leukemia cell line, HL-60. Delta psi was detected with 2 lipophilic cationic fluorochromes: 3,3'-dihexyloxacarbocyanine iodide [DiOC6(3)] or 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolylcarbocyanine iodide (JC-1). Mitochondrial mass was measured with nonyl acridine orange (NAO). Protonophore carbonyl cyanide m-chlorophenylhydrazone (CCCP) depolarized mitochondria in control experiments. Cell viability was determined by propidium iodide uptake. Hoechst 33342 at 10-20 mg/L decreased fluorescence for DiOC6(3) at 0.5 hr. The fluorescence partially normalized at 3 hr and then progressively decreased at 5-24 hr, resulting in cell shrinkage and death. Mitochondrial mass decreased 40-70% by 1 hr and 70-90% at 24 hr. A lower concentration of Hoechst 33342, 5 mg/L, reduced the delta psi at 0.5 hr, but delta psi returned to control values after 3 hr. Mitochondrial mass decreased 30-40% and then partially normalized, and cell viability was > 92% at 24 hr. Protonophore carbonyl cyanide m-chlorophenylhydrazone lowered delta psi with little cell death. Thus, at high concentration, Hoechst 33342 induces depolarization of delta psi and subsequent apoptosis. Lack of apoptosis at low concentration of Hoechst 33342, despite depolarization of delta psi, indicates that mitochondrial membrane depolarization alone is insufficient to induce apoptosis.     

The absence of delayed-type hypersensitivity reactivity in a syngeneic murine tumour system

In different murine systems, delayed-type hypersensitivity (DTH) swelling responses at 24-48 hr after antigen challenge were preceded by an early 2-hr swelling response. The 24-hr DTH response is thought to depend on this early (DTH-initiating) hypersensitivity response. In this paper we show that in the syngeneic DBA/2-SL2 murine tumour system only an early 2-hr swelling response can be evoked. This early hypersensitivity response was tumour specific and serotonin dependent. The early hypersensitivity response in contact hypersensitivity has been ascribed to antigen-specific T-cell factors. To test whether similar T-cell factors were involved in the early hypersensitivity response in this syngeneic tumour system, we have transferred lymph node, spleen lymphocytes and serum from immunized mice into naive recipients. The serum was fractionated in two fractions, a 50,000-80,000 MW fraction, and a 120,000-190,000 MW fraction. In recipients of lymphocytes, total serum and the 50,000-80,000 MW fraction of the serum, an early hypersensitivity response can be evoked. So, these data suggest the involvement of specific T-cell factors in the development of an early hypersensitivity response against syngeneic tumour cells. Despite the development of an early (DTH initiating) hypersensitivity swelling response these immunized animals cannot develop a classical 24-hr swelling response. This absence of the 24-hr response in the presence of the 2-hr response is discussed in relation to the frequently observed immune suppression in tumour-bearing mice.     

Fever alters characteristics of sleep in rats

This study examined the effects of a fungal infection on body temperature (Tb) and sleep states. Tb and sleep were recorded in male rats for 24 hr after a saline injection and 48 hr after a subcutaneous injection of live brewer's yeast, at ambient temperatures (Ta's) of 20 degrees and 30 degrees C. Peak fevers of 1.6-3.1 degrees C occurred within 6-10 hr at both Ta's. The rats remained febrile for the next 12-24 hr. For the first 24 hr postyeast, amounts of SWS increased by 19 +/- 3% at 20 degrees C and 12 +/- 2% at 30 degrees C. Specifically, SWS was significantly increased from hr 5-8 (lights-on) and 13-24 (lights-off) at 20 degrees, and from hr 5-8 and 17-24 at 30 degrees C. Ta did not affect the changes in Tb or the changes in SWS after either saline or yeast. Duration of REMS varied with Ta after saline. After yeast, REMS increased by 21 +/- 12% at 20 degrees and decreased by 28 +/- 6% at 30 degrees C, with the net result that REMS at the two Ta's was equal during the fever. Furthermore, while the rats were febrile the normal diurnal variation in REMS was eliminated. Sleep and Tb returned to control values during the second fever day. These results suggest that an activated immune system both increases SWS and overrides the diurnal and thermoregulatory modulations of REMS.     

