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Antihypertensive effect of thyroidectomy in SHR: associated changes in heart performance.

Effects of thyroidectomy (TX; 10 wk) on the performance of perfused hearts from spontaneously hypertensive rats (SHR) were compared with effects on hearts from normotensive Wistar-Kyoto (WKY) controls. TX prevented the development of hypertension in SHR and moderately reduced arterial pressure of WKY, confirming previous observations. TX also reduced heart-to-body-weight ratio (relative left ventricular hypertrophy) but not left-to-right ventricular weight ratio (absolute hypertrophy) of SHR. The performances of euthyroid SHR and WKY hearts were similar to each other. TX reduced maximum left ventricular pulse pressure to the same extent in both strains and had no effect on hydraulic work, O2 consumption, or efficiency of contraction in either strain. However, TX reduced maximum left ventricular +dP/dt of SHR but not of WKY hearts. The results show that hypothyroidism selectively depresses the contractility (LV +dP/dt) of SHR hearts but otherwise has similar effects on the performance of hypertensive and normotensive rat hearts.