1. A rapid colorimetric and apparently specific micromethod for the determination of total glutathione in small amounts of tissue is described. Generally, less than 30mg. of tissue is sufficient and this is homogenized in ice-cold 3% metaphosphoric acid. The product is filtered through sintered glass and neutralized or diluted before being added to a cuvette containing phosphate buffer, pH7.1, 5,5'-dithiobis-(2-nitrobenzoic acid), EDTA and glutathione reductase. Addition of NADPH(2) to the system initiates a progressive reduction of 5,5'-dithiobis-(2-nitrobenzoic acid) by catalytic amounts of GSH, and this causes a colour increase at 412mmu. The rate of this change, calculated over 5min., is proportional to the total amount of glutathione present, and consequently unknown concentrations may be determined by reference to standards. 2. A preparation (based on that of Racker, 1955) of a suitable sample of glutathione reductase from yeast is described. 3. A less specific and less sensitive determination of extracted thiol groups with 5,5'-dithiobis-(2-nitrobenzoic acid) at pH8.0, based on observations of Ellman (1959) and Jocelyn (1962), is also described. 4. Although the precise nature of the reaction is not known, evidence is put forward to support a process of cyclo-reduction. GSSG is reduced enzymically to GSH, which reacts with 5,5'-dithiobis-(2-nitrobenzoic acid) to produce a coloured ion: [Formula: see text] (E(max.) 412mmu) and a mixed disulphide. This disulphide reacts with further quantities of GSH to liberate another ion and GSSG, which then re-enters the cycle.

Diuretics can result in various undesired biochemical changes, such as impotence, skin rashes, nausea, dizziness and lethargy as well as subjective side effects. The side effects are mostly predictable, their effects depending on both the circulatory blood volume and on the transport of water and solute in the renal tubules. Two of the commonest side effects are mild hypovolaemia, when any diuretic is used, and mild hypokalaemia when the non-potassium-sparing diuretics, such as thiazides and frusemide are used. Its occurrence is dose dependent and can be corrected by potassium supplements, but potassium-retaining diuretics, which also correct the often associated fall in serum magnesium, are preferable. Many reports link hypokalaemia with cardiac arrhythmias, but some dispute this association in the absence of the concomitant use of digoxin. Hyponatraemia rarely occurs, but can be life threatening. Calcium excretion is markedly reduced, but unlike other electrolyte disturbances from diuretics, this may be valuable: some suggest diuretics have an anti-osteoporotic action. Diuretics increase glucose and insulin resistance and should be used sparingly in diabetics. They rarely cause a non-ketotic hyperosmolar coma. Urate is raised, but clinical gout is not common. Cholesterol elevation has been reported in some studies, but long-term studies indicate that lipid changes are minor. Other rare side effects are not predictable from their pharmacological actions and these include the occurrence of skin rashes, thrombocytopenia, pancreatitis and interstitial nephritis; and ototoxicity from frusemide.

We describe an apparatus modified for the chemiluminescent estimation of nitrogen in biological and clinical samples. Analytical characteristics have been assessed and results compared with those by the traditional Kjeldahl method. The chemiluminescence method, much faster and more sensitive than the traditional method, is at least as accurate, precise, and reproducible. Costs are low, and the method should find a place in laboratories needing, for example, rapid assessments of nitrogen balance in surgical patients and renal function in patients with renal failure, or estimations of small amounts of specific nitrogen-containing chemical substances in biological samples.

Summary:We describe a case of hypercalcaemia secondary to recurrent malignant phaeochromocytoma. Parathyroid-related protein (PTHrp 1-86) immunoreactivity was identified in plasma and PTHrp was identified by immunocytochemistry in tumour tissue.Correspondence: J.A. Bridgewater

1. A method is described for the serial determination of renal tubular reabsorption of amino acids in the ethanol-anaesthetized rat. It utilizes intravenous radio-labelled inulins, automated amino acid analysis and forced diuresis. 2. Intravenous loading with phenylalanine and infusion of phenylalanine analogues in this preparation decrease reabsorption of endogenous amino acids in accordance with existing concepts of amino acid transport. 3. Maximal tubular reabsorption (Tmax) could not be demonstrated for phenylalanine at plasma concentration below 9 mmol/l. 4. Infusion of phenylalanine analogues into phenylalanine-loaded ('phenylketonuric') rats did not specifically inhibit tubular reabsorption of phenylalanine and it is unlikely that any of the substances tested have a potential therapeutic use in man. 5. p-Guanidino derivatives of phenylalanine, in contrast to p-amino derivatives, appear to cause a dose-related basic aminoaciduria. 6. Consideration of urinary flow rates and sodium excretion suggests that the ethanol anesthesia does not modify amino acid reabsorption through effects on sodium transport or antidiuretic hormone.