Igh allotype-linked control of immune complex-type hypersensitivity induced by hepatitis B surface antigen.

Hepatitis B surface antigen (HBsAg) induced an immune complex-type hypersensitivity which developed at 5-6 hr after the challenge and could be transferred by anti-HBs antisera, in addition to the delayed-type hypersensitivity in B10.BR mice. The pre-S region of HBsAg influenced this induction because the pre-S-depleted HBsAg or recombinant major S protein could not stimulate this 5-hr ear swelling. The male B10.BR mice responded better than the female ones, probably due to the inhibition by female hormone. Furthermore, HBsAg could also induce an early-occurring hypersensitivity which appeared within 1 hr of the antigen challenge. However, B10.BR mice did not exhibit this hypersensitivity; B6 mice expressed all three types of hypersensitivity (1 hr, 5 hr and 24 hr) and BALB/c mice showed only 1-hr and 24-hr responses. The expression of the immune complex-type seems to be determined by the Ighb gene or gene(s) closely associated to it. Mice bearing the Igh-1b allotype could be stimulated by HBsAg to induce the immune-complex type hypersensitivity. Moreover, it was the high specific binding not the titre of anti-HBs antibodies that influenced the exhibition of immune complex-type hypersensitivity.     

The cultured fetal mouse heart as a model for studying myocardial ischemic necrosis

A flow-independent model of anoxic injury employing the whole fetal mouse heart in organ culture was used to define the extent of ultrastructural damage and eventual necrosis resulting from hypoxia alone or hypoxia plus substrate depletion. In order to assess early ultrastructural damage fetal mouse hearts either received 1, 3 or 5 hr of hypoxia with or without substrate, following which the hearts were processed for electron microscopy. In order to assess extent of necrosis another group of hearts received 1, 3 or 5 hr of hypoxia with or without substrate followed by a recovery phase which consisted of 24 hr of reoxygenation with substrate. The percent of the fetal hearts which showed histologic necrosis was determined from 1 μm thick toluidine blue stained sections. Several ultrastructural changes were seen during the early phases of anoxic injury including nuclear chromatin clumping and margination, loss of glycogen, intracellular swelling and vacuolization which became progressively worse as the duration of hypoxia increased from 1 to 5 hr. In hearts submitted to substrate deprivation as well as hypoxia intracellular swelling was more severe with 3 to 5 hr of injury. In hearts which received 1 to 5 hr of hypoxia plus 24 hr of recovery well delineated areas of necrosis could be visualized. In hearts with 1 hr of hypoxia plus recovery 4 ± 2% of the myocardium was necrotic; with 3 hr of hypoxia plus recovery 15 ± 3% was necrotic, and with 5 hr of hypoxia plus recovery 52 ± 3% of the myocardium was necrotic. With the addition of substrate depletion hearts developed more necrosis at 3 hr (29±4%) and 5 hr (64 ± 4%) compared to exposure to hypoxia alone (P < 0.05).In conclusion, the fetal mouse heart is a flow-independent model which can be used to test the effects of hypoxia and substrate deprivation on the extent of myocardial damage; the duration of hypoxia is the major determinant of the extent of necrosis in this model while substrate depletion also increases damage.     

Kinetics of induction of DNA damage and lacZ gene mutations in stomach mucosa of mice treated with beta-propiolactone and N-methyl-N'-nitro-N-nitrosoguanidine, using single-cell gel electrophoresis and MutaMouse models.

