Sympathetic nervous activity and arterial pressure responses during rest and acute behavioral stress in SHR versus WKY rats

The object of this experiment is to compare changes in renal sympathetic nerve activity (SNA), mean arterial blood pressure (MAP) and heart rate (HR) during rest and behavioral stress in 12-14 week old spontaneously hypertensive rats (SHR; N=12) and normotensive Wistar-Kyoto (WKY; N=12) controls. Animals were behaviorally trained by following a 15 s auditory conditional stimulus (CS +) with a 1/2 s tail shock. Resting MAP was higher (p < 0.001) in SHR (154 +/- 3 mmHg, mean +/- SEM) compared to WKY (116 +/- 3 mmHg); conversely, there was no difference in the average resting HR. The pattern of the SNA and MAP changes during the CS + was similar across groups, but the amplitude was larger in the SHR. The CS + stress stimulus evoked an initial transient MAP increase averaging 14 +/- 2 mmHg in the SHR compared to 4 +/- 1 mmHg in the WKY. This presser response was preceded by a sudden burst of SNA averaging 177 +/- 22% over baseline in SHR versus 105 +/- 13% for the WKY. HR decreased in SHR only during the second component of the CS + trial despite the large increase in SNA. We conclude that (1) SHR have higher reactivity than WKY to stress in SNA and MAP; (2) both SHR and WKY have greater SNA and MAP responses to CS + than CS - (i.e., the discriminative paradigm was effective); (3) control of sympathetic and parasympathetic nervous activity during sustained stress differs remarkably in hypertensive and normorensive subjects; and (4) SHR blood pressure effector mechanisms may have a higher responsiveness to sympathetic nervous activity as compared to WKY.