AJP - Endocrinology and Metabolism, Vol 260, Issue 4 E608-E612, Copyright © 1991 by American Physiological Society
Compensatory changes in thyroid blood flow are only partially mediated by thyrotropin
M. Michalkiewicz, J. M. Connors, L. J. Huffman, Z. Pietrzyk and G. A. Hedge
Department of Physiology, West Virginia University Health Sciences Center, Morgantown 26506.
It has been shown that the compensatory growth of the thyroid gland and the
compensatory increase in hormone secretion that occur after
hemithyroidectomy are preceded by a dramatic increase in thyroid blood flow
(BF). These alterations in the thyroid remnant may be due to the
concomitant increase in plasma thyrotropin (TSH) concentrations. It has
been suggested, however, that the compensatory thyroid growth may also
involve a neural reflex. In this study we have investigated the role of TSH
in mediating the compensatory alterations in thyroid BF and mass after
subtotal thyroidectomy. Male Sprague-Dawley rats were anesthetized with
ether for surgical or sham hemithyroidectomy. One-half of the
hemithyroidectomized rats (HTX) received no further treatment; in the other
one-half of the HTX rats (Clamp), plasma TSH levels were maintained at
levels comparable with those in sham-operated animals by initiating
constant thyroid hormone replacement beginning at the time of
hemithyroidectomy. Plasma samples for TSH, 3,5,3'-triiodothyronine, and
thyroxine radioimmunoassays were obtained 2, 7, 14, and 21 days after
surgery. Thyroid BF was determined at 1, 2, and 3 wk after surgery by the
reference sample version of the radioactive microsphere technique (141Ce,
15 microns diameter). Plasma TSH levels and thyroid lobe weight were
significantly elevated in HTX rats but not in Clamp rats. Thyroid BF was
markedly increased in HTX rats. Thyroid BF was also significantly increased
in Clamp rats despite the suppression of the rise in plasma TSH
concentration, but this increase was less than that in HTX rats. Neither
hemithyroidectomy nor Clamp treatments had any effect on arterial blood
pressure or BF to other tissues (e.g., kidney).(ABSTRACT TRUNCATED AT 250
WORDS)
