TOXlCOLQGYANDAPPLIEDPHARMACOLCGY35,341-346(1976)

The Effect of Povidone-Iodine on Thyroid Function in Rats

MAX GOLDMAN AND DAVID LANDRY

Department of Biology, University of South Dakota, VermiNion, South Dakota 57049

Received June 26,1975; accepted September 19,1975

The Effect of Povidone-Iodine on Thyroid Function in Rats. GOLDMAN,

M., AND LANDRY, D. (1976). Toxicol. Appl. Pharmacol. 35, 341-346. Young male, Sprague-Dawley rats, 60-70 days of age, and adult male Long-Evans rats, 1 yr old, were injected with povidone-iodine (Betadine) at two different dosages. The characteristic pattern of the Wolff-Chaikoff block followed exposure to the free iodine liberated by the povidone-iodine complex causing a reduction in thyroid 1311 uptake, depression of the thyroid-to-serum radioiodide ratio, and inhibition of organic iodinations. The marked reduction in the percentages of labeled mono- and di-iodo- tyrosines (MIT and DIT), and iodothyronines (T3 + T4), the large increase in percentage of labeled iodide and the increase in MIT/DIT ratios are changes which are considered as a classic illustration of the consequences of a reduction in thyroid hormone synthesis. This is an example of what is termed the Wolff-Chaikoff effect which usually follows the presence of high concentrations of inorganic iodine.

Povidone-iodine (Betadine) is an antiseptic bactericide that is utilized extensively as a surgical scrub and a general topical microbicide and for preoperative preparation for surgery. It is an iodophore of a water-soluble complex of polyvinylpyrrolidone and iodine which slowly releases free iodine.

Quagliana (1963) has reported that administration of povidone-iodine as a pre- operative skin preparation and as a vaginal douche prior to various surgical procedures induced an elevation in serum protein-bound iodine (PBI). However, neither Garnes et al. (1959) nor Kearns (1965) were able to find any measurable effect of povidone- iodine on either serum protein-bound iodine or butanol-extractable iodine (BEI). Recently, King and Diddle (1970) have reported that application of povidone-iodine to patients undergoing vaginal surgery resulted in a significant elevation in serum protein-bound iodine 24 hr later which returned to preoperative values the following week. Concomitant determinations of serum thyroxine showed no significant elevation due to the treatment. The present study was undertaken to ascertain the influence of povidone-iodine on thyroid function by examining some of the kinetics of iodine metabolism.

METHODS

Male Sprague-Dawley rats, 190-220 g, 60-70 days old, and male Long-Evans rats, 480-500 g, 1 yr old, were used in this study. Both strains of rats were bred in our labora- tory and maintained on Purina laboratory chow and water ad libitum. Copyright 0 1976 by Academic Press, Inc. 341 All rights of reproduction in any form reserved. Printed in Great Britain

342 GOLDMAN AND LANDRY

Povidone-iodine’ (Betadine, PVP-I) contained 10 g of available iodine per 100 g of product and was used at two different dosages, 500 pg and 5 mg/animal. Appropriate dilutions were made such that each animal received an ip injection of 0.5 ml. All control animals were injected ip with 0.5 ml of physiological saline.

Thyroid radioiodide concentration ratios. The determination of the thyroid-to-serum radioiodide ratio (T/S) was performed on two groups of rats: a group of Sprague- Dawley rats, 60-70 days of age, and a group of Long-Evans rats, 1 yr old. Each rat was injected ip with 10 mg of methimazoleZ followed 1 hr later by an ip injection of 0.5 ml of povidone-iodine containing 500 pg or 5 mg of available iodine or 0.5 ml of physiological saline. Five minutes later all animals received an ip injection of 3 pCi of carrier-free 1311.3 Blood was obtained from the dorsal aorta, and the thyroid glands were removed under light ether anesthesia and weighed 1 hr after radioiodine administration. After homogenization in 0.5 ml of NaCl-Tris buffer, pH 8.5, the radioactivity in aliquots of homogenate and in serum were counted in a Nuclear Chicago well-type scintillation counter. The T/S ratio was calculated as the ratio of radioiodide per gram of thyroid to radioiodide per milliliter of serum (Goldman, 1973).

