The effect of pinealectomy on plasma vasopressin response to isotonic, hypertonic and hypovolemic treatments in rats supplemented with L-thyroxine

Mogulkoc, R. and Baltaci, A. (2008) The effect of pinealectomy on plasma vasopressin response to isotonic, hypertonic and hypovolemic treatments in rats supplemented with L-thyroxine. Acta Biologica Hungarica, 59 (2). pp. 163-172. ISSN 0236-5383

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Abstract

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-Lthyroxine + 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 (TT ₃ ) and total thyroxine (TT ₄ ) levels were examined in plasma by RIA. Hematocrit and osmolality levels were also determined. It was found that the TT ₃ and TT ₄ 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 Lthyroxine 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.

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