Search PubMed⌕ Search

Biomedical subjects

R Levinson

Publications and source records attributed to R Levinson.

28 records · Page 2Linked to original sources
PubMed1984

A carcinogenic potency database of the standardized results of animal bioassays.

The preceding paper described our numerical index of carcinogenic potency, the TD50 and the statistical procedures adopted for estimating it from experimental data. This paper presents the Carcinogenic Potency Database, which includes results of about 3000 long-term, chronic experiments of 770 test compounds. Part II is a discussion of the sources of our data, the rationale for the inclusion of particular experiments and particular target sites, and the conventions adopted in summarizing the literature. Part III is a guide to the plot of results presented in Part IV. A number of appendices are provided to facilitate use of the database. The plot includes information about chronic cancer tests in mammals, such as dose and other aspects of experimental protocol, histopathology and tumor incidence, TD50 and its statistical significance, dose response, author's opinion and literature reference. The plot readily permits comparisons of carcinogenic potency and many other aspects of cancer tests; it also provides quantitative information about negative tests. The range of carcinogenic potency is over 10 million-fold.

Animals↗
PubMed1976

Effects of water immersion to the neck on pulmonary circulation and tissue volume in man.

Utilizing the rebreathing of a gas mixture containing C2H2, C180, He O2, and N2, we obtained serial measurements of the pulmonary capillary blood flow (Qc), diffusing capacity per unit of alveolar volume (DL/VA), functional residual capacity (FRC), pulmonary tissue plus capillary blood volume (VTPC), and O2 comsumption (VO2) in five normal subjects under the following conditions: 1) 6 h of sitting, 2) 4 h of sitting while immersed in thermoneutral water to the neck, and 3) 4 h of lying in thermoneutral water to the neck. Water immersion (NI) was preceded and followed by 1-h prestudy and 1-h recovery periods. The measurements were made at 30-min intervals. Seated NI produced a fourfold increase in sodium excretion (UNaV), a 25-36% increase in Qc, a 45-59% increase in DL/VA, and a 30-36% decrease in FRC. This occurred as early as the 1st h of NI and persisted throughout the 4-h period of study. Throughout the seated control and NI periods, VO2, heart rate, and VTPC remained constant. During supine NI, Qc, HR, DL/VA, FRC, and VO2 did not differ significantly from supine prestudy. These date demonstrate that seated NI causes a significant increase of Qc and DL/VA which persists throughout the immersion period. Furthermore, the lack of change of VTPC suggests that the central vascular engorgement induced by seated NI is not accompanied by extravasation of fluid into the pulmonary interstitial space.

Adolescent↗
PubMed1976

Effects of water immersion on renal hemodynamics in normal man.

Although previous studies have demonstrated that water immersion to the neck (NI) results in a significant natriuresis and diuresis, the mechanisms are incompletely delineated. Since recent studies have demonstrated that NI induces a marked increase in cardiac index, it is possible that, as a consequence, renal hemodynamics may be augmented markedly during NI thereby mediating the encountered renal changes. The present study was undertaken to delineate the effects of NI on renal plasma flow and glomerular filtration rate as assessed by the clearance of PAH (CPAH) and inulin (CIn), respectively. Nine normal male subjects were studied on two occasions, control and NI. The conditions of seated posture and time of day were identical. Immersion did not alter CIn or CPAH at a time when sodium excretion was increasing markedly. The constancy of CPAH during NI suggests that renal blood flow is unaltered and that the natriuresis of NI is mediated independently of alterations in overall renal perfusion. The sluggish decline of a naturiuresis during recovery is consistent with the presence of a humoral factor contributing to the encountered natriuresis.

Adult↗
PubMed1976

Determinants of deranged sodium and water homeostasis in decompensated cirrhosis.

Previous studies from this laboratory have demonstrated that the redistribution of blood volume and concomitant central hypervolemia induced by water immersion to the neck (NI) results in a significant natriuresis, kaliuresis, and diuresis. The NI model was utilized to assess the role of "effective volume" and hyperaldosteronism in the impairment of sodium and water handling in cirrhosis. Eleven cirrhotic patients were studied twice while in balance on a 10 mEq. Na, 100 mEq. K diet: control and NI. The conditions of seated posture and time of day were identical. UNaV was constant throughout C, ranging from 1 to 2 muEq per minute. During NI, UNaV increased progressively from 1 +/- 1 (S.E.M.) during the prestudy hour to 89 +/- 32 muEq per minute during hour 5 of NI (p less than 0.02), greatly exceeding the comparable value found in normal subjects on an identical diet. (See article).

Adult↗
PubMedDate not supplied

Prolongation of skin allograft survival by pretreatment of allograft with monoclonal antibody and steroids.

Treatment of large burns would be simplified by the development of a nonsensitizing allograft which would survive permanently. In our hands, in vitro immune modification of the allograft has prolonged graft survival in mice across major histocompatibility barriers (H-2d to H-2b) by 36% (steroid pretreatment) and 25% (monoclonal antibody to the Iad antigen found on donor Langerhans cells). To our knowledge, monoclonal antibody has not been employed in this capacity previously. Double grafting studies suggest that neither MK-D6 nor steroids enhance graft survival by systemic immunosuppression. Moreover, MK-D6 acts upon the afferent limb of the immune response while steroids interrupt the efferent limb (and probably afferent limb). These effects are not additive. This modest improvement in allograft survival may have profound importance since allografts supported briefly by host immunosuppression have gone on to indefinite survival in burn victims without further immunologic intervention. This improvement in allograft survival is of fundamental immunologic interest. If synergistic pretreatments can be found, it may ultimately allow allografting of burn victims with the expectation of indefinite graft survival.

Animals↗