The Effect of Pinealectomy on Plasma Vasopressin Response to Isotonic, Hypertonic and Hypovolemic Treatments in Rats Supplemented with L-Thyroxine
The present study was conducted to determine the effects of basal, isotonic as well as hypertonic and hypovolemic treatments on fluid-electrolyte balance and plasma AVP levels in rats supplemented with L-thyroxine and pinealectomized L-thyroxine. The animals were initially separated into 4 groups: control (n = 24), L-thyroxine treated (n = 24); L-thyroxine + sham-pinealectomy (n = 24) treated and 4-L-thyroxine + pinealectomy (n = 24) treated. L-thyroxine was given for 4 weeks. At the end of the 4-week experimental period, the sub-groups were formed before decapitation, which were classified as unstimulated (n = 6), isotonic (n = 6), hypertonic (n = 6) and hypovolemic (n = 6) stimulation. Plasma AVP, total triiodothyronine (TT3) and total thyroxine (TT4) levels were examined in plasma by RIA. Hematocrit and osmolality levels were also determined. It was found that the TT3 and TT4 levels showed significant increases in L-thyroxine treated groups (P < 0.001). Also, plasma AVP levels increased in the group subjected to L-thyroxine treatment. However, this increase was depicted to be significantly more prominent in L-thyroxine + pinealectomy treated group (P < 0.001). The results of the present study indicate that L-thyroxine treatment increases the basal and stimulated AVP release, which became more significant in the pinealectomy plus L-thyroxine treatment group. Moreover, the results indicate that AVP response to hypertonic and hypovolemic stimulations does not undergo any change due to supplementation by L-thyroxine treatment and/or pinealectomy plus L-thyroxine.
KeywordsAVP L-thyroxine treatment pinealectomy hypertonic and hypovolemic stimulation osmolality rat
Unable to display preview. Download preview PDF.
This study was supported by Scientific Research Projects Coordinatorship of Selcuk University (SUBAPK). (Project No: TF 2002/089). Authors would like to thanks Dr. Esma Oztekin for hormones analysis.
- 16.Juszczak, M., Kopotowska, A., Stempniak, B., Guzek, J. W. (1993) Hypothalamic and neurohypophyseal vasopressin and oxytocin content as influenced by haemorrhage in melatonin-treated male rats. Pathol. Pol. 44, 55–59.Google Scholar
- 18.Konakchieva, R., Mitev, Y., Almeida, O. F., Patchev, V. K. (1997) Chronic melatonin treatment and the hypothalamo-pituitary-adrenal axis in the rat: attenuation of the secretory response to stress and effects on hypothalamic neuropeptide content and release. Biol. Cell. 89, 587–596.CrossRefGoogle Scholar
- 19.Marcisz, C., Jonderko, G., Kucharz, E. J. (2001) Changes of plasma arginine-vasopressin level in patients with hyperthyroidism during treatment. Med. Sic. Monit. 7, 409–414.Google Scholar
- 30.Zimmerman, R. S., Ryan, J., Edwards, B. S., Klee, G., Zimmerman, D., Scott, N., Burnett, J. C. Jr. (1988) Cardiorenal endocrine dynamics during volume expansion in hypothyroid dogs. Am. J. Physiol. 255, R. 61–66.Google Scholar
This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.