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Influence
of hypovolemic and hypertonic treatments on plasma vasopressin
levels and fluid balance in the thyroidectomy-induced hypothyroid
rats
by Rasim MogulkoÁ, Osman Dogru, A. Kasim Baltaci, Bayram
Yilmaz & Haluk Kelestimur
Keywords:
vasopressin, fluid balance, thyroidectomy, hypothyroidism,
rat
Abstract:
OBJECTIVES: This study was undertaken to investigate the effects
of hypovolemic and hypertonic treatments on plasma vasopressin
(AVP) levels and fluid balance in thyroidectomy-induced hypothyroidism
in the rat. The influence of hypothyroidism on AVP responsiveness
to hypertonic and hypovolemic stimuli were compared.
MATERIALS
& METHODS: Adult male rats were divided into two groups. The
rats were surgically thyroidectomized (hypothyroid) or sham-operated
(euthyroid). Two weeks later these groups were further divided
in three subgroups each containing six rats. The first subgroup
consisted of unchallenged rats. The second group underwent hypovolemic
treatment by using I.P. 700 mg polyethylene glycol. The third
subgroup consisted of hypertonic (1.5 M NaCl; 1 ml/100 g) stimulated
animals. All rats were decapitated and trunk blood collected
in heparinized tubes. Plasma samples were stored at -20oC until
assayed. Plasma AVP, T3 and T4 levels were measured by radioimmunoassay.
Hematocrit values and plasma Na and K concentrations were also
determined.
RESULTS: In the hypothyroid rats, hypovolemic treatment significantly
reduced the expected increases in plasma AVP levels (p<0.05)
compared to the respective intact animals. In the hypertonic
group, similar increases occurred in plasma AVP levels of hypothyroid
and euthyroid rats. Hematocrit values and plasma Na concentrations
were not significantly different in the hypothyroid rats compared
to euthyroid rats.
CONCLUSION: In conclusion, thyroidectomy-induced hypothyroidism
may affect AVP response to hypovolemic stimulus although it
has no important effect on basal AVP levels nor AVP response
to hypertonic stimulus.
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