Effects of an Acute Bacterial Infection on Serum Thyroid Hormones and Nuclear Triiodothyronine Receptors in Mice*

Abstract

Serum T3, T4, and rT3 levels as well as liver nuclear T3 receptors (NT3R) were measured in mice with a bacterial infection. Pseudomonas aeruginosa were injected into one thigh of ICR mice, resulting in a severe infection at sacrifice 15 h later. Since food intake, which influences serum thyroid hormone levels and NT3R, was 75% lower in infected than in control mice, infected mice were either fed and compared with pair-fed controls or fasted and compared with fasted and fed controls. Fasting induced a fall in serum T3 and T4 levels, which was even more pronounced in infected fasted animals. However, while fasting caused an approximately 80% increase in serum rT3 concentrations, serum rT3 levels in infected fasted animals were not different from those in fed controls. The combination of infection and fasting thus prevented the rise in serum rT3 otherwise invariably associated with fasting. NT3R measurements on isolated nuclei revealed the presence of NT3R in mouse liver similar to those reported in rat liver. The NT3R Kd (approximately 2 X 10(-10) M) was not affected by decreased food intake, infection, or a combination thereof. The NT3R maximum binding capacity (MBC) was decreased in fasted animals (460 vs. 306 pg/mg DNA). However, the MBC of infected fasted mice was not different from that of fasted mice. Similarly, no difference in MBC was found between infected fed and pair-fed control mice. In mice injected with heat-killed P. aeruginosa to evaluate potential effects of endotoxins, neither serum thyroid hormone levels nor hepatic NT3R were different from those of controls. These data show that in mice, a severe bacterial infection with P. aeruginosa has effects on serum hormone levels not explained by the disease-associated diminished food intake, whereas it has no effects on liver NT3R beyond those due to the disease-related decreased food intake.