The oxygen‐18 content of precipitation in the Amazon basin is characterized by a very small inland gradient, 0.75 × 10−3 ‰ km−1. This is a consequence of the large contribution of reevaporated moisture to the basin's water balance. A distinct seasonal and regional pattern of stable isotope composition has been recognized and shows the basin to be inhomogeneous from the hydrometeorological point of view. The occasional appearance of very low δ values is believed to be related to the position of the ITCZ rather than to interbasin processes.

An increase of 3‰ in the “d” value of the isotopic composition of precipitation over the Amazon Basin suggests that an isotopically fractionated evapotranspiration flux contributes to the atmospheric water balance over the region. A steady state evapotranspiration model for the Amazon Basin was developed, and it is shown that the observed increase in the “d” value corresponds to a situation where 20–40% of the total evapotranspiration flux is accompanied by an isotopic fractionation, such as by evaporation from an open water surface. The site of this fractionation, whether by evaporation from the flood plains, canopy interception or lakes, cannot be resolved with the presently available data set.

No abstract

The antitumor effect of oenothein B, a macrocyclic ellagitannin from Oenothera erythrosepala Bordas, on rodent tumors was studied, Oenothein B exhibited a strong antitumor activity against MM2 ascites tumors upon intraperitoneal administration to the mice before or after the tumor inoculation. The tannin also inhibited the growth of Meth‐A solid type tumor in mice. This antitumor effect of the tannin could not be attributed to its direct cytotoxic action on tumor cells, because the cytotoxicity was very weak in the presence of serum protein. When oenothein B was injected into the peritoneal cavity of mice, peritoneal exudate cells, including cytostatic macrophages, were induced. Furthermore, in the in vitro treatment of macrophages from mice and humans, the tannin stimulated release of an interleukin 1 (IL‐1)‐like activity and IL‐1β from the cells. These results suggest that oenothein B exerts its antitumor effect through potentiation of the host‐immune defense via activation of macrophages.

No abstract