Early changes in the levels of serum triiodothyronine (T3), thyroxine (T4), T3/T4 ratio and microsomal carboxylesterase activity in rats following treatment with CCL4.

To study the relationship between the activity of nonspecific carboxylesterase located in the smooth endoplasmic reticulum (SER) of hepatocytes, and serum thyroid hormones including triiodothyronine (T3), thyroxine (T4), and T3/T4 ratio, we determined these hormones, liver carboxylesterase activity, and serum alanine amino-transferase (SGPT) before, and 5 to 720 min after treatment with a single oral dose of CC14 (1 ml/kg) in rats. The serum T3/T4 ratio decreased 5 to 10 min after administration. Each of 16 male and 16 female rats showed a significant correlation between carboxylesterase activity and T3/T4 ratio (male, r = 0.79, p less than 0.01; female, r = 0.84, p less than 0.01), but revealed no correlation between carboxylesterase and T3 or T4, alone. SGPT contents were elevated 6 to 12 h after, whereas T3/T4 ratio decreased gradually during the course. The SER increased mildly 5 min after, but was irregularly distended 6 h after. Changes in the microvilli were not found 5 min after, but the disruption was seen 6 h after. These results suggest that serum T3/T4 ratio is closely correlated with microsomal carboxylesterase activity in CC14-treated rats and represents a microsomal function.