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Metabolism of zinc and copper in the neonate: Zinc thionein in developing rat brain, heart, lung, spleen, and thymus
Life Sciences, Vol. 32, pp. 2981-2987 Printed in the U.S.A.
Pergamon Press
METABOLISM OF ZINC AND COPPERIN THE NEONATE: ZINC THIONEIN IN DEVELOPING RAT BRAIN, HEART, LUNG, SPLEEN, AND THYMUS Frank O. Brady Department of Biochemistry School of Medicine University of South Dakota Vermillion, South Dakota 57069 (Received in final form April 15, 1983)
SummarX In a continuing study of the importance of metallothionein (MT) in the growth and development of neonates, zinc and copper metabolism in rat brain, heart, lung, spleen, and thymus has been analyzed in 5,10,15,20, and 25 day old rats. Total, cytosol, and MT zinc and copper concentrations and organ contents were determined. Zinc, but very l i t t l e , i f any copper was associated with MT in these organs. Concentrations ranged from 0.03 to 3.3 ~g Zn in MT/g; organ contents ranged from 0.003 to 2.2 ~g Zn in MT/organ. Brain exhibited the highest concentrations and contents of zinc in MT, approaching the levels found in kidneys. Rank order of organ contents of zinc in MT was brain > lung > heart, spleen, thymus, during this neonatal growth period. Whenorgan growth was rapid, a large percentage (20-95%) of the cytosolic zinc present in these organs was associated with MT, as has been previously observed with liver, kidneys, and testes. Noneof these organs undergoes the dramatic changes in zinc and copper metabolism previously observed in neonatal rat liver and gastrointestinal tract, and in maturing testes. They are more comparable to kidneys in their concentrations of zinc in MT. Like testes, l i t t l e copper is found in these organs. In a continuing investigation of the function and role of metallothionein in zinc and copper metabolism, the levels of (Zn,Cu)-thionein have been systematically studied in various tissues of the neonatal and developing rat. The working hypothesis has been that high levels of metallothionein would be present in tissues, which were undergoing rapid growth and development, in order to supply zinc, and possibly copper, for nucleic acid metabolism, protein synthesis, and other metabolic processes. Previous studies were completed on the liver ( I ) , the gastrointestinal tract (2), the kidneys (3), and the testes (3). This study presents the results for neonatal brain, heart, lung, spleen, and th~nnus in rats from 5 to 25 days of age. Several reviews of the properties of metallothionein are available (4-8). Methods Female, pregnant Sprague-Dawley rats were purchased from Sasco, Inc., O~ha. Individual n~thers with their pups were maintained in separate cages without l i t t e r changes. Purina rat chow and tap water were provided ad l i b i rum. 0024-3205/83 $3.00 + .00 Copyright (c) 1983 Pergamon Press Ltd.
2982
Rat Xeonatal Zinc Thionein
Vol. 32, No. 26,
1983
L i t t e r sizes were kept at lO-12 pups. 4 to 6 pups were removed at appropriate time points and were killed on days 5, l~, 15, 20, and 25 after birth. Organs were removed, weighed, and stored at -20 C. Because of the small size of the tissues in this study, organs from pups from several l i t t e r s were pooled for analysis. See Tables I and II for details of number of animals, number of l i t t e r s , body weights, and organ weights. Organs were p a r t i a l l y thawed at room temperature and were homogenized in two volumes of ice cold, lO mM Tris-HCl, pH 8.6, 0.25 M sucrose. An aliquot (2 x 0.5 ml) of the homogenate was removed for total zinc and copper analysis, and the remainder was centrifuged at 140,000 x g for 45 minutes in a Beckman L5-75 ultracentrifuge. An aliquot of the cytosol (2 x 50 ~l) was removed and diluted 20-fold in water for zinc and copper analysis. Duplicate aliquots of the cytosol (2.0 to 5.0 ml) were chromatographed