Methods of measuring available nutrients in West Indian soils

Summary Methods of measuring available N have been compared using response and uptake data from maize grown on 155 West Indian soils in greenhouse experiments. Total soil N and Cornfield's alkaline hydrolysable N gave best estimates of available N when all soils were considered together. Correlations between test data and N uptake were best for acid soils, for soils with large cation exchange capacities and for soils with between 80 and 99 per cent base saturation. Differences between correlations for soils from different islands could usually be related to these soil properties.     

THE SUMMER CONDITION OF THREE EASTERN TRANSVAAL RESERVOIRS AND SOME CONSIDERATIONS REGARDING THE ASSESSMENT OF TROPHIC STATUS

SUMMARY

Summer temperature, oxygen and light penetration profiles in the Da Gama, Klipkopje and Witklip Reservoirs are presented. Analysis of waters from different depths showed the presence of chemical stratification despite the absence of clear thermal stratification. An algal bioassay procedure also confirmed the presence of increasing quantities of available nutrients with depth in all three reservoirs. The significance of the results in assessing trophic status is discussed and it is concluded that for South African impoundments, an anaerobic hypolimnion is not exclusively associated with eutrophy.     

Characterization of sodium transport in gustatory epithelia from the hamster and rat

The transduction of sodium salts occurs through a variety of mechanisms, including sodium influx through amiloride-sensitive sodium channels, anion-dependent sodium movement through intercellular junctions and unidentified amiloride-insensitive mechanisms. Characterizations of sodium transport in lingual epithelium mounted in Ussing chambers have focused almost exclusively on epithelia containing only fungiform taste buds. In the present study we have investigated sodium transport by measuring NaCl-induced short-circuit current from lingual epithelia containing fungiform, foliate, vallate and palatine taste buds in the hamster and the rat. All areas show measurable sodium transport, yet significant differences were noted between the epithelia from the rat and the hamster and among the different epithelia within a single species in terms of current density, transepithelial resistance and mucosal amiloride sensitivity. In general, epithelia from the anterior tongue were of a lower resistance and transported sodium more effectively than from the posterior tongue. Moreover, fungiform- and vallate-containing epithelia in the rat had a greater current density than did the corresponding tissues in the hamster. Amiloride sensitivity also differed between the rat and the hamster. In the hamster all gustatory areas showed some amiloride sensitivity, while in the rat the vallate-containing epithelia were devoid of amiloride- sensitive sodium transport. The results are consistent with the interpretation that all chemosensitive areas may participate in the detection of salts but the degree of salt transport and the mechanism of transport is variable among different lingual epithelia and different species.      

Determination of bumetanide in the plasma of non-human primates by high-performance liquid chromatography

A simple, sensitive and specific method for the determination of bumetanide in the plasma of non-human primates has been developed using high-performance liquid chromatography in a reversed-phase mode. The limit of accurate measurement for bumetanide in plasma was 1 ng/ml although lower concentrations could be detected. The method has been applied to plasma samples obtained from cynomolgus monkeys after intravenous doses of bumetanide of 0.03 mg/kg. In this species, mean plasma concentrations declined from 300 ng/ml at 2 min after dosing to 1 ng/ml at 180 min; the half-life of the terminal linear phase was 43 min.