Forest systems cover more than 4.1 x 10(9) hectares of the Earth's land area. Globally, forest vegetation and soils contain about 1146 petagrams of carbon, with approximately 37 percent of this carbon in low-latitude forests, 14 percent in mid-latitudes, and 49 percent at high latitudes. Over two-thirds of the carbon in forest ecosystems is contained in soils and associated peat deposits. In 1990, deforestation in the low latitudes emitted 1.6 +/- 0.4 petagrams of carbon per year, whereas forest area expansion and growth in mid- and high-latitude forest sequestered 0.7 +/- 0.2 petagrams of carbon per year, for a net flux to the atmosphere of 0.9 +/- 0.4 petagrams of carbon per year. Slowing deforestation, combined with an increase in forestation and other management measures to improve forest ecosystem productivity, could conserve or sequester significant quantities of carbon. Future forest carbon cycling trends attributable to losses and regrowth associated with global climate and land-use change are uncertain. Model projections and some results suggest that forests could be carbon sinks or sources in the future.

No abstract

AICA-riboside (5-amino-4-imidazole carboxamide ribonucleoside) is a novel adenosine-regulating agent that is currently being investigated for the treatment of ischemic heart disease. In a placebo-controlled, double-blind study in healthy men, we evaluated the safety and kinetics of the drug after oral and IV administration of 10, 25, 50, and 100 mg/kg doses. At each dose level, four subjects received active drug and two subjects received placebo with a 1-week wash-out period between the IV and oral doses. The drug was well tolerated at all dose levels with only mild and transient side effects reported in some instances by the subjects who received placebo and those patients who received the drug. The post-infusion plasma concentrations of AICA-riboside declined rapidly in a biphasic fashion, and the terminal elimination phase had a harmonic mean t1/2 beta of 1.4 hours. Total plasma clearance (CL), mean residence time (MRTIV), and volume of distribution at steady-state (VSS) were 2.5 L/hr/kg, 0.7 hr, and 1.6 L/kg, respectively. The drug was not protein bound, and there was rapid uptake and phosphorylation in RBCs to its 5'-monophosphate nucleotide. Renal clearance (CLR) was 0.2 L/hr/kg with only 8% of the IV dose excreted in the urine as intact AICA-riboside. Although there was a trend towards a decrease in CL with increasing dose, there were no significant differences (P greater than .05) in the mean estimates of t1/2 beta, CL, CLR, MRTIV and VSS associated with dose. The drug was poorly bioavailable (less than 5%) when administered orally in solution.

No abstract

No abstract

No abstract

Attempts to relate plant metabolic activity with developmental stage are often hindered by lack of an appropriate developmental index. Existing indices of morphological development are unsuitable for use with plants having a semideterminate, recurrently flushing pattern of growth as displayed by Quercus seedlings. We propose the following morphological index (QMI) to define the stages of Quercus seedling ontogeny: (1) radicle emergence; (2) epicotyl emergence from the soil; and (for each flush) (3) termination of elongation of the second internode, which corresponds with the period of most rapid stem elongation; (4) completion of elongation by all internodes, which corresponds with the period of most rapid leaf elongation; and (5) completion of elongation of the last leaf but one, which usually precedes closely the pause between one growth flush and another. The relationship between QMI and net photosynthesis by individual leaves of Quercus rubra L. seedlings was determined. Net photosynthesis increased with QMI during a flush, but at a particular QMI stage, generally decreased from one flush to the next.

The aim of these two studies was to evaluate the safety and pharmacokinetics of oral nalmefene, a new orally effective opioid antagonist. In the first study, single ascending doses of 50, 100, 200, and 300 mg of nalmefene HCl were administered in double-blind fashion to four groups of healthy men. There were six subjects in each group; four received nalmefene and two received placebo. The drug was well tolerated at all dose levels with only mild and transient side effects, such as lightheadedness, at the higher doses. Model-independent pharmacokinetic analysis of the plasma concentration-time data showed that nalmefene was rapidly absorbed and had an elimination half-life that ranged from seven to 15 hours (mean, 10.7 hr). There was a good linear relationship (r = .97) between administered dose and total area under the curve at each dose level. Only about 4% of the dose was excreted in the urine as unchanged nalmefene, whereas up to 60% was excreted as a beta-glucuronidase/sulfatase hydrolysable conjugate(s) of nalmefene. In the second study, six healthy men were initially administered a single 50-mg dose of drug, and plasma samples were obtained at selected time intervals for 48 hours. A dosing schedule of 20 mg q12h was then started and continued for seven days. Plasma samples were collected immediately before each dose and at selected times for up to 48 hours after the last dose. The drug was well tolerated by all subjects, and no clinically significant adverse effects were observed during the seven-day administration period.(ABSTRACT TRUNCATED AT 250 WORDS)