Compartmental analysis of the efflux of l-[3H]norepinephrine from isolated perfused rat lungs

Isolated rat lungs, pretreated with 100 microM pargyline and 100 microM U-0521 (3',4'-dihydroxy-2-methylpropriophenone) to block metabolism of norepinephrine (NE), were perfused with 0.3 microM 3H-labeled l-norepinephrine (1-[3H]-NE) for 30 min. Efflux samples were then collected for 30 min during washout of the tissue with amine-free Krebs solution. Compartmental analysis (nonlinear least-squares regression) of the efflux of tissue l-[3H]NE content vs. time indicates that NE is accumulated in a large slowly equilibrating compartment (t 1/2 = 58.15 +/- 6.84 min) in addition to distribution in the vascular (blue dextran tracer) and extracellular ([3H]sorbitol tracer) fluid compartments of the lung. Pretreatment of the lungs with 100 microM cocaine hydrochloride reduces the total l-[3H]NE space from 7.44 +/- 1.91 to 2.48 +/- 0.23 ml/g (P less than 0.05) by selectively decreasing the size of the slow NE compartment from 6.99 +/- 1.97 to 1.67 +/- 0.14 ml/g (P less than 0.05). The large size, cocaine sensitivity, and long efflux half time of this compartment suggest that neuronal uptake contributes to the pulmonary vascular inactivation of l-[3H]NE.     

Multiple components of split-dose repair in plateau-phase mammalian cells: a new challenge for phenomenological modelers

Split-dose experiments using starved plateau-phase Chinese hamster ovary cells have been used to investigate the kinetics of repair, expressed in terms of enhancement of reproductive survival. The results show two distinct components of repair, one having a characteristic time of just over 1 h for the removal of a lesion, the other, about 18 h. The rate at which each component removes damage and the fraction of the total damage that each removes appear to be independent of the initial amount of damage produced, i.e., dose. This lack of dose dependence is not consistent with some simple models of ionizing radiation damage and repair, such as those which assume that saturation of a repair process, depletion of enzyme pools, or the interaction of pairs of sublesions is responsible for the curvature in the dose-response relationship. However, the relationship between the amounts of each type of damage and dose appears to be consistent with models that assume that only a portion of the initial damage is directly accessible to the repair systems or that the initial damage consists of a mixture of potentially lethal and sublethal lesions.     

Adaptive response and the bystander effect induced by radiation in C3H 10T(1/2) cells in culture.

This paper discusses two phenomena of importance at low doses that have an impact on the shape of the dose-response relationship. First, there is the bystander effect, the term used to describe the biological effects observed in cells that are not themselves traversed by a charged particle, but are neighbors of cells that are; this exaggerates the effect of small doses of radiation. Second, there is the adaptive response, whereby exposure to a low level of DNA stress renders cells resistant to a subsequent exposure; this reduces the effect of low doses of radiation. The present work was undertaken to assess the relative importance of the adaptive response and the bystander effect induced by radiation in C3H 10T(1/2) cells in culture. When the single-cell microbeam delivered from 1 to 12 alpha particles through the nuclei of 10% of C3H 10T(1/2) cells, more cells were inactivated than were actually traversed by alpha particles. The magnitude of this bystander effect increased with the number of particles per cell. An adaptive dose of 2 cGy of gamma rays, delivered 6 h beforehand, canceled out about half of the bystander effect produced by the alpha particles.     

Spectrum of aerobic endurance running performance in eleven inbred strains of rats

The goal of this study was to identifyinbred rat strains that could serve as useful models for exploration ofthe genetic basis of aerobic endurance performance. Six rats of eachgender from 11 different inbred strains were tested for1) maximal running capacity on atreadmill and 2) isolated cardiacperformance. Running performance was estimated from1) duration of the run,2) distance run, and3) vertical work performed. Cardiacoutput, during constant preload and afterload, was taken as a measureof cardiac performance from an isolated working heart preparation. TheCOP rats were the lowest performers and the DA rats were the bestperformers by all estimates of running performance. Across the 11 strains, the distance run correlated positively with isolated cardiacperformance (r = 0.87). Estimates ofperformance were as follows (COP vs. DA strain, respectively): durationof run, 19.9 ± 1.8 vs. 41.5 ± 2.2 min; distance run, 298 ± 30 vs. 840 ± 64 m; vertical work, 15 ± 1.7 vs. 40 ± 4.4 kg/m. These ~2.5-fold differences in running performancebetween the COP and DA suggest that these strains could serve as modelsfor evaluation of the genetic basis of variance in aerobicperformance.