on a column of Sephadex G-75 (I.5 x 90 cm), equilibrated and eluted with O.Ol M Tris. HCl, pH 8.6, l mM NAN3. Fractions (3.0 ml) were collected and analyzed for zinc and copper. The metal content of the metallothionein peak (Ve/Vo of 2.0 to 2.5) was quantitated and expressed as ug metal in metallothionein per g tissue or per total organ. Zinc and copper were determined by atomic absorption spectroscopy, using a Perkin Elmer 303 or an Instrumentation Laboratories 551 in the flame mode. Column fractions were assayed for metals d i r e c t l y , cytosol samples were assayed for metals after dilution, and homogenate samples were assayed for metals after wet ashing at 90°C with 3.0 ml of a n i t r i c acid/perchloric acid mixture (4:1), the ash being redissolved in 3.0 ml of 5% HCI. The presence of metallothionein in cytosolic fractions was supported using the [2°3Hg]-displacement of zinc technique (9). A two fold excess of mercury to zinc was incubated with a cytosol sample from each of the tissues for 60 minutes at 4°C. The mixture was then chromatographed on Sephadex G-75, as described above. Fractions were then counted with a Packard gamma counter for the quantitation of mercury before assaying for zinc by atomic absorption spectroscopy. Results and Discussion In Tables I and II are shown the zinc concentrations (ug/g tissue wet weight) and contents (ug/organ) for neonatal rat brain, heart, lung, spleen, and thymus. The data are presented as total metal, cytosol metal, and metallothionein metal, as a function of age after birth. Very l i t t l e total copper is present in these tissues (Table I l l ) , as compared to l i v e r , kidneys, and gastrointestinal tract (I-3). The metallothionein fractions contained undetectable levels of copper, a situation previously observed with rat testes (3). The metallothionein zinc concentrations and contents in these tissues are summarized in Figures l and 2, respectively, and are also compared with the levels previously observed in l i v e r (1), kidneys (3), and testes (3). Neonatal rat brain, heart, lung, spleen, and thymus do not undergo the dramatic changes in zinc and copper metabolism that occur in neonatal rat l i v e r and gastrointestinal tract (2), and in maturing rat testes. Metallothionein organ content in brain is comparable to kidneys, while heart, lung, spleen, and thymus are lower. The metallothionein concentrations in these tissues are s t i l l higher, though, than that found in adult rat l i v e r . Although lower in metallothionein concentration than neonatal l i v e r and kidneys and maturing testes, these tissues s t i l l have a large percentage (20-95%) of t h e i r cytosolic zinc bound to metallothionein (Table I), when they are undergoing rapid growth and development. Because of the small sizes of the tissues examined in this study,
Vol. 32, No. 26, 1983
Rat Neonatal Zinc Thionein
2983
TABLE I Zinc Concentrationa Age (Days) 5 Number of animals ( l i t t e r s ) Brain: Total
34(7) 39(7) 5.95
6.60
15
20
25
21(4)
28(6)
19(5)
5.70
5.15
8.45
Cytosol
3.42
3.66
3.05
2,95
3.09
Metallothionein
3.26
1.48
1.97
1.62
0.59
%b
95.3
40.4
64.6
54.5
19.1
11.70
Heart: Total
ll.lO
12.35
9.95
Cytosol
7.12
4.01
2.50
2.50
2.13
Metallothionein
0.04
0.64
1.64
0.51
0.49
0.6
16.0
65.6
20.4
23.0
% Lung:
I0
li.55
Total
9.30 I0.40
Cytosol
4.92
4.50
Metallothionein
0.75
0.23
l.ll
0.68
1.28
%
15.2
5.1
20.7
12.9
24.2
Spleen:Total
15.30 12.55
12.35 12.90 I0.60 5.37
5.28
5.29
13.45 14.80 15.10
Cytosol
6.67
8.00
5.33
8.05
9.01
Metallothionein
1.65
1.12
1.72
0.61
0.55
%
24.7
14.0
32.3
7.6
6.1
Thymus:Total
8.60 14.45
13.60 I ¢ . 0 5
12.65
Cytosol
3.98
8.76
4.78
5.50
5.52
Metallothionein %
0.47 If.8
0.86 9.8
0.58 12.1
1.03 18.7
0.03 0.5
a(pg/g wet weight) The data for zinc concentration are presented as the average for two determinations. b% is the percentage of cytosolic zinc present as metallothionein.
