Toxicology Letters, 63 (1992) 135-139 0 1992 Elsevier Science Publishers B.V. All rights reserved 0378-4274/92/$05.00
135
TOXLET 02796
Zinc and copper in tissues of rats with blood hypertension induced by long-term lead exposure
Paolo Boscoloa, Marco Carmignanib, Giovanni Carelli”, Vincent N. Finellid and Giovanni Giuliano” “Center of Occupational Safety and Ergophthalmology, University of Chieti, Chieti (Italy), bDepartment of Cell Biology and Physiology, University ojL’Aquila, L’Aquila (Italy), ‘Institute of Occupational Medicine, Catholic University, Roma (Italy), dEnvironmental Health & Safety, Florida Atlantic University, Boca Raton, FL (USA) and ‘Insitute OccupationalMedicine, University of Florence, Florence (Italy)
of
(Received 4 May 1992) (Accepted 22 July 1992) Key words: Copper; Zinc; Lead; Blood hypertension SUMMARY Male Sprague-Dawley rats received for 14 months 0, 15,30 and 60 @ml of lead in drinking water. Both blood pressure and tissue lead were augmented with a dose-response effect, while cardiac inotropism was increased only in the rats treated with 60 ppm of lead. In the exposed animals, zinc and copper were unchanged in kidneys and testicles and augmented in the brain, while copper, but not zinc, was reduced in the heart. These data suggest a possible relation between the modifications of copper and zinc metabolism and the effects of lead on cardiovascular homeostasis.
INTRODUCTION
In the past three decades numerous reports have associated exposure to toxic metals with the development of hypertension [la]. Toxic metals have also been found to alter the metabolism of essential metals [5-71. Dietary levels of iron, copper and zinc have been reported to affect the absorption and toxicity of lead [7-91 and, vice versa, the intake of lead has been found to alter the levels and some biological activities of zinc [ 10,111. The competitive inhibition of the zinc-dependent b-aminolevulinic acid dehydratase (ALA-D) activity by lead has been extensively investigated [ 1l-l 31.
Correspondence to: Dr. Vincent N. Finelli, Director, Environmental University, 500 NW 20th Street, Boca Raton, FL 33431, USA.
Health & Safety, Florida Atlantic
136
The essential trace metals zinc and copper play vital roles in living organisms and, among other functions, are involved in cardiovascular homeostasis. Zinc is involved in protein metabolism and in this function plays a role in the synthesis and catabolism of vasoactive peptides, e.g., the zinc-dependent converting enzyme and kininase activities. Copper also participates in the regulation of cardiovascular functions through monoamine oxidase and dopamine+hydroxylase which are metalloenzymes involved in the metabolism of vasoactive amines and neurotransmitters. This study was designed to investigate whether chronic exposure to lead can affect blood pressure in rats and concurrently alter the trace metal content of organs which are important in the homeostasis of cardiovascular functions. MATERIALS AND METHODS
Twenty-four weaning male Sprague-Dawley rats were randomly divided into four groups of six animals, housed in stainless steel cages and fed a standard laboratory diet with a lead content below 1.5 ppm, copper ranging from 8 to 15 ppm and zinc from 55 to 65 ppm. The four groups of animals received for 14 months, starting from weaning, 0, 15, 30 or 60 pug/ml of lead (as lead acetate) in deionized drinking water. At the end of the exposure, the rats were anaesthetized with sodium thiopental(50 mg/kg body weight, i.p.); thereafter the trachea was cannulated to allow spontaneous breathing. A polyethylene catheter was placed in the left femoral artery for recording aortic systolic and diastolic blood pressure by means of P23Db Statham pressure transducer, as reported in a previous study [ 141.A Biotronex derivative computer was used for determining (by differentiating the pulsatile aortic blood pressure) the maximum rate of rise of blood pressure (dP/dt), an index of cardiac inotropism. Heart rate was measured by a Beckman cardiotachometer coupler, which was triggered by the R-peak of the lead II electrocardiogram. The cardiovascular parameters were monitored on a Beckman type dynograph recorder. After determination of the cardiovascular parameters, tissue specimens of kidney, heart, brain, testicles and other organs were excised for histopathological examination by light microscopy, and for determining the content of lead, zinc and copper utilizing atomic absorption spectrophotometry after wet acid digestion [15,16]. The concentration of the metals was referred to the wet weight of the tissues. The Dunnett t-test for multiple comparison was used for statistical analysis of the data. RESULTS
