Psychopharmacology
Psychopharmacology 56, 113 - 114 (1978)
9 by Springer-Verlag 1978
Circadian Rhythm of Lithium Toxicity in Mice R I C H A R D H A W K I N S , D A N I E L F. K R I P K E , and DAVID S. J A N O W S K Y Group in Physiology and Pharmacology and Department of Psychiatry, University of California at San Diego; and Veterans Administration Hospital, San Diego, California, U.S.A..
Abstract. The existence of cyclical (circadian) variations in lithium toxicity in mice was determined. Mice, standardized to a light-dark cycle, were injected with lithium chloride (940 mg/kg) at one of six times (20:00, 24:00, 4:00, 8:00, 12:00, and 16:00) and subsequently observed for mortality over 28 h. A significant (P < 0.01) time-of-day effect was found for lithium-induced lethality, with highest lethality following injection at 12:00. Key words." Lithium - Toxicity -- Circadian rhythm Mice -
Lithium is widely used in the treatment of affective disorders. Unfortunately, lithium has a rather low therapeutic index (Goodman and Gilman, 1975), and hence it is desirable to minimize toxic side effects. Recent research indicates that biosusceptibility to a variety of toxic agents follows circadian rhythms (Reinberg and Halberg, 1971; Haus et al., 1972; Reinberg, 1974).
animals were removed at each observation. A chi-square (Z2) test was used to determine whether mortality differed significantly among the six injection times.
RESULTS Considering all times of injection together, 50 % of the mice had died by 16 h after injection of 940 mg/kg lithium. At this LDso point, there was a highly significant variation in mortality depending on the time of injection (Z2 = 17.20, P < 0.01). Peak mortality was found in animals injected at 12:00, toward the middle of the lights-on phase, when mice are quiescent. Lowest mortality was found in animals injected at 24: 00, toward the middle of the lights-off or activity phase. Figure 1 illustrates differences in mortality depending on time of injection. 100 90 80 70
MATERIALS AND METHODS
60
Male Swiss-Webster (Hilltop) mice, weighing 35 - 4 0 g, were housed five per box in a light-controlled room (lights on from 8 : 00 - 20: 00) for four weeks in December. Food and water were continuously available. A pilot dose response-toxicity study determined that 940 mg/kg of lithium chloride, injected at 16:00, was approximately a 24-h LD50 dosage. In the present experiment, groups of 20 animals each were injected at one of six times: 20: 00, 24: 00, 4: 00, 8 : 00, 12:00, and 16:00. Each animal was given 0.16 ml lithium chloride i.p. (225 mg/ml) dissolved in distilled water for an average dose of 940 mg/kg. After injection, animals were returned to their cages and observed at 4-h intervals for at least 28 h after injection. Dead
50
Address for offprint requests: David S. Janowsky, M.D., Department of Psychiatry, University of California at San Diego, P.O. Box 109, La Jolla, CA 92037, U.S.A.
40 30
~
28h
16h
20
j
10 0
9
9
9
e
Dark
_
Light
~\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\~ " ~
20:00 24:00 04:00
4h
I
08:00 12100 16'.00 20:00
TIME OF INJECTION
Fig. 1. Cumulative percentage of Swiss-Webster mice dead between 4 and 28 h after i.p. injection of lithium chloride (940 mg/kg)
0033-3158/78/0056/0113/$1.00
114
Similarly, in a separate 24-h pilot study in which injections began earlier (at 14:00 rather than 20:00), greater mortality was noted in animals injected with lithium during the lights-on phase.
DISCUSSION The specific cause of lithium's toxicity was not obvious from this study. Although Saron and Gaind (1973) suggested that lithium's effects on brain are the major source of toxicity and lethality, it is also possible that peripheral lithium effects contributed. The mechanism underlying the observed 24-h fluctuations in lithium toxicity may only be speculated upon. Possibly, fluctuations in toxicity might be based on interactions between lithium and neurotransmitters such as acetylcholine (Samples et al., 1977), sleep-activity state, or water or food consumption during the lights-on and lights-off phases. Alternatively, the fluctuations in toxicity may be due to direct circadian fluctuations in lithium metabolism and clearance, perhaps related to 24-h rhythms in plasma aldosterone (Hilfenhaus, 1976; Grim et al., 1974). It is possible that circadian influences also affect lithium levels in man. L. Huey et al. (personal communication) have noted that serum lithium levels are highest in man following evening lithium carbonate administration, as compared to levels following morning or afternoon administration This agrees with the higher lethality noted in our mice following morning administration, since mice are nocturnal animals
Psychopharmacology 56 (1978)
and their 24-h rhythms are generally opposite in phase to that of man. Thus the toxic effects of lithium in man, as in mice, might vary with the time of administration, a consideration that might have clinical significance. Acknowledgements. Supported by the Medical Research Service of the Veterans Administration and by NIMH 1 KO2 MH00117-01 and 1 P50 MH 30914-01 and MIRS No. 4576.
