COMPLETE ADAPTATION TO CHRONIC POTASSIUM LOADING AFTER ADRENALECTOMY - POSSIBLE HUMORAL MECHANISMS

This study was designed to evaluate the mechanisms of adaptation to ch ronic potassium loading after bilateral adrenalectomy. Studies were pe rformed in Sprague-Dawley rats subjected to 3 days of normal diet and 9 days of high KCl diet followed by adrenalectomy or sham operation on the thirteenth day and 9 additional days of potassium loading (groups 1 and 2, respectively). Animals that underwent adrenalectomy and inta ct animals, both receiving a normal diet, served as the control groups (groups 3 and 4, respectively). Plasma potassium, urinary potassium a nd sodium excretion rates, plasma aldosterone and insulin, and Na+-KATPase activity in renal cortical and medullary homogenates were measu red. Within 5 days of adrenalectomy the urinary potassium excretion ra te in potassium-loaded rats that underwent adrenalectomy (group 1) rea ched the level observed in potassium-loaded intact rats (group 2), but a significant elevation in plasma potassium levels among rats in grou p 1 was noticed. In both of the potassium-loaded groups plasma insulin levels and renal cortical and medullary Na+-K+ ATPase activity were s ignificantly higher compared with those in respective control groups r eceiving a normal diet. Acute clearance experiments carried out in adr enalectomized rats infusing the sera of the potassium-adapted rats tha t underwent adrenalectomy (obtained at the end of the chronic experime nt) showed an uprise in urinary potassium excretion. This result was n ot observed after the infusion of control sera. These findings suggest that full renal adaptation to chronic potassium loading can be achiev ed in the absence of aldosterone through mechanisms that might be rela ted to elevated plasma insulin levels (extrarenal); also, a humoral fa ctor associated with the renal adaptation cannot be ruled out.