Throughout the experiment, body weight and general appearance of the animals were not affected by the lead treatment. The rats which received 15 ppm of lead did not demonstrate modifications of the cardiovascular parameters in relation to the controls (Table I). Systolic blood pressure was significantly augmented in the animals treated with 30 ppm of lead, while
137
TABLE I BLOOD PRESSURE (BP), MAXIMUM RATE OF INCREASE IN LEFT VENTRICULAR PRESSURE (dP/dt) AND HEART RATE IN RATS CHRONICALLY EXPOSED TO 15,30, OR 60 ppm OF LEAD
Control 15 ppm of lead 30 ppm of lead 60 ppm of lead
Systolic BP
Diastolic BP
(mmHg)
(mmHg)
dPldt (mmHgis)
Heart rate (beatsimin)
112f 118k 128 k 136 +
85 + 932 97f 105 F
4134 + 4236 f 4451 f 5632 +
330 k 342 2 361 f 341 k
8 5 10* 12*
10 7 12 10*
621 742 542 812*
16 14 22 18
Values represent means f SD. *Significantly different from control group, P < 0.05
both systolic and diastolic blood pressures, along with cardiac inotropism (dP/dt), were increased in the rats exposed to 60 ppm lead. Heart rate was not affected in any of the lead-exposed groups. The histopathological examination, performed on heart, aorta, brain, kidney, liver, testicles and other organs did not show any evidence of significant alterations. Lead was augmented in kidneys, heart, brain and testicles with a dose-response effect (Table II). The content of copper was increased in the brain of all the exposed rats, while that of zine was significantly anymented only in those treated with 60 ppm lead (Table II). Copper, but not zinc, was reduced in the heart of the animals exposed to either 30 or 60 ppm lead. However, lead exposure did not affect the levels of copper and zinc in kidneys and testicles. DISCUSSION
This research demonstrates that long-term lead exposure increases the content of lead, zinc and copper in the brain. An increase of these essential elements in the nervous system may be related to morphological alterations at ultrastructural level, as an increase in density of astrocytes and microglia and a reduction of oligodendrocytes were observed in rats which received from birth for 3 months 100 ppm of lead in food [ 171.It may be suggested that the increase of copper in the brain may affect the activity of copper-containing enzymes such as monoamine oxidase and dopamine-/?hydroxylase involved in the metabolism of neurotransmitters. This is also in agreement with the increased responsiveness to stimulation of qadrenoreceptors (acting at the level of both central and peripheral sympathetic junctions) previously observed by us in rats treated with 30 and 60 ppm of lead in drinking water for 18 months [ 181. In these animals lead did not affect the response induced by the a,-adrenoreceptors; however, it potentiated the effects following activation of cardiac and vascular /Iadrenoreceptors and of the vascular dopaminergic receptors. Moreover, it altered the
138
TABLE
II
LEAD,
ZINC
AND
RATS CHRONICALLY
COPPER
CONTENTS
EXPOSED
IN KIDNEY,
BRAIN,
HEART
AND
TESTICLE
OF
TO 15,30 OR 60 ppm OF LEAD
Metal contents
@g/g, wet weight)
lead
zinc
copper
4.6 2 0.8
Kidney Control 15 ppm of lead 30 ppm of lead 60 ppm of lead
0.1 * 0.1
20.4 f 0.2
0.3 f 0.1*
21.5 k 1.4
5.2 + 0.9
1.0 f 0.4*
23.8 k 2.1
5.2 k 1.7
2.1 2 0.3*
21.4 + 4.4
5.7 * 3.1
Brain Control
< 0.03
12.3 + 2.0
2.2 k 0.3
15 ppm of lead 30 ppm of lead
i 0.03
12.7 + 1.0
3.7 + 0.6*
< 0.08
14.2 + 1.2
4.0 k 0.9*
60 ppm of lead
0.05 + 0.03*
15.9 t 0.9*
3.9 k 0.6*
Control
< 0.03
15.5 k 1.1
7.1 k 2.1
15 ppm of lead 30 ppm of lead
< 0.06
14.9 + 1.3
5.5 + 1.6
< 0.08
16.8 t 1.5
4.1 t 0.4*
60 ppm of lead
0.07 i 0.03*
15.4 f 1.4
4.6 f 0.7*
< 0.03 0.05 f 0.03
25.8 + 0.9 28.7 f 3.0
2.8 + 0.9 2.2 f 0.6
Heart
Testicle Control 60 ppm of lead Values represent *Significantly
means k SD.
different
from control
group,
P < 0.05.
