1. In order to elucidate the mechanisms by which parathyroidectomy (PTX), performed in young spontaneously hypertensive rats (SHR), delays the development and attenuates the level of hypertension, we studied, in vivo, cardiovascular reactivity (CVR, blood pressure response to bolus noradrenaline administration), aortic calcium distribution and cardiac calcium content in SHR with or without parathyroid glands.

2. PTX was performed in 6-week-old animals and experiments were done in pretreated anaesthetized animals 2 and 22 weeks after surgery. A significantly decreased CVR was observed 22 weeks after PTX in SHR-PTX as compared with controls.

3. These data are not specific for hypertensive animals since similar data are also obtained on nor-motensive Wistar rats treated in an identical fashion. In addition, after PTX in SHR and Wistar rats myocardial (auricle and ventricle) calcium content was more rapidly reduced (after 2 weeks) than aortic membrane-bound and cellular calcium fractions.

4. The present studies established that PTX decreases CVR and alters calcium content and distribution in the cardiovascular systems of rats from hypertensive and normotensive strains. Furthermore, the results confirm a requirement for the parathyroid glands in the pathogenesis of spontaneous hypertension in SHR and for the normal CVR.

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