POSSIBLE GENETIC INFLUENCE ON THE STRENGTH OF HUMAN MUSCLE NERVE SYMPATHETIC ACTIVITY AT REST

Large reproducible interindividual differences in the strength of huma n muscle nerve sympathetic activity have been demonstrated previously without satisfactory explanation. We undertook the present study to in vestigate whether a genetic influence may be a factor of importance. M icroneurographic recordings of sympathetic impulse traffic were made i n the peroneal nerve in nine pairs of monozygotic male twins and eight pairs of age-matched male subjects without family relationship. The s trength of the sympathetic activity was quantitated as number of sympa thetic bursts per 100 heart beats and bursts per minute. Group mean va lues of muscle sympathetic activity, heart rate, and blood pressure we re similar in the two groups. Intrapair differences (mean+/-SEM) of sy mpathetic activity were 5.4+/-1.7 bursts per 100 heart beats (1.7+/-0. 5 bursts per minute) for the twins and 19.4+/-3.2 bursts per 100 heart beats (11.8+/-2.5 bursts per minute) for the control subjects (P<.01 for both). The degree of reproducibility between twins is similar to t hat reported previously between repeated recordings in the same subjec t. The finding may indicate that the strength of sympathetic outflow t o muscle is controlled genetically. If so, we speculate that this may contribute to the heritability of blood pressure in both normotensive and hypertensive subjects.