CAMP-dependent availability of calcium for contractile processes in both vascular and cardiac myocells in all exposed rats, including those receiving 15 ppm Pb. The increase of cardiac inotropism observed in the animals exposed to 60 ppm Pb may be related to the energetics of the myocells, since the copper content of the heart in this group was significantly lowered and this metal plays an important role in the mitochondrial oxidative phosphorylation. REFERENCES 1 Schroeder, H.A. and Vinton, Am. J. Physiol. 202, 515.
Jr., W.H. (1962) Hypertension
induced
in rats by small doses of cadmium.
2 Perry, Jr., H.M. and Erlanger, M.W. (1976) Mechanism of cadmium-induced Hemphill (Ed.), Trace Substances in Environmental Health. Vol. 10, Univerity pp. 339-348.
hypertension. In: D.D. of Missouri, Columbia,
139
3 Boscolo, P., Porcelh, G., Carmignani, M. and Finelli, V.N. (1981) Urinary kallikrein and hypertension in cadmium-exposed rats. Toxicol. Lett. 7, 189-194. 4 Carmignani, M., Finelli, V.N. and Boscolo, P. (1983) Mechanisms in cardiovascular regulation following chronic exposure of male rats to inorganic mercury. Toxicol. Appl. Pharmacol. 69,442450. 5 Petering, H.G. (1974) The effects of cadmium and lead on copper and zinc metabolism. In: W.G. Hoekstra, J.W. Suttie, H.E. Ganther and W. Mertz (Eds.), Trace Element Metabolism in Animals, University Park Press, Baltimore, pp. 31 l-325. 6 Cerklewski, F.L. and Forbes, R.M. (1976) Influence of dietary zinc on lead toxicity in the rats. J. Nutr. 106,689-696. 7 Klauder, D.S., Murthy, L. and Petering, H.G. (1973) Effect of dietary intake of lead acetate on copper metabolism in male rats. In: D.D. Hemphill (Ed.), Trace Substances in Environmental Health, Vol. 1, University of Missouri, Columbia, pp. 131-136. 8 Six, K.M. and Goyer, R.A. (1972) The influence of iron deficiency on tissue content and toxicity of ingested lead in the rats. J. Lab. Clin. Med. 79, 128-136. 9 El-Gazzar, R.M., Finelli, V.N., Boiano, J. and Petering, H.G. (1978) Influence of dietary zinc on lead toxicity in rats. Toxicol. Lett. 1,.227-234. 10 Finelli, V.N. and El-Gazzar, R.M. (1977) The interaction of lead and zinc on the prothrombin activity in rats. Toxicol. Lett. 1, 33-39. 11 Finelli, V.N., Klauder, D.S., Karaffa, M.A. and Petering, H.G. (1975) Interaction of zinc and lead on &aminolevulinate dehydratase. Biochem. Biophys. Res. Commun. 65,303-311. 12 Finelli, V.N., Lerner, S., Hong, C. and Lohiya, G. (1980) Effect of zinc supplementation during chelation therapy in plumbism: A case report. Med. Lavaro 71 (2), 149-156. 13 Boscolo, P., Di Martino, G., Carelli, G., Vitale, I. and Finelli, V.N. (1986) Effects of zinc treatment in lead-exposed humans. In: M. Anke, W. Baumann, et al. (Eds.), 5. Spurenelement Symposium, Jena, 1986, University of Jena, pp. 10541061. 14 Boscolo, P., Carmignani, M., Sacchettoni-Logroscino, G., Rannelletti, F.O., Artese, L. and Preziosi, P. (1988) Ultrastructure of the testis in rats with blood hypertension induced by long-term lead exposure. Toxicol. Lett. 41, 1299137. 15 Selander, S. and Cramer, K. (1968) Determination of lead in blood by atomic spectrophotometry. J. Ind. Med. 25,209-213. 16 Kopito, L.W. (1970) Atomic Absorption Manual. Vol. 3, Jarrel-Ash Division, Fisher Scientific Company. 17 Reyners, H., Gainfelici de Reyners, E. and Maisin, J.R. (1979) An ultrastructural study of the effects of lead in the central nervous system of the rat. In: R. Perry (Ed.), Heavy Metals in the Environment, Int. Conference, London, 1979, CEP Consultants Ltd., Edinburgh, pp. 58861. 18 Boscolo, P. and Carmignani, M. (1988) Neurohumoral blood pressure regulation in lead exposure. Environ. Health Perspect. 78, 101-105.
