The effect of Streptococcus pneumoniae infection on the binding of triiodothyronine to nuclei isolated from rat liver.

Hepatic nuclei were isolated from control and Streptococcus (S.) pneumoniae-infected rats to determine the effect of S. pneumoniae infection on the binding capacity and affinity of hepatic nuclei for T3. Infection did not affect the purity or yield of the isolated nuclei. A significant decrease in serum total T3 was observed 40 h after inoculation with S. pneumoniae. Serum free T3 was significantly decreased by 20 h after inoculation, but returned to control levels by 40 h after inoculation. Scatchard analysis of nuclear T3 binding, determined under optimal conditions, confirmed the presence of high affinity, low capacity sites for T3 on nuclei isolated from both control and infected rats. During infection, the maximum binding capacity of the purified nuclei for T3 decreased significantly, but infection had no significant effect on the affinity of the receptor for T3. These results suggest that the decrease in serum T3 observed during infection is not contributed to by increased hepatic nuclear T3 receptor concentration and that the increased hepatic RNA, protein, and lipid synthesis observed during S. pneumoniae infection in the rat is not the result of increased binding or affinity of T3 to the nuclear receptor.