Cell kinetics of the marine sponge Halisarca caerulea reveal rapid cell turnover and shedding.

This study reveals the peculiar in vivo cell kinetics and cell turnover of the marine sponge Halisarca caerulea under steady-state conditions. The tropical coral reef sponge shows an extremely high proliferation activity, a short cell cycle duration and massive cell shedding. Cell turnover is predominantly confined to a single cell population, i.e. the choanocytes, and in this process apoptosis only plays a minor role. To our knowledge, such fast cell kinetics under steady-state conditions, with high turnover by shedding in the absence of apoptosis, has not been observed previously in any other multicellular organism. The duration of the cell cycle in vivo resembles that of unicellular organisms in culture. Morphological and histochemical studies demonstrate compartmentalization of choanocytes in the sponge tissue, which corresponds well with its remarkable cellular kinetics. Coral reef cavity sponges, like H. caerulea, inhabit low nutrient tropical waters, forcing these organisms to filter large volumes of water and to capture the few nutrients efficiently. Under these oligotrophic conditions, a high cell turnover may be considered as a very useful strategy, preventing permanent damage to the sponge by environmental stress. Halisarca caerulea maintains its body mass and keeps its food uptake system up to date by constantly renewing its filter system. We conclude that studies on cell kinetics and functional morphology provide new and essential information on the growth characteristics and the regulation of sponge growth in vivo as well as in vitro and the role of choanocytes in tissue homeostasis.

Calibration of lichen transplants considering faint memory effects.

Biomonitoring, among other purposes, can be used as a tool to study the dispersion of trace elements through the atmosphere and back to the earth's surface again. In this sense it has been used for more than 20 years now. Yet, the calibration of biomonitors elemental contents against other atmospheric element dispersion variables like deposition or airborne concentration is still an open subject. The knowledge of a calibration nevertheless represents a qualitative improvement upon the use of biomonitors. Biomonitors elemental contents are usually assumed to depend in a linear way on the average values of atmospheric element dispersion variables, thus a linear regression is assumed to provide a good calibration. In this work: the element dispersion variables like deposition or airborne concentration will be referred in general as availability variables due to reasons that will be clarified; an uptake experiment using transplants of lichen Parmelia sulcata carried out in Portugal during a 2-year period (1994/1996) is described; and new concepts and calibration methods are presented. Lichen and aerosol samples were analysed by nuclear analytical techniques PIXE and INAA, and total deposition dry residue samples were analysed by ICP-MS. A database of roughly 70,000 values was thus created and biomonitor calibration carried out considering that biomonitors are not mechanical instruments but that they rather describe their exposure with a non-perfect memory. Data shows that surveying lichens four times within 1 year, with a period of 3 months in between sampling campaigns, allows the recovery of availability mean, maxima and standard deviation for many elements.

Influence of salinity and eutrophication on bioaccumulation of 99technetium in duckweed.

This study concerns the bioaccumulation of the long-lived nuclear waste product 99Tc in duckweed (Lemna minor L.). 99Tc was present as the oxyanion TcO4-, being the main chemical form of technetium in aerobic water systems. In contrast with terrestrial plants, bioaccumulation in duckweed proved to be independent of the nitrate concentration in the medium. However, uptake is controlled by electrostatic effects in the cell wall, which affects the bioaccumulation of 99Tc in duckweed in natural environments. These waters are characterized by a range of salinity and hardness, and this study suggests that this may result in up to a threefold difference in 99Tc accumulation. Because of screening of negative charges in the cell wall, the highest accumulation may be expected in hard, brackish water. This behavior can be described by a general model, which includes electrostatic effects and binding of cations at the cell wall. The model also explains why cationic radionuclides are preferably taken up in soft, fresh water while anionic species are concomitantly taken up in hard, chlorine-rich waters.

In-target production of high specific radioactivity [15O]nitrous oxide by deuteron irradiation of nitrogen gas.