Thyroid 1311 uptake and distribution of 1311 in hydrolyzed thyroid glands. Long-Evans rats (60-70 days of age) received an ip injection of 0.5 ml of povidone-iodine containing 500 pug or 5 mg of available iodine or 0.5 ml of physiological saline 5 min prior to an ip injection of 10 pCi of 1311 The thyroid glands were removed and homogenized in . an NaCl-Tris buffer, pH 8.5,l hr later and the radioactivity in an aliquot of homogenate counted to determine the thyroid 1311 uptake as a percentage of the injected dose. The homogenate was hydrolyzed with Pronase 4 for 8 hr and the iodinated amino acids were fractionated by paper chromatography in a collidine-3 N ammonia (3: I, v/v) solvent system for 16 hr. The positions of the radioactive zones were located by auto- radiography and the radioactivity in the bands determined according to the procedure of Rosenberg et al. (1964).

The radioactivity in an aliquot of serum was also counted. Values are expressed as the means +SE, and analysis of the significance of differences

between groups was done by means of Student’s t test. Ap value co.01 was considered statistically significant.

RESULTS

Thyroid: Serum Radioiodide Concentration Ratio (T/S)

The data obtained in two separate experiments in which two different strains of rats, Sprague-Dawley (60-70 days of age) and Long-Evans (1 yr old), were used are shown in Table 1. The T/S values for the control animals are typical of rats of these ages in our colony. Povidone-iodine injected at a total dosage of 500 pg of available iodine per rat lowered the T/S ratio in the Sprague-Dawley and the Long-Evans rats from their control values to 11.1 and 12.5 respectively. Moreover, when the dose was raised to 5 mg of available iodine per animal a further and even more marked suppression in

1 Obtained from Purdue Frederick Company, Norwalk, Connecticut. * I-Methyl-2-mercaptoimidazole, donated by Eli Lilly and Company, Indianapolis, Indiana. 3 Obtained from New England Nuclear, Boston, Massachusetts. 4 Strepromyces griseus protease, Calbiochem, Los Angeles, California.

POVIDONE-IODINE ON THYROID 343

TABLE 1

EFFECT OF POVIDONE-IODINE ON T/S IODIDE RATIO IN MALE RATS’

Strain Treatment Number Body weight Thyroid weight of rats (d bg) T/S

Sprague-Dawley Saline injection 10 203 i- 7.0” 12.3 + 0.7 27.7 _+ 3.1 Sprague-Dawley mo I43 13 198 + 4.8 13.2 _+ 0.6 11.1 + 0.5’ Sprague-Dawley 5mi3 14 201 +_ 6.1 12.5 f 0.7 2.1 + 0.4’ Long-Evans Saline injection 10 447 + 20.7 29.2 + 3.1 45.1 _+ 4.4 Long-Evans 500 .a 10 450 + 13.4 23.9 + 3.8 12.5 + 2.2d Long-Evans 5mg 10 487 k 14.2 26.8 _+ 2.3 1.9 + 0.26

a Rats received a single ip injection of 0.5 ml of providone-iodine 5 min before ip injection of lJII; thyroid glands were removed 1 hr later and thyroid: serum radioiodide concentration ratio (T/S) was calculated.

b Values are expressed as means &SE. c Significantly different from treated and saline-injected Sprague-Dawley controls; p < 0.001. d Significantly different from treated and saline-injected Long-Evans controls; p < 0.001.

TABLE 2

EFFECT OF POVIDONE-IODINE ON THYROID 13’1 UPTAKE AND SERUM 1311 IN MALE SPRAGUE-DAWLEY RATS’

Treatment Number of

rats Thyroid IJII uptake

(% injected dose) Serum 1311

(‘A injected dose/ml)

Saline injection 10 1.12 + 0.1” 0.47 5 0.06 500 Pug 10 0.09 + 0.01’ 0.48 + 0.06 5mg 10 0.07 k 0.01’ 0.91 + 0.07d

0 Rats received a single ip injection of 0.5 ml of povidone-iodine 5 min before ip injection of 1311; thyroid glands removed 1 hr later and thyroid uptake and serum radioactivity calculated.

* Values are expressed as means GE. c SignificantIy different from treated and saline-injected controls; p < 0.001. d Significantly different from treated and saline-injected controls and between treated groups;

p < 0.01.

T/S ratio occurred, equivalent to that observed in hypophysectomized rats (Taurog et al., 1958).

Although the serum radioactivity in rats injected with povidone-iodine at a dose level of 500 pg of available iodine per animal was not dissimilar from the serum values observed in control animals, the thyroid uptake of 13’1 was depressed (Table 2). Injec- tion of povidone-iodine at the higher dose of 5 mg of available iodine was associated with a significant elevation in serum radioactivity together with a reduction in uptake of radioiodine by the thyroid gland.

