摘要:

SummaryDNA methylase from Ehrlich's ascites tumour cells preferentially methylates DNA with high GC content. The methylase activity was not affected by the presence of the oligonucleotides, dCdG or dCdCdGdG, which are known to be part of the methyl‐acceptor sequence for mammalian DNA methylase. DNA from 5‐azacytidine‐treated ascites cells was a good methyl acceptor Actinomycin D, ethydium bromide and quinacrine inhibited the methylase activity. Distamycin A also inhibited the methylation of DNA from 5‐azacytidine‐treated ascites cells, but did not inhibit the methylation of (dG.dC)n. The inhibitory effect of all these drugs was overcome by increasing the DNA concentration. Non‐competitive type inhibition in regard to S‐adenosylmethionine was observed with all the DNA‐binding drugs.

ISSN:0004-945X    

DOI:10.1038/icb.1982.27

出版商:Nature Publishing Group    

年代:1982

数据来源: WILEY

摘要:

SummaryToxic substances are generated by microsomes undergoing NADPH‐dependent lipid peroxidation. In the present experiments the nature of the haemolytic material extracted from peroxidized microsomes is further examined. Suspensions of peroxidized rat liver microsomes were extracted with lipid solvents and the haemolytic material obtained subjected to gel exclusion chromatography. The haemolytic activity eluted as a single broad peak with an average size of 720 daltons. There was no evidence of haemolytic compounds less than 500 daltons. On a silicic acid column the activity eluted with the phospholipid. In both separations the presence of haemolytic activity correlated well with the peroxide content.

ISSN:0004-945X    

DOI:10.1038/icb.1982.28

出版商:Nature Publishing Group    

年代:1982

数据来源: WILEY

摘要:

SummaryPhomopsin, the mycotoxin produced byPhomopsis leptostromiformis, was found to have a very high toxicity for sheep. When administered as a single, subcutaneous injection over the dose range 1·25 to 98 μg/kg body weight, all sheep given 37·5 μg/kg or more died. Some, though not all, died following lower doses, the minimum lethal dose being 10 μg/kg. The time course of hepatic response over 21 days after phomopsin administration was followed by plasma biochemical analyses including those for some enzymes (glutamate dehydrogenase, γ‐glutamyl transpeptidase, aspartate aminotransferase and alkaline phosphatase), total bilirubin and the determination of bromosulphophthalein clearance rates. Hepatobiliary impairment was apparent after all dosages of 2·5 μg/kg and above while 1·25 μg/kg approximated the ‘no effect’ level.

ISSN:0004-945X    

DOI:10.1038/icb.1982.29

出版商:Nature Publishing Group    

年代:1982

数据来源: WILEY

摘要:

SummaryAcute intraperitoneal doses of spongiatriol, a compound extracted from marine sponges, caused blood pressure but not heart rate to fall in conscious hypertensive rats in a dose‐dependent manner up to 50 mg/kg at which dose mean blood pressure fell 24%. Diarrhoea also resulted. Chronic oral doses (50 mg/kg every 3 h) lowered blood pressure by 73 mmHg after 48 h in conscious hypertensive rats and caused severe diarrhoea. Spongiatriol was an atrial stimulantin vitroand this effect could be greatly reduced by prior reserpinization or by β‐adrenoceptor blockade. In anaesthetized cats spongiatriol (50 mg/kg i.p.) caused reductions in blood pressure (19%), heart rate (11%) and cardiac output (12%). Spongiatriol 10−5g/ml had no effect on the response to noradrenaline in isolated rat tail arteries, markedly inhibited the response ofin vitroguinea‐pig ilea to acetylcholine and had a slight potentiating effect on the response ofin vitrorat fundus stomach to serotonin and prostaglandin E2.

ISSN:0004-945X    

DOI:10.1038/icb.1982.30

出版商:Nature Publishing Group    

年代:1982

数据来源: WILEY

摘要:

SummaryThe neurohypophysial hormones vasopressin (the antiduiretic hormone) and oxytocin have been quantified in xerophilic and mesophilic rodents under normal and dehydrated conditions in order to study the relative contribution of these hormones to survival under drought conditions. The ability to cope adequately with water deprivation or saline ingestion was found to be closely related to the magnitude (relative to body size) of pre‐existing hormone stores in the neural lobe and to the subsequent ability to enhance hypothalamic biosynthesis of vasopressin and oxytocin sufficiently in maintain those stores at near‐normal levels despite a continuing high level of demand for vasopressin and, apparently, also oxytocin.The possible role(s) of the release of oxytocin in these conditions is discussed.Attempts have been made to explain differences observed between laboratorybredNotomysand those taken from the wild in their relative abilities to withstand water deprivation, the former seeming to be more dependent upon acutely accelerated hormone biosynthesis than on previous adaptationviarenal medullary ‘work‐load’ hypertrophy.

