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1.
Pinealectomized Syrian hamsters were injected thrice daily with 25 micrograms of melatonin per injection. The injections were administered at 3-hour intervals either during the day or during the night of a photoperiodic cycle of 14 hours of light and 10 hours of darkness. After 6 weeks of treatment with melatonin during the night, both pinealectomized and intact hamsters had reduced testis weight, and pinealectomized hamsters showed decreased levels of serum gonadotropins. Injection of melatonin during the day for 7 weeks either once (75 micrograms) a day or thrice (25 micrograms per injection) daily caused a reduction in testis weight in pinealectomized hamsters. Both pinealectomized and intact females injected with melatonin thrice daily during the day became anovulatory by week 7 of treatment. These results are similar to those observed when hamsters are exposed to a short photoperiod, suggesting that melatonin may be acting as a hormone in mediating the effects of photoperiod on the reproductive system of the Syrian hamster. 相似文献
2.
Quinacrine (atebrin): mode of action 总被引：5，自引：0，他引：5
Quinacrine at a concentration of 8 x 10(-4) mole per liter is bactericidal for Escherichia coli, blocks DNA synthesis, and inhibits the syntheses of RNA and protein strongly. At a concentration of 2x 10(-4) mole per liter, the drug is bacteriostatic, the syntheses of protein and DNA (but not that of RNA) are partially inhibited, and the bacteria grow into giant filaments. Impairment of DNA replication is proposed as the mode of action of quinacrine. 相似文献
3.
Subcutaneous injection of 240 micrograms of acetoxycycloheximide in mice rapidly produces marked inhibition of cerebral protein synthesis. Treated mice were trained to escape shock by choosing the lighted limb of a T-maze. When trained five or more minutes after injection, they had a normal capacity to learn. They remembered normally 3 hours after training, but 6 hours after training they had markedly impaired retention. Amnesia persisted thereafter. Injections immediately after training had a less marked but significant amnesic effect. These studies suggest that protein synthesis is not necessary for learning or for memory for 3 hours after training but that it is required for long-term memory. The protein synthesis which appears to be necessary for long-term e3memory occurs during training, or within minutes after training, or both. 相似文献
4.
The amount of phenacetin in plasma was determined in nine control subjects (nonsmokers) and nine subjects who smoked at least 15 cigarettes per day. The mean plasma concentration of phenacetin at 1, 2, 3(1/2), and 5 hours after its administration was markedly lower in cigarette smokers than in nonsmokers. At 2 hours after the oral administration of 900 milligrams of phenacetin, the plasma concentration (+/- standard error) of unchanged drug was 2.24 +/- 0.73 micrograms per milliliter in the controls and 0.48 +/- 0.28 micrograms per milliliter in the smokers. The rate of excretion in urine of the major metabolite of phenacetin, N-acetyl-p-aminophenol, was the same in both groups. These results indicate for the first time decreased concentrations of a drug in plasma of persons who smoke cigarettes, and the results suggest that the decrease in the amount of Phenacetin in plasma may result from increased metabolism of phenacetin in cigarette smokers. 相似文献
5.
Suppressed RNA synthesis exceeded control rates 2 hours after removal of actinomycin from serial lines of green monkey kidney cells in exponentially dividing monolayer cultures. Enhanced synthesis was directly related to the dose of actinomycin, and release from inhibition was temperature dependent. A broad range of RNA sizes was made after removal of drug, but cytoplasmic and nucleolar sedimentation profiles were abnormal for at least 20 hours. 相似文献
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Antibody formation: initiation in "nonresponder" mice by macrophage synthetic polypeptide RNA 总被引：3，自引：0，他引：3
The RNA extracted from normal peritoneal macrophages exposed to a linear, random synthetic polypeptide, Glu(60)Ala(30)Tyr(10), initiated an immune response in C57B1/6J mice, although this strain responds very poorly to the antigen itself. From 10 to 150 micrograms of RNA obtained from mouse, rat, or rabbit macrophages was injected intraperitoneally into recipient mice, and specific antibody was detectable by passive hemagglutination 3 to 4 weeks later. Treatment of the RNA with ribonuclease destroyed its ability to initiate a specific immune response. The RNA contained by weight 0.02 percent of the (specific) antigen. The RNA obtained from cells incubated with a second polypeptide, Glu(36)Lys(24)Ala(40), initiated a response specific for this polymer. This RNA even when incubated in vitro with Glu(60)Ala(30)Tyr(10) failed to initiate antibody formation specific for Glu(60)Ala(30)Tyr(10). 相似文献
8.
A toxin isolated from apple fruit tissue infected by Erwinia amylovora is 98 percent galactose in polymeric form, 0.375 percent protein, and has an average molecular weight of approximately 165,000. Young shoots of rosaceous, but not nonrosaceous, species wilt in a manner characteristic of the disease when placed in toxin solutions with concentrations as low as 10 micrograms per milliliter. Varieties of apple and pear susceptible to Erwinia amylovora wilt in 1 to 3 hours, whereas resistant varieties display symptoms 12 to 24 hours after treatment. 相似文献
9.
D A Booth 《Science (New York, N.Y.)》1967,158(800):515-517
Injection of 6 micrograms of aqueous norepinephrine elicits eating only when it takes place at sites within a limited region of the rat brain. The distribution of effective sites coincides with that of systems connected to an extrahypothalamic pathway between the limbic forebrain and tegmental motor systems. It does not correspond to those parts of the lateral hypothalamus thought to control normal feeding. 相似文献
10.
