Dynamics and distribution of microphytobenthic chlorophyll-a in the Western Scheldt estuary (SW Netherlands)

The temporal dynamics and spatial distribution of microphytobenthic chlorophyll-a in the layer 0–1 cm were determined in the Western Scheldt estuary over the period 1991–1992. Connections between the annually averaged benthic chlorophyll-a and station elevation and sediment composition (as a measure of the hydrodynamic energy caused by currents and waves) were also examined.Microphytobenthic chlorophyll-a showed one main peak in early summer and a smaller peak in autumn. The mean chlorophyll-a concentration of 113 mg Chl-a m^–2 in the upper centimeter is of the same order of magnitude as in other estuarine areas. The average annual primary production of the microphytobenthos has been estimated at 136 g C m^–2 y^–1 The primary production of sediment inhabiting microalgae is at least 17% of the total primary production in the estuary.Considerable differences in annually averaged chlorophyll-a emerges between the stations. These differences are related mainly to the interaction between station elevation and clay content of the sediment.     

Urinary mercury levels in females: Influence of skin-lightening creams and dental amalgam fillings

The influence of application of skin-lightening creams and dental amalgam fillings on the urinary mercury (Hg) level was evaluated in 225 females (ages 17 to 58 years) living in Riyadh, capital of Saudi Arabia. The arithmetic mean of the urinary Hg level was 6.96 ± 20.43 g l, in the range 0 to 204.8 g l. The mean urinary Hg level adjusted by creatinine (Cr) was 11.22 ± 37.23 g g Cr, in the range 0 to 459.37 g g. No significant difference in urinary Hg was noted between the females regarding the use of skin-lightening creams. On the other hand, results showed that urinary Hg concentration was influenced by the use and number of dental amalgam fillings. No women were identified with symptoms or signs that could be attributed to Hg intoxication. Urine analyses for creatinine, urea, uric acid, phosphorus, magnesium, glucose and calcium showed significant correlation with urinary Hg. This suggests that chronic exposure to Hg may be associated with a deterioration of renal function.     

Feedback inhibition of sodium uptake in K+-depolarized toad urinary bladders

Ouabain-blocked toad urinary bladders were maintained in Na⁺-free mucosal solutions, and a depolarizing solution of high K⁺ activity containing only 5 mM Na⁺ on the serosal side. Exposure to mucosal sodium (20 mM activity) evoked a transient amiloride-blockable inward current, which decayed to near zero within one hour. The apical sodium conductance increased in the initial phase of the current decay and decreased in the second phase. The conductance decrease required Ca²⁺ to be present on the serosal side and was more rapid when the mucosal Na⁺ activity was higher. At 20 mM mucosal Na⁺ and 3 mM serosal Ca²⁺ the initial (maximal) rate of inhibition amounted to 20% in 10 min. The conductance decrease could be accelerated by raising the serosal Ca²⁺ activity to 10 mM. The inhibition reversed on lowering the serosal Ca²⁺ to 3 μM and, in addition, the mucosal Na⁺ to zero. Exposure of the mucosal surface to the ionophore nystatin abolished the Ca²⁺ sensitivity of the transcellular conductance, showing that the Ca²⁺-sensitive conductance resides in the apical membrane. The data imply that in the K⁺-depolarized epithelia, cellular Ca²⁺, taken up from the serosal medium by means of a Na⁺-Ca²⁺ antiport, cause feedback inhibition by blockage of apical Na⁺ channels. However, the rate of inhibition is small, such that this regulatory mechanism will have little effect at 1 mM serosal Ca²⁺ and less than 20 mM cellular Na⁺.     