A simple and rapid production method for high specific radioactivity [15O]N2O has been developed based on the 14N(d,n)15O reaction on high-purity nitrogen gas in a flow-through target irradiated with a 0.5 microA beam of 7 MeV deuterons. The [15O]N2O formed during irradiation is selectively concentrated from the target effluent by adsorption on a zeolite during 150 s and subsequently released by rapid heating into a pulse with a full width at half maximum of 3.5 s. The radioactivity and specific radioactivity in the pulse amount to 4 MBq [15O]N2O and 4.5 x 10(13) Bq/mol respectively with a radiochemical purity >99.95%. A tenfold higher specific radioactivity may be feasible at larger beam currents. It was shown that stable N2O was also formed during irradiation. Based on responses to variations in various parameters during irradiation and on analyses performed on the products, an explanation is given on the mechanisms of in-target [15O]N2O and N2O formation, involving reaction of a particular excited state of O3 with N2.

Microbeam PIXE analysis of Na, K, Mg, and Ca in severely damaged cardiac tissue.

The aim of the study was to measure with microbeam PIXE elements such as Na, K, Mg, and Ca in cardiac tissue after various treatments in vivo, which affect the cardiomyocyte integrity. It was assumed that local deviations from normal electrolyte levels indicate the degree of cardiac damage. The first step in this feasibility study was comparison of severely damaged cardiac tissues with controls. Severe cardiac damage was introduced by the so-called Ca paradox. Experiments were performed with isolated rat hearts, perfused retrogradely with an oxygenated crystalloid buffer. Results indicated that severe cardiac damage was accompanied with almost complete disappearance of the normal intracellular electrolyte composition as a result of the loss of membrane integrity. Identifications of smaller and more locally present ischemic damages on basis of altered electrolyte levels appeared to be feasible. However, the prerequisite was that the mobility of electrolytes be kept under control during tissue sampling and sample preparation, when physiological mechanisms stop to maintain gradients.

Radiochemical neutron activation analysis in the life sciences. A look back and ahead.

The contribution of radiochemical neutron activation analysis (RCNAA) to a better understanding of trace element analytics and physiology in the life sciences is outlined. Now, various non-nuclear powerful techniques for trace element analysis have become available, competing with RCNAA. This necessitates re-evaluation of the position of RCNAA, in particular versus inductively coupled plasma--mass spectrometry (ICP-MS). On basis of the characteristic features of RCNAA and the capabilities of various competing non-nuclear analytical techniques, future niches for RCNAA in the analytical market are indicated.

Effects of theophylline on tolerance to the bronchoprotective actions of salmeterol in asthmatics in vivo.

Long-term treatment with salmeterol produces tolerance for its protective effects against bronchoconstrictor stimuli in patients with asthma. There is human in vitro evidence that theophylline may prevent beta2-adrenoceptor downregulation. Therefore, we investigated the effect of theophylline on the tolerance to the protective effect of salmeterol against histamine challenge in asthma in vivo. In a parallel 6-wk study, 25 asthmatics were treated with theophylline (mean serum level +/- SEM: 9.9 +/- 1.1 mg/L, Days 1 to 40) or placebo, combined with inhaled salmeterol (50 microgram twice daily, Days 8 to 36). Histamine challenges were carried out by tidal breathing method at entry, and at Days 4, 8, 22, 36, and 40. The response was measured by PC20. There was no significant change in PC20 after 4 d monotherapy with theophylline or placebo (mean difference +/- SEM: 0.54 +/- 0.39 and -0.02 +/- 0.41 doubling dose [DD], respectively; p > 0.15). One hour after the first dose, salmeterol afforded significant protection against histamine, as shown by an increase in PC20 in both the theophylline and placebo group (by 3.49 +/- 0.28 and 3.36 +/- 0.32 DD, respectively; p < 0. 001). However, after 2 and 4 wk salmeterol treatment, the improvements in PC20 by salmeterol were significantly reduced to 1. 80 +/- 0.35 and 1.69 +/- 0.36 DD, respectively, in the theophylline group (p < 0.001), and to 1.55 +/- 0.47 and 1.52 +/- 0.56 DD, respectively, in the placebo group (p < 0.002). These changes were not significantly different between the groups (p > 0.80). After cessation of salmeterol treatment, PC20 was not significantly different from the values at entry in either group (p > 0.90). We conclude that regular theophylline treatment neither prevents, nor worsens, the development of tolerance to the bronchoprotective effect of salmeterol in asthmatics in vivo.

Gastric transit and pharmacodynamics of a two-millimeter enteric-coated pancreatin microsphere preparation in patients with chronic pancreatitis.