2984
Rat Neonatal
Zinc Thionein
Vol.
32, No. 26, 1983
TABLE II Zinc Contenta Age (Days) 5
lO
15
20
25
Average body weight (g)
I0.4
17.7
36.8
45.6
55.9
Brain:
Average weight (g)
0.45
0.74
1.12
1.26
1.29
Total
2.68
4.85
6.39
6.46
I0.93
Cytosol
1.54
2.69
3.42
3.71
4.01
Metallothionein
1.47
1.09
2.21
2.04
0.76
Average weight (g)
0.09
O. l l
0.22
0.25
0.29
Total
1.06
1.34
2.45
3.12
2.93
Heart:
Lung:
Cytosol
0.67
0.47
0.55
0.63
0.63
Metallothionein
0.003 0.07
0.36
0.13
0.14
Average weight (g)
0.20
0.35
0.59
0.58
0.60
Total
1.87
3.67
7.33
7.42
6.31
Cytosol
0.98
1.58
3.21
3.04
3.15
Metallothionein
0.15
0.08
0.66
0.39
0.76
0.07
O. lO
0.20
0.18
0.23
Total Cytosol
1.03 0.45
1.21 0.77
2.64 1.05
2.73 1.49
3.45 2.05
Metallothionein
O. l l
O. l l
0.34
O. l l
0.13
Spleen: Average weight (g)
Thymus : Average weight (g)
0.03
0.08
0.22
0.26
0.28
Total
0.24
1.14
2.99
3.70
3.52
Cytosol
Q.12
0.69
1.06
1.46
1.55
Metallothionein
O.Oi
0.07
0.13
0.27
O, Ol
a(~g/organ) The data for zinc content are presented as the average of two determinations.
Vol. 32, No. 26, 1983
Rat Neonatal Zinc Thioneln
2985
Rat Organs Metallothlonetn Concentration
50
40
30
Zinc
(~ill)
I
l
/
^. :.--
.
""- .--,,, . . . .
)kl I ft ,.,Ibm"" ~ "
".
Age (Days)
Metallothionein zinc concentration in neonatal and developing rat organs. Liver I l l I H ) , kidneys (3) (~ ~), testes (3) ( t - - - o ) , brain ( & - - ~ ) , heart (~ ~), lungs ( D - - o ) , spleen (o o), and thymus ( ~ - - ~ ) . insufficient amounts of [~sS]-cysteine could be incorporated into the metallothionein fractions for detection and confirmation of these zinc proteins as truly metallothioneins. Instead the [2°3Hg]-displacement of zinc technique (9) was used. All of the zinc in the putative metallothionein G-75 peak of each of ~he tissues examined was displaced by a 60 minute incubation at 4° C with Hg2T before chromatography on Sephadex G-75. This is a property indicative of authentic metallothioneins and is in support of the conclusion that these are indeed zinc thioneins. The results of this study add to the catalog of metallothionein concentrations in tissues of the neonatal and developing rat. Although these smaller tissues do not exhibit the large fluctuations in zinc and copper concentrations that occur in the liver during this same growth period, significant amounts of cytosolic zinc are present in them bound to metallothionein. As the neonatal liver probably functions as a reservoir of metals for the whole
2986
Rat Neonatal Zinc Thionein
Vol. 32, No. 26, ]983
Rat Organs Metallothioneln Content
11-
,i L
',,
\
Zinc (pg/Organ)
,t "'o
/ /
3~ I
i
..
2-
I
//A
/
"'-A
;Idney
!
