D. Villar et al., EFFECT OF PROPYLTHIOURACIL-INDUCED HYPOTHYROIDISM ON THYROID-HORMONE PROFILES AND TISSUE DEIODINASE ACTIVITY IN CASHMERE GOATS, Small ruminant research, 29(3), 1998, pp. 317-324
The relationships between dose of propylthiouracil (PTU), circulating
plasma thyroid hormone concentrations and 5'-monodeiodinase enzyme act
ivity were investigated to determine the dose and duration of PTU trea
tment required to suppress plasma thyroid hormone levels in cashmere g
oats. Six groups of four cashmere goats were orally dosed for 2 months
with between 1.1 and 35 mg/kg/bw per day of PTU. Mean thyroxine (T4)
concentrations in goats treated with 1.1 mg/kg of PTU did not differ s
ignificantly from the control animals at any time during the study. Ho
wever, in goats treated with 2.2 to 35 mg/kg/day of PTU, T4 concentrat
ions declined in a dose dependent manner and plateaued after approxima
tely 1 month of treatment. Mean plasma triiodothyronine (T3) concentra
tions were not significantly affected by any of the PTU doses. Type I
5'-monodeiodinase (type I 5'-MDI) activity in liver and kidney in the
1.1 mg/kg group was suppressed to 25 and 37%, respectively, of values
recorded in control animals (24.3 vs. 98.4 for liver, and 15.7 vs. 42.
4 pmol iodine released/h/mg protein for kidney), and was below assay s
ensitivity at doses of PTU > 4 mg/kg, Type II 5'-monodeiodinase activi
ty in goat skin was detected at approximately 11.5 fmol iodine release
d/h/mg/protein and was not apparently affected by PTU treatment. It is
concluded that a dose I 1 mg/kg/bw PTU can be used in long-term studi
es in goats, to inhibit extrathyroidal conversion of T4 to T3 via type
I 5'-MDI without influencing circulating thyroid hormone profiles. (C
) 1998 Elsevier Science B.V. All rights reserved.