Section of Measurement in Medicine
473
cave in which are housed three plastic scintillation detectors; a separate control room contains the electronic equipment for measurement and analysis of the radioactivity. The cave was constructed by excavating an REFERENCES area 6 m deep by 5 m wide into an existing chalk Alexander F W, Clayton B E & Delves H T bank. The excavation was lined and roofed with (1974) Quarterly Journal ofMedicine 43, 89 Delves H T corrugated steel sheets on a steel joist framework, (1976) Clinica ch,imica acta (in press) and then further protected with chalk. The roof Delves H T, Shepherd G & Vinter P (1971) Analyst 96, 260 was weather proofed with 15 cm of sealed Kawaguchi H & Auld D S (1975) Clinical Chlemistry 21, 591 Masironi S concrete. The interior of the cave was lined with (1969) Bulletin ofthe World Health Organization 40, 305 3 mm steel sheets covered with 3 mm lead. The Sharrett A R & Feinleib,M (1 975) Preventive Medicine 4, 20 floor and the walls were then coated with polyWalsh A (1955) Spectrochimica Acta 7, 108 urethane to provide an impervious and easily Wester P O (1971) Acta medica Scandinavica 190, 155 cleaned surface. The detection system was designed for high sensitivity rather than high resolution and therefore has three large plastic scintillation heads, each of which is viewed by two 17.8 cm diameter photomultiplier tubes. To obtain a good approximation to whole-body geometry and to reduce variations due to the Mr M J Vagg redistribution of isotope within the body after (Agricultural Research Council, administration, the heads are arranged symInstitute for Research on Animal Diseases, metrically in a vertical plane around the animal. Compton, Newbury, Berkshire, RG16 ONN) The complete detector assembly is mounted on a rectangular frame carried on tracks in the roof Assessment of Trace Element of the cave. The frame is motor driven and is Metabolism in Farm Animals designed to traverse the length of a cow at a preset speed. In farm animals the estimation of the absorption Signals from the photomultiplier tubes pass to a of a mineral or trace element from the diet is signal mixing unit, then to an amplifier and finally important in the context of 'production disease' to a single channel pulse height analyser and as discussed by Payne (1970). scaler. The absorption of an element can be measured A 144-channel pulse height analyser (Nuclear provided the net retention of a radioisotope of the Enterprises, NE 6900) is used in the initial setting element is known, that is the difference between up of the detector for each isotope to be counted. the input, the quantity administered, and the Method of operation: The cow is restrained in a output or quantity excreted in urine, faces and mobile steel crush which is then drawn into the milk in a period of 7-10 days. However, if the cave of the whole-body counter by means of an element is poorly absorbed this difference is small electric winch. Both forward and reverse scans and cannot be accurately determined because of of the animal are made and a printout obtained the considerable errors involved in the measure- of the total count and the duration of each scan. ment of both input and output of radioisotope. Application of a whole-body counter to the estimaA whole-body counter can measure directly and tion of the absorption coefficient for manganese-54 accurately the retention of a radioisotope of even in the dairy cow: A whole-body counter can a poorly absorbed element and thus give a accurately measure the retention of an oral dose measure of its absorption. The absorption of a radioisotope at various times after its coefficient of the element, defined as the fraction administration but this retention is not equal to of the dietary content of the element absorbed the absorbed fraction of that isotope for two through the gastrointestinal tract, may then be reasons: (1) Because of the unabsorbed isotope calculated from the whole-body retention values still present in the gastrointestinal tract. (2) as described below. Because of the isotope which has been absorbed This paper describes the construction of a but subsequently resecreted. into the gastrowhole-body counter suitable for cattle, and its intestinal tract and excreted in fices. application to the study of the trace element These two factors were taken into account in metabolism of farm animals. this work by oral administration of 54MnCI2 Construction: The Compton whole-body counter followed by an intravenous injection of the same consists principally of a shielded low background radioisotope about one month later, at which
possible with the new developments in atomic spectroscopy, and will no doubt be used more frequently in future studies of trace metals in human diseases.
