Key result
Specific angiotensin II binding sites matching the AT1 receptor subtype were identified in plasma membrane preparations from the rat thyroid gland.
First demonstration of AT1 receptor subtypes in the rat thyroid gland, suggesting a potential reciprocal regulation of thyroid function by the renin-angiotensin system.
Hypothesis-generating for RAS-thyroid interactions in rodents; leaves open any human relevance or clinical translation.
In this study we showed, for the first time, the existence of a moderate density of specific angiotensin II (Ang II) binding sites (Kd=3.9+/-1.7 nM and Bmax=467.2 130.0 fmol/mg protein) in plasma membrane preparations from rat thyroid gland. Reverse transcriptase/polymerase chain reactions, using primers based on the cloned AT1 and AT2 receptor subtypes, and pharmacological characterization, using the Ang II receptor subtype antagonists Losartan and PD 123319, revealed that these Ang II binding sites match with the AT1 receptor subtypes. To obtain more information on the molecular structure of this Ang II receptor, immunoblotting analyses were carried out using a polyclonal rabbit anti-AT1 antiserum. Western analysis of fresh plasma membrane preparations from thyroid tissue showed three prominent bands of approximately 60, 45 and 40 kDa which appear to be related to different degrees of glycosylation of the receptor molecule. The functional significance of the Ang II receptors in thyroid gland is currently not known. Nevertheless, since Ang II receptors play a pivotal role in the co-ordinated actions of the renin-angiotensin system (RAS), our findings support a reciprocal regulation of thyroid function by the RAS.
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Montiel et al. (1998) studied this question. Angiotensin II receptor characterization was evaluated on Angiotensin II binding sites. Specific angiotensin II binding sites matching the AT1 receptor subtype were identified in plasma membrane preparations from the rat thyroid gland.
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