REFERENCES Goodman, L. S., Gilman, A. (eds.): The pharmacological basis of therapeutics, 5th ed. New York: MacMillan 1975 Grim, C., Winnacker, J., Peters, T., Gilbert, G. : Low renin, normal aldosterone and hypertension: circadian rhythm of renin, aldosterone, cortisol, and growth hormone. J. Ctin. Endocrinol. Metab. 39, 247-256 (1974) Haus, E., Halberg, F., Scheving, L., Pauly, J., Carduso, S., Kuhl, J., Sothern, R., Shiotsuka, R., Hwang, D. : Increased tolerance of leukemic mice to arabinosyl cytosine with schedule adjusted to circadian system. Science 177, 80-82 (1972) Hilfenhaus, M.: Circadian rhythms of plasma renin activity, plasma aldosterone and plasma corticosterone in rats. Int. J. Chronobiol..3, 213 - 229 (1976) Reinberg, A. : Chronopharmacology in man. In: Chronobiological aspects of endocrinology, symposium Capri, J. Aschoff, F. Ceresa, and F. Halbert, eds., pp. 305 - 337. Stuttgart-New York: Schattauer-Verlag 1974 Reinberg, A., Halberg, F. : Circadian chronopharmacology. Annu. Rev. Pharmacol. 11, 455-492 (1971) Samples, A., Janowsky, D. S., Pechnick, R., Judd, L. L. : Lethal effects of physostigmine plus lithium in rats. Psychopharmacology 52, 307- 309 (1977) Saron, B. M., Gaind, R. : Lithium. Clin. Toxicol. 6, 257-269 (1973) Received March 28, 1977; Final Version July 28, 1977
Psychopharmacology 56, 113 - 114 (1978)
9 by Springer-Verlag 1978
Circadian Rhythm of Lithium Toxicity in Mice R I C H A R D H A W K I N S , D A N I E L F. K R I P K E , and DAVID S. J A N O W S K Y Group in Physiology and Pharmacology and Department of Psychiatry, University of California at San Diego; and Veterans Administration Hospital, San Diego, California, U.S.A..
Abstract. The existence of cyclical (circadian) variations in lithium toxicity in mice was determined. Mice, standardized to a light-dark cycle, were injected with lithium chloride (940 mg/kg) at one of six times (20:00, 24:00, 4:00, 8:00, 12:00, and 16:00) and subsequently observed for mortality over 28 h. A significant (P < 0.01) time-of-day effect was found for lithium-induced lethality, with highest lethality following injection at 12:00. Key words." Lithium - Toxicity -- Circadian rhythm Mice -
Lithium is widely used in the treatment of affective disorders. Unfortunately, lithium has a rather low therapeutic index (Goodman and Gilman, 1975), and hence it is desirable to minimize toxic side effects. Recent research indicates that biosusceptibility to a variety of toxic agents follows circadian rhythms (Reinberg and Halberg, 1971; Haus et al., 1972; Reinberg, 1974).
animals were removed at each observation. A chi-square (Z2) test was used to determine whether mortality differed significantly among the six injection times.
RESULTS Considering all times of injection together, 50 % of the mice had died by 16 h after injection of 940 mg/kg lithium. At this LDso point, there was a highly significant variation in mortality depending on the time of injection (Z2 = 17.20, P < 0.01). Peak mortality was found in animals injected at 12:00, toward the middle of the lights-on phase, when mice are quiescent. Lowest mortality was found in animals injected at 24: 00, toward the middle of the lights-off or activity phase. Figure 1 illustrates differences in mortality depending on time of injection. 100 90 80 70
MATERIALS AND METHODS
60
Male Swiss-Webster (Hilltop) mice, weighing 35 - 4 0 g, were housed five per box in a light-controlled room (lights on from 8 : 00 - 20: 00) for four weeks in December. Food and water were continuously available. A pilot dose response-toxicity study determined that 940 mg/kg of lithium chloride, injected at 16:00, was approximately a 24-h LD50 dosage. In the present experiment, groups of 20 animals each were injected at one of six times: 20: 00, 24: 00, 4: 00, 8 : 00, 12:00, and 16:00. Each animal was given 0.16 ml lithium chloride i.p. (225 mg/ml) dissolved in distilled water for an average dose of 940 mg/kg. After injection, animals were returned to their cages and observed at 4-h intervals for at least 28 h after injection. Dead
50
Address for offprint requests: David S. Janowsky, M.D., Department of Psychiatry, University of California at San Diego, P.O. Box 109, La Jolla, CA 92037, U.S.A.