Daily rhythm in tyrosine concentration in human plasma: persistence on low-protein diets 总被引：2，自引：0，他引：2
The concentration of tyrosine in the plasma of normal males varies diurnally. It is lowest (9.5 +/- 0.35 micrograms per milliliter) between 0130 and 0230 hours and rises to a peak of 16.2 +/- 0.82 micrograms per milliliter by 1030 hours. This rhythm persists when subjects are maintained for 2 weeks on a diet that is very low in protein. 相似文献
11.
The interspecific fusion of normal bovine lymphocytes with a nonsecreting mouse hybridoma produced stable cell lines secreting bovine immunoglobulins. One of these lines has continued to secrete immunoglobulin G1 (5 to 10 micrograms per milliliter) for over 16 months. The bovine x mouse hybrid cells can be expected to provide bovine monoclonal immunoglobulins for sequencing studies and for use as serological standards as well as to provide messenger RNA for cloning bovine immunoglobulin genes. 相似文献
12.
Injection of potassium chloride into the hippocampus produces a disruption of electrical activity; a concomitant of this disruption is a deficit in retention of conditioned suppression learned 24 hours before injection. 相似文献
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Interferon inducers protect mice against plasmodium berghei malaria 总被引：23，自引：0，他引：23
Injection of mice with two interferon inducers, Newcastle disease virus or statolon, 20 hours after inoculation with Plasmodium berghei sporozoites, prevented or delayed the development of detectable malarial parasitemia and death. 相似文献
15.
Ovulation in hamster: induction by subunit of ovine interstitial cell stimulating hormone 总被引：3，自引：0，他引：3
As little as 5 micrograms of interstitial cell stimulating hormone (ICSH) or 20 micrograms of ICSH-beta is effective for the induction of ovulation in 100 percent of hamsters treated at 0500 hours on day 4 after lordosis, whereas as much as 800 micrograms of ICSH-alpha is ineffective. Both ICSH and ICSH-beta are also effective for induction of ovulation in hypophysectomized animals. Thus, the ovulation-inducing activity of the ICSH molecule resides in its beta subunit. 相似文献
16.
Chworos A Severcan I Koyfman AY Weinkam P Oroudjev E Hansma HG Jaeger L 《Science (New York, N.Y.)》2004,306(5704):2068-2072
One challenge in supramolecular chemistry is the design of versatile, self-assembling building blocks to attain total control of arrangement of matter at a molecular level. We have achieved reliable prediction and design of the three-dimensional structure of artificial RNA building blocks to generate molecular jigsaw puzzle units called tectosquares. They can be programmed with control over their geometry, topology, directionality, and addressability to algorithmically self-assemble into a variety of complex nanoscopic fabrics with predefined periodic and aperiodic patterns and finite dimensions. This work emphasizes the modular and hierarchical characteristics of RNA by showing that small RNA structural motifs can code the precise topology of large molecular architectures. It demonstrates that fully addressable materials based on RNA can be synthesized and provides insights into self-assembly processes involving large populations of RNA molecules. 相似文献
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The purine analog azaguanine does not inhibit the initial induction of hepatic tyrosine transaminase by hydrocortisone. However, the continued induced synthesis of tyrosine transaminase, elicited by repeated doses of hydro-cortisone, is inhibited approximately 64 percent in the presence of the analog after 7 to 8 hours and appears to be almost completely inhibited by 9 to 10 hours; this suggests that the induction cycle involves the activation and renewal of a pool of preexisting messenger RNA. 相似文献
18.
Topical application of 25, 50, or 100 micrograms of 10,11-epoxy-farnesenic acid methyl ester in peanut oil induced male Ips confusus to produce sex pheromone in the hindgut Malpighian tubule region. Twenty-four hours aftertreatment of male beetles with 100 micrograms of hormone, their hindgut Malpighian tubule extract was more attractive to female beetles in a laboratory bioassay than was extract from males producing pheromone naturally in ponderosa pine logs. 相似文献
19.
Cytokinin activity: localization in transfer RNA preparations 总被引：15，自引：0，他引：15
F Skoog D J Armstrong J D Cherayil A E Hampel R M Bock 《Science (New York, N.Y.)》1966,154(754):1354-1356
Transfer RNA from yeast, liver, and Escherichia coli has cytokinin activity in the tobacco callus bioassay, whereas ribosomal RNA from yeast is inactive. In contrast to fractions of yeast transfer RNA rich in serine acceptor and cytokinin activity, preparations (70 to 90 percent pure) of arginine transfer RNA(2), glycine transfer RNA, phenylalanine transfer RNA, and valine transfer RNA(1) and of highly purified alanine transfer RNA from yeast were inactive at concentrations of 20 to 2500 micrograms per liter. One molecule of 6-(gamma,gamma-dimethylallylamino) purine per 20 molecules of yeast tRNA would account for the observed cytokinin activity. The number of major molecular species contributing to cytokinin activity of transfer RNA, therefore, must be small. 相似文献
20.
25-hydroxycholecalciferol: direct effect on calcium transport 总被引：5，自引：0，他引：5
The perfused small intestine from a vitamin D deficient rat exhibits about one-half the calcium transport of the intestine from a rat given vitamin D. These levels of calcium transport can be maintained for at least 4 hours. Addition of 2.5 micrograms of 25-hydroxycholecalciferol added to the vitamin D deficient intestine via the arterial blood perfusate induces a rise in calcium transport to +D levels within 2 hours. In contrast, 250 micrograms of vitamin D(3) given in the same manner has no effect on the calcium transport level overa 4-hour period. These data provide strong evidence that 25-hydroxycholecalci ferol represents the metabolically active form of vitamin D(3). 相似文献