Accurate and efficient method for quantification of urinary histamine by gas chromatography negative ion chemical ionization mass spectrometry

Because of the recognized inaccuracy and unreliability of currently available methods for the quantification of histamine in biological fluids, a method for quantification of urinary histamine by stable isotope dilution assay with negative ion chemical ionization mass spectrometry has been developed. Following the addition of [²H₄]histamine to 1 ml of urine, histamine is extracted into butanol, back-extracted into HCl, derivatized to the pentafluorobenzyl derivative (CH₂C₆F₅)₃-histamine, extracted into methylene chloride, and then quantified with negative ion chemical ionization mass spectrometry by selected ion monitoring of the ratio of ions $\text{m}\text{z}$$\text{430}\text{434}$. Twenty samples can be assayed in 2 days. Precision of the assay is ±2.7% and the accuracy is 97.6%. Lower limits of sensitivity are approximately 100–500 fg injected on-column. This assay provides a very sensitive, accurate, and efficient method for the quantification of histamine in human urine.     

Purification of a human urinary carboxypeptidase (kininase) distinct from carboxypeptidases A, B, or N

A carboxypeptidase which cleaves basic C-terminal amino acids from peptides was purified from concentrated human urine by a three-step procedure: chromatography on Affi-Gel Blue, arginine-Sepharose affinity chromatography, and gel filtration by HPLC on a TSK-G3000SW column. Urinary carboxypeptidase was purified 406-fold with an 11% yield and a specific activity of 49 mumol/min/mg with benzoylglycylargininic acid as substrate. It migrated as a single band of Mr 75,700 in polyacrylamide gel electrophoresis with sodium dodecyl sulfate. It cleaved benzoylglycylarginine, benzoylglycyllysine, benzoylglycylargininic acid, benzoylalanyllysine, and benzoylphenylalanyllysine at different relative rates than human plasma carboxypeptidase N, the Mr 48,000 active subunit of carboxypeptidase N or human pancreatic carboxypeptidase B. Urinary carboxypeptidase did not hydrolyze benzoylglycylphenylalanine, a substrate of carboxypeptidase A, but readily cleaved bradykinin with a Km of 46 microM and a Kcat of 32 min-1. Its activity was enhanced by CoCl2 and inhibited by cadmium acetate, o-phenanthroline, or DL-2-mercaptomethyl-3-guanidinoethylthiopropanoic acid. The enzyme had a pH optimum of 7.0 and its activity dropped at pH 6.0 by 60%. It was stable for at least 2 h at 37 degrees C (pH 8.0) but was unstable at room temperature below pH 4.5. The molecular weight, electrophoretic mobility, and activity of urinary carboxypeptidase was not affected by trypsin. The effect of pH and stability further distinguished the urinary carboxypeptidase from other human carboxypeptidases. Urinary carboxypeptidase was immunologically distinct from carboxypeptidase N when analyzed by the "Western blot" technique. Thus, human urine contains a basic carboxypeptidase, different from known carboxypeptidases, which may be released into the urine by the kidney. Here it could inactivate kinins and other peptides containing a basic C-terminal amino acid.     

Excretion of radiolabeled estradiol in the cat (Felis catus,L): A preliminary report

The time course and end products of estradiol metabolism were studied in the domestic cat, which has been chosen as a model for steroid metabolism studies in nondomestic felidae. Radiolabeled estradiol was injected intravenously into three adult female cats; one had a spontaneous estrus, one was induced with follicle-stimulating hormone, and one had been ovariohysterectomized; feces, urine, and blood were collected daily, and the radioactivity content was determined. Feces and urine contained 47 and 1% of the injected dose (0.33 μCi), respectively. Metabolites appeared earlier in the urine than in feces (d 1 vs d 2 postinjection), and excretion was completed on d 5; no radioactivity was detected in plasma 24 h postinjection. Estradiol metabolites were excreted as unconjugated estrogens (22%) and as conjugates hydrolyzable with β-glucuronidase and acid solvolysis (7 and 50%, respectively); the remaining 14% were not recoverable with any of the above methods. The major portion of the conjugates was estradiol-17β (64–80%) while 11–16% appeared as estrone. Endogenous cycles related to the spontaneous and induced ovarian activity were monitored by observation of estrous behavior, vaginal epithelium cornification, and plasma estradiol determination. The reproductive state of each animal had no effect on the time course or type of metabolite excreted. We found low proportions of injected radioactivity excreted in the urine and high residual levels remaining after hydrolysis and extraction in the feces. These findings suggest that although feces are an abundant source of estradiol metabolite in the cat, and probably in the exotic felidae, development of noninvasive methods for monitoring ovarian cycles in these species will depend on more efficient methods for urine hydrolysis, on the resolution of problems encountered in fecal steroid analysis, or on the identification of metabolites which may be measured directly in the urine without hydrolysis or extraction.     