/
10
/"
15
"'"
/
20
Age Days
h
,/
i
/
,p,
-
5
/
',
/
-
j"
;
A
1~-
4..T~stes
eart
25
3o~.~o.~
Fi 9. 2 Metallothionein zinc organ content in neonatal and developing rat organs. Liver ( I ) ( 0 - - - 4 ) , kidneys (3) (~ ~), testes (3) ( ~ - - ~ ) , brain ( k - - i ) , heart (A---A), lungs ( ~ - - ~ ) , spleen, (~ o), and thymus ( ~ - ~ ) .
animal, i t would not be unexpected to have these other tissues exhibiting a lesser reservoir of zinc. This present work concludes our study of the concentrations and organ contents of metallothionein in neonatal and developing rat tissues.
Vol. 32, No. 26, 1983
Rat Neonatal Zinc Thionein
2987
TABLE I I I Total Copper Concentration And Content In Neonatal Rat Tissues a Age (Days) 5
lO
15
Brain Heart Lung
0.30/0.14 1.40/0.13 0.90/0.18
0.35/0.26 0.95/0. I I 1.35/0.48
Spleen Thymus
0.70/0.05 0.20/0.01
O. ll/O.Ol O.15/O.Ol
20
25
O.90/l.Ol 1.80/0.40 1.45/0.86
0.80/I.00 1.90/0.48 1.40/0.81
0.55/0.71 1.80/0.53 1.45/0.51
0.03/0.01 0.30/0.07
0.03/0.01 0.45/0.12
O.O3/O.Ol 0.25/0.07
aThe f i r s t number is concentration (ug/g wet weight); the second number is content (ug/organ). The data are presented as the average of two determinations.
Acknowledgement During part of this work the author was the recipient of a Research Career Development Award (ES 00022) from the DHHS, USPHS, NIH, National I nst i t ut e of Environmental Health Sciences. References I. 2. 3. 4. 5. 6. 7. 8. 9.
R. MASON, A. BAKICA, G.P. SAHAWICKRAMA, and M. WEBB, Br. J. Nutr. 45 375389 (1981) R. MASON, F.O. BRADY, and M. WEBB, Br. J. Nutr. 45 391-399 (1981) F.O. BRADYand M. WEBB, J. Biol. Chem. 256 3931-3~35 (1981) Y. KOJI~ and J.H.R. KAGI, Trends Biochem. Sci. 3 90-93 (1978) J.H.R. KAGI and M. NORDBERG(Eds.), Metallothionein, Birkh~user Verlag, Basel (1979) M. WEBB (Ed.), The Chemistry, Biochemistry, and Biology of Cadmium, Elsevier/North-Holland, New York (1979) F.O. BRADY, Trends Biochem. Sci. 7 143-145 (1982) M. WEBB and K. CAIN, Biochem. Pha~macol. 31 137-142 (1982) D. HOLT, L. MAGOS, and M. WEBB, Chem.-Biol. Interactions 32 125-135 (1980)
Pergamon Press
METABOLISM OF ZINC AND COPPERIN THE NEONATE: ZINC THIONEIN IN DEVELOPING RAT BRAIN, HEART, LUNG, SPLEEN, AND THYMUS Frank O. Brady Department of Biochemistry School of Medicine University of South Dakota Vermillion, South Dakota 57069 (Received in final form April 15, 1983)
SummarX In a continuing study of the importance of metallothionein (MT) in the growth and development of neonates, zinc and copper metabolism in rat brain, heart, lung, spleen, and thymus has been analyzed in 5,10,15,20, and 25 day old rats. Total, cytosol, and MT zinc and copper concentrations and organ contents were determined. Zinc, but very l i t t l e , i f any copper was associated with MT in these organs. Concentrations ranged from 0.03 to 3.3 ~g Zn in MT/g; organ contents ranged from 0.003 to 2.2 ~g Zn in MT/organ. Brain exhibited the highest concentrations and contents of zinc in MT, approaching the levels found in kidneys. Rank order of organ contents of zinc in MT was brain > lung > heart, spleen, thymus, during this neonatal growth period. Whenorgan growth was rapid, a large percentage (20-95%) of the cytosolic zinc present in these organs was associated with MT, as has been previously observed with liver, kidneys, and testes. Noneof these organs undergoes the dramatic changes in zinc and copper metabolism previously observed in neonatal rat liver and gastrointestinal tract, and in maturing testes. They are more comparable to kidneys in their concentrations of zinc in MT. Like testes, l i t t l e copper is found in these organs. In a continuing investigation of the function and role of metallothionein in zinc and copper metabolism, the levels of (Zn,Cu)-thionein have been systematically studied in various tissues of the neonatal and developing rat. The working hypothesis has been that high levels of metallothionein would be present in tissues, which were undergoing rapid growth and development, in order to supply zinc, and possibly copper, for nucleic acid metabolism, protein synthesis, and other metabolic processes. Previous studies were completed on the liver ( I ) , the gastrointestinal tract (2), the kidneys (3), and the testes (3). This study presents the results for neonatal brain, heart, lung, spleen, and th~nnus in rats from 5 to 25 days of age. Several reviews of the properties of metallothionein are available (4-8). Methods Female, pregnant Sprague-Dawley rats were purchased from Sasco, Inc., O~ha. Individual n~thers with their pups were maintained in separate cages without l i t t e r changes. Purina rat chow and tap water were provided ad l i b i rum. 0024-3205/83 $3.00 + .00 Copyright (c) 1983 Pergamon Press Ltd.
