Cysteine sulfinic acid decarboxylase activity in response to thyroid hormone administration in rats

The modulation of hepatic and renal cysteine sulfinic acid decarboxylase (EC 4.1.1.29) activities by triiodothyronine (T3) was studied in a series of experiments. In a dose--response study, hepatic cysteine sulfinic acid decarboxylase activity (CSAD) was depressed by 65% and renal activity was increased threefold in rats injected with 100 micrograms T3/100 g body wt for 7 days when compared to rats injected with 0.3 micrograms T3/100 g body wt. Western blot analysis indicated that these changes in CSAD activity were due to changes in the quantity of CSAD protein. Changes in hepatic and renal activities were not evident until 24 h after T3 administration. In response to T3 clearance, hepatic and renal CSAD activities approached euthyroid values 4-7 days after cessation of T3 injections although serum T3 concentrations were no different from euthyroid values 48 h after T3 injections were stopped. These data indicate that thyroid hormone effects persist after T3 clearance. The response of CSAD to thyroid status may be related to its role in taurine biosynthesis.