Effect of distension on ADH-induced osmotic water flow in toad urinary bladder

Summary We recently described a method by which the resistance to water flow of the luminal membrane of ADH-stimulated toad bladder can be quantitatively distinguished from that of barriers lying in series with it. This method requires estimates of both total bladder water permeability (assessed by transbladder osmotic water flow at constant gradient) and luminal membrane water permeability (assessed by quantitation of the frequency of ADH-induced luminal membrane particle aggregates). In the present study we examined the effect of bladder distension on transepithelial osmotic water flow before and during maximal ADH stimulation. Base-line water flow was unaffected by bladder distension, but hormonally stimulated flow increased systematically as bladders became more distended. Distension had no effect on the frequency of ADH-induced intramembranous particle aggregates. By comparing the relationships between aggregate frequency and hormonally induced water permeability in distended and undistended bladders, we found that distension appeared to enhance ADH-stimulated water flow by decreasing the resistance of the series permeability barrier while the apparent water permeability associated with each single luminal membrane aggregate was unaffected. In that bladder distension causes tissue thinning, the series resistance limiting ADH-stimulated water flow appears to be accounted for by deformable barriers within the bladder tissue itself, probably unstirred layers of water.     

The sediment column as a record of trophic status: examples from Bosherston Lakes,SW Wales

Bosherston Lakes are a series of interconnected, mesotrophic to hypereutrophic, artificially-created coastal marl lakes in Dyfed, South West Wales. Progressive eutrophication of the lake system has been produced by a high external phosphorus loading which includes phosphorus-rich effluent from a sewage treatment works (STW) in the catchment of the Lakes.Cores were taken from four sites of varying eutrophic status within the Lakes. In the surface sediment layer, organic C, N and P concentrations generally correlate directly with trophic status and reflect distance from the source of P input. At one site, sediment stratigraphy records a clear transition at 20–15 cm depth, marked by a sharp upward increase in porosity, organic C, N, and P, and iron-associated-P; decreases in organic matter C/N, C/P and N/P ratios; a sharp decrease in carbonate, and a change in the subfossil diatom assemblage. Lead-210 dating indicates that this change occurred in the period 1919 to 1938.The diatom stratigraphy and sediment geochemistry suggest that this transition reflects an increase in trophic status at this site, probably as a result of the influx of nutrient-rich water. This took place when the management of the Stackpole estate surrounding the lake system, fell into decline during the period 1919–1938.     

Paleolimnology of Qilu Hu,Yunnan Province,China

Qilu Hu is a large (A = 36.9 km²), shallow (z_max = 6.8 m) lake that lies at an elevation of 1797 m above msl on the Yunnan Plateau, southern China. Lake waters are hard (Mg = 3.2m eq L^–1, Ca = 1.3 meq L^–1 ), fresh (conductivity = 380 S cm ^–1), and productive (Secchi < 40 cm). An 11-m sediment core has a basal ¹⁴C age of 30960 ± 860 B.P. Sediments between 11 m and 6 m are high in % dry weight, rich in clay components Al₂O₃, Fe₂O₃, K₂O, MgO, and low in organic C (6.1%), carbonate-C (<1.0%), total N (<3.2 mg g^–1), and total S (<-1.7 mg g^–1). Diatoms and pollen indicate open-water conditions between 9.0 m and 6.0 m (1342011790 B.P.). Above 6.0 m, CaCO₃ and organic matter concentrations increase relative to clastics. The transition marks a change to shallow-water conditions as inferred from diatoms and pollen, and probably reflects a shift to drier climate. Uppermost (80-0 cm) red clays were deposited rapidly, probably as a consequence of recent (decades to centuries) riparian disturbances (e.g. agriculture, lake-bottom reclamation, urban development). Dates assigned to events in the Qilu Hu profile are tentative because of potential hard-water-lake error.