474
Proc. roy. Soc. Med. Volume 69 July 1976
14
time the radioactivity due to the orar dose had Table I virtually disappeared. Following administration Comparison of the percentage retention of orally administered of radioisotope by either route, the animal was 5'Mn by two cows as determined by whole-body counting (WBC) subjected to whole-body counting at 5 and 12 and conventional balance methods (B) Cow I Cow 2 hours after dosing and then at daily intervals for 15 days. Days alier dosing WBC B WBC B Due to redistribution of radioisotope during 1 77.1 75.6 82.9 85.5 32.8 35.0 43.6 47.6 the first 12 hours after dosing, minor variations 2 12.8 18.2 21.8 28.0 in count rate occurred which resulted in some- 43 5.4 10.3 10.3 16.6 times the 5 hour and sometimes the 12 hour count 5 2.7 7.9 5.5 11.8 indicating the higher apparent retention. The higher measurement was then taken to indicate 100 % retention of radioisotope and all subsequent The use of the gut absorption-resecretion whole-body counts were related to this figure. model provides a more reliable estimate of The whole-body retention curves obtained relative absorption rates because it makes a were then subjected to a mathematical deconvolu- quantitative allowance for the effects of variations tion process using the gut absorption-resecretion in endogenous secretion rate and rate of passage model derived by Sansom (1972). This model is of food through the gut. based on two assumptions: (1) That the quantity In Table I the results obtained for retention of of isotope absorbed during any day is proportional orally administered 54Mn by whole-body counting to the amount of isotope present in the gut on the are compared with those obtained by the conprevious day. (2) That the absorbed isotope is ventional radioisotope balance method. The available for resecretion at the same rate as that results show that there is good agreement for the which has been administered intravenously. first two days after dosing, but that subsequently Fig 1 shows the whole-body retention curves the balance method increasingly oVerestimates of 54.Mn in two cows after oral and intravenous retention. It was this overestimate that previously administration. Net retentions at 13 days derived led to the belief that absorption of manganese from the oral dose retention curves are 0.39 % was of the order of 5 % of dietary content. in Cow 1 and 0.14% in Cow 2. However, the REFERENCES calculated absorption coefficient in Cow I is less Payne M than in Cow 2 and the absorption of 54Mn during (1970) JInternational Review of Fxperimental Pathology 9, 191 13 days is 0.36% and 0.57% respectively. The Sansom B F (1972) In: Assessment of Radioactive Contamination retention curves of the orally administered 54Mn in Man. IAEA, Vienna; p 563 are thus misleading if used as a measure of relative absorption rates in the two cows. The low estimate of absorption in Cow 1 is due to a higher rate of endogenous secretion and faster rate of passage of radioisotope through the gastroDr G S Fell and Dr R R Burns intestinal tract. (Royal Infirmary, Glasgow, G4 OSF) Zinc
Zinc metalloenzymes are of basic importance to many intracellular biochemical mechanisms; in particular they regulate various stages of protein and nucleic acid synthesis. Modern analytical methods, such as atomic absorption spectrophotometry (AAS) and studies with radioactive 6f5Zn, have allowed widespread study of zinc metabolism in human health and disease, and much is now known of the role of zinc in human medicine (Halsted et al. 1974, Fell 1975, Lancet 1973, 1975).
0
Oral do.
Ih dose
CowlI Cow22- 1
10
S
Days after dosini
Fig 1 Whole-body retention of 54Mn in two cows
oral and intravenous administration of following isotope
15
Causes of Human Zinc Deficiency Failure of zinc supply: Absolute dietary zinc insufficiency is not likely since zinc occurs in most foodstuffs. However, the reduced bio-availability
473
cave in which are housed three plastic scintillation detectors; a separate control room contains the electronic equipment for measurement and analysis of the radioactivity. The cave was constructed by excavating an REFERENCES area 6 m deep by 5 m wide into an existing chalk Alexander F W, Clayton B E & Delves H T bank. The excavation was lined and roofed with (1974) Quarterly Journal ofMedicine 43, 89 Delves H T corrugated steel sheets on a steel joist framework, (1976) Clinica ch,imica acta (in press) and then further protected with chalk. The roof Delves H T, Shepherd G & Vinter P (1971) Analyst 96, 260 was weather proofed with 15 cm of sealed Kawaguchi H & Auld D S (1975) Clinical Chlemistry 21, 591 Masironi S concrete. The interior of the cave was lined with (1969) Bulletin ofthe World Health Organization 40, 305 3 mm steel sheets covered with 3 mm lead. The Sharrett A R & Feinleib,M (1 975) Preventive Medicine 4, 20 floor and the walls were then coated with polyWalsh A (1955) Spectrochimica Acta 7, 108 urethane to provide an impervious and easily Wester P O (1971) Acta medica Scandinavica 190, 155 cleaned surface. The detection system was designed for high sensitivity rather than high resolution and therefore has three large plastic scintillation heads, each of which is viewed by two 17.8 cm diameter photomultiplier tubes. To obtain a good approximation to whole-body geometry and to reduce variations due to the Mr M J Vagg redistribution of isotope within the body after (Agricultural Research Council, administration, the heads are arranged symInstitute for Research on Animal Diseases, metrically in a vertical plane around the animal. Compton, Newbury, Berkshire, RG16 ONN) The complete detector assembly is mounted on a rectangular frame carried on tracks in the roof Assessment of Trace Element of the cave. The frame is motor driven and is Metabolism in Farm Animals designed to traverse the length of a cow at a preset speed. In farm animals the estimation of the absorption Signals from the photomultiplier tubes pass to a of a mineral or trace element from the diet is signal mixing unit, then to an amplifier and finally important in the context of 'production disease' to a single channel pulse height analyser and as discussed by Payne (1970). scaler. The absorption of an element can be measured A 144-channel pulse height analyser (Nuclear provided the net retention of a radioisotope of the Enterprises, NE 6900) is used in the initial setting element is known, that is the difference between up of the detector for each isotope to be counted. the input, the quantity administered, and the Method of operation: The cow is restrained in a output or quantity excreted in urine, faces and mobile steel crush which is then drawn into the milk in a period of 7-10 days. However, if the cave of the whole-body counter by means of an element is poorly absorbed this difference is small electric winch. Both forward and reverse scans and cannot be accurately determined because of of the animal are made and a printout obtained the considerable errors involved in the measure- of the total count and the duration of each scan. ment of both input and output of radioisotope. Application of a whole-body counter to the estimaA whole-body counter can measure directly and tion of the absorption coefficient for manganese-54 accurately the retention of a radioisotope of even in the dairy cow: A whole-body counter can a poorly absorbed element and thus give a accurately measure the retention of an oral dose measure of its absorption. The absorption of a radioisotope at various times after its coefficient of the element, defined as the fraction administration but this retention is not equal to of the dietary content of the element absorbed the absorbed fraction of that isotope for two through the gastrointestinal tract, may then be reasons: (1) Because of the unabsorbed isotope calculated from the whole-body retention values still present in the gastrointestinal tract. (2) as described below. Because of the isotope which has been absorbed This paper describes the construction of a but subsequently resecreted. into the gastrowhole-body counter suitable for cattle, and its intestinal tract and excreted in fices. application to the study of the trace element These two factors were taken into account in metabolism of farm animals. this work by oral administration of 54MnCI2 Construction: The Compton whole-body counter followed by an intravenous injection of the same consists principally of a shielded low background radioisotope about one month later, at which
possible with the new developments in atomic spectroscopy, and will no doubt be used more frequently in future studies of trace metals in human diseases.
