A unified theory of impact crises and mass extinctions: quantitative tests.

Several quantitative tests of a general hypothesis linking impacts of large asteroids and comets with mass extinctions of life are possible based on astronomical data, impact dynamics, and geological information. The waiting times of large-body impacts on the Earth derived from the flux of Earth-crossing asteroids and comets, and the estimated size of impacts capable of causing, large-scale environmental disasters, predict the impacts of objects > or = 5 km in diameter (> or = 10(7) Mt TNT equivalent) could be sufficient to explain the record of approximately 25 extinction pulses in the last 540 Myr, with the 5 recorded major mass extinctions related to impacts of the largest objects of > or = 10 km in diameter (> or = 10(8) Mt events). Smaller impacts (approximately 10(6) Mt), with significant regional environmental effects, could be responsible for the lesser boundaries in the geologic record. Tests of the "kill curve" relationship for impact-induced extinctions based on new data on extinction intensities, and several well-dated large impact craters, also suggest that major mass extinctions require large impacts, and that a step in the kill curve may exist at impacts that produce craters of approximately 100 km diameter, smaller impacts being capable of only relatively weak extinction pulses. Single impact craters less than approximately 60 km in diameter should not be associated with detectable global extinction pulses (although they may explain stage and zone boundaries marked by lesser faunal turnover), but multiple impacts in that size range may produce significant stepped extinction pulses. Statistical tests of the last occurrences of species at mass-extinction boundaries are generally consistent with predictions for abrupt or stepped extinctions, and several boundaries are known to show "catastrophic" signatures of environmental disasters and biomass crash, impoverished postextinction fauna and flora dominated by stress-tolerant and opportunistic species, and gradual ecological recovery and radiation of new taxa. Isotopic and other geochemical signatures are also generally consistent with the expected after-effects of catastrophic impacts. Seven of the recognized extinction pulses seem to be associated with concurrent (in some cases multiple) stratigraphic impact markers (e.g., layers with high iridium, shocked minerals, microtektites), and/or large, dated impact craters. Other less well-studied crisis intervals show elevated iridium, but well below that of the K/T spike, which might be explained by low-Ir impactors, ejecta blowoff, or sedimentary reworking and dilution of impact signatures. The best explanation for a possible periodic component of approximately 30 Myr in mass extinctions and clusters of impacts is the pulselike modulation of the comet flux associated with the solar system's periodic passage through the plane of the Milky Way Galaxy. The quantitative agreement between paleontologic and astronomical data suggests an important underlying unification of the processes involved.

Efficacy of fluvastatin, a totally synthetic 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor. FLUENT Study Group. Fluvastatin Long-Term Extension Trial.

The Fluvastatin Long-Term Extension Trial (FLUENT) was designed to assess the safety and efficacy of fluvastatin over a prolonged period of time. In this way, FLUENT represents a clinical scenario that is closer to office-based chronic treatment of hyperlipidemic patients. A total of 918 patients with severe primary hypercholesterolemia (mean baseline low density lipoprotein cholesterol [LDL-C], 227 mg/dL) were enrolled into the study and received open-label fluvastatin, 20 or 40 mg daily, depending on response. Results of the first year of treatment have been published previously and showed statistically significant changes in LDL-C (-30.7%), total cholesterol (-21.9%), and high density lipoprotein cholesterol (HDL-C; +3.5%). Of the original number of patients completing the 1-year study, 761 completed a second year of evaluation; the results are presented here. Any patient who did not achieve LDL-C levels of < or = 130 mg/dL could receive cholestyramine (usually 8 g/day) or fluvastatin up to 80 mg/day. At the end of the 2-year period there were significant changes in LDL-C with fluvastatin (20 mg/day, -25.4%; 40 mg/day, -30.6%; 80 mg/day, -33.7%; p < 0.001 vs baseline for all values). The combination of fluvastatin and cholestyramine changed LDL-C by -34.6%. Similar dose-response results were seen with reductions in total cholesterol and the LDL-C: HDL-C ratio. There were no unexpected or severe adverse events or laboratory abnormalities. In conclusion, fluvastatin offers a range of LDL-C reduction (25-34%) similar to other HMG-CoA reductase inhibitors, that conforms with guideline recommendations for over 90% of hypercholesterolemic patients.

Dicarboxylate diamide dimercaptide (N2S2) technetium-99m complexes: synthesis and biological evaluation as potential renal radiopharmaceuticals.

Novel diamide dimercaptide (N2S2) ligands 4, 5, and 8 have been synthesized and evaluated as potential renal radiopharmaceuticals. The target compounds were prepared in modest overall yields of 22%, 19%, and 20%, respectively, using readily available starting materials. Following in situ deprotection, 99mTc complexes of high radiochemical purity were obtained in excellent yield and were found to be stable for up to 6 h. The 99Tc complex of ligand 8 was isolated as the AsPh4 salt. The X-ray crystallographic data for [99TcO(8)]AsPh4 (space group P2(1)/n: Z = 4, a = 9.342(3) A; b = 18.594(5) A; c = 18.417(7) A; beta, deg = 90.61(3); V, A3 = 3199.1(20)) show that the Tc is bound to both thiolate sulfur atoms and to two deprotonated amide nitrogen atoms. The coordination geometry about the Tc is square-pyramidal with an -yl oxygen atom in the apical position. The Tc-N bond distances (2.002(12) and 1.984(12) A), the Tc-S bond distances (2.300(5) and 2.286(5) A), and the Tc-O bond distance (1.667(11) A) are in good agreement with bond lengths reported for similar complexes. The carboxylate groups are not bonded to the Tc atom in the solid state, nor in CDCl3 solution, as evidenced by X-ray crystal data and solution NMR data, respectively. In the solid state, [99TcO(8)]AsPh4 is monoanionic, therefore, at physiological pH, [99mTcO(8)] is presumably trianionic. Biodistribution studies performed in rats with the 99mTc complexes revealed slow blood clearance and high muscle uptake for these agents. Modest hepatobiliary excretion was observed, and low quantities of the complexes were found in the heart, lungs, and spleen after 1 h. The urinary excretion of the 99mTc complexes of ligands 4, 5, and 8 was found to be slow when compared to the excretion of [131I]OIH in rats (22%, 22%, and 32% vs 85-86%, respectively). Protein binding of 99mTc complexes of ligands 4, 5, and 8 in both rat and monkey plasma was found to be similar to MAG3. While the synthetic schemes reported here supply facile routes to novel N2S2 ligands, biodistribution studies of the 99mTc complexes performed on rats revealed slow renal excretion rates, accompanied by slow blood clearance and high uptake in muscle tissue. Preliminary planar imaging studies in monkeys also revealed slow renal excretion for these agents. The 99mTc complexes evaluated here are poor candidates as renal radiopharmaceuticals.

Prevention and differential of scrotal cancer.

Testicular self-examination is the most efficient method for early detection of scrotal cancer. These tumors are the most common neoplasm in young adult males, yet health teaching in this area is often overlooked. Several types of testicular cancer and associated risk factors have been identified. The examination is explained and teaching strategies are discussed using a developmental approach with adolescents and young adults.