PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Periodicity”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2Linked to original sources
PubMed1975

Catch-up growth in rats undernourished for different periods during the suckling period.

Catch-up in body weight, nose-rump length and tail length has been examined in male rats. At birth, pups from several females were pooled and reallocated to provide litters of 16 pups. In group 1, the number was reduced to 8 at day 8, in group 2 on day 15, group 3 were raised in large litters until weaning. Animals reared in litters of 8 were termed controls. All animals were weaned at 22 days, placed two to a cage and provided with food and water ad libitum. They were examined at intervals to day 120. Animals rehabilitated at 8 days had caught up in body weight and 97% of the length of controls on day 120. Rats rehabilitated on day 22 were 88% of the body weight and 97% of the body length of the controls at 120 days. None of the experimental groups achieved the same tail length as the controls. It was concluded that the data do not support the "time tally" mechanism of catch-up growth. This may be due to early timing of the experiment or an oversimplification of the mechanism. It was also concluded that catch-up following neonatal undernutrition in rats is greatly influenced by the normal growth pattern.

Animals↗
PubMed1976

Effects of sodium periodate modification of lymphocytes on the sensitization and lytic phases of T cell-mediated lympholysis.

Sensitization of mouse splenic lymphocytes in vitro with sodium borohydride, suggesting that the biologic effects of sodium periodate are-treated autologous spleen cells stimulated a one-way mixed lymphocyte reaction and led to the generation of thymus-derived cytotoxic effector cells. These effectors were capable of lysing in 4 hr periodate-treated syngeneic and, to a lesser extent, periodate-treated allogeneic target cells. These results suggest that sensitization by periodate-treated autologous cells could result either from a specific reaction to modified self components or from a nonspecific mitogenic stimulation. Effector cells generated by allogeneic sensitization were detected on periodate-modified targets, irrespective of the H-2 antigens expressed by the targets. The effects of periodate modification on both stimulator and target cells were reversible by sodium periodate are dependent on the formation of a free aldehyde group on cell surface glycoproteins. Pretreatment of stimulator cells with neuroaminidase prevented the effect of periodate treatment, suggesting that the sensitization involves oxidized sialic acid residues. During the 4-hour 51Cr-release assay periodate-treated targets could be used to detect cytotoxic effector cells of any specificity. Fresh spleen cells and lymphocytes cultured for 5 days without antigen or in the presence of lipopolysaccharide did not lyse periodate-treated targets. An increasing level of cytotoxicity was detected on periodate-treated targets when the effector cells were generated, respectively, by stimulation with concanavalin A, by sensitization with periodate-modified autologous cells. Although the lysis of periodate-treated targets is itself nonspecific, effector cell specificity could be determined by selective blocking of the lytic phase with cells syngeneic to the stimulators. These results indicate that a nonspecific interaction can occur between lymphocytes and periodate-treated target cells, but that this interaction leads to lysis only when the lymphocytes were activated to become cytotoxic effectors.

Animals↗
PubMed1976

A strain of Plasmodium vivax characterized by prolonged incubation: the effect of numbers of sporozoites on the length of the prepatent period.

The North Korean strain of Plasmodium vivax was characterized by its extraordinarily prolonged incubation period in certain circumstances. It was clearly demonstrated by quantitative observations that the phenomenon may be elicited by the inoculation of small numbers of sporozoites. After the intradermal inoculation of 10 or 100 sporozoites, the incubation period was delayed for periods varying between 262 and 628 days; after u,000 sporozoites, with one exception, the same delay occurred; after 100,000 sporozoites, the incubation period was always of normal duration (13--16 days). Two laboratory-acquired infections in workers who had taken a prophylactic drug showed incubation periods of 315 and 329 days, respectively. Various theories for the phenomenon of prolonged prepatent periods are examined, and the most satisfactory one is based on the presumed existence of two populations of sporozoites in P. vivax. In temperate strains, sporozoites requiring long prepatent periods (LPP) for development are present in great excess over a much smaller proportion of sporozoites characterized by short prepatent periods (SPP); thus small doses will elicit the phenomenon, though doses of over 1,000 sporozoites will mask the effect as the few SPP sporozoites will produce an infection with a normal (i.e. short) prepatent period. In tropical strains, the relative proportions are different, perhaps in equal numbers, and even in small doses some SPP sporozoites will be present and normal prepatent periods should ensure whatever the dosage."

Humans↗
PubMed1977

An analysis of Wenkebach periodicity during atrial pacing.

