Abstract
We have recently demonstrated that the iv administration of acidic fibroblast growth factor(a‐FGF) to rats for 6 days results in a marked increase in thyroid weight colloid accumulation and flat, quiescent follicular cells. Whereas a‐FGF administration consistently increases thyroid weight, there are only minor alterations in serum TSH and thyroid hormones, and no change in intrathyroidal metabolism of ^125^l metabolism. In the present work, we studied the effects of 1 or 6 daily injections of a‐FGF (60 μ/kg BW) or vehicle on the mRNA levels for histone, c‐fos, actin, type I 5′ deiodinase (5′D‐1), thyroid peroxidase, and thyroglobulin and cathepsin D in the thyroid, liver and bone. Rats were sacrificed 0.5, 2, 4, 8 and 24 h after the 1st or the 6th a‐FGF injection and thyroid, liver and calvarium were removed. The relative amounts of mRNAs were determined by slot blot analysis. There was a 43% increase in thyroid weight in rats treated with a‐FGF for 6 days compared to vehicle‐treated rats. We observed an increase in c‐fos mRNA content in the thyroid gland 0.5 to 4 h after 1 or 6 injections of a‐FGF. In contrast, treatment with a‐FGF for 1 or 6 days did not affect histone mRNA content, a marker of proliferative activity or actin mRNA levels. Treatment with a‐FGF caused a marked decrease in thyorid 5′ D‐I mRNA content in the thyroid. The decrease was present 2 h after the first injection and reached a nadir 8 h. After 6 daily injections, the decrease in 5′ D‐I mRNA was present throughout the whole day. In the liver, there was a significant decrease in 5′ D‐1 mRNA only 2 and 4 h after the 6daily injection of a‐FGF. There was no effect of a‐FGF treatment on the mRNA content of thyorid peroxidase, thyroglobulin, or a marker of lysosomal activity, cathepsin D. These data indicate that a‐FGF induces colloid accumulation in the rat thyroid without changes in proliferative or lysosomal activites, or alteration in the regulation of the thyroid specific genes thyroid peroxidase and thyroglobulin. Modification in gene expression and induction are reflected by the upregulation of the early response gene c‐fos. The marked and persistent decrease in 5′ deiodinase mRNA content after a‐FGF treatment suggests that a‐FGF may be involved in the regulation of 5′ D‐1 activity in the thyroid. © 1992 Wiley‐Liss, Inc.