Cardiovascular alteration by nucleus locus coeruleus in spontaneously hypertensive rat

Biphasic electrical stimulation of the nucleus locus coeruleus (LC) produced frequency-related pressor responses associated with increased heart rate in normotensive rats (WKY) at both 50 and 100 microamperemeter. In contrast, spontaneously hypertensive rats (SHR) demonstrated small depressor responses at 50 microamperemeter and 50 Hz, but no consistent pressure or heart rate changes at either 50 or 100 muA stimulation. The LC pressor threshold current (current necessary to increase arterial pressure by greater than or equal 10 mm Hg) was higher in SHR than WKY (136 +/- 5 muA vs. 84 +/- 7 muA; P less than 0.001); and only the SHR LC demonstrated a depressor threshold (current necessary to reduce arterial pressure by greater than or equal to 10 mm Hg) (53 +/- 3 muA). These threshold current levels did not seem to change with acute alterations of arterial pressure produced by either bilateral carotid artery occlusion or caortid sinus stimulation. Therefore, these studies indicate altered levels of responsiveness of the SHR LC to stimulation but that the pressor function of the LC does not seem to be importantly involved in further elevation of abnormally high arterial pressure in the SHR.