ISSN:0004-945X    

DOI:10.1038/icb.1982.31

出版商:Nature Publishing Group    

年代:1982

数据来源: WILEY

摘要:

SummaryThe putative central catecholamine neurotransmitters, adrenaline, noradrenaline and dopamine, have been quantified by enzyme radiochemical methods in the hypothalamo‐neurohypophysial system (HNS) of the xeric rodents,Notomys alexisandPseudomys australis, using the laboratory rat for comparison. All three catecholamines were found (noradrenaline>dopamine>adrenaline) in the hypothalami of the three species. The hypothalami of the two xeric rodents contained some 5–10 times as much of each of the catecholamines (when expressed as ng per body weight) as the rat. The ratio of noradrenaline to dopamine was constant (3·8–4·2) between species. Posterior pituitary contents of the catecholamines were generally inconsistent within and between species, with only dopamine being invariably and consistently present. It was also found that, like the antidiuretic hormone content, the dopamine content of the neural lobe was significantly correlated with the body surface area of the animal.Withdrawal of drinking water or its replacement with 2·5% saline increased hypothalamic noradrenaline synthesis and dopamine utilisation. In the neural lobe, saline ingestion produced a significant increase in all three catecholamines, but with water deprivation only dopamine was increased (relative to body weight).The results of these studies are interpreted as indicating a possible role for catecholamine neurotransmitters, particularly dopamine, in the control of neurohypophysial hormone release in the HNS.

ISSN:0004-945X    

DOI:10.1038/icb.1982.32

出版商:Nature Publishing Group    

年代:1982

数据来源: WILEY

摘要:

SummaryThe intermediate or “pre‐progenitor” B‐cell subpopulation giving primary adoptive responses has been found by this laboratory to be s‐IgD−, whereas other laboratories have reported the progenitors of primary adoptive responses to be s‐IgD+. This difference appears to depend on the recent history of environmental stimuli received by the mice. Deliberate administration of a complex non‐specific stimulus, designed to mimic the effects of infection or certain types of experimental manipulation, shifted “pre‐progenitor” activity from the s‐IgD−compartment to the s‐IgD+compartment within 24 h. Neither horse erythrocytes (HRC) nor lipopolysaccharide (LPS) alone produced a reproducible effect, but the combination of HRC with low doses of LPS produced a marked shift to s‐IgD+activity. Some earlier experiments from this laboratory suggesting a striking effect with HRC alone probably resulted from suspension of HRC in saline contaminated by LPS‐like material. Priming with HRC alone, under conditions which did not induce s‐IgD, nevertheless stimulated the “pre‐progenitors” to enter cell cycle. Three conclusions are drawn: (1) The stimulus for induction of s‐IgD is not identical with the non‐specific stimulus which selectively induces cell division in this intermediate B‐cell subset; (2) the presence of IgD on the surfaceper sedoes not prevent the non‐specific activation of these cells into division; (3) the absence of s‐IgD is only a useful marker of the “pre‐progenitor” subset if the mice are maintained under specific pathogen‐free conditions and exogenous stimuli are controlled.

ISSN:0004-945X    

DOI:10.1038/icb.1982.33

出版商:Nature Publishing Group    

年代:1982

数据来源: WILEY

摘要:

SummarySensitive biological assays of toxin/antitoxin potency have been developed to assist in research on characterization of salivary toxins of the Australian paralysis tickIxodes holocyclusand on immunity to tick paralysis.The toxin assay utilizes suckling mice (4–5 g); a quantitative paralysis index is applied over a range of doses. The antitoxin assay is based on anin vitro/in vivoneutralization test which required a sensitive toxin assay and methods of standardization of toxin preparations. This assay permits the monitoring of blood antibody levels in animals during the course of development and loss of immunity and is assisting a study into the feasibility of producing an anti‐paralysis vaccine. The method also allows standardization of commercial tick paralysis antiserum.The methods and applications are described and comparisons made with previous assays. Sample data are examined statistically by regression and variance analyses; parallelism of dosage‐response lines is tested and relative toxicities (toxin) or potencies (antiserum) calculated.

ISSN:0004-945X    

DOI:10.1038/icb.1982.34

出版商:Nature Publishing Group    

年代:1982

数据来源: WILEY

摘要:

SummaryThe faecal egg counts and worm burdens of mice selected over 7 generations as refractory (R), random (Rd) or liable (L) to primary infection withNemataspiroides dubiuswere significantly different, but the antibody titres (generation 8 mice) after 21 days infection were similar, demonstrating that selection had separated populations of mice which differed in their innate immunity. Variations in adaptive immunity were also shown between the three colonies in terms of protection after challenge infections, self‐cure reactions, humoral antibody titres and ability of immune serum from R, Rd and L donors to passively protect recipient Quackenbush (Q) strain mice. R mice were more refractory to primary infection and more proficient in acquiring protective levels of adaptive immunity than L colony mice. Correlation of the faecal parasite egg count after primary with that after secondary infection supported the conclusion that the genetic control of liability to primary infection and of the adaptive immune response following challenge infections were at least partially linked.

ISSN:0004-945X    

DOI:10.1038/icb.1982.35

出版商:Nature Publishing Group    

年代:1982

数据来源: WILEY

摘要:

SummaryThe present study investigated the nature of ablastin, a factor present in the serum of rats infected withTrypanosoma lewisiand which inhibits the parasites' division. Ablastin was unstable to dialysis at pH 1·8, was not adsorbed from serum by trypanosomes and could not be inducedin vivoby means other than a natural infection. Attempts to purify ablastin from serum by conventional chromatographic techniques were unsuccessful. Removal of over 90% of the immunoglobulins from ablastinic serum did not reduce the ablastin titre. It is concluded that ablastin is unlikely to be an immunoglobulin as has been previously suggested.

ISSN:0004-945X    

DOI:10.1038/icb.1982.36

出版商:Nature Publishing Group    

年代:1982

数据来源: WILEY