Growth impairment caused by dietary nitrate intake regulated via hypothyroidism and decreased somatomedin.

The effect of 2 days or 6 weeks administration of the diet containing 3 per cent potassium nitrate on serum level of thyroxine (T4), triiodothyronine (T3), nitrate, methemoglobin and somatomedin activity was investigated in piglets aged 56 days. Sufficient iodine intake by mothers prevented a decrease of T4 level in piglets after 2 days administration of nitrate. However, after 6 weeks of nitrate administration a striking decrease of T4 level was found (average level less than 10 nmol l-1) which could not be prevented even by the addition of 0.5 mg iodide per kg diet. No adaptation to nitrate administration was observed. After long-term administration of nitrate a significant decrease of serum somatomedin activity was found which also showed a positive correlation with a decrease of body weight gain.