Distribution of 1311 in Components of Pronase-Hydrolyzed Thyroid

A marked disparity in distribution of radioiodine among the iodinated amino acids of the hydrolysates of thyroglobulin of control and povidone-iodine-injected animals is

344 GOLDMAN AND LANDRY

TABLE 3

DISTRIBUTION OF 13’1 PERCENT IN CHHOMATOGRAMS OF THYROID HYDROLYSATES OF MALE

SPRAGUE-DAWLEY RATS INJECTED WITH POVIDONE-IODINE”

Number MIT/ Treatment of rats Origin MIT DIT Ts+TJ 1311 DIT

-I_

Saline injection 8 1.6+_0.2b 30.7+1.1 50.2f1.6 8.6kO.2 8.9kO.2 0.6fO.l

500 Piit 10 1 S&O.2 5.9kO.4 4.1kO.3” 6.6kO.4’ 79.9+1.4” 1.4+0.1” 5mg 10 0.2kO.3 2.7k0.2d 2.0_+0.2d 2.6k0.1d 91.5+1.7d 1.4_+0.1’

a Rats received a single ip injection of 0.5 ml of povidone-iodine 5 min before ip injection of 1311; thyroid glands removed 1 hr later, homogenized with Pronase and chromatographed. MIT, monoiodo- tyrosine; DIT, diiodotyrosine; Ta, triiodothyronine; T4, thyroxine.

b Values are expressed as means *SE c Significantly different from saline-injected controls; p < 0.001. d Significantly different from saline-injected controls and treated groups; p < 0.001.

shown in Table 3. The incorporation of 13’ into a number of thyroidal components was severely inhibited as noted by the restriction in labeling of both iodotyrosines (MIT and DIT) and iodothyronines (T, + T,). Concomitantly, the fraction of labeled iodide increased greatly together with an increase of r311-labeled MIT to 1311-labeled DIT (MIT/DIT) leading to an MIT/DIT ratio above unity due to a greater deficit in labeling of DIT. The effect of povidone-iodine on these parameters was even more marked with the large dose of injected povidone-iodine.

DISCUSSION

Iodide in excess induces an acute inhibition in organic iodine synthesis termed the Wolff-Chaikoff effect (Morton et al., 1944; Wolff and Chaikoff, 1948; Nagataki and Ingbar, 1964). However, the suppression in thyroid hormone synthesis is only temporary since, eventually, adaptation to the large iodide loads occurs and escape from this block follows with consequent resumption in organic binding of the iodide remaining in the gland (Wolff et al., 1949). The Wolff-Chaikoff effect has also been demonstrated in humans (Stanley, 1949) and is believed to impart some measure of protection from precipitous and toxic increases in thyroid hormone formation. Braverman and Ingbar (1963) have suggested that, as a consequence of inhibited organic binding of excess iodide, an intrinsic mechanism exists in the thyroid gland which reduces the capacity of the thyroid to transport iodide actively. This results in a decline in intrathyroidal iodide to a concentration which is inadequate to inhibit further the organic binding of iodide, and so escape, or adaptation, ensues.

The data obtained in our study indicate that povidone-iodine at two different dosages elicited the characteristic pattern of the classic Wolff-Chaikoff blockade induced by large iodide loads in rats (Wolff and Chaikoff, 1948) and in man (Stanley, 1949). Table 3 shows that the acute response to povidone-iodine at the lowest dosage administered evoked a depression in organic binding of iodide resulting in an increase in the 13rI-

POVlDONE-IODINE ON THYROID 345

labeled iodide fraction, marked diminuation in thyroid labeling of iodothyronines and iodotyrosines with an elevation in the MIT/DIT ratio indicative of the reduction in thyroid hormone synthesis (Galton and Pitt-Rivers, 1959). Demonstration of the Wolff-Chaikoff effect was even more vivid with the higher dosage given, evoking further suppression in organification of iodide (Table 3), reduction in thyroidal 1311 uptake (Table 2) with a severe depression in thyroidal iodide-transport capacity as evidenced by the T/S ratios (Table 1). Furthermore, the tremendous increase in total serum radioactivity obtained with the larger dose of povidone-iodine (Table 2) is related to the marked reduction in thyroidal radioiodine uptake and depressed T/S ratios.