Seventy-six atrial pacing induced Wenckebach periods in 20 patients were analyzed. They were divided into 5 types according to the manner of increment change of P'V prolongation. Fifty-four % of the periods were atypical (Types II-V). There was a significant increase in the incidence of atypical periods as the length of the periods increased. The recovery curve of the A-V node was obtained by plotting P'V against preceding VP'. The curve was convex and the slope became greater than 45 degrees near the absolute refractory period in the majority of the cases, although there was 1 case in which the slope was less than 45 degrees throughout the curve. The P'V interval was found to be determined mainly by the preceding VP' interval. The mechanism by which these different types of Wenckebach periods develop can be explained by the relationship between the shape of the recovery curve and the pacing rate. The types II, III, and IV periods which have been dealt with as atypical periods were understood to develop by the same mechanism as type I (typical) periods.

Adult↗
PubMed1975

Control of proliferation in mitogen responsive human peripheral blood lymphocytes: restimulation of cells stimulated by sodium periodate.

Human peripheral blood lymphocytes are stimulated to a greater extent by sodium periodate when cells are incubated in medium containing human serum than when incubated in medium with fetal calf serum. NaIO4 STIMULATION CAN BE REVERSED BY TREATMENT WITH SODIUM BOROHYDRIDE BUT CELLS ALREADY COMMITTED TO DIVISION ARE NOT AFFECTED BY BOROHYDRATE TREATMENT. Maximal commitment to DNA synthesis of a NaIO4 oxidized cell suspens-on occurs after about 28 hr of incubation in medium. The committal time after periodate stimulation is identical to that after stimulation with concanavalin A. Cells treated with periodate and then reduced with borohydride immediately after oxidation are refractory to further per-odate stimulation. Cells stimulated with periodate and then incubated for 6 hr before treatment with borohydride can be restimulated with periodate, indicating a turnover of membrane sites in the 6 hr period. Periodate-stimulated cells divide only once in response to the stimulation. The progeny of cells which were stimulated with periodate can be restimulated by treatment with either periodate or concanavalin A.

Animals↗
PubMed1977

Citation characteristics of periodical literature in veterinary science.

The usage of periodical literature in veterinary science was measured by means of citation analysis. Eighty-two percent of the citations in the source of this study, Advances in Veterinary Science and Comparative Medicine (1970-1974), were from periodicals, and 70 of the 743 periodical titles cited (9.4%) contributed 66% of the total periodical citations. Periodical literature cited in the source of the study appeared to have a half-life of 6.1 years, and to double its size approximately every 20 years. The aging patterns of the periodical literature seemed to vary with the publishing age of the periodical, i.e., the literature in the periodicals which have been in publication for more than 40 years showed a more gradual aging pattern than did that in the newer periodicals.

Periodicals as Topic↗
PubMed1978

The changing trends of uterine cancer and cytology: a study of morbidity and mortality trends over a twenty year period.

Data on squamous carcinoma of the cervix from a 20 year study period (1955 to 1974) in metropolitan Toledo revealed a 66% reduction of the average annual age-adjusted incidence rate and a 61% reduction in death rate of cervical squamous carcinoma when the first time period (1955 to 1958) was compared with the last time period (1971 to 1974). The decrease for both morbidity and mortality rates was more pronounced in women age 50 years and younger. The age-adjusted death rate during this study period revealed 15.5/100,000 for black women and 8.7/100,000 for white women. The reduction in death rate of 83% in black women is more prominent than 54.5% in white women. The decrease in both morbidity and mortality for cervical squamous carcinoma has a close relation to cytologic screening activity. The factors of age and race, probably related to socioeconomic status, are two known determinants of risk for cervical squamous carcinoma. Data for endometrial carcinoma during this study period revealed 15.5/100,000 women in the average age-adjusted incidence and an increase of 13.8% in average yearly rates when the first time period (1955 to 1958) were compared with the last time period (1971 to 1974). The peak age was 60 to 64 years old in the first time period and shifted to 70 to 74 years old in the last time period. The trend in metropolitan Toledo is comparable to that of Louisville, Kentucky. The mass cytologic screening program which contributed to a remarkable reduction in morbidity and mortality for the cervical squamous carcinoma, did not have any beneficial effect on endometrial carcinoma.

Adult↗
PubMed1977

Oxidation of tissue polysaccharides by periodic acid in dimethyl sulfoxide and its anhydrous and aqueous mixtures.

