The renin response to aortic occlusion is enhanced by stimulation of the hypothalamus

The sympathetic nervous system is an important factor that can induce increased renin secretion by the kidney. In recent years, the notion has arisen that the sympathetic nervous system may also function to set the level of responsiveness of the kidney to nonneural stimuli for renin secretion. However, evidence in favor of this possibility has come primarily from studies employing direct electrical stimulation of renal nerves, and no attempt has been made to determine if central neural sites can also influence the responsiveness of the kidney. In the present study, the ability of hypothalamic activation to enhance the renin response to suprarenal aortic occlusion was investigated. Conscious, freely moving rats with an inflatable cuff placed around the aorta were used to determine the relationship between renal-perfusion pressure and plasma renin activity in the control state and during continuous low-level stimulation of the paraventricular nucleus. The stimulation resulted in a rightward shift in the curve that related renal perfusion pressure to plasma renin activity; that is, for any given decrease in renal perfusion pressure, the plasma renin activity was greater during the ongoing stimulation. This rightward shift appeared to be mediated by increased renal nerve activity, since renal denervation prevented the shift. These data indicate that the hypothalamus, which plays an important role in regulating sympathetic activity, is capable of increasing the sensitivity of the kidney to a nonneural stimulus for renin secretion. This effect may become important in certain hypertensive and prehypertensive states where central neural activity is thought to be enhanced.