Acute Effects of Short‐term Fasting on Blood Pressure, Circulating Noradrenaline and Efferent Sympathetic Nerve Activity

Abstract

Eleven moderately obese women, aged 46–62 years, with a body mass index of 29–34 and with borderline hypertension (repeated diastolic blood pressure >90 mmHg) fasted for 48 hours. Before the fast and after 48 hours of fasting, plasma noradrenaline, urinary noradrenaline, urine potassium, urine sodium and weight were measured. In six of the patients muscle nerve sympathetic activity was recorded from the peroneal nerve by tungsten micro‐electrodes for 15 min each time. The efferent muscle sympathetic activity (MSA) was expressed as the number of bursts/min. The recordings were done before the fast and after 48 hours of fasting. We found significant decreases in body weight from 88.4±2.5 kg to 86.4±2.5 kg. Systolic blood pressure (BP) was reduced from 158±3 mmHg to 146±5 mmHg (p<0.001) and diastolic BP from 96±3 mmHg to 89±3 mmHg (p<0.01) during the fast. MSA was significantly increased from 42.0±5.5 bursts/min to 44.5±5.8 (n=6), while plasma and urine noradrenaline concentrations (n = 11) showed a non‐significant tendency to increase. We conclude that the hypotensive response during the first days of extensive caloric reduction is not due to a decreased sympathetic activity. If anything, there may be weak increase of efferent sympathetic nerve activity and venous plasma levels of circulating noradrenaline. The mechanisms behind the acute hypotensive response to negative caloric balance are thus still unclear, but obviously different from long‐term adaptation of the blood pressure.

Effect of 48 h Fasting on Autonomic Function, Brain Activity, Cognition, and Mood in Amateur Weight Lifters

“…In accordance with Andersson et al [13], we observed a hypotensive response (decreased BP) to 48 h fasting. In addition, we observed a decrease in HR, which is in accordance with a predominant increase in the activity of the parasympathetic nervous system [29, 30].…”

“…It is noteworthy that 48 h fasting increased sympathetic activity and was indicated as stress [3, 13]. The observed common hypotensive response during the first days of fasting is not due to a decreased sympathetic activity [13].…”

“…The observed common hypotensive response during the first days of fasting is not due to a decreased sympathetic activity [13]. It is well established that the brain is a target of stress and that the prefrontal cortex is the brain area that is most sensitive to its effects [14, 15]; the prefrontal complex is responsible for highest-order cognitive abilities, such as executive functions [14, 16].…”

Human cardiac autonomic responses to head-up tilting during 72-h starvation

“…Others (Webber and MacDonald 1994) reported that during a 3-day fast in healthy humans, elevations in resting metabolic rate, heart rate, and forearm blood flow were consistent with an increased sympathetic nervous system activity. Also, starvation-induced increases in muscle sympathetic nerve activity (Andersson et al 1988) and an increased heart rate with reduced vagal modulation (Chan et al 2007) are further evidence of an increase in sympathetic autonomic nervous system activity with short periods of starvation in humans. In contrast, decreased resting sympathetic activation in acutely anorexic and fasting These data were obtained from subject 6 on Day 3 p.m., where mean supine heart rate was 55.6 beats min -1 , and mean heart rate during head-up tilt was 86 beats min -1…”

“…For example, a 48-h fast caused suppression of centrally mediated sympathetic activity in the rat as evidenced by the reduced turnover of norepinephrine in the heart and other organs (Young and Landsberg 1977). Similarly in obese humans, the decrease in blood pressure which accompanies short-term calorie restriction has been attributