Effects of dehydration on the vasopressin response to immersion

Nine healthy volunteers underwent three experimental procedures in random order. The protocols were 4 h of thermal dehydration followed by 2 h of head-out water immersion, 4 h of thermal dehydration followed by 2 h of chair rest, and 6 h of rest in the supine position. Four hours of heat exposure (50 degrees C) resulted in a body weight loss of approximately 3.5%. Plasma osmolality rose by approximately 5 mosmol/kg, mean arterial pressure (MAP) decreased from 85 to 78 mmHg, and body temperature increased from 36.8 to 38.6 degrees C. As a consequence of the combined action of hypertonicity, hypovolemia, hypotension, and hyperthermia, plasma arginine vasopressin (AVP) increased from 2.1 to 8.1 pg/ml after 4 h thermal dehydration. Changes in body weight, plasma osmolality, body temperature, and MAP were similar after either a subsequent 2 h of water immersion or 2 h of chair rest. However, during chair rest plasma AVP remained elevated (8.4 pg/ml), whereas during immersion plasma AVP decreased from 8.1 to 4.7 pg/ml. This was probably due to the central hypervolemia induced by immersion. Our results support the hypothesis that central hypervolemia rather than hypotonicity is the primary stimulus for AVP suppression during water immersion in dehydrated subjects. During the early immersion period hypoosmolality might contribute to the AVP suppression.     

Juvenile hormone biosynthesis and oocyte development in adult female Blattella germanica: Effects of grouping and mating

The roles of grouping and mating in modulating the activity of the corpora allata (CA) in adult female cockroaches were investigated using the in vitro radiochemical assay of juvenile hormone (JH) biosynthesis. Isolated virgin females have longer, asynchronous cycles of CA activity and oocyte maturation than do isolated females mated on day 8. Three factors were identified as the major contributors to this difference: (1) an experimental artifact of selection for sexually receptive females, (2) a positive effect of grouping on JH synthesis and oocyte maturation, and (3) a positive effect of copulation on oviposition and retention of the ootheca. Mated females constitute a subpopulation of receptive females that differ significantly from other females by having higher rates of JH synthesis prior to mating. The relative importance of such selection is substantial when the rate of mating is low, as in experiments with isolated females that are exposed to males for a short period of time. Long-term exposure of females to males introduces a grouping effect, which obscures any additional effect of mating on CA activity and oocyte development. However, mating influences ootheca formation and its retention. The effect of grouping can be mimicked in isolated females by transection of the nerves connecting the CA–corpora cardiaca complex to the brain, suggesting that in this insect isolation causes brain inhibition of the CA, and grouping provides disinhibitory stimuli that release the CA from brain inhibition.     

Stand microclimate and physiological activity of tree leaves in an oak-hornbeam forest

Summary In an uneven-aged, multi-species oak-hornbeam forest at Báb, SW Slovakia (former IBP Forest Research Site), a series of micrometeorological and ecophysiological measurements started in 1985. The aims of the work are to improve understanding of physiological processes (photosynthesis, respiration, and transpiration) of adult trees and stand microclimate, to collect data for simulation of the canopy (stand) photosynthesis and for ecological synthesis of the functioning of the forest ecosystem. In this paper, photosynthetically active radiation (PAR), air temperature (AT) and relative humidity (RH), wind speed (WS), and CO₂ concentration ([CO₂]) in and above the forest are characterized for the fully leaved season, using diurnal courses, vertical profiles and isodiagrams (isopleths). Approximately 50% of incident PAR was absorbed by the upper 4–5 m layer of leaves and only approximately 5% or less penetrated to the forest floor. Vertical gradients of AT and RH were generally low, but large differences in diurnal ranges of AT and RH were observed between vertical levels. The upper leaf canopy greatly reduced WS, and at a height of about 14 m above the ground it was close to zero. The highest diurnal [CO₂] maximum and variations occurred at 1 m above the ground, and the lowest above the forest. In good light conditions in the forest, the entire leaf canopy (overstorey and understorey canopy) is a large sink of CO₂. At night the forest stand is a source of CO₂, the largest internal source being the soil and forest floor.     

Carbohydrates on human Fc gamma receptors. Interdependence of the classical IgG and nonclassical lectin-binding sites on human Fc gamma RIII expressed on neutrophils

To explore the molecular basis for the ability of aggregated IgG to block the phagocytosis by human polymorphonuclear leukocytes of Con A-opsonized E and of nonopsonized Escherichia coli with mannose-binding adhesins, we examined specific aspects of the glycoprotein structure of both the 40- to 43-kDa receptor for the Fc portion of IgG (Fc gamma RII) and the 50- to 78-kDa receptor for the Fc portion of IgG (Fc gamma RIIIPMN) from human polymorphonuclear leukocytes. Fc gamma RIIIPMN isolated by both mAb and ligand affinity chromatography, but not Fc gamma RII, binds Con A in Western blots. This binding is specifically inhibitable by alpha-methylmannoside. Digestion of Fc gamma RIIIPMN by recombinant endoglycosidase H, which is specific for high mannose-type (Con A-binding) oligosaccharides, alters the epitope recognized by mAb 3G8 in or near the IgG ligand-binding site of the receptor. Similarly, the ability of Fc gamma RIIIPMN to bind human IgG ligand is sensitive to endoglycosidase H digestion. Our data indicate that ligands other than the classical IgG opsonins can bind to human Fc gamma RIIIPMN per se through lectin-carbohydrate interactions. Furthermore, Fc gamma RIIIPMN contains a high mannose type oligosaccharide chain which contributes importantly to the integrity of the classical IgG ligand-binding site. Thus, specific glycosylations of the receptor are important for both classical and nonclassical engagement of Fc gamma RIII and may play a role in determining the properties of the ligand-binding site.     

Metabolism of 20-hydroxyeicosatetraenoic acid by cyclooxygenase. Formation and identification of novel endothelium-dependent vasoconstrictor metabolites

We recently demonstrated that 20-hydroxyeicosatetraenoic acid (20-HETE) constricts rat aortic rings. The contractile response was partially dependent on the presence of endothelium and was abolished by pretreatment of the rings with either indomethacin or the endoperoxide/thromboxane receptor antagonist, SQ29548. Addition of GSH or SnCl2 to the organ bath diminished the contractile response of 20-HETE, whereas preincubation of the rings with a thromboxane synthase inhibitor did not affect the 20-HETE induced contractions. Short time incubation (2 min) of 20-HETE with ram seminal vesicle microsomes in the presence of p-hydroxymercurybenzoate yielded metabolites which migrated similarly on thin layer chromatography to the known arachidonate endoperoxides prostaglandin (PG) G2 and PGH2 and possess vasoconstrictory properties. The vasoconstriction was dose-dependent with a half-life of approximately 6.3 +/- 0.6 min. Addition of SQ29548 to the aortic ring bath 1 min after metabolite elicited vasoconstriction produced immediate relaxation. Furthermore, pretreatment of the rings with SQ29548 totally abolished the contraction. SnCl2 reduction of the metabolites produced in incubation of rat seminal vesicles with 20-HETE and p-hydroxymercurybenzoate resulted in a single radioactive peak which was further identified by gas chromatography/mass spectrometry as 20-hydroxy-PGF2 alpha. The inhibitory effect of SQ29548, the appearance of labile metabolites with a half-life of approximately 6 min and the production of 20-hydroxy-PGF2 alpha by SnCl2 reduction clearly indicate that the vasoconstrictor metabolites of 20-HETE are the labile endoperoxides of 20-HETE, 20-hydroxy-PGG2, and 20-hydroxy-PGH2.     

The Roles of CRE, TRE, and TRE-Adjacent S1 Nuclease Sensitive Element in the Regulation of Tyrosine Hydroxylase Gene Promoter Activity by Angiotensin II

Abstract: The cis elements mediating activation of the tyrosine hydroxylase gene by angiotensin II were examined by transfecting tyrosine hydroxylase promoter-luciferase constructs into cultured bovine adrenal medullary cells. Angiotensin II-responsive elements are located within −54/+25-bp and −269/−55-bp promoter regions and were identified, respectively, as cyclic AMP (CRE)- and 12- O -tetradecanoylphorbol 13-acetate responsive element (TRE)-like sequences. Unlike CRE, TRE also supports basal promoter activity. Mutations of TRE or CRE that reduced angiotensin II stimulation abolished in vitro binding of nuclear proteins to those elements, suggesting that proteins forming CRE- and TRE-inducible complexes may mediate angiotensin II stimulation. The TRE is adjacent to a dyad symmetry element. Those two sites form a common regulatory unit in which the dyad symmetry element acts as a repressor of the TRE site. Isolated dyad symmetry element did not bind nuclear proteins in vitro. In supercoiled DNA it exhibited S1 nuclease sensitivity and was recognized by a DNA cruciform-specific antibody consistent with the extrusion of a cruciform structure that overlaps with the TRE. A mutation that abolished formation of the cruciform correlated with a loss of repressor activity. We propose a novel model of tyrosine hydroxylase gene regulation in which functions of the TRE are modulated via structural transition in the adjacent DNA.     

Overall Informativity,OI, in DNA Polymorphisms Revealed by inter-AluPCR: Detection of Genomic Rearrangements

We studied two systems of multilocus markers revealed by PCR using primers directing amplification betweenAlurepeats in a tail-to-tail orientation. Genomic polymorphisms were detected as the presence or absence of the electrophoretic bands representing DNA fragments of a given length. A total of 104 such fragments segregating as Mendelian markers in a panel of eight CEPH families were analyzed by two-point linkage analysis. Fifty-one of these fragments were localized with respect to CEPH markers; they represented 33 loci, 7 of which were multiallelic. Locus-specific oligonucleotides were developed and used as hybridization probes to identify the mapped loci within a complex pattern of inter-AluPCR products. A great proportion of inter-AluPCR polymorphisms represented length variants within amplified DNA segments, while others were presumably due to mutations within the priming sites. To describe the expected number of informative loci per typing experiment we introduced a parameter called overall informativity (OI), which provides a single measure of the multiplex ratio and the informativity of markers contributing to a multilocus system (OIof a single locus is equivalent to its heterozygosity and cannot exceed 0.5 for a biallelic codominant marker). HighOIvalues (5.8 and 11.5) of the two presented systems of inter-AluPCR markers of random chromosomal distribution render them suitable for mapping genomic rearrangements such as genomic deletions in tumoral tissues. This was illustrated by the detection of loss of heterozygosity in the 9q22–qter region in sporadic colon cancer.