Periodic acid (1% w/v) solvated by anhydrous dimethyl sulfoxide (DMSO) readily induced a strong Schiff reaction in a variety of structures containing polysaccharides, but not glycogen. With the increasing amounts of water added to DMSO, glycogen was also oxidized, while the selective localization of other polysaccharides remained unimpaired. Periodate, solvated in the anhydrous acetic acid-DMSO mixture, rapidly induced concomitant oxidation of nucin and glycogen-containing structures. Sodium bisulfite addition derivatives of carbonyls, induced by periodate oxidation in DMSO, were stained meta- and orthochromatically with toluidine blue at controlled pH. Certain metachromatic tissue components were strongly birefringent in polarized light in contrast to the identical structures oxidized by aqueous periodate. Marked differences in staining reactions elicited in identical structures by periodate in DMSO as compared with aqueous periodate suggest that DMSO-periodate method considerably enhances the range of histochemical oxidations by periodate.

Animals↗
PubMed1979

Restoration of corticosteroid periodicity in obese rats by limited a.m. food access.

Absence of circadian periodicity of plasma corticosteroid levels has previously been reported to occur in animals maintained under constant light and in animals with suprachiasmatic nuclear lesions. Such animals also exhibit aperiodic rather than normal nocturnal eating. Restricted a.m. access to food (09.30--11.30 h) in such animals results in appearance of circadian corticosteroid periodicity (peak at 08.00 h) similar to that seen in normal animals on a similar food restriction regimen. The present study investigated the nature of adrenal circadian periodicity in obese rats who are reported to exhibit aperiodic feeding. Such aperiodic feeding occurred in obese male, but not in obese female, animals. These obese male animals manifested absent corticosteroid circadian periodicity. Restricted a.m. access to food was associated with the appearance of such periodicity similar to that described above in the two other experimental situations. These studies indicate differences in eating behavior and corticosteroid periodicity between obese male and obese female rats. They provide additional confirmation, in animals under normal light--dark conditions and in the absence of CNS lesions, of the role of periodic feeding in the generation of adrenal circadian periodicity.

Adrenal Cortex Hormones↗
PubMed1977

Heavy water as a tool for study of the forces that control length of period of the 24-hour clock of the hamster.

In alternating 12-hr periods of light and darkness, start of the dark period entrains the hamster's 24-hr clock. Blinding or constant darkness frees the clock of entrainment by allowing it to run faster or slower than 24 hr. Constant light frees the clock from entrainment and permits it to run slower than 24 hr--that is, lengthening its period. Heavy water given in drinking water linearly lengthens the period of the 24-hr clock of blinded hamsters or of hamsters kept in constant darkness in direct proportion to concentration of heavy water (1--50%). Heavy water (1-35%) has very different effects on length of the periods of the 24-hr clock when given under conditions of alternating 12-hr periods of light and darkness. Under these conditions, length of the period is controlled by three factors: (i) heavy water which slows the 24-hr clock; (ii) constant light which also slows the 24-hr clock; (iii) the counteracting effects of entrainment. It is thus possible to observe the effects of all three forces simultaneously in the same animal. The clock slowed by heavy water (1--20%) showed a strong tendency to return to a 24-hr entrainment whenever possible. On a 50% concentration of heavy water, the length of period of the clock became markedly lengthened but very constant and apparently independent of all external and internal disturbances.

Animals↗
PubMed2026

Distinct YY dinucleotide periodicity in adeno-associated virus DNA.

Dinucleotide periodicity is a hallmark of genome organization, yet its role in single-stranded (ss)DNA viruses remains poorly understood. Here, we systematically analyzed dinucleotide spacing patterns in adeno-associated virus (AAV) genomes and other viruses. Across 13 primate AAV serotypes, we identified a pronounced and highly conserved ∼15-bp periodicity specific to pyrimidine-pyrimidine (YY) dinucleotides and their reverse complements (RR). Comparative analyses across >25,000 viral sequences demonstrate that this 15-bp YY/RR periodicity is unique to the genus Dependoparvovirus and absent from other ssDNA viruses, satellite viruses, and helper viruses, which predominantly exhibit canonical ∼10- to 11-bp periodicities. Upon disruption of the YY/RR pattern using DNA family shuffling of AAV capsid genes, and subsequent iterative selection for viral production or cell entry, we found that the pattern is under positive selection. Selected sequences display increased periodicity alongside reduced sequence diversity, supporting a functional role for this genomic feature. Finally, engineered recombinant AAV genomes containing YY periodic motifs exhibit enhanced production and, for some designs, improved transduction efficiency, demonstrating that YY periodicity can modulate viral replication and infectivity. Our findings uncover a unique DNA-encoded signal in dependoparvoviruses that contributes to AAV fitness, expands our knowledge of virus biology, and has implications for vector engineering.

Dependovirus↗