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Regulation by thyroid hormone of the concentration of substance P in the rat anterior pituitary.

The content of immunoreactive substance P (iSP) in the male rat anterior pituitary was measured after thyroidectomy and excess T4 administration. Baseline values for iSP content (mean +/- SE, 400 +/- 37 fmol/mg protein) increased progressively after thyroidectomy (4 days, 893 +/- 100; 6 days, 1321 +/- 242; 14 days, 1897 +/- 509). Administration of pharmacological doses of T4 (50 micrograms daily) for 2 and 14 days significantly decreased anterior pituitary iSP content (2 days, 196 +/- 30; 14 days 138 +/- 12). Thyroid status did not affect iSP content in the hypothalamus, caudate nucleus, amygdala, or brainstem. Partial chemical characterization of SP immunoreactivity in the anterior pituitary was obtained by gel permeation chromatography on Sephadex G-25, high pressure liquid chromatography, and the use of two antisera in RIAs, one directed against the amino-terminus and one directed against the carboxyl-terminus of the peptide. SP in the anterior pituitary was readily releasable in vitro by 44 mM potassium chloride in a calcium-dependent manner. The present study demonstrates that the concentration of iSP in the rat anterior pituitary is affected by the thyroid status of the animal and supports the probability that thyroid hormones participate in the regulation of the synthesis and/or release of iSP from the anterior pituitary.