GLOMERULAR FILTRATION RESPONSE TO ACUTE PROTEIN LOAD

838 fraction exaggerates our procedural deficiency because no account is taken of the fact that the samples loaded onto the DEAE columns also had no detectable infectivity and that these columns per se have 2 a considerable capacity for removing infectivity.2 Our paper showed that the biochemistry of the extraction can be run safely, even when massive amounts of infectivity are present in the starting material (at least 1000 times the potential infectivity in an HGH production run). Our replicated results clearly showed a progressive reduction of infectivity in successive stages of the protocol, but it is important to emphasise that the reduction is probably by removal of infectivity rather than by inactivation. In translating the degree of safety of our model runs into any assurance that HGH production methods have been or will be safe, there are many weaknesses to be considered of much more importance than Brown’s point. Some of these need to be mentioned in view of many questions which we have been asked. Our experiments showed that processes such as membrane and gel filtration remove considerable amounts of infectivity: the latter (G 100 column) may have been able to remove much more infectivity than the very reduced amount loaded at this late stage of the protocol. Furthermore, although on theoretical grounds the final ion-exchance column would be expected to be capable of adsorbing infectivity, we were unable to demonstrate this because the material we loaded had already lost all detectable infectivity. Although the adsorption of infectivity onto filters and column materials is potentially a great safeguard against contamination of the hormone end product, the fact that infectivity may well be concentrated on such materials makes them potentially hazardous in their own right. If decontamination is not employed before disassembly, reassembly, re-packing, and so on, these processes represent a serious source of potential environmental contamination which could affect an otherwise clean end product. Since little is known of the maximum adsorptive capacity of these systems for infectivity there exists the problem of deciding a safe working life for each column, before it becomes saturated and infectivity starts to leach into the product. If very high standards are not adhered to there will be further opportunities for large aggregates of infectivity to "leapfrog" down the production process from spillages, contamination of hands, inadequately decontaminated equipment and reagents, or failure to handle the lyophilised end product by the rigorous aseptic standards that are necessary. Brown’s comments may divert attention from what was our crucial conclusion-namely, that the greatest risk from agents such as that of CJD, in the production of HGH from human pituitary glands, is likely to be through cross-contamination between stages of the process. This will arise from lack of appreciation of the extreme aseptic standards which are necessary. AFRC and MRC Neuropathogenesis Unit, West Mains Road, Edinburgh EH9 3JF

D. M. TAYLOR A. G. DICKINSON

P, Rohwer RG, Gajdusek DC. Sodium hydroxide decontamination of Creutzfeldt-Jakob disease virus. N Engl J Med 1984; 310: 727. Hunter GD, Millson GC. Studies on the heat stability and chromatographic behaviour of the scrapie agent. J Gen Microbiol 1964; 37: 251-58.

1 Brown

2.

GLOMERULAR FILTRATION RESPONSE TO ACUTE PROTEIN LOAD

SIR,-Dr Rodriguez-Iturbe and colleagues (Aug 31, p 461) describe the acute effect of protein load on glomerular filtration rate (GFR) in healthy volunteers, in kidney donors, and in patients who had apparently recovered from poststreptococcal glomerulonephritis. We report here our preliminary findings in a study of the effect of protein on GFR in healthy subjects. We have investigated the effect of 90 g meat protein and non-meat (milk) protein on the GFR in ten healthy men aged 26-41 (51-73 kg) who had no evidence of renal disease. At the beginning of the study the men drank 500 ml water and thereafter drank 200 ml every half-hour; urine was collected half-hourly. Five men consumed 90 g protein as lightly cooked red meat (raw weight 540 g) and eight (in nine experiments) consumed 100 g non-meat protein (’Casilan’, Glaxo) containing 90 g protein, after a control period. In 3 of the

Changes in creatinine clearance after ingestion of meat protein. Vertical bars indicate SEM. *p<0-05, **p<0-01, ***p<0-001, cantly different from pre-meal clearance by paired t test.

or

milk

signifi-

subjects in the casilan study and in all five in the meat study blood samples were taken half-hourly. In the others one blood sample was taken. Plasma and urine were analysed for creatinine by an automated Jaffe reaction. Changes in creatinine clearance from the mean pre-protein value were calculated and analysed by paired t test. Meat protein caused a significant increase in creatinine clearance 11/2 hours after ingestion and clearances remained high after 4 hours (figure). Non-meat protein did not affect creatinine clearance. The increase in creatinine clearance seen here after ingestion of 90 g of meat protein differs in magnitude and duration from that reported by others, who observed increases of 60-68% (RodriguezIturbe et al) and 63%,1 whereas a sustained but smaller increase (18%) was seen in2 our study. This sustained increase was similar to that seen in dogs.2 The failure of non-meat protein to increase the GFR could be due to differences in aminoacid composition.z In view of the possible and importance of protein in the development of in the management of chronic renal it is important to be aware of the possible differences between different kinds of protein.

disease lomerulosclerosis ,4

We thank the volunteers and Mrs Priscilla Chin, Mr David Lo, and the staff of department of chemical pathology for technical assistance.

Department of Chemical Pathology, Chinese University of Hong Kong

G. JONES

Department of Chemical University of Leeds

KAREN LEE

Pathology,

Department of Chemical Pathology, Chinese University of Hong Kong, Hong Kong

R. SWAMINATHAN

1. Bosch JP, Saccaggi A, Lauer A, Ronco C, Belledonne M, Glabman S. Renal functional reserve in human Effect of protein intake on glomerular filtration rate. Am J Med 1983; 75: 943-50. 2. Lee K, Summerhill RA. Glomerular filtration rate following administration of individual amino acids in conscious dogs. Quart J Exp Physiol 1982; 67: 459-65. 3. Rosman JB, ter Wee PM, Meijer S, Piers-Becht TPhM, Sluiter WJ, Donker AbJM. Prospective randomised trial of early dietary protein restriction in chronic renal failure. Lancet 1984; ii: 1291-95. 4. Brenner BM, Meyer TW, Hostetter TH. Dietary protein intake and the progressive nature of kidney disease: The role of hemodynamically mediated glomerular injury in the pathogenesis of progressive glomerular sclerosis in aging, renal ablation and intrinsic renal disease. N Engl J Med 1982; 307: 652-59.

PROTEINURIA AND BLOOD PRESSURE IN KIDNEY DONORS

SIR,-Dr Robitaille’s report (June 8, p 1297) and Dr Zucchelli’s letter (July 27, p 212) raise the question of long-term sequelae of unilateral nephrectomy; this matter is very important in clinical transplantation, especially from living related donors. As part of a study of the characterisation (by sodium dodecylsulphatepolyacrylamide gel electrophoresis, SDS-PAGE) of urinary proteins excreted by healthy volunteers (6 male and 5 female, aged 41±4) we studied 20 kidney donors (11 male and 9 female, aged