2982
Rat Xeonatal Zinc Thionein
Vol. 32, No. 26,
1983
L i t t e r sizes were kept at lO-12 pups. 4 to 6 pups were removed at appropriate time points and were killed on days 5, l~, 15, 20, and 25 after birth. Organs were removed, weighed, and stored at -20 C. Because of the small size of the tissues in this study, organs from pups from several l i t t e r s were pooled for analysis. See Tables I and II for details of number of animals, number of l i t t e r s , body weights, and organ weights. Organs were p a r t i a l l y thawed at room temperature and were homogenized in two volumes of ice cold, lO mM Tris-HCl, pH 8.6, 0.25 M sucrose. An aliquot (2 x 0.5 ml) of the homogenate was removed for total zinc and copper analysis, and the remainder was centrifuged at 140,000 x g for 45 minutes in a Beckman L5-75 ultracentrifuge. An aliquot of the cytosol (2 x 50 ~l) was removed and diluted 20-fold in water for zinc and copper analysis. Duplicate aliquots of the cytosol (2.0 to 5.0 ml) were chromatographed on a column of Sephadex G-75 (I.5 x 90 cm), equilibrated and eluted with O.Ol M Tris. HCl, pH 8.6, l mM NAN3. Fractions (3.0 ml) were collected and analyzed for zinc and copper. The metal content of the metallothionein peak (Ve/Vo of 2.0 to 2.5) was quantitated and expressed as ug metal in metallothionein per g tissue or per total organ. Zinc and copper were determined by atomic absorption spectroscopy, using a Perkin Elmer 303 or an Instrumentation Laboratories 551 in the flame mode. Column fractions were assayed for metals d i r e c t l y , cytosol samples were assayed for metals after dilution, and homogenate samples were assayed for metals after wet ashing at 90°C with 3.0 ml of a n i t r i c acid/perchloric acid mixture (4:1), the ash being redissolved in 3.0 ml of 5% HCI. The presence of metallothionein in cytosolic fractions was supported using the [2°3Hg]-displacement of zinc technique (9). A two fold excess of mercury to zinc was incubated with a cytosol sample from each of the tissues for 60 minutes at 4°C. The mixture was then chromatographed on Sephadex G-75, as described above. Fractions were then counted with a Packard gamma counter for the quantitation of mercury before assaying for zinc by atomic absorption spectroscopy. Results and Discussion In Tables I and II are shown the zinc concentrations (ug/g tissue wet weight) and contents (ug/organ) for neonatal rat brain, heart, lung, spleen, and thymus. The data are presented as total metal, cytosol metal, and metallothionein metal, as a function of age after birth. Very l i t t l e total copper is present in these tissues (Table I l l ) , as compared to l i v e r , kidneys, and gastrointestinal tract (I-3). The metallothionein fractions contained undetectable levels of copper, a situation previously observed with rat testes (3). The metallothionein zinc concentrations and contents in these tissues are summarized in Figures l and 2, respectively, and are also compared