THE EFFECTS OF INSULIN AND INSULIN-LIKE MATERIALS IN THE BRAIN ON CENTRAL CARDIOVASCULAR REGULATION - WITH SPECIAL REFERENCE TO THE CENTRAL EFFECTS OF SODIUM-CHLORIDE

The present study investigated the roles of insulin on central cardiovascular regulation. When rats were fed with a high-salt diet for 4 weeks, hypothalamic and pituitary contents of insulin-like immunoreactive substance (ILI) significantly decreased. The plasma concentration of ILI remained unaltered, however. Intracerebroventricular injections of insulin significantly decreased both the blood pressure and the heart rate, with corresponding decreases in renal sympathetic nervous activity in urethane-anesthetized rats. Microinjections of insulin into the ventromedial nucleus in the hypothalamus caused greater vasodepression and bradycardia compared with the intracerebroventricular injections. Intracerebroventricular infusions of insulin inhibited the pressor effects of simultaneously-infused hypertonic saline, and the digitalis-like immunoreactivity in both the plasma and the hypothalamus were significantly decreased by the insulin. These results indicate that ILI in the brain affects the central cardiovascular regulation through the suppression of both sympathetic nervous system activity and the release of digitalis-like substances. These mechanisms may operate particularly during a sodium load.