Radiocarbon ages of lacustrine deposits in volcanic sequences of the Lomas Coloradas area, Socorro Island, Mexico.

Extensive eruptions of alkalic basalt from low-elevation fissures and vents on the southern flank of the dormant volcano, Cerro Evermann, accompanied the most recent phase of volcanic activity on Socorro Island, and created the Lomas Coloradas, a broad, gently sloping terrain comprising the southern part of the island. We obtained 14C ages of 4690 +/- 270 BP (5000-5700 cal BP) and 5040 +/- 460 BP (5300-6300 cal BP) from lacustrine deposits that occur within volcanic sequences of the lower Lomas Coloradas. Apparently, the sediments accumulated within a topographic depression between two scoria cones shortly after they formed. The lacrustine environment was destroyed when the cones were breached by headward erosion of adjacent stream drainages. This was followed by the eruption of a thin basaltic flow from fissures near the base of the northernmost cone. The flow moved downslope for a short distance and into the drainages that presently bound the study area on the east and west. The flow postdates development of the present drainage system and may be very recent. Our 14C data, along with historical accounts of volcanic activity over the last century, including submarine eruptions that occurred a few km west of Socorro in early 1993, underscore the high risk for explosive volcanism in this region and the need for a detailed volcanic hazards plan and seismic monitoring.

Gender and developmental differences in adolescents' conceptions of moral reasoning.

Eighth graders, 11th graders, and college sophomores wrote open-ended essays that characterized their own approaches to moral reasoning. Their essays were scored for the presence of various themes. Students also responded to three dilemmas from the Defining Issues Test (Rest, 1979). Students then rated their own use of justice and care orientations in moral reasoning, using a previously developed instrument (Ford and Lowery, 1986; Lyons, 1983). Characterizations of moral reasoning became more multifaceted and thorough with grade, and correlated with many traditional measures of moral reasoning. Males and females showed some, but relatively few, differences in characterizing their own moral reasoning, although females tended to respond more thoroughly to the open-ended task. Gender differences, when they occurred, were mostly found on measures that assessed so-called feminine issues or concerns, but not on traditional measures of moral reasoning. Characterizations of moral reasoning clustered into five dimensions, raising questions about the utility of the constructs of justice and care orientations.

Liposome-encapsulated hemoglobin: a synthetic red cell.

Liposome-encapsulated hemoglobin (LEH) is being developed at the Naval Research Laboratory as a universally transfusable oxygen-carrying blood replacement. A chemical engineering scale-up feasibility study has been completed recently. We report here the development of an encapsulation method which produces liters of phospholipid/cholesterol liposomes containing at least 16 g% hemoglobin in a few hours. The 0.2 micron liposomes are produced with a Microfluidizer TM (Microfluidics Corp., Newton, MA) adapted for this purpose, and then washed and sterile filtered using a Pellicon (Millipore, Bedford, MA) tangential flow filtration device. Previously, production limitations and lack of sterility have been serious barriers to toxicity testing for all the researchers engaged in related investigations. The biophysical properties of the LEH thus produced are ideal for use as a blood substitute, resembling those of red blood cells. The oxygen-binding affinity of LEH can be maintained at the level of fresh whole blood for many weeks by co-encapsulation of pyridoxal-5-phosphate. The circulation persistence time of liposomes is a function of the type of phospholipid. We have developed a formulation which has a circulation persistence time of 15-20 hours. The LEH oxygen binding characteristics, circulation half-life and its lipid composition dependence, scale-up preparation method, and a sterilization method are presented.

The reduction of methemoglobin levels by antioxidants.

Preventing the oxidation of hemoglobin in solution is one of the major requirements for the successful production and long-term storage of hemoglobin-based blood substitutes. To this end we have studied the effects of antioxidants on the rate of methemoglobin formation and disappearance in solutions of human and bovine hemoglobin at 4 degrees C and 37 degrees C. Ascorbate and desferal (5 mM) were observed to act as prooxidants, increasing the rate of methemoglobin formation at 37 degrees C. Trehalose, mannitol, glucose, and EDTA (5 mM) had no significant effect. Glutathione and NADH (10 mM) were the most effective antioxidants tested, causing a significant decrease in the rate of methemoglobin formation at 37 degrees C for periods of up to 50 hours. The combination of these antioxidants in bovine hemoglobin at 4 degrees C resulted in the reduction of methemoglobin levels to nearly undetectable levels in approximately 150 hours. In addition, NADH and glutathione were found to reduce methemoglobin levels to 10% over a period of 100 hours in a sample of human hemoglobin that had been stored at 4 degrees C for one year and had 60% methemoglobin. These results suggest that the prevention and reversal of methemoglobin formation during the long-term storage of hemoglobin solutions and hemoglobin-based blood substitutes may now be possible.

Liposome-encapsulated hemoglobin: oxygen binding properties and respiratory function.

Lipid bilayer membranes have been used to encapsulate hemoglobin and organic phosphates, resulting in a synthetic red cell with oxygen-binding properties very similar to red blood cells (RBCs). In addition to the oxygen-binding parameters, we report here an improvement in the lipid formulation that confers upon the liposome-encapsulated hemoglobin (LEH) a circulation retention half-time of 15 to 20 hours in mice. Cooperative oxygen binding of the encapsulated hemoglobin is retained and the oxygen-binding affinity can be maintained at or below the level of fresh whole blood for many weeks by co-encapsulation of an appropriate concentration of pyridoxal-5-phosphate. A comparison of the kinetics of oxygen exchange across the membranes of the synthetic red cells and RBCs indicates that the increased surface to volume ratio of the much smaller synthetic red cells, coupled with their somewhat lower concentration of hemoglobin, results in more rapid rates of oxygen uptake and release than are seen with RBCs. Efficacy studies have begun and we report here the successful transfusion of rats with LEH. After greater than 90% exchange, LEH transfused rats were able to maintain activity with normal respiratory and cardiac function parameters.