Recently Lavelle er al. (1975) have suggested a more cautious use of povidone-iodine since topical application to bum patients resulted in elevated serum concentrations of inorganic iodide, indicating that povidone-iodine is readily absorbed. Under such circumstances, the acute inhibition of thyroid hormone synthesis would follow (Wolff and Chaikoff, 1948; Stanley, 1949) in order to preclude the formation of massive toxic increases in thyroid hormones. However, the suppression in thyroid hormone formation which ensues is temporary since hormonal synthesis resumes as the concentration of plasma iodide declines below a critical concentration, according to Wolff and Chaikoff (1948). It has since been shown that the depression in organic binding of iodide is dependent on the intrathyroidal rather than on the plasma iodide concentration (Raben, 1949). Consequently, reports of increased amounts of serum protein-bound iodine after povidone-iodine administration might simply reflect escape from the Wolff- Chaikoff effect or adaptation to the high plasma iodide concentrations with consequent resumption of thyroid hormone synthesis (Wolff et al., 1949; Braverman and Ingbar, 1963).

REFERENCES

BRAVERMAN, L. E , AND INGBAR, S. H. (1963). Changes in thyroidal function during adaptation to large doses of iodide. J. Clin. Invest. 42, 1216-1231.

GALTON, V. A., AND PINT-RIVERS, R. (1959). The effect of excessive iodine on the thyroid of the rat. Endocrinology 64,835-839.

GARNES, A. L., DAVIDSON, E., TAYLOR, L. E., FELIX, A. J., SHIDLOVSKY, B. A., AND PRIGOT A. (1959). Clinical evaluation of povidone iodine aerosol spray in surgical practice. Amer. J. Surg. 97,49-53.

GOLDMAN, M. (1973). Failure of dimethyl sulfoxide (DMSO) to alter thyroid function in the rat. Toxicol. Appl. Pharmacol. 24,73-80.

KEARNS, J. E. (1965). The effect of new iodophors on protein bound iodine and butinol extract- able iodine in humans. Amer. J. Surg. 109, 457-459.

KING, K. R., AND DIDDLE, A. W. (1970) Protein-bound iodine and T4 tests after vaginal application of povidone-iodine. Amer. J. Obstet. Gynecol. 108, 1175-l 177.

LAVELLE, K. J., DOEDENS, D. J., KLEIT, S. A., AND FORNEY, R. B. (1975). Iodine absorption in burn patients treated topically with povidone-iodine. Clin. Pharrnacol. Ther. 17,355362.

MORTON, M. E., CHAIKOFF, I. L., AND ROSENFELD, S. (1944). Inhibiting effect of inorganic iodide on the formation in vitro of thyroxine and diiodotyrosine by surviving thyroid tissue. J. Biol. Chem. 154,381-387.

NAGATAKI, S., AND INGBAR, S. H. (1964). Relation between qualitative and quantitative alterations in thyroid hormone synthesis induced by varying doses of iodide. Endocrinology 74,73 1-736.

QIJAGLIANA, J. M. (1963). Effect of topical povidone-iodine (Betadine) on serum protein- bound iodine. J. Clin. Endocrinol. 23, 395-397.

346 GOLDMAN AND LANDRY

RABEN, M. S. (1949). The paradoxical effects of thiocyanate and of thyrotropin on the organic binding of iodine by the thyroid in the presence of large amounts of iodide. Endocrinology 45,296-304.

ROSENBERG, L. L., GOLDMAN, M., LAROCHE, G., AND DIMICK, W. K. (1964). Thyroid function in rats and chickens: Equilibrium of injected iodide with existing thyroidal iodine in Long- Evans rats and white Leghorn chickens. Endocrinology 14,212-225.

STANLEY, M. M. (1949). The direct estimation of the rate of thyroid hormone formation in man. The effect of the iodide ion on thyroid iodine utilization. J. Clin. Endocrinol. 9,941-954.

TAUROG, A., TONG, W., AND CHAIKOFF, I. L. (1958). Thyroid 1311 metabolism in the absence of the pituitary: The untreated, hypophysectomized rat. Endocrinology 62,646-663.

WOLFF, J., AND CHAIKOFF, I. L. (1948). Plasma inorganic iodide as a homeostatic regulator of thyroid function. J. Biol. Gem. 174,555-%X.

WOLFF, J., CHAIKOFF, I. L., GOLDBERG, R. C., AND MEIER, J. R. (1949). The temporary nature of the inhibitory action of excess iodide on organic iodine synthesis in the normal thyroid. Endocrinology 45, 504-5 13.