Interrelationships between athyreotic and manganese-deficient states in rats.

Possible interrelationships of manganese-deficient and hypothyroid (thiouracil treatment) states in rats were examined. Clinical signs, necropsy changes, and plasma thyroxine concentrations were determined in control rats (group A), thiouracil-treated (hypothyroid) rats (group B), rats given manganese-deficient feed (group C), and rats given thiouracil and manganese-deficient feed (group D). Clinical signs observed included a hyperemic condition of the ears in group C and D rats that was considerably more severe in the latter group. One rat from group D also had middle ear changes, as reflected by a tilting of the head. Fluid intake was severely reduced in group D rats near the end of the 60-day experimental period and resulted in marked dehydration. Pathologic change (fatty liver) was observed at necropsy in only 1 rat from group D. Thiouracil treatment of rats reduced plasma thyroxine concentration to 48 to 68% of base line from experimental days 20 to 60. The same thiouracil treatment combined with feeding a manganese-deficient ration significantly reduced plasma thyroxine concentrations to 37% of base line at day 20 and 5% of base line at day 40; the concentration at day 60 was 76% of base line, apparently approaching normal because of concentration of the plasma (and thyroxine) in the dehydrated rats. Mean adrenal gland weight was significantly less than normal in group D rats, whereas mean thyroid gland weight in this group was increased, although less than that of group B rats treated with thiouracil only. Thus, clinical signs of deficiency were enhanced when athyreotic and manganese-deficient states were combined, and plasma thyroxine concentrations were markedly decreased, giving added meaning to the need for awareness of hormonal and trace mineral status of animals.