Absent aldosterone response to metoclopramide in patients with high spinal cord transection: evidence that metoclopramide stimulates aldosterone secretion through central pathways

This study evaluates dopaminergic regulation of aldosterone secretion in 6 patients with high spinal cord transections. Administration of the dopamine antagonist metoclopramide resulted in a marked rise in plasma aldosterone and 18-hydroxycorticosterone levels in 12 normal individuals, but no change in plasma levels of these zona glomerulosa corticosteroid products in spinal cord patients. Spinal cord transected patients also did not have the rise in plasma renin activity that was observed in normals following metoclopramide administration. Basal levels of aldosterone, 18 hydroxycorticosterone, corticosterone and renin activity as well as the aldosterone responses to graded dose infusion of adrenocorticotropin were similar in the spinal cord patients and the normals. These data suggest that dopaminergic regulation of adrenal zona glomerulosa corticosteroid and renal renin secretion is absent in patients with high spinal cord transections, suggesting that intact neural pathways from the central nervous system are necessary for metoclopramide stimulation of aldosterone and renin secretion in men. Since basal plasma aldosterone levels were normal in spinal cord transected patients, it appears that the absence of dopaminergic control does not result in elevated secretion.     

Human impact on vegetation at the Alpine tree-line ecotone during the last millennium: lessons from high temporal and palynological resolution

Three mires and a small lake in the Swiss and Austrian Alps were studied palynologically at high resolution, covering the last 1,000, 400, 50 and 1,200 years, respectively. Methodological lessons include: (1) Sub-decadal resolution in upper, little-decomposed peat layers reveals recurrent marked fluctuations in both percentages and influx of regional tree-pollen types, reflecting variations in pollen production rather than in plant-population sizes. (2) Intermittent, single-spectrum pollen maxima in samples of sub-decadal resolution indicate pollen transport in clumps. This type of pollen transport may remain unrecognized in sections with lower sampling resolution, which may then lead to inappropriate interpretation in terms of plant-population sizes. (3) The detection of short-lived phases of human impact in decomposed peat requires sampling intervals as close as 0.2 cm. (4) PAR (pollen influx) may reflect vegetation dynamics more faithfully than percentages. Reliable PAR, however, is difficult to achieve in Alpine mires due to past human impact on peat growth, even when complex depth–age modelling techniques are used. Critical comparison of PAR with percentages is therefore essential. (5) Careful consideration of spatial scales in pollen signals (local–regional and subdivisions) is essential for a realistic palaeo-ecological interpretation. Results in terms of past human impact on vegetation are summarized as follows: (1) Trends in pollen types reflecting regional human action are in general agreement with earlier findings for the western Swiss Alps, allowing for regional differences. (2) All mires in the Alps investigated here and in an earlier study experienced human impact during the last millennium. The studied small lake, lying in sub-alpine pasture, records forest dynamics at a lower elevation since a.d. 800.     

Drosophila ATP6AP2/VhaPRR functions both as a novel planar cell polarity core protein and a regulator of endosomal trafficking

Planar cell polarity (PCP) controls the orientation of cells within tissues and the polarized outgrowth of cellular appendages. So far, six PCP core proteins including the transmembrane proteins Frizzled (Fz), Strabismus (Stbm) and Flamingo (Fmi) have been identified. These proteins form asymmetric PCP domains at apical junctions of epithelial cells. Here, we demonstrate that VhaPRR, an accessory subunit of the proton pump V‐ATPase, directly interacts with the protocadherin Fmi through its extracellular domain. It also shows a striking co‐localization with PCP proteins during all pupal wing stages in Drosophila. This localization depends on intact PCP domains. Reversely, VhaPRR is required for stable PCP domains, identifying it as a novel PCP core protein. VhaPRR performs an additional role in vesicular acidification as well as endolysosomal sorting and degradation. Membrane proteins, such as E‐Cadherin and the Notch receptor, accumulate at the surface and in intracellular vesicles of cells mutant for VhaPRR. This trafficking defect is shared by other V‐ATPase subunits. By contrast, the V‐ATPase does not seem to have a direct role in PCP regulation. Together, our results suggest two roles for VhaPRR, one for PCP and another in endosomal trafficking. This dual function establishes VhaPRR as a key factor in epithelial morphogenesis.     

Interaction of phosphoinositide cycle intermediates with the plasma membrane-associated clathrin assembly protein AP-2.

Several components of the phosphoinositide cycle have been found to interact specifically and at physiological concentrations with the plasma membrane-associated clathrin assembly (adaptor) protein AP-2. These include phosphatidylinositol 4,5-bisphosphate and inositol 1,4,5-trisphosphate, which are present at the plasma membrane, as well as other polyphosphoinositols. ATP and other polyphosphate molecules complete with the polyphosphoinositols, however, they are at least 80-fold less potent. Also, the effect of ATP, unlike the polyphosphoinositols, is blocked by physiological concentrations of Mg2+. Photoaffinity labeling of AP-2 by [alpha-32P]8-azidoadenosine 5'-triphosphate and its competition by polyphosphoinositols has been used to identify the alpha subunit of the AP-2 complex as the site of specific interaction with the polyphosphoinositols and to confirm direct ultrafiltration binding experiments. Proteolytic dissection of the labeled AP-2 demonstrated that binding occurred exclusively on the N-terminal portion of the alpha subunit. Interaction of purified AP-2 with sub-microM concentrations of polyphosphoinositols has inhibitory effects on a novel AP-2 self-association described in the accompanying paper (Beck, K. A., and Keen, J. H., J. Biol. Chem. 266, 4437-4441), and at higher concentrations on the binding of AP-2 to dissociated clathrin trimers as well as AP-2-mediated clathrin coat assembly. Review of the literature shows that several physiological stimuli that are known to result in increased coat pit formation in intact cells correlate with increased phosphoinositide turnover. These in vivo correlations and the in vitro observations reported here suggest that coated membrane and phosphoinositide cycles may be interdependent within cells.     

The use of biochemical parameters for a qualitative and quantitative assessment of ischemic damage to the small-intestinal mucosa

Lactate dehydrogenase has been measured in the small-intestinal mucosa in order to assess its value as a marker for the effects of ischemia and of reperfusion. The decrease in specific activity of the enzyme illustrates the deleterious effect of reperfusion on the quality of the remaining epithelial cells. However, this parameter fails to detect the loss of epithelial cells, which is the major event during ischemia as well as during reperfusion. In contrast, the expression of enzyme activity per g protein of the underlying intestinal muscle allowed us, in addition, to assess quantitatively the loss of epithelial cells, in good agreement with the histological data.