Study of the Kinetics of the Thyroid Hormones and the Peripheral Conversion Rate of Thyroxine to Triiodothyronine in Acute Renal Insufficiency under Experimental Conditions

Summary

We studied the kinetic behavior of triiodothyronine (T₃) and thyroxine (T₄) in two groups of 10 sheep. One was used as the control group (I) and the other consisted of sheep with acute renal failure (A.R.F.) induced by an iv. injection of mercuric dichloride. Five sheep of each group were injected with ¹²⁵IT₃ and the remaining five with ¹²⁵IT₄, later taking periodical extractions throughout the first 96 hours. The radioactive contaminants in the plasma were eliminated by extracting the hormones through immunoextraction. The mathematical calculation of the kinetics was based on the open two-compartment model.

The A.R.F. caused a decrease in the disposition constant of the slow phase in the T₃ kinetics, while at the same time prolonging the plasma half-life of the phase. The steady state distribution volume increases and the distribution constant K₂₁ decreases in the group suffering from renal insufficiency.

As regards the T₄, all the kinetic parameters were altered with the exception of the distribution volumes, the most significant changes being the shortening of the plasma half-life in the end phases, the rise of the elimination constant K₁₃ and the increase in the plasma clearance and thyroxine turnover rates.

The analysis of the peripheral conversion rate revealed, with a great amount of variation, that there is evidence of the conversion of T₄ to T₃ in the healthy group while this phenomenon remains undetected in the sick animals.

Key-Words

Kinetics - Acute Renal Failure - Thyroid Hormones