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Title: Hypothyroid state reduces calcium channel function in 18-day pregnant rat uterus
Authors: Parija, S C
Mishra, S K
Raviprakash, V
Keywords: Calcium
Issue Date: Jan-2006
Publisher: CSIR
Abstract: Hypothyroidism significantly reduced the mean amplitude and increased the mean frequency of spontaneous rhythmic contractions in 18day pregnant rat uterus. Nifedipine (10<sup>-12</sup>-10<sup>-9</sup> <i style="">M</i>) and diltiazem (10<sup>-10</sup>-10<sup>-6</sup><i style="">M</i>) caused concentration related inhibition of the myogenic responses of the uterine strips obtained from both pregnant and hypothyroid state. However, nifedipine was less potent (IC<sub>50</sub>:2.11×10<sup>-11</sup> <i style="">M</i>) in pregnant hypothyroid state as compared to pregnant control (IC<sub>50</sub>: 3.1×10<sup>-12</sup><i style="">M</i>). Similarly, diltiazem was less potent (IC<sub>50</sub> : 3.72×10<sup>-9 </sup><i style="">M</i>) in inhibiting the uterine spontaneous contractions in hypothyroid than in pregnant rat uterus (IC<sub>50</sub>:5.37×10<sup>-10</sup> M). A similar decrease in the sensitivity to nifedipine and diltiazem for reversal of K<sup>+ </sup>(100 m<i style="">M</i>)–induced tonic contraction and K<sup>+</sup>-stimulated <sup>45</sup>Ca<sup>2+</sup> influx was observed with these calcium channel antagonists in uterus obtained from hypothyroid pregnant rats compared to the controls. Nifedipine–sensitive influx of <sup>45</sup>Ca<sup>2+</sup>-stimulated either by K<sup>+</sup> (100 m<i style="">M</i>) or by Bay K8644 (1,4-dihydro-2,6-methyl-5-nitro-4-[2'-(tri-fluromethyl)phenyl]-3-pyridine carboxylic acid methyl ester) (10<sup>-9</sup> <i style="">M</i>) was significantly less in uterine strips from hypothyroid rats compared to controls. The results suggest that the inhibition of uterine rhythmic contractions may be attributable to a reduction in rat myometrial Ca<sup>2+ </sup>channel function in the hypothyroid state.<b style=""></b>
Description: 19-27
ISSN: 0975-1009 (Online); 0019-5189 (Print)
Appears in Collections:IJEB Vol.44(01) [January 2006]

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