     

Models for evaluating agents intended for the prophylaxis, mitigation and treatment of radiation injuries. Report of an NCI Workshop, December 3-4, 2003

To develop approaches to prophylaxis/protection, mitigation and treatment of radiation injuries, appropriate models are needed that integrate the complex events that occur in the radiation-exposed organism. While the spectrum of agents in clinical use or preclinical development is limited, new research findings promise improvements in survival after whole-body irradiation and reductions in the risk of adverse effects of radiotherapy. Approaches include agents that act on the initial radiochemical events, agents that prevent or reduce progression of radiation damage, and agents that facilitate recovery from radiation injuries. While the mechanisms of action for most of the agents with known efficacy are yet to be fully determined, many seem to be operating at the tissue, organ or whole animal level as well as the cellular level. Thus research on prophylaxis/protection, mitigation and treatment of radiation injuries will require studies in whole animal models. Discovery, development and delivery of effective radiation modulators will also require collaboration among researchers in diverse fields such as radiation biology, inflammation, physiology, toxicology, immunology, tissue injury, drug development and radiation oncology. Additional investment in training more scientists in radiation biology and in the research portfolio addressing radiological and nuclear terrorism would benefit the general population in case of a radiological terrorism event or a large-scale accidental event as well as benefit patients treated with radiation.     

Dose-rate evidence for two kinds of radiation damage in stationary-phase mammalian cells

Survival based on colony formation was measured for starved plateau-phase Chinese hamster ovary (CHO) cells exposed to 250 kVp X rays at dose rates of 0.0031, 0.025, 0.18, 0.31, and 1.00 Gy/min. A large dose-rate effect was demonstrated. Delayed plating experiments and dose response experiments following a conditioning dose, both using a dose rate of 1.00 Gy/min and plating delays of up to 48 hr, were also used to investigate the alternative repair hypotheses. There is clearly a greater change in survival in dose-rate experiments than in the other experiments. Thus we believe that a process which depends on the square of the concentration of initial damage, and which alters the effect of initial damage on cell survival is being observed. We have applied the damage accumulation model to separate the single-event damage from this concentration-dependent form and estimate the repair rate for the latter type to be 70 min for our CHO cells. Use of this analysis on other published dose-rate studies also yields results consistent with this interpretation of the repair mechanisms.     

Enzymatic formation of angiotensins II and III in the hindlimb circulation of dogs

Experiments were performed in 14 anesthetized dogs to (1) to determine if the reductions in hindlimb blood flow produced by [des-Asp1] angiotensin I were due to its local enzymatic (kininase II) conversion to angiotensin III and (2) to quantitate the extent of conversion of angiotensin I to angiotensin II and of [des-Asp1] angiotensin I to angiotensin III in the hindlimb circulation. Graded doses of these peptides were administered as bolus injections directly into the left external iliac artery while measuring flow in this artery electromagnetically. Dose-response relationships were determined before and during the inhibition of kininase II activity with captopril or antagonism of angiotensin receptor sites with [Ile7] angiotensin III. Captopril inhibited the vasoconstrictor responses to angiotensin I and [des-Asp1] angiotensin I, but did not affect the responses to angiotensins II or III, or norepinephrine. [Ile7] angiotensin III inhibited the vasoconstrictor responses to all four angiotensin peptides but did not alter the responses to norepinephrine. These findings indicate that the hindlimb vasoconstrictor responses to [des-Asp1] angiotensin I were due to the local formation of angiotensin III. The extent of conversion of [des-Asp1] angiotensin I to angiotensin III that occurred in one transit through the hindlimb arterial circulation was estimated to be 36.7%, which was not different from the estimated 36.4% conversion of angiotensin I to angiotensin II. We conclude that angiotensin I and [des-Asp1] angiotensin I are converted to their respective vasoactive forms (angiotensins II and III) to a similar extent in the hindlimb circulation via the action of kininase II.     

CONSPICUOUS ALGAL COLONIZATION OF THE ASH FROM MOUNT ST. HELENS1

Conspicuous growth of green and yellow-green algae developed in arid steppe communities in eastern Washington on the silt-sized ash from the 18 May 1980 eruption of Mount St. Helens. In a veneer on the ash, cell numbers per gram dry ash of these aerial immigrants equaled or exceeded the highest reported values for terrestrial chlorophytes (10⁸ cells · g^?1 dry soil). Such pronounced growth was restricted largely to three microsites (under the canopy of Artemisia tridentata, along the runways of the vole, Microtus montanus, and surrounding emergent agarics), apparently in response to water-holding properties of the ash, localized nutrient input and possible reduction of predation by nematodes. Highest algal counts were in Microtus runways where daily water and urea-N input per adult animal may be 8 mL and 23 mg, respectively. Cyanophytes, commonly considered early colonizers of volcanic ash, were extremely rare. The role of blue-green algae in succession on volcanic materials may be more restricted geographically than previously recognized.