135
TOXLET 02796
Zinc and copper in tissues of rats with blood hypertension induced by long-term lead exposure
Paolo Boscoloa, Marco Carmignanib, Giovanni Carelli”, Vincent N. Finellid and Giovanni Giuliano” “Center of Occupational Safety and Ergophthalmology, University of Chieti, Chieti (Italy), bDepartment of Cell Biology and Physiology, University ojL’Aquila, L’Aquila (Italy), ‘Institute of Occupational Medicine, Catholic University, Roma (Italy), dEnvironmental Health & Safety, Florida Atlantic University, Boca Raton, FL (USA) and ‘Insitute OccupationalMedicine, University of Florence, Florence (Italy)
of
(Received 4 May 1992) (Accepted 22 July 1992) Key words: Copper; Zinc; Lead; Blood hypertension SUMMARY Male Sprague-Dawley rats received for 14 months 0, 15,30 and 60 @ml of lead in drinking water. Both blood pressure and tissue lead were augmented with a dose-response effect, while cardiac inotropism was increased only in the rats treated with 60 ppm of lead. In the exposed animals, zinc and copper were unchanged in kidneys and testicles and augmented in the brain, while copper, but not zinc, was reduced in the heart. These data suggest a possible relation between the modifications of copper and zinc metabolism and the effects of lead on cardiovascular homeostasis.
INTRODUCTION
In the past three decades numerous reports have associated exposure to toxic metals with the development of hypertension [la]. Toxic metals have also been found to alter the metabolism of essential metals [5-71. Dietary levels of iron, copper and zinc have been reported to affect the absorption and toxicity of lead [7-91 and, vice versa, the intake of lead has been found to alter the levels and some biological activities of zinc [ 10,111. The competitive inhibition of the zinc-dependent b-aminolevulinic acid dehydratase (ALA-D) activity by lead has been extensively investigated [ 1l-l 31.
Correspondence to: Dr. Vincent N. Finelli, Director, Environmental University, 500 NW 20th Street, Boca Raton, FL 33431, USA.
Health & Safety, Florida Atlantic
136
The essential trace metals zinc and copper play vital roles in living organisms and, among other functions, are involved in cardiovascular homeostasis. Zinc is involved in protein metabolism and in this function plays a role in the synthesis and catabolism of vasoactive peptides, e.g., the zinc-dependent converting enzyme and kininase activities. Copper also participates in the regulation of cardiovascular functions through monoamine oxidase and dopamine+hydroxylase which are metalloenzymes involved in the metabolism of vasoactive amines and neurotransmitters. This study was designed to investigate whether chronic exposure to lead can affect blood pressure in rats and concurrently alter the trace metal content of organs which are important in the homeostasis of cardiovascular functions. MATERIALS AND METHODS
Twenty-four weaning male Sprague-Dawley rats were randomly divided into four groups of six animals, housed in stainless steel cages and fed a standard laboratory diet with a lead content below 1.5 ppm, copper ranging from 8 to 15 ppm and zinc from 55 to 65 ppm. The four groups of animals received for 14 months, starting from weaning, 0, 15, 30 or 60 pug/ml of lead (as lead acetate) in deionized drinking water. At the end of the exposure, the rats were anaesthetized with sodium thiopental(50 mg/kg body weight, i.p.); thereafter the trachea was cannulated to allow spontaneous breathing. A polyethylene catheter was placed in the left femoral artery for recording aortic systolic and diastolic blood pressure by means of P23Db Statham pressure transducer, as reported in a previous study [ 141.A Biotronex derivative computer was used for determining (by differentiating the pulsatile aortic blood pressure) the maximum rate of rise of blood pressure (dP/dt), an index of cardiac inotropism. Heart rate was measured by a Beckman cardiotachometer coupler, which was triggered by the R-peak of the lead II electrocardiogram. The cardiovascular parameters were monitored on a Beckman type dynograph recorder. After determination of the cardiovascular parameters, tissue specimens of kidney, heart, brain, testicles and other organs were excised for histopathological examination by light microscopy, and for determining the content of lead, zinc and copper utilizing atomic absorption spectrophotometry after wet acid digestion [15,16]. The concentration of the metals was referred to the wet weight of the tissues. The Dunnett t-test for multiple comparison was used for statistical analysis of the data. RESULTS