It has been suggested that enteric-coated pancreatin microsphere (ECPM) preparations with sphere sizes larger than 1.7 mm pass through the stomach at a slower rate than a meal and therefore may be less efficacious in restoring pancreatic enzyme activity than preparations with smaller sphere sizes. The aim of this study was to investigate the gastric transit profile of a 2-mm ECPM preparation in relation to that of a solid meal and to simultaneously measure enzyme activities in eight patients with pancreatic exocrine insufficiency due to chronic pancreatitis. Gastric transit was assessed by double-isotope scintigraphy. A pancake was labeled with 99mTc. A 2-mm ECPM preparation was labeled with 171Er. Intraluminal pancreatic enzyme activities were assessed during a 6-hr period with the cholesteryl-[14C]octanoate breath test (for carboxyl ester lipase activity) and the N-benzoyl-L-tyrosyl-p-aminobenzoic acid/p-aminosalicylic acid (NBT-PABA/PAS) test (for chymotrypsin activity). The ECPM preparation passed through the stomach more rapidly (median 24 min) than the pancake (median 52 min, P < 0.05). During ECPM therapy, mean cumulative 14CO2 outputs rose significantly from 30% to 70% (P < 0.05), but remained below outcomes in healthy volunteers. Mean cumulative plasma PABA concentrations rose significantly from 46% to 87% (P < 0.05) and were not significantly different from outcomes in healthy volunteers. In chronic pancreatitis, a 2-mm ECPM preparation does not pass through the stomach more slowly than a solid meal, but in fact faster. Digestion of ester lipids and proteins showed an improvement to subnormal and normal levels, respectively.

Comparative effects of enteric-coated pancreatin microsphere therapy after conventional and pylorus-preserving pancreatoduodenectomy.

BACKGROUND: A comparative study was performed between patients with exocrine pancreatic insufficiency after conventional pancreatoduodenectomy (Whipple's procedure) and pylorus-preserving pancreatoduodenectomy (PPPD). In these patients the pharmacodynamics of 2-mm enteric-coated pancreatin microspheres (ECPMs) and their gastric transit time in relation to that of a solid meal were investigated. The efficacy of ECPM preparations may differ after Whipple's procedure compared with PPPD, because the latter procedure does not include gastrectomy. METHODS: Gastric transit was assessed by double-isotope scintigraphy. A pancake meal was labelled with 99mTc. ECPMs were cold-labelled with 170Er and neutron activated shortly before ingestion to enable imaging with a gamma camera. Intraluminal pancreatic enzyme activity was assessed during a 6-h period with two indirect tests: the cholesteryl [14C]octanoate breath test and the N-benzoyl-L-tyrosyl-p-aminobenzoic acid-p-aminosalicylic acid (NBT-PABA-PAS) test. RESULTS: In patients who had Whipple's procedure, the gastric transit time of ECPMs and of the pancake meal was not significantly different. The outcome of the indirect pancreatic function tests during enzyme supplementation was comparable, and not significantly different, from that in healthy volunteers. In patients who had PPPD, however, the gastric transit time of microspheres was greatly delayed compared with that of the pancake meal (P < 0.05). Improvement in the outcome of the indirect pancreatic function tests during enzyme supplementation was much less and remained well below that of healthy volunteers (P < 0.05). CONCLUSION: In cases of exocrine pancreatic insufficiency after Whipple's procedure, 2-mm ECPM treatment adequately restores pancreatic enzyme activity. Following PPPD, however, ECPM treatment is often ineffective because the microspheres are retained in the stomach. In these patients, use of conventional powdered pancreatin enzyme preparations may improve the efficacy of treatment.

Pixe microanalysis of trace elements of normoxic, ischemic and reperfused rat hearts.

With a 3 x 3 mu m(2) proton microbeam spatial distributions of Na, Mg, P, S, K, Ca and Fe were measured via PIXE in 50 x 50 mu m(2) areas of rat heart, sliced into 10-15 mu m thick cryosections. The isolated rat hearts were subjected to normal perfusion, ischemia and reperfusion. Substantial changes in the elemental distribution were found in tissue after 40 min. of reperfusion, particularly indicated by locally elevated Ca and decreased K levels. Electron microscopic examination was used for assessment of artefacts due to sample preparation and handling. Results of stained cryosections analyzed via STIM demonstrated that this latter technique can be employed prior to PIXE analysis to localize individual cells in freeze-dried cryosections.