ABSTRACT
Objective To define the effect and mechanism of hyperkalemic solution on atrial natriuretic peptide (ANP) secretion in rabbits. Methods Eighteen rabbits were selected and the chest was opened under anes-thetization to remove the heart. The left atrium was isolated and fixed in the atrial perfusion system with proper electric stimulation for beating. The following experiments were carried out on beating rabbit atria: ①The atrium was perfused for 60 min to stabilize parameters of ANP secretion and atrial dynamics. The control period (12 min as an experimental cycle) was followed by an infusion of hyperkalemic solution (K+ concentration of hyperkalemic solution was 5.64 mmol/L and the osmolarity of hyperkalemic solution was unchanged) for three cycles, then normal K+ cancentration was recovered for two cycles;②The control period was followed by an infusion of L type Ca2+ channel blocker nifedipine (1.0 μmol/L) for three cycles;③L type Ca2+ channel inhibitor nifedipine (1.0 μmol/L) was infused for 36 rain prior (three cycles) to infusion of hyperkalemic solution. Atrial stroke volume was determined and the ANP secretion was measured by radioimmtmoaasay. Results (1)Hyperkalemic solution increased atrial ANP secretion (P<0.01) and reduced the atrial stroke volume,hut the difference was not statistically significant as compared with that of the control cycle(P>0.05). The recovery trend was to the normal level of ANP secretion and atrial stroke volume was to become normal gradually when solution level recovered to normal ,which was not significantly different from that of the control cycle (P>0.05) ;②Nifedipine (1.0 μmol/L) also increased the atrial ANP secretion (P<0.01 or P <0.05) while decreasing atrial stroke volume (P<0.01 or P < 0.05 ) ; ③Nifodipine (1.0μmol/L) completely blocked the effect of hyperkalemic solution so to increase the ANP secretion (P <0.01 ). Conclusion Hyperkalemic solution significantly increases atrial ANP secretion via extracellular high K+ competitive inhibition of extracellular Ca2+ inflow in beating rabbit atria.