Throughout the experiment, body weight and general appearance of the animals were not affected by the lead treatment. The rats which received 15 ppm of lead did not demonstrate modifications of the cardiovascular parameters in relation to the controls (Table I). Systolic blood pressure was significantly augmented in the animals treated with 30 ppm of lead, while
137
TABLE I BLOOD PRESSURE (BP), MAXIMUM RATE OF INCREASE IN LEFT VENTRICULAR PRESSURE (dP/dt) AND HEART RATE IN RATS CHRONICALLY EXPOSED TO 15,30, OR 60 ppm OF LEAD
Control 15 ppm of lead 30 ppm of lead 60 ppm of lead
Systolic BP
Diastolic BP
(mmHg)
(mmHg)
dPldt (mmHgis)
Heart rate (beatsimin)
112f 118k 128 k 136 +
85 + 932 97f 105 F
4134 + 4236 f 4451 f 5632 +
330 k 342 2 361 f 341 k
8 5 10* 12*
10 7 12 10*
621 742 542 812*
16 14 22 18
Values represent means f SD. *Significantly different from control group, P < 0.05
both systolic and diastolic blood pressures, along with cardiac inotropism (dP/dt), were increased in the rats exposed to 60 ppm lead. Heart rate was not affected in any of the lead-exposed groups. The histopathological examination, performed on heart, aorta, brain, kidney, liver, testicles and other organs did not show any evidence of significant alterations. Lead was augmented in kidneys, heart, brain and testicles with a dose-response effect (Table II). The content of copper was increased in the brain of all the exposed rats, while that of zine was significantly anymented only in those treated with 60 ppm lead (Table II). Copper, but not zinc, was reduced in the heart of the animals exposed to either 30 or 60 ppm lead. However, lead exposure did not affect the levels of copper and zinc in kidneys and testicles. DISCUSSION
This research demonstrates that long-term lead exposure increases the content of lead, zinc and copper in the brain. An increase of these essential elements in the nervous system may be related to morphological alterations at ultrastructural level, as an increase in density of astrocytes and microglia and a reduction of oligodendrocytes were observed in rats which received from birth for 3 months 100 ppm of lead in food [ 171.It may be suggested that the increase of copper in the brain may affect the activity of copper-containing enzymes such as monoamine oxidase and dopamine-/?hydroxylase involved in the metabolism of neurotransmitters. This is also in agreement with the increased responsiveness to stimulation of qadrenoreceptors (acting at the level of both central and peripheral sympathetic junctions) previously observed by us in rats treated with 30 and 60 ppm of lead in drinking water for 18 months [ 181. In these animals lead did not affect the response induced by the a,-adrenoreceptors; however, it potentiated the effects following activation of cardiac and vascular /Iadrenoreceptors and of the vascular dopaminergic receptors. Moreover, it altered the
138
TABLE
II
LEAD,
ZINC
AND
RATS CHRONICALLY
COPPER
CONTENTS
EXPOSED
IN KIDNEY,
BRAIN,
HEART
AND
TESTICLE
OF
TO 15,30 OR 60 ppm OF LEAD
Metal contents
@g/g, wet weight)
lead
zinc
copper
4.6 2 0.8
Kidney Control 15 ppm of lead 30 ppm of lead 60 ppm of lead
0.1 * 0.1
20.4 f 0.2
0.3 f 0.1*
21.5 k 1.4
5.2 + 0.9
1.0 f 0.4*
23.8 k 2.1
5.2 k 1.7
2.1 2 0.3*
21.4 + 4.4
5.7 * 3.1
Brain Control
< 0.03
12.3 + 2.0
2.2 k 0.3
15 ppm of lead 30 ppm of lead
i 0.03
12.7 + 1.0
3.7 + 0.6*
< 0.08
14.2 + 1.2
4.0 k 0.9*
60 ppm of lead
0.05 + 0.03*
15.9 t 0.9*
3.9 k 0.6*
Control
< 0.03
15.5 k 1.1
7.1 k 2.1
15 ppm of lead 30 ppm of lead
< 0.06
14.9 + 1.3
5.5 + 1.6
< 0.08
16.8 t 1.5
4.1 t 0.4*
60 ppm of lead
0.07 i 0.03*
15.4 f 1.4
4.6 f 0.7*
< 0.03 0.05 f 0.03
25.8 + 0.9 28.7 f 3.0
2.8 + 0.9 2.2 f 0.6
Heart
Testicle Control 60 ppm of lead Values represent *Significantly
means k SD.
different
from control
group,
P < 0.05.
