COMPARATIVE EFFECTS OF NICKEL AND IRON DEPLETION ON CIRCULATING THYROID-HORMONE CONCENTRATIONS IN RATS

Trace elements have important metabolic functions, particularly as com ponents of enzymes and hormones (KIRCHGESSNER 1987). Relationships bet ween trace elements and thyroid hormone metabolism have been first rep orted for iodine, which is an integral component of thyroxine (T-4) an d triiodothyronine (T-3) (HETZEL and MABERLY 1986; NEVE 1992a) and for selenium as a component of type-I-deiodase (ARTHUR et al. 1990; BERRY et al. 1991; NEVE 1992b). However, in a few experiments it has been s hown that also essential trace elements including iron, copper, zinc a nd manganese may alter the concentrations of thyroid hormones in blood (DILLMAN et al. 1980; MORLEY et al. 1980; WADA and KING 1986; KIRCHGE SSNER et al. 1995; KRALIK et al. 1995, 1996a,b; LUKASKI et al. 1995). In the 1970s, findings consistent with nickel being a 'new' essential nutrient have been reported (NIELSEN et al. 1975; SCHNEGG and KIRCHGES SNER 1975; SPEARS et al. 1978). Since, no information about the effect of nickel deprivation on thyroid hormone status was available, this s tudy was primarily conducted to test whether dietary nickel deficiency may alter the concentrations of total thyroxine, free thyroxine and t riiodothyronine in plasma. Since, nickel depletion has been shown to s lightly impair iron status of animals (SCHNEGG and KIRCHGESSNER 1975, STANGL and KIRCHGESSNER 1996), it is difficult to delimit nickel defic iency effects from iron deficiency symptoms. Therefore, a second exper iment inducing moderate iron depletion was carried out to distinguish between the effect of nickel deficiency and iron deficiency on circula ting thyroid hormones.