TOXICOLOGY

AND

APPLIED

PHARMACOLOGY

s&259-263

(1979)

Biliary Excretion and Tissue Distribution of Penta- and Hexavalent Molybdenum in Rats JAROSLAV

Institute

LENER

AND BED~~ICH B~BR’

of Hygiene and Epidemiology,

Srobrirova 100 42 Praha 10. Czechoslovakia

Received March

48,

9, 1979; accepted July 3, 1979

Biliary Excretion and Tissue Distribution of Penta- and Hexavalent Molybdenum in Rats. LENER, J., AND B~BR, B. (1979). Toxicol. Appl. Pharmacol. 51, 259-263. Biliary excretion, whole-body excretion, and distribution of pentavalent and hexavalent forms of molybdenum in blood, liver, and jejunoileocecum were studied in rats at 1, 2, 3, and 4 hr after iv administration of 0.08 and 4.6 mg of molybdenum/kg. The excretion of both valence forms of molybdenum was found to be dose dependent. No difference was observed between the two valence forms in the biliary and whole-body excretion after the dose of 0.08 mg MO/kg, whereas after the administration of 4.6 mg MO/kg the excretion of pentavalent molybdenum was considerably decreased. This was accompanied by a slower decline in the content of pentavalent molybdenum in all the analyzed tissues.

Growing interest in molybdenum metabolism and toxicity is most certainly associated with its continuously increasing involvement in the industrial and agricultural environment. Besides the risk of occupational exposure there is also a risk of increased molybdenum intake in nonworker populations living in areas with an increased occurrence of this element in the natural environment. It has been already demonstrated that heavy metals or metalloids, such as lead (Klaassen and Shoeman, 1974), copper (Klaassen, 1973), manganese (Klaassen, 1974a), mercury (Cikrt, 1972; Klaassen, 1976), zinc (Methfessel and Spencer, 1973), cadmium (Nordberg et al., 1977), tin (Hiles, 1974), beryllium (Cikrt and Bencko, 1974), arsenic (Klaassen, 1974b), selenium (Levander and 1 Present address: Isotope Laboratory of the Institutes for Biological Research, Czechoslovak Academy of Sciences, Budejovicka 1083, 140 00 Praha 4, Czechoslovakia.

Baumann, 1966), and cerium (Kitani et al., 1977) are excreted from the organism via bile. The biliary excretion of organic anions has been so far studied by Abou el Makarem et al. (1967) and Abdel Aziz et al. (1971). The results of our experiments concerning molybdenum excretion from the organism as a whole and from individual organs of experimental animals have been already reported in previous papers (Bibr and Lener, 1973, 1974). This paper deals with the biliary excretion, whole-body excretion and tissue distribution in the liver, blood, and jejunoileocecum of molybdenum in the form of inorganic anion, or pentavalent complexes, depending upon the molybdenum valence. METHODS Animals (substrain were used groups of 259

and anesthesia. Male Wistar strain rats Konarovice), mean body weight 230 g, in the experiments. The animals, kept in five were anesthetized by urethane (900 All

0041-008x/79/140259-05s02.00/0 Copyright @ 1979 by Academic Press, Inc. rights of reproduction in any form reserved. Printed in Great Britain

260

LENER

AND

BfBR

man, 1958; Levander, 1965). The solution of pentaand hexavalent molybdenum was injected into the tail vein of rats 1 hr after cannulation; the doses used were 0.08 and 4.6 mg MO/kg. Bile was collected in the first 2 hr after molybdenum injection at 3-min intervals and in the next 2 hr at 30-min intervals. The amount of bile excreted was determined gravimetrically. Molybdenum content in tissues. The molybdenum content in the whole blood, liver, and jejunoileocecum was determined at 1, 2, 3, and 4 hr after iv dose of 4.6 mg of penta- and hexavalent molybdenum/kg. Whole-body excretion. The whole-body excretion of both valence forms of molybdenum was determined at 1, 2, 3, and 4 hr after doses of 0.08 and 4.6 mg MO/kg, administered SC. Radioactivity measurement. The bile and body

mg/kg, ip) and their constant body temperature, monitored rectally, was maintained using an infrared heating lamp. Solutions. Hexavalent molybdenum was applied in the form of sodium molybdate (labelled with 99Mo, Radiochemical Centre, Amersham, U.K., 2 mg MO/ml, specific activity 5 mCi/ml). Pentavalent molybdenum was prepared by reducing the above solution with hydrazine hydrate at boiling point in 4 M hydrochloric acid medium. After the breakdown of excessive hydrazine, the solution of pentavalent molybdenum was neutralized to pH = 6.5 by caustic soda in the presence of ascorbic acid (MO : Asc.A. = 1 : 4). Biliary

excretion of molybdenum. The bile duct of anesthetized animals was cannulated through an abdominal incision, using the PE-10 cannula (Gross-

b.w.

008mgMo/kg

Mov, I

0.20

.0.20

0.15 (D z 0 B P 0.10 8 P

0.15

.O.lO

0.05

0.05

t 4 0

0. I

0

I

2

,

t

I

3

4

0

4.6mq MO”

I

I

2

#

3

4

MO/kgb.w.

6

6

---r--1 0

I

2

3

I 0

4

I

, 2

3

4

hours

FIG. 1. Biliary excretion of penta- and hexavalent molybdenum Each value represents mean + SE for five animals.

after 0.08 and 4.6 mg MO/kg.