CAMP-dependent availability of calcium for contractile processes in both vascular and cardiac myocells in all exposed rats, including those receiving 15 ppm Pb. The increase of cardiac inotropism observed in the animals exposed to 60 ppm Pb may be related to the energetics of the myocells, since the copper content of the heart in this group was significantly lowered and this metal plays an important role in the mitochondrial oxidative phosphorylation. REFERENCES 1 Schroeder, H.A. and Vinton, Am. J. Physiol. 202, 515.
Jr., W.H. (1962) Hypertension
induced
in rats by small doses of cadmium.
2 Perry, Jr., H.M. and Erlanger, M.W. (1976) Mechanism of cadmium-induced Hemphill (Ed.), Trace Substances in Environmental Health. Vol. 10, Univerity pp. 339-348.
hypertension. In: D.D. of Missouri, Columbia,
139
3 Boscolo, P., Porcelh, G., Carmignani, M. and Finelli, V.N. (1981) Urinary kallikrein and hypertension in cadmium-exposed rats. Toxicol. Lett. 7, 189-194. 4 Carmignani, M., Finelli, V.N. and Boscolo, P. (1983) Mechanisms in cardiovascular regulation following chronic exposure of male rats to inorganic mercury. Toxicol. Appl. Pharmacol. 69,442450. 5 Petering, H.G. (1974) The effects of cadmium and lead on copper and zinc metabolism. In: W.G. Hoekstra, J.W. Suttie, H.E. Ganther and W. Mertz (Eds.), Trace Element Metabolism in Animals, University Park Press, Baltimore, pp. 31 l-325. 6 Cerklewski, F.L. and Forbes, R.M. (1976) Influence of dietary zinc on lead toxicity in the rats. J. Nutr. 106,689-696. 7 Klauder, D.S., Murthy, L. and Petering, H.G. (1973) Effect of dietary intake of lead acetate on copper metabolism in male rats. In: D.D. Hemphill (Ed.), Trace Substances in Environmental Health, Vol. 1, University of Missouri, Columbia, pp. 131-136. 8 Six, K.M. and Goyer, R.A. (1972) The influence of iron deficiency on tissue content and toxicity of ingested lead in the rats. J. Lab. Clin. Med. 79, 128-136. 9 El-Gazzar, R.M., Finelli, V.N., Boiano, J. and Petering, H.G. (1978) Influence of dietary zinc on lead toxicity in rats. Toxicol. Lett. 1,.227-234. 10 Finelli, V.N. and El-Gazzar, R.M. (1977) The interaction of lead and zinc on the prothrombin activity in rats. Toxicol. Lett. 1, 33-39. 11 Finelli, V.N., Klauder, D.S., Karaffa, M.A. and Petering, H.G. (1975) Interaction of zinc and lead on &aminolevulinate dehydratase. Biochem. Biophys. Res. Commun. 65,303-311. 12 Finelli, V.N., Lerner, S., Hong, C. and Lohiya, G. (1980) Effect of zinc supplementation during chelation therapy in plumbism: A case report. Med. Lavaro 71 (2), 149-156. 13 Boscolo, P., Di Martino, G., Carelli, G., Vitale, I. and Finelli, V.N. (1986) Effects of zinc treatment in lead-exposed humans. In: M. Anke, W. Baumann, et al. (Eds.), 5. Spurenelement Symposium, Jena, 1986, University of Jena, pp. 10541061. 14 Boscolo, P., Carmignani, M., Sacchettoni-Logroscino, G., Rannelletti, F.O., Artese, L. and Preziosi, P. (1988) Ultrastructure of the testis in rats with blood hypertension induced by long-term lead exposure. Toxicol. Lett. 41, 1299137. 15 Selander, S. and Cramer, K. (1968) Determination of lead in blood by atomic spectrophotometry. J. Ind. Med. 25,209-213. 16 Kopito, L.W. (1970) Atomic Absorption Manual. Vol. 3, Jarrel-Ash Division, Fisher Scientific Company. 17 Reyners, H., Gainfelici de Reyners, E. and Maisin, J.R. (1979) An ultrastructural study of the effects of lead in the central nervous system of the rat. In: R. Perry (Ed.), Heavy Metals in the Environment, Int. Conference, London, 1979, CEP Consultants Ltd., Edinburgh, pp. 58861. 18 Boscolo, P. and Carmignani, M. (1988) Neurohumoral blood pressure regulation in lead exposure. Environ. Health Perspect. 78, 101-105.