474
Proc. roy. Soc. Med. Volume 69 July 1976
14
time the radioactivity due to the orar dose had Table I virtually disappeared. Following administration Comparison of the percentage retention of orally administered of radioisotope by either route, the animal was 5'Mn by two cows as determined by whole-body counting (WBC) subjected to whole-body counting at 5 and 12 and conventional balance methods (B) Cow I Cow 2 hours after dosing and then at daily intervals for 15 days. Days alier dosing WBC B WBC B Due to redistribution of radioisotope during 1 77.1 75.6 82.9 85.5 32.8 35.0 43.6 47.6 the first 12 hours after dosing, minor variations 2 12.8 18.2 21.8 28.0 in count rate occurred which resulted in some- 43 5.4 10.3 10.3 16.6 times the 5 hour and sometimes the 12 hour count 5 2.7 7.9 5.5 11.8 indicating the higher apparent retention. The higher measurement was then taken to indicate 100 % retention of radioisotope and all subsequent The use of the gut absorption-resecretion whole-body counts were related to this figure. model provides a more reliable estimate of The whole-body retention curves obtained relative absorption rates because it makes a were then subjected to a mathematical deconvolu- quantitative allowance for the effects of variations tion process using the gut absorption-resecretion in endogenous secretion rate and rate of passage model derived by Sansom (1972). This model is of food through the gut. based on two assumptions: (1) That the quantity In Table I the results obtained for retention of of isotope absorbed during any day is proportional orally administered 54Mn by whole-body counting to the amount of isotope present in the gut on the are compared with those obtained by the conprevious day. (2) That the absorbed isotope is ventional radioisotope balance method. The available for resecretion at the same rate as that results show that there is good agreement for the which has been administered intravenously. first two days after dosing, but that subsequently Fig 1 shows the whole-body retention curves the balance method increasingly oVerestimates of 54.Mn in two cows after oral and intravenous retention. It was this overestimate that previously administration. Net retentions at 13 days derived led to the belief that absorption of manganese from the oral dose retention curves are 0.39 % was of the order of 5 % of dietary content. in Cow 1 and 0.14% in Cow 2. However, the REFERENCES calculated absorption coefficient in Cow I is less Payne M than in Cow 2 and the absorption of 54Mn during (1970) JInternational Review of Fxperimental Pathology 9, 191 13 days is 0.36% and 0.57% respectively. The Sansom B F (1972) In: Assessment of Radioactive Contamination retention curves of the orally administered 54Mn in Man. IAEA, Vienna; p 563 are thus misleading if used as a measure of relative absorption rates in the two cows. The low estimate of absorption in Cow 1 is due to a higher rate of endogenous secretion and faster rate of passage of radioisotope through the gastroDr G S Fell and Dr R R Burns intestinal tract. (Royal Infirmary, Glasgow, G4 OSF) Zinc
Zinc metalloenzymes are of basic importance to many intracellular biochemical mechanisms; in particular they regulate various stages of protein and nucleic acid synthesis. Modern analytical methods, such as atomic absorption spectrophotometry (AAS) and studies with radioactive 6f5Zn, have allowed widespread study of zinc metabolism in human health and disease, and much is now known of the role of zinc in human medicine (Halsted et al. 1974, Fell 1975, Lancet 1973, 1975).
0
Oral do.
Ih dose
CowlI Cow22- 1
10
S
Days after dosini
Fig 1 Whole-body retention of 54Mn in two cows
oral and intravenous administration of following isotope
15
Causes of Human Zinc Deficiency Failure of zinc supply: Absolute dietary zinc insufficiency is not likely since zinc occurs in most foodstuffs. However, the reduced bio-availability
