Cardiovascular and sympathetic responses to ouabain injected into the hypothalamus in rats

To investigate the effects of sodium-potassium activated adenosine triphosphatase inhibition on central cardiovascular regulation a microinjection of ouabain was given into the hypothalamus of urethane anaesthetised rats. Doses of 0.01-1.0 micrograms per rat injected into the posterior hypothalamus produced a rise in blood pressure within 1 min, the maximum rise occurring 15-20 min later in a dose dependent manner. Both heart rate and abdominal sympathetic nerve activity increased with the rise in blood pressure. Ouabain injected into either the anterior preoptic hypothalamus or the ventromedial hypothalamus produced no notable cardiovascular responses. These results suggest that an endogenous digitalis like substance produced in the hypothalamus as a result of sodium loading may participate in central cardiovascular regulation by increasing sympathetic outflow in the discrete area of the brain, as does ouabain.