Pituitary-thyroid axis in short- and long-term experimental diabetes mellitus.
Short-term experimental diabetes mellitus (DM) produces a significant decrease in serum thyroid hormones, a decreased or normal serum thyroid-stimulating hormone (TSH) and a reduction in hepatic and renal T4-5'-deiodination. However, little is known about the effects of chronic diabetes mellitus on the pituitary-thyroid axis function. We evaluated the changes induced by very short-term (6 days), short-term (15 days) and chronic (6 months) streptozotocin-induced diabetes mellitus in 3-month old female Dutch-Miranda rat serum T4, serum TSH and T4-5'-deiodinase activity in the thyroid and pituitary glands. Serum hormones were determined by specific radioimmunoassays. Iodothyronine-5'-deiodinase activities were assayed in the thyroid and pituitary microsomal fractions using 2 microM T4 as substrate. Mean serum T4 was significantly decreased from 3.3 to 2.0 micrograms/dl 6 days after diabetes mellitus induction, and from 2.2 to 1.5 micrograms/dl after 15 days of DM, with no significant changes in serum TSH, indicating a decreased pituitary TSH responsiveness to the diminished suppression by T4, even though pituitary T4-5'-deiodinase activity was unchanged. Thyroid T4-5'-deiodinase was unchanged after 6 days of diabetes mellitus, but was significantly increased from 20.6 to 37.0 pmol T3/mg protein after 15 days. Six months after diabetes mellitus induction, both serum T4 and thyroid T4-5'-deiodinase returned to normal ranges and serum TSH was unchanged, although pituitary T4-5'-deiodinase was now significantly decreased from 2.7 to 1.7 pmol T3/mg protein. These findings indicate that some kind of adaptation to chronic insulinopenia may occur at the thyroid level, but this does not seem to be true for the pituitary.
Nascimento-Saba
C C
CC
Laboratório de Fisiologia Endócrina, Instituto de Biofísica Carlos Chagas Filho, Centro de Cièncias da Saúde, Universidade Federal do Rio de Janeiro, Brasil.
Breitenbach
M M
MM
Rosenthal
D
D
D000818:Animals; D015496:CD4-Positive T-Lymphocytes / Q000378:metabolism; D003921:Diabetes Mellitus, Experimental / Q000097:blood / Q000503:physiopathology*; D005260:Female; D010902:Pituitary Gland / Q000503:physiopathology*; D051381:Rats; D013961:Thyroid Gland / Q000503:physiopathology*; D013972:Thyrotropin / Q000097:blood* / Q000378:metabolism
D013972:Thyrotropin