with the levels previously observed in l i v e r (1), kidneys (3), and testes (3). Neonatal rat brain, heart, lung, spleen, and thymus do not undergo the dramatic changes in zinc and copper metabolism that occur in neonatal rat l i v e r and gastrointestinal tract (2), and in maturing rat testes. Metallothionein organ content in brain is comparable to kidneys, while heart, lung, spleen, and thymus are lower. The metallothionein concentrations in these tissues are s t i l l higher, though, than that found in adult rat l i v e r . Although lower in metallothionein concentration than neonatal l i v e r and kidneys and maturing testes, these tissues s t i l l have a large percentage (20-95%) of t h e i r cytosolic zinc bound to metallothionein (Table I), when they are undergoing rapid growth and development. Because of the small sizes of the tissues examined in this study,
Vol. 32, No. 26, 1983
Rat Neonatal Zinc Thionein
2983
TABLE I Zinc Concentrationa Age (Days) 5 Number of animals ( l i t t e r s ) Brain: Total
34(7) 39(7) 5.95
6.60
15
20
25
21(4)
28(6)
19(5)
5.70
5.15
8.45
Cytosol
3.42
3.66
3.05
2,95
3.09
Metallothionein
3.26
1.48
1.97
1.62
0.59
%b
95.3
40.4
64.6
54.5
19.1
11.70
Heart: Total
ll.lO
12.35
9.95
Cytosol
7.12
4.01
2.50
2.50
2.13
Metallothionein
0.04
0.64
1.64
0.51
0.49
0.6
16.0
65.6
20.4
23.0
% Lung:
I0
li.55
Total
9.30 I0.40
Cytosol
4.92
4.50
Metallothionein
0.75
0.23
l.ll
0.68
1.28
%
15.2
5.1
20.7
12.9
24.2
Spleen:Total
15.30 12.55
12.35 12.90 I0.60 5.37
5.28
5.29
13.45 14.80 15.10
Cytosol
6.67
8.00
5.33
8.05
9.01
Metallothionein
1.65
1.12
1.72
0.61
0.55
%
24.7
14.0
32.3
7.6
6.1
Thymus:Total
8.60 14.45
13.60 I ¢ . 0 5
12.65
Cytosol
3.98
8.76
4.78
5.50
5.52
Metallothionein %
0.47 If.8
0.86 9.8
0.58 12.1
1.03 18.7
0.03 0.5
a(pg/g wet weight) The data for zinc concentration are presented as the average for two determinations. b% is the percentage of cytosolic zinc present as metallothionein.
2984
Rat Neonatal
Zinc Thionein
Vol.
32, No. 26, 1983
TABLE II Zinc Contenta Age (Days) 5
lO
15
20
25
Average body weight (g)
I0.4
17.7
36.8
45.6
55.9
Brain:
Average weight (g)
0.45
0.74
1.12
1.26
1.29
Total
2.68
4.85
6.39
6.46
I0.93
Cytosol
1.54
2.69
3.42
3.71
4.01
Metallothionein
1.47
1.09
2.21
2.04
0.76
Average weight (g)
0.09
O. l l
0.22
0.25
0.29
Total
1.06
1.34
2.45
3.12
2.93
Heart:
Lung:
Cytosol
0.67
0.47
0.55
0.63
0.63
Metallothionein
0.003 0.07
0.36
0.13
0.14
Average weight (g)
0.20
0.35
0.59
0.58
0.60
Total
1.87
3.67
7.33
7.42
6.31
Cytosol
0.98
1.58
3.21
3.04
3.15
Metallothionein
0.15
0.08
0.66
0.39
0.76
0.07
O. lO
0.20
0.18
0.23
Total Cytosol
1.03 0.45
1.21 0.77
2.64 1.05
2.73 1.49
3.45 2.05
Metallothionein
O. l l
O. l l
0.34
O. l l
0.13
Spleen: Average weight (g)
Thymus : Average weight (g)
0.03
0.08
0.22
0.26
0.28
Total
0.24
1.14
2.99
3.70
3.52
Cytosol
Q.12
0.69
1.06
1.46
1.55
Metallothionein
O.Oi
0.07
0.13
0.27
O, Ol
a(~g/organ) The data for zinc content are presented as the average of two determinations.
