EFFECT OF PARATHYROIDECTOMY ON DEVELOPMENT OF HYPERTENSION AND ATRIAL RESPONSIVENESS IN SPONTANEOUS HYPERTENSIVE RATS

1. In order to further clarify the relationships between parathyroid function and development of hypertension, the effects of parathyroidectomy (PTX) on blood pressure and on responsiveness of atria isolated from spontaneous hypertensive rats (SHR) were examined. 2. PTX was carried out in 6-week-old SHR and normotensive Wistar rats. The experiments were performed 2 weeks after surgery. 3. PTX reduced the plasma calcium concentration and decreased atrial calcium content in SHR. On the other hand, basal contractile force and beat frequency of isolated atria were higher in PTX SHR than in sham-operated SHR. In response to cumulative addition of isoprenaline, atria from PTX SHR displayed diminished inotropic and chronotropic responses compared with sham-operated SHR. Similar results were obtained in atria isolated from Wistar rats. When calcium sensitivity was studied in atria from Wistar rats, basal and isoprenaline-induced maximum contractile forces were higher in PTX group than in the sham-operated group. Nevertheless, basal and isoprenaline-induced maximum contractile forces, determined at the respective plasma ionized calcium concentration of PTX and sham-operated groups (0.83 and 1.22 mmol/L), were not significantly different. 4. Our results do not favour a role for alteration in atrial activity as a causal mechanism in delayed development of experimental genetic hypertension after parathyroidectomy.