TSH SYNTHESIS AND RELEASE IN THE THYROIDECTOMIZED RAT:

Publisher Website
Google Scholar
Abstract
Groups of surgically thyroidectomized (.hivin.T) male rats were sacrificed at intervals during the period of 1-5 and 30-180 days after .hivin.T. Plasma T3 [triiodothyronine], T4 [thyroxine] and TSH [thyroid stimulating hormone] levels and pituitary TSH content were measured by RIA [radioimmunoassay]. A drop of plasma T3 and T4 from normal to undetectable values occurred by day 3 post .hivin.T. There was a progressive increase of plasma TSH from the normal value of 136 .+-. 14 ng/ml to 1623 .+-. 186 ng/ml (mean .+-. SE) at day 5 post .hivin.T, reaching at 30 days a new plateau of 8618 .+-. 527 ng/ml. These levels remained unchanged up to 130 days post .hivin.T. At 180 days, plasma TSH (4123 .+-. 991 ng/ml) fell significantly below the plateau level. Pituitary TSH content fell from the normal value of 80.9 .+-. 15.9 .mu.g/mg to a nadir of 12.7 .+-. 1.4 .mu.g/mg at day 4 post .hivin.T and then slowly rose to 98.6 .+-. 5.9 .mu.g/mg at 100 days, remaining at this level for another 30 days and finally declining significantly at 180 days post .hivin.T. The rates of TSH release and synthesis were calculated using the metabolic clearance rates (MCR), determined from the curves of disappearance of injected [125I]-TSH by a noncompartmental analysis. The MCR values decreased, starting at 8 days after .hivin.T, and reached about half the normal value from 30 days onwards (0.257 .+-. 0.03 to 0.144 .+-. 0.001 mg/min per 100 g body wt).