Search

A self-instructional audit package for the identification and management of hypertensive patients was developed. The materials were field tested in the clinics of seven institutions to assess their clarity and collect data to illustrate the usefulness of an audit as an educational tool.

Previous work has shown that thymocytes of rats receiving two i.v. injections, 4 days apart, of large numbers of xenogeneic erythrocytes become tolerant of the injected cells whereas peripheral T cells in the same recipients make a vigorous response to the injected antigen. Results are herein presented of experiments on the effect of splenectomy on the induction of thymocyte tolerance produced in this way. Splenectomy performed either immediately before the first injection of erythrocytes, or between the two injections, completely prevented tolerance induction and tolerance was still incomplete when splenectomy was performed as late as a few hours after the second injection of tolerogen. Sham splenectomy had no effect on the erythrocyte-induced thymocyte tolerance. The results demonstrate an essential role for the spleen in the tolerization of thymocytes in this system. Possible mechanisms and the implications for self tolerance are discussed.

We use molecular mechanics to calculate the conformational properties of a cyclic urea mimetic of alpha-chymotrypsin proposed, but not yet synthesized, by Cram and co-workers. We find that, in order to bring the structural elements of the catalytic triad into a spatial orientation suitable for proton transfer, the proposed enzyme mimetic must adopt a highly strained conformation. We redesign that part of the molecular architecture holding the catalytic triad in position and suggest two alternative enzyme mimetics. Of these, we find that the mimetic containing a fused ring structure positions the components of the catalytic triad at reasonable distances for proton transfer. We study the effect of these structural alterations on the recognition pattern presented by the enzyme mimetic to the substrate, as illustrated by the molecular electrostatic potential of the artificial enzyme.

The intravenous injection of large doses of xenogeneic erythrocytes into rats completely abrogated the ability of thymocytes from such animals to provide help for antierythrocyte antibody responses in an adoptive transfer system. Thymocyte tolerance developed at a time when the thymocyte donors were producing antibody to the tolerizing antigen, and spleen helper T cells were not tolerized by the injection protocol. A minimum of two injections of 1 ml of packed erythrocytes, spaced 4 - 5 days apart, was required to induce loss of helper activity. Tolerance was fully developed within 16 h of the last injection of antigen. Helper activity recovered over a 24-h period starting 5 days after this injection but could be delayed by giving further injections of antigen. These results suggest that the intrathymic pool of cells with assayable helper activity turns over in about one day and that precursors of this pool are probably also tolerable. Suppressor cells could not be detected in tolerant thymocyte populations indicating that the loss of helper activity was either a consequence of clonal inactivation or that an antigen-specific mechanism existed for the recruitment of helper cells from the thymus. The significance of these findings to the acquisition of self-tolerance is discussed.

Large underestimates of the limitation to photosynthesis imposed by stomata can occur because of an error in the standard method of calculating average substomatal pressures of carbon dioxide when heterogeneity of those pressures occurs across a leaf surface. Most gas exchange data supposedly indicating nonstomatal inhibition of photosynthesis by water stress could have this error. However, if no stomatal closure occurs, any reduction in photosynthesis must be due to nonstomatal inhibition of photosynthesis. Net carbon dioxide exchange rates and conductances to water vapor were measured under field conditions in upper canopy leaves of tomato plants during two summers in Beltsville, Maryland, USA. Comparisons were made near midday at high irradiance between leaflets in air with the ambient water vapor content and in air with a higher water content. The higher water content, which lowered the leaf to air water vapor pressure difference (VPD), was imposed either one half hour or several hours before measurements of gas exchange. In both seasons, and irrespective of the timing of the imposition of different VPDs, net photosynthesis increased 60% after decreasing the VPD from 3 to 1 kPa. There were no differences in leaf conductance between leaves at different VPDs, thus transpiration rates were threefold higher at 3 than at 1 kPa VPD. It is concluded that nonstomatal inhibition of photosynthesis did occur in these leaves at high transpiration rate.

Light-saturated photosynthetic rates at air levels of carbon dioxide were measured about weekly in upper canopy leaves of two soybean cultivars grown at stand densities of 40 and 100 plants per square meter. Early in the season, when leaf area indices differed between stand densities, plants of both cultivars grown at high stand density had photosynthetic rates which averaged 23% lower than plants at low stand density. Later in the season, when there were no differences in leaf area index between stand densities, there were no differences in photosynthetic rates in the cultivar Kent, but rate differences of about 14% persisted in the cultivar Williams. In Williams mainstem leaves emerged into full sunlight later in their development at high than at low stand density. In both cultivars the oldest fully exposed leaves were photosynthetically immature for much of the season, as higher rates could be achieved by lower leaves which were shaded in situ. The results identify shading of young developing leaves and photosynthetic immaturity of fully exposed leaves as factors limiting canopy photosynthesis in soybeans, and indicate cultivar differences in how much high stand density reduces photosynthetic capacity.

Net photosynthetic rates and mesophyll conductances were measured under standardized conditions for leaves of two C3 and one C4 annual species grown at temperatures of 20 to 32°C. Plants were grown with varying day and night temperatures, and also at constant temperatures equal to all the day and night temperatures used. Plants were grown with 8, 12, and 16 hours of light per day. This design allowed determination of whether photosynthetic characteristics were best correlated with day, night, mean, or time-weighted mean temperatures, The results showed that for Glycine max (L.) Merr. (C3) night temperature was most important in determining photosynthetic characteristics, while in Helianthus annuus L. (C3) and Amaranthus hypochondriacus L. (C4) the time-weighted mean temperature was most important. The results for all species were consistent with the hypothesis that development of photosynthetic characteristics is related to a balance between the rate of leaf expansion and the rate of photosynthesis under the growth conditions.

A number of tertiary and secondary homoallylic amines, i.e. (Z)- and (E)-4-(4-bromophenyl)-4-(3-pyridyl)-3-buten-1-ylamines, were synthesized in diastereomerically pure forms. The compounds were evaluated as neuronal norepinephrine (NE) and serotonin (5-HT) uptake inhibitors under in vitro and ex vivo conditions and compared with the tricyclics amitriptyline and nortriptyline having homoallylic side chains and with the corresponding diastereomers in the zimeldine series having allylic side chains. The Z isomers of the new homoallylic derivatives (3Z, 4Z) were specific 5-HT uptake inhibitors in analogy with the corresponding allylic derivatives zimeldine (1Z) and norzimeldine (2Z). Likewise, the selectivity profile of the homoallylic (3E, 4E) and the allylic (1E, 2E) derivatives was comparable. In general, the homoallylic compounds were less potent inhibitors than their allylic counterparts. The similarities and discrepancies were evaluated in terms of conformational preferences determined by CAMSEQ molecular mechanics calculations. Homonorzimeldine (4Z) can accommodate energetically favored, but less populated, conformations having amino nitrogen atom to aromatic ring center distances comparable to those in norzimeldine. These facts correlate to retained 5-HT selectivity but diminished potency of 4Z compared to 2Z.

Mesophyll resistance to CO(2) uptake was calculated from gas exchange data on intact leaves of 12 species of woody plants. Plants studied were native to habitats ranging from streamsides to deserts. Gas exchange measurements were made at light saturation and constant temperature to eliminate possible effects of light and temperature on estimates of mesophyll resistance. Cuticular transpiration was measured and used in calculation of stomatal resistances from whole leaf transpiration rates. In all species examined, an increase in mesophyll resistance was observed as leaves dried. The increase in mesophyll resistance in all cases occurred at the same water potential as the initial decline in net photosynthesis, and was accompanied by an increase in stomatal resistance.