AJP - Endocrinology and Metabolism, Vol 245, Issue 1 32-E37, Copyright © 1983 by American Physiological Society
In vitro TSH and PRL secretion from eutopic and heterotopic rat pituitaries: effects of hypothyroidism
H. Ikeda and M. A. Greer
Five adenohypophyses from donors of the same strain, age, and sex were
transplanted under the renal capsule of young adult female rats. At least 3
wk later, enzymatically dispersed cells from eutopic or heterotopic
adenohypophyses from the same rat were perifused in vitro in a small
chamber. Thyrotropin (TSH) and prolactin (PRL) secretion per 10(6) cells
were significantly less from heterotopic than from eutopic cells under all
conditions. In cells from euthyroid animals, TRH induced TSH secretion only
in the eutopic cells but induced PRL secretion in both eutopic and
heterotopic cells. Hypothyroidism increased TRH-induced TSH secretion and
content in the cell lysate in both eutopic and heterotopic cells but
increased TRH-induced PRL secretion only in the eutopic cells. The increase
in TSH secretion induced by hypothyroidism in the heterotopic cells was of
borderline statistical significance. The inability of TRH to induce TSH
secretion in heterotopic pituitary cells from euthyroid rats may be due to
a lower set point for thyroid hormone inhibition of TSH secretion in the
heterotopic thyrotrophs. Heterotopic pituitary TSH secretion is probably
suppressed by the normal plasma thyroid hormone concentration maintained by
the eutopic pituitary and may be stimulated by TRH only in the presence of
a subnormal plasma thyroid hormone concentration.