BILIARY

EXCRETION

organ radioactivity measurements were conducted using an automatic gamma counting system (Searle and Co.) in the 99mTc peak at 0.140 meV, after reaching the 99Mo-99mT~ isotopic balance. The whole-body molybdenum excretion was measured in the 9gM~ peak at 0.704 meV, using a whole-body counter of our own construction, composed of two axially localized NaI(T1) crystals 15x 10 and 10x 10 cm. Details of the method have been described elsewhere (Babicky et al., 1970).

RESULTS Biliary

Excretion

The biliary excretion of penta- and hexavalent molybdenum is shown in Fig. 1. The upper part of the figure shows an increase in the molybdenum content in bile during the first 2 hr after administration of 0.08 mg MO/kg. No influence of molybdenum valence was observed. While the biliary excretion of hexavalent molybdenum administered at a dose of

0

I

261

OF MOLYBDENUM

2

4.6 mg/kg follows practically the samepattern as that of the O.O%mg/kg dose, the excretion of the pentavalent form differs significantly not only in the total amount of molybdenum excreted

in bile but also in the time course

of

biliary excretion (lower part of Fig. 1). Excretion

of Molybdenum

from

the Organism

The results of whole-body counting are presented in Fig. 2. The upper part of the figure shows that after the dose of 4.6 mg/kg of penta- and hexavalent molybdenum there is an accelerated excretion rate of the hexavalent form, whereas after 0.08 mg MO/kg (lower part of the figure) both molybdenum valence forms are excreted at an identical rate. Molybdenum

Tissue Concentration

Molybdenum concentrations in the whole blood, liver, and jejunoileocecum after the

3

4

hours

FIG. 2. Whole-body counting of penta- and hexavalent molybdenum excretion from the rat organism after SCdoses of 0.08 and 4.6 mg MO/kg. Solid circles (0) represent mean + SE values of excreted MO”‘, open circles (0) mean f SE values of excreted MO” (for five animals).

262

IBNER AND BfBR

P

BLOOD

T

LIVER

dose of 4.6 mg MO/kg are shown in Fig. 3. There is apparently a steep decrease in the hexavalent molybdenum concentration in all the tissues studied, particularly in blood, while the pentavalent molybdenum concentration decreases at a much slower rate; in the liver the pentavalent molybdenum is retained for 3 and 4 hr after administration. 0 MO” .

MO”’

Concentration Gradients

The molybdenum concentration gradients (according to Brauer (1959) showing the correlations among the liver, jejunoileocecum, bile, and blood as well as between the bile and liver are indicated in Table 1. It is quite apparent from Table 1 that even 4 hr after the administration of pentavalent molybdenum it had not reached the gradient value of 1.O, indicating the state of concentration equilibrium between the tissues in question. On the other hand, starting with the second hour after the administration of hexavalent molybdenum the concentration gradients for bile-blood and bile-liver became higher than 1.0 and their values further increased during the time period under study.

JEJUNOILEOCOECUM

I I

2

3

4

hours

FIG. 3. Penta- and hexavalent molybdenum content in the whole blood, liver, and jejunoileoceoum of rats after a dose of 4.6 mg MO/kg. Solid circles (0) represent mean f SE values of MO”‘, open circle (0) mean + SE values of MO” (for five animals).

TABLE MOLYBDENUM

1

CONCENTRATION

GRADIENTS

Hours

Concentration gradient

1

2

3

4

MO” Liver/blood JIC*/blood Bile/blood Bile/liver

0.37kO.17”

0.5OkO.28

0.62kO.05

0.79+0.14

0.27+0&I

0.6250.17

0.69?-0.07

0.73kO.07

0.01 0.23kO.10

0.36kO.02

0.50*0.03

0.56kO.05

0.72kO.38

0.80+0.05

0.71+0.13

0.59kO.14

0.44kO.20

0.74+0.10

0.86kO.06

0.54kO.07

0.67kO.80

0.73

0.89kO.07

1.60+0.17

2.46kO.24

3.27kO.20

1.53k0.36

3.67k1.61

3.31kO.29

3.81kO.15

0.09*

MoV’ Liver/blood JIG/blood Bile/blood Bile/liver

’ Means f SE for five individual animals. b Jejunoileocecum.

+0.10

0.61+0.09

'

BILIARY EXCRETION OF MOLYBDENUM

DISCUSSION The process of biliary excretion has now become the subject of intensive studies as one of the important detoxification and excretion mechanisms in the organism. According to Brauer’s scheme of biliary excretion, the group of B substances should involve only those compounds for which the bileblood concentration ratio ranges from 10 to 1000. In spite of the fact that this ratio for hexavalent molybdenum is 3 (Table 1) it seems justifiable to include this molybdenum valence form among the B substances and to presume the existence of an active secretion mechanism involved in its transfer from blood to bile. The biliary excretion of hexavalent molybdenum apparently involves the secretory activity of hepatic cells which in case of MO” and MO’” excretion participate in oxidation-reduction processes by which most of the pentavalent molybdenum is oxidized to the hexavalent form and which is then excreted in bile. In spite of the fact that only 1% of the total amount of molybdenum administered is excreted via bile, this mechanism of excretion cannot be underestimated in cases of massive molybdenum intoxication.

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263

BfBR, B., AND LENER, J. (1973). Excretion of moiybdenum by experimental animals. Physiol. Bohemoslov. 22, 167-178.

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METHFESSEL, A. H., AND SPENCER, H. (1973). Zinc metabolism in the rat. II. Secretion of zinc into intestine. J. AppI. Physiol. 34, 63-67. NORDBERG, G. F., ROBERT, K. H., AND PANNONE, M. K. (1977). Pancreatic and biliary excretion of cadmium in the rat. Acta Pharmacol. Toxicol. 41, 84-88.