beta-Propiolactone (BPL) and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) are two direct alkylating agents that induce multiple genetic lesions and tumors in the rodent stomach. We measured the kinetics of the induction of DNA damage by using the single-cell gel electrophoresis assay (SCGE) and the induction of gene mutations by using the MutaMouse model in the glandular stomach mucosa of mice exposed to a single oral administration of BPL or MNNG. The aims were to determine the optimal sampling time and to investigate the cause-effect relationship between DNA damage and gene mutations. The induction of comets, evaluated in individual cells with the tail moment, was analyzed 1, 2, 4, 24, and 72 hr after a single oral administration of 25 mg/kg BPL or 20 mg/kg MNNG. The effects of both compounds were most intense at the earlier sampling times (1-2 hr), tailing off 4 hr after treatment and becoming undetectable at 72 hr. The lacZ mutant frequency (MF) was measured 3, 7, 14, 28, and 50 days after a single oral administration of 150 mg/kg BPL or 100 mg/kg MNNG, and 3 and 14 days after a single administration of 25 mg/kg BPL or 20 mg/kg MNNG. The MF was strongly enhanced at the highest doses and all sampling times, the most marked effects being observed 14 days (11.1-fold) and 28 days (19.0-fold) after BPL and MNNG administration, respectively. At the lowest doses, only a small increase in MF ( approximately 2.5- to 3.5-fold) was found at both sampling times. Primary DNA damage detected with SCGE shortly after treatment (1-2 hr) was rapidly (3 days) transformed into stable gene mutations that remained detectable for 50 days. These results illustrate the ability and complementarity of the SCGE and MutaMouse models to assess the genotoxicity of direct alkylating agents in the mouse gastric mucosa in vivo.     

Fat metabolism and heat production in young rabbits

1. The rates of oxygen consumption were measured in 6-8-day-old rabbits at 34 and 15 degrees C after varying periods of starvation and cold exposure. At the start of the experiment the rabbits had been fasted for 24 hr. Eight rabbits were studied immediately, six after 24 and six after 48 hr in a cold environment (20 degrees C), and twelve after a further 48 hr in a warm environment (34 degrees C). All the animals had a similar increase in oxygen consumption during the final hour of cold exposure (15 degrees C).2. The rabbits kept at 20 degrees C lost 83% of the fat stored in their brown adipose tissue within 24 hr and a further 11% in the next 24 hr. The fat content of white adipose tissue had fallen by 75% at 48 hr. In contrast rabbits kept unfed at 34 degrees C had lost 47% of the fat in brown adipose tissue and 44% of the fat in white adipose tissue after 48 hr.3. In six rabbits subcutaneous thermocouples demonstrated that local heat production continued in brown adipose tissue after 48 hr cold exposure.4. In the rabbits kept at 34 degrees C the final cold exposure caused a large increase in the serum free fatty acid and glycerol concentrations. Much lower concentrations were found in rabbits kept at 20 degrees C.5. The results show that the fat stored in the brown adipose tissue of young rabbits exposed to cold is preferentially used for heat production. When this store of fat is exhausted, brown adipose tissue still produces heat presumably by oxidizing fat and glucose taken from the circulation.     

The effect of intracerebroventricular hypertonic infusion on sodium appetite in rats after peritoneal dialysis

Sixty minute peritoneal dialysis (PD) against isotonic glucose decreased sodium concentration [Na+] in serum and cerebrospinal fluid (CSF) to 14% and 7% of their initial values, respectively. About 3 to 4 hours after PD, [Na+] began to increase slowly, reaching the initial level 24 hr afterwards. Central restoration of Na+ was made by infusing isotonic or hypertonic fluid into the 3rd brain ventricle (3BV) of rats at different times after dialysis. Continuous infusion (1 microliter/hr) of artCSF, 150 mM Na+, from -1 to 24 hr after PD decreased sodium intake as compared with uninfused control or control receiving Na+-free infusate or distilled water. Hypertonic central sodium infusions (1 microliter/hr) administered from -1 to 8 hr after PD, did not modify sodium intake; however an infusion made from 8 to 24 hr or from 16 to 24 hr post-dialysis decreased sodium intake by 38% and 67%, respectively. The volumes of sodium ingested were compared with those of the same animal infused with CSF 150 mM Na+. The results suggest that the fall in CSF [Na+] after sodium depletion by itself does not seem to be a critical factor in the onset of specific sodium appetite.