Abstract
1. An investigation has been made into factors regulating the secretion of thyroid hormones into bile. The preparation employed was the isolated rat liver perfused with a modified Tyrode solution.
2. Tracer amounts of radioactive thyroxine were injected into the Tyrode solution just before its entry into the liver. This allowed the thyroxine-binding sites in the tissue to capture most of the injected hormone. It was found that this tissue-bound hormone was then gradually secreted into the bile and that the process could be resolved into two components. There was a steady, continuous secretion of hormone, which maintained a fairly constant bile:liver ratio in thyroxine concentration of about 2·3. There was also, superimposed upon this, an extra transient secretion of thyroxine occurring just after the injection. This transient effect was abolished by injecting the hormone at 22° C and it was probably due to the sudden flood of free thyroxine into the tissue during the 15 sec injection period.
3. Very similar results were obtained with tri-iodothyronine except that the secretion process maintained a higher bile:liver ratio of about 3·7.
4. The secretion mechanism was extremely sensitive to changes in temperature and it was able to generate very high concentrations of free thyroxine in the bile. It was concluded that the over-all process was probably an active one.
5. The presence of 30% bovine serum in the perfusion fluid did not reduce the bile:liver thyroxine ratio even though it caused a massive fall in the amount of thyroxine in the tissue.
6. These results show that the rate of thyroxine secretion into bile is determined by the total amount of thyroxine trapped in the tissue. It is not directly related to the concentration of free thyroxine in the perfusing medium.
7. It is suggested that the secretion mechanism works from a small intracellular pool of free thyroxine which is in rapid exchange with the large pool of tissue-bound hormone, and that thyroxine exchange between this small intracellular pool and the free thyroxine pool in the plasma is relatively slow.
Full text
PDF
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Hillier A. P. Autoregulation of thyroxine secretion into bile. J Physiol. 1972 Mar;221(2):471–476. doi: 10.1113/jphysiol.1972.sp009762. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hillier A. P. Free thyroxine in bile. J Endocrinol. 1971 May;50(1):181–182. doi: 10.1677/joe.0.0500181. [DOI] [PubMed] [Google Scholar]
- Hillier A. P. The binding of thyroid hormones to phospholipid membranes. J Physiol. 1970 Dec;211(3):585–597. doi: 10.1113/jphysiol.1970.sp009295. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hillier A. P. The rates of release and binding of thyroxine by bovine serum. J Physiol. 1970 Jun;208(2):473–483. doi: 10.1113/jphysiol.1970.sp009132. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hillier A. P. The release of thyroxine from serum protein in the vessels of the liver. J Physiol. 1969 Aug;203(2):419–434. doi: 10.1113/jphysiol.1969.sp008872. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hillier A. P. The uptake and release of thyroxine and triiodothyronine by the perfused rat heart. J Physiol. 1968 Nov;199(1):151–160. doi: 10.1113/jphysiol.1968.sp008644. [DOI] [PMC free article] [PubMed] [Google Scholar]
- INGBAR S. H., FREINKEL N. Regulation of the peripheral metabolism of the thyroid hormones. Recent Prog Horm Res. 1960;16:353–403. [PubMed] [Google Scholar]
- Oppenheimer J. H., Surks M. I., Schwartz H. L. The metabolic significance of exchangeable cellular thyroxine. Recent Prog Horm Res. 1969;25:381–422. doi: 10.1016/b978-0-12-571125-8.50011-9. [DOI] [PubMed] [Google Scholar]