Regulation of thyrotropin secretion in rats bearing the Walker 256 carcinoma

Journal Article · Sun Nov 01 04:00:00 EST 1981 · Endocrinology; (United States)

DOI:https://doi.org/10.1210/endo-109-5-1760· OSTI ID:5574535

Kumara-Siri, M H ^[1]; Lee, K; Surks, M I

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1. Montefiore Hospital and Medical Center, Bronx

To evaluate the mechanisms whereby serum TSH was maintained in the normal range in tumor-bearing rats in association with decreased serum T/sub 4/ and T/sub 3/ concentrations, we studied the regulation of TSH secretion in groups of control (C) and T rats. The pituitary TSH contents were similar in the two groups of animals, and an iv injection of TRH (5 ..mu..g/100 g BW) resulted in a 10-fold increase in plasma TSH concentrations in the control group 15 min after injection. The TSH concentrations achieved after TRH injection were significantly greater in T rats than in the C group. A progressive 5- to 8-fold increase in plasma TSH was noted in both C and T rats after thyroidectomy. There was no difference in the integrated TSH response between these groups. Similarly, a smaller stimulus to TSH secretion did not produce significantly different effects on plasma TSH between groups of C and T rats. This was demonstrated in a study in which both groups of rats were fed 1-methyl-2-mercaptoimidazole (methimazole(MMI)) (10 ..mu..g/ml) in their drinking water. 5 days after the addition of MMI the mean plasma T/sub 4/ level decreased from 3.6 +/- 0.5 to 2.7 +/- 0.6 (SEM) ..mu..g/dl (P<0.01). The mean plasma TSH level increased significantly (P<0.001) from 150 +/- 20 to 629 +/- 135 ng/ml in C rats and from 208 +/- 58 to 868 +/- 196 ng/ml in T rats after MMI treatment. The local production of T/sub 3/ from T/sub 4/ was studied in homogenates of pituitaries obtained from C and T rats. A mean 2.1-fold increase in the rate of T/sub 3/ formation from T/sub 4/ was noted in tissue from T rats. Lastly, the concentration of pituitary T/sub 3/ in C and T rats was determined directly by RIA. The mean T/sub 3/ content of T rats (18 +/- 1 pg/pituitary) was significantly decreased (P<0.001) from that of C rats (41 +/- pg/pituitary).

• OSTI ID: 5574535
• Journal Information: Endocrinology; (United States), Journal Name: Endocrinology; (United States) Vol. 109:5; ISSN ENDOA
• Country of Publication: United States
• Language: English

Related Subjects

550601* -- Medicine-- Unsealed Radionuclides in Diagnostics
62 RADIOLOGY AND NUCLEAR MEDICINE
AMINO ACIDS
ANIMALS
BODY
CARBOXYLIC ACIDS
DISEASES
DOSE-RESPONSE RELATIONSHIPS
ENDOCRINE GLANDS
GLANDS
HORMONES
ISOTOPE APPLICATIONS
MAMMALS
METABOLISM
NEOPLASMS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
ORGANIC IODINE COMPOUNDS
ORGANS
PEPTIDE HORMONES
PITUITARY GLAND
PITUITARY HORMONES
RADIOASSAY
RADIOIMMUNOASSAY
RATS
RESPONSE MODIFYING FACTORS
RODENTS
THYROID HORMONES
THYROXINE
TRACER TECHNIQUES
TRIIODOTHYRONINE
TSH
VERTEBRATES