Increased Activation of Sympathetic Nervous System and Endothelin by Mental Stress in Normotensive Offspring of Hypertensive Parents

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Abstract
Background The pathogenesis of essential hypertension is still uncertain, but genetic factors and the sympathetic nervous system are likely to be involved. Sympathetic nerve activity and hormonal circulatory control mechanisms, however, are affected by blood pressure itself. Hence, early functional changes are best investigated in normotensive subjects at risk to develop hypertension, such as normotensive offspring of hypertensive parents. Methods and Results Muscle sympathetic nerve activity (MSA) was measured in the peroneal nerve of 10 normotensive offspring of parents with essential hypertension and 8 offspring of normotensive parents. Measurements were performed under resting conditions, during a 10-minute period of hypoxia (12.5% O2/87.5% N2), and during a 3-minute mental stress test. The tests were separated by a 30-minute resting period. Plasma samples for determination of norepinephrine and endothelin were collected before and after the tests. Baseline values of MSA were comparable in offspring of hypertensive and normotensive parents. During hypoxia, MSA, heart rate, and norepinephrine and endothelin plasma levels increased in offspring of hypertensive and normotensive parents to a comparable degree, whereas no significant changes in blood pressure and plasma norepinephrine levels were observed in either group. During mental stress, MSA and plasma norepinephrine and endothelin increased only in offspring of hypertensive parents (P<.001 to .01). In parallel, blood pressure increased significantly only in offspring of hypertensive parents (P<.001 to .05), but heart rate increased in both groups (P<.001 to .05). Conclusions The activity of the sympathetic nervous system and plasma norepinephrine and endothelin levels are increased during mental stress only in offspring of hypertensive parents, whereas the response to hypoxia was similar in offspring of hypertensive and normotensive parents, suggesting a genetically determined abnormal regulation of the sympathetic nervous system to certain stressful stimuli in offspring of hypertensive parents. This may play a role in the pathogenesis of essential hypertension.