AJP - Endocrinology and Metabolism, Vol 255, Issue 3 E280-E286, Copyright © 1988 by American Physiological Society
Effect of postweaning thyroid status on endocrine and adipose development in rats
M. Q. Robert and E. Herrera
Departamento de Bioquimica y Fisiologia, Facultad de Biologia, Universidad de Barcelona, Spain.
We previously reported that 6 wk after thyroidectomy, rat fat cell diameter
and number were 86 and 32% of values in age-matched controls. This study
aims to 1) determine the time course of these changes and of parallel
changes in the levels of several hormones known to participate in adipose
differentiation and 2) try to normalize the altered cellularity with
thyroxine (T4) treatment. Rats were thyroidectomized (T) or sham-operated
and studied 2, 5, or 6 wk later. At 5 wk some T rats received L-T4.
Epididymal fat cells were sized and used to estimate fat cell number.
Triiodothyronine (T3), T4, thyroid-stimulating hormone, somatotropin (GH),
and insulin plasma levels were assayed. In T rats fat cell hypertrophia was
blunted uniformly with time, whereas fat cell hyperplasia was slow for 2 wk
and zero thereafter. Insulinemia was less drastically reduced than T4, T3,
and GH levels. The fat cell number-to-body weight ratio always stayed close
to the ratio present at thyroidectomy. In T rats receiving a T4
substitution dose for 1 wk, fat cell number and body weight increased, but
not when the T4 dose was lower even though the plasma thyroid hormone
levels were increased. These thyroid hormone effects on adipose tissue are
probably secondary to other endocrine changes that occur in hypothyroidism.
