Effect of thyroid hormones and analogues on ammonia and urea excretion in Lata fish ( Ophicephalus punctatus)

Abstract

The influence of single intraperitoneal injection of thyroxine (T 4), triiodothyronine (T 3), tetraiodothyroacetic acid (TETRAC), and triiodothyroacetic acid (TRIAC) were studied on the nitrogen excretion (urea-N and NH 3N) of Lata fish acclimatized at 25 or 30°. The actions of T 4 and the iodinated analogs, studied at these temperatures on nitrogen excretion of these animals, appear to be temperature-specific. The NH 3N as well as urea-N excretion of normal Lata fish was also found to be directly proportional to the environmental temperature (10 to 30°). Thyroxine (T 4) injection at lower doses (0.5 or 1 μg/g) caused anabolic effect with respect to NH 3N and urea-N excretions at 25°. With higher doses of T 4 (2 μg/g or 4 μg/g) at 25° C, the results on nitrogen excretion were not significantly different from the control. At 30°, T 4 (1, 2, or 4 μg/g) increased NH 3N and urea-N excretion. Triiodothyronine (T 3) with higher doses (2 or 4 μg/g) was effective in causing increased NH 3N excretion at 25°. The responses of T 3 with a dose of 4 μg/g with respect to nitrogen excretion was about at the same level as found with 10 μg/g of T 4/g of body wt at this temperature. Tetraiodothyroacetic acid, or TETRAC, (1, 2, or 4 μg/g) enhanced NH 3N excretion, but not urea-N excretion, at 25°. Triiodothyroacetic acid (TRIAC) even with 4 μg/g was ineffective in this respect, at 25°. Both TETRAC and TRIAC with 1, 2, or 4 μg/g at 30° significantly increased NH 3N excretion. Compared to the controls, urea excretion remained unchanged with 1 μg of TRIAC/g at 30°. This nitrogen excretion (urea-N) was enhanced with higher doses of this analog (2 and 4 μg/g) at 30°. TETRAC with all doses used (1, 2, or 4 μg/g) increased urea-N excretion at this temperature. The results shown that TETRAC was more potent than TRIAC.