Vol. 32, No. 26, 1983
Rat Neonatal Zinc Thioneln
2985
Rat Organs Metallothlonetn Concentration
50
40
30
Zinc
(~ill)
I
l
/
^. :.--
.
""- .--,,, . . . .
)kl I ft ,.,Ibm"" ~ "
".
Age (Days)
Metallothionein zinc concentration in neonatal and developing rat organs. Liver I l l I H ) , kidneys (3) (~ ~), testes (3) ( t - - - o ) , brain ( & - - ~ ) , heart (~ ~), lungs ( D - - o ) , spleen (o o), and thymus ( ~ - - ~ ) . insufficient amounts of [~sS]-cysteine could be incorporated into the metallothionein fractions for detection and confirmation of these zinc proteins as truly metallothioneins. Instead the [2°3Hg]-displacement of zinc technique (9) was used. All of the zinc in the putative metallothionein G-75 peak of each of ~he tissues examined was displaced by a 60 minute incubation at 4° C with Hg2T before chromatography on Sephadex G-75. This is a property indicative of authentic metallothioneins and is in support of the conclusion that these are indeed zinc thioneins. The results of this study add to the catalog of metallothionein concentrations in tissues of the neonatal and developing rat. Although these smaller tissues do not exhibit the large fluctuations in zinc and copper concentrations that occur in the liver during this same growth period, significant amounts of cytosolic zinc are present in them bound to metallothionein. As the neonatal liver probably functions as a reservoir of metals for the whole
2986
Rat Neonatal Zinc Thionein
Vol. 32, No. 26, ]983
Rat Organs Metallothioneln Content
11-
,i L
',,
\
Zinc (pg/Organ)
,t "'o
/ /
3~ I
i
..
2-
I
//A
/
"'-A
;Idney
!
/
10
/"
15
"'"
/
20
Age Days
h
,/
i
/
,p,
-
5
/
',
/
-
j"
;
A
1~-
4..T~stes
eart
25
3o~.~o.~
Fi 9. 2 Metallothionein zinc organ content in neonatal and developing rat organs. Liver ( I ) ( 0 - - - 4 ) , kidneys (3) (~ ~), testes (3) ( ~ - - ~ ) , brain ( k - - i ) , heart (A---A), lungs ( ~ - - ~ ) , spleen, (~ o), and thymus ( ~ - ~ ) .
animal, i t would not be unexpected to have these other tissues exhibiting a lesser reservoir of zinc. This present work concludes our study of the concentrations and organ contents of metallothionein in neonatal and developing rat tissues.
Vol. 32, No. 26, 1983
Rat Neonatal Zinc Thionein
2987
TABLE I I I Total Copper Concentration And Content In Neonatal Rat Tissues a Age (Days) 5
lO
15
Brain Heart Lung
0.30/0.14 1.40/0.13 0.90/0.18
0.35/0.26 0.95/0. I I 1.35/0.48
Spleen Thymus
0.70/0.05 0.20/0.01
O. ll/O.Ol O.15/O.Ol
20
25
O.90/l.Ol 1.80/0.40 1.45/0.86
0.80/I.00 1.90/0.48 1.40/0.81
0.55/0.71 1.80/0.53 1.45/0.51
0.03/0.01 0.30/0.07
0.03/0.01 0.45/0.12
O.O3/O.Ol 0.25/0.07
aThe f i r s t number is concentration (ug/g wet weight); the second number is content (ug/organ). The data are presented as the average of two determinations.
Acknowledgement During part of this work the author was the recipient of a Research Career Development Award (ES 00022) from the DHHS, USPHS, NIH, National I nst i t ut e of Environmental Health Sciences. References I. 2. 3. 4. 5. 6. 7. 8. 9.
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