Summary
Dietary nitrate significantly inhibits the growth of male and female rats. To test
the possibility that the growth hormone-releasing factor (GRF) content in hypothalamic
tissue is deranged under these conditions, male and female rats were fed a diet containing
3% KNO3for 6 weeks, compared to a normal diet (4 × 5 animals). The food intake of rats fed
nitrate was reduced significantly (23 and 28% resp.). Weight gain was also decreased
by 35 and 41% in male and female rats. The mean Sm—C/IGF—I concentration was 1.61
and 1.03 rU/ml in male and female control rats, whereas the concentrations in nitrate-exposed
rats were 0.92 and 0.64, respectively (P < 0.01). The GRF content of hypothalamic
tissue also decreased significantly from 407 and 533 ng/g protein in controls to 174
and 229 in treated male and female rats. Nitrate exposure is characterized by hypothyroidism,
food intake depression, low Sm—C/IGF—I concentrations in plasma and a decreased hypothalamic
GRF content. Independent of the peripheral changes, the content of Sm—C/ IGF—I in
the brain remains constant. The results of the study demonstrate that thyroid hormone
deficiency leads to an inhibition of GH axis already at the hypothalamic level.
Key words
Nitrate - Hypothyroidism - Relapse - Growth hormone releasing factor - Somato-medin
- C/Insulin-like growth factor