Increase in muscle nerve sympathetic activity after glucose intake is blunted in the elderly

Muscle nerve sympathetic activity (MSA; involved in blood pressure regulation) was recorded by microneurography in the peroneal nerve for 90 min after ingestion of 100 g D-glucose in three groups of healthy subjects: young subjects (mean age 26 years) and 70-year-old men with normal and reduced insulin sensitivity as assessed by euglycaemic insulin clamp. Muscle nerve sympathetic activity at rest was lowest in the young and highest in the insulin-resistant subjects (burst frequencies 19.8 +/- 6.0, 47.7 +/- 7.0 and 55.1 +/- 11.5 bursts/min for the three groups, respectively). The young subjects responded to glucose intake with a pronounced increase in MSA, a response that was blunted in the elderly and weakest in the insulin-resistant subjects. A similar relationship was observed during a Valsalva manoeuvre, indicating that the blunted response in the elderly is a generalized phenomenon. Blood pressure remained stable in the young subjects but fell slightly and significantly in the elderly subjects. It is concluded that old subjects utilize their total capacity for MSA close to maximum at rest. Thus, the reserve for response to stimuli normally evoking a strong increase in MSA is restricted. This restriction may contribute to postprandial hypotension in the healthy elderly.