40 30
~
28h
16h
20
j
10 0
9
9
9
e
Dark
_
Light
~\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\~ " ~
20:00 24:00 04:00
4h
I
08:00 12100 16'.00 20:00
TIME OF INJECTION
Fig. 1. Cumulative percentage of Swiss-Webster mice dead between 4 and 28 h after i.p. injection of lithium chloride (940 mg/kg)
0033-3158/78/0056/0113/$1.00
114
Similarly, in a separate 24-h pilot study in which injections began earlier (at 14:00 rather than 20:00), greater mortality was noted in animals injected with lithium during the lights-on phase.
DISCUSSION The specific cause of lithium's toxicity was not obvious from this study. Although Saron and Gaind (1973) suggested that lithium's effects on brain are the major source of toxicity and lethality, it is also possible that peripheral lithium effects contributed. The mechanism underlying the observed 24-h fluctuations in lithium toxicity may only be speculated upon. Possibly, fluctuations in toxicity might be based on interactions between lithium and neurotransmitters such as acetylcholine (Samples et al., 1977), sleep-activity state, or water or food consumption during the lights-on and lights-off phases. Alternatively, the fluctuations in toxicity may be due to direct circadian fluctuations in lithium metabolism and clearance, perhaps related to 24-h rhythms in plasma aldosterone (Hilfenhaus, 1976; Grim et al., 1974). It is possible that circadian influences also affect lithium levels in man. L. Huey et al. (personal communication) have noted that serum lithium levels are highest in man following evening lithium carbonate administration, as compared to levels following morning or afternoon administration This agrees with the higher lethality noted in our mice following morning administration, since mice are nocturnal animals
Psychopharmacology 56 (1978)
and their 24-h rhythms are generally opposite in phase to that of man. Thus the toxic effects of lithium in man, as in mice, might vary with the time of administration, a consideration that might have clinical significance. Acknowledgements. Supported by the Medical Research Service of the Veterans Administration and by NIMH 1 KO2 MH00117-01 and 1 P50 MH 30914-01 and MIRS No. 4576.
REFERENCES Goodman, L. S., Gilman, A. (eds.): The pharmacological basis of therapeutics, 5th ed. New York: MacMillan 1975 Grim, C., Winnacker, J., Peters, T., Gilbert, G. : Low renin, normal aldosterone and hypertension: circadian rhythm of renin, aldosterone, cortisol, and growth hormone. J. Ctin. Endocrinol. Metab. 39, 247-256 (1974) Haus, E., Halberg, F., Scheving, L., Pauly, J., Carduso, S., Kuhl, J., Sothern, R., Shiotsuka, R., Hwang, D. : Increased tolerance of leukemic mice to arabinosyl cytosine with schedule adjusted to circadian system. Science 177, 80-82 (1972) Hilfenhaus, M.: Circadian rhythms of plasma renin activity, plasma aldosterone and plasma corticosterone in rats. Int. J. Chronobiol..3, 213 - 229 (1976) Reinberg, A. : Chronopharmacology in man. In: Chronobiological aspects of endocrinology, symposium Capri, J. Aschoff, F. Ceresa, and F. Halbert, eds., pp. 305 - 337. Stuttgart-New York: Schattauer-Verlag 1974 Reinberg, A., Halberg, F. : Circadian chronopharmacology. Annu. Rev. Pharmacol. 11, 455-492 (1971) Samples, A., Janowsky, D. S., Pechnick, R., Judd, L. L. : Lethal effects of physostigmine plus lithium in rats. Psychopharmacology 52, 307- 309 (1977) Saron, B. M., Gaind, R. : Lithium. Clin. Toxicol. 6, 257-269 (1973) Received March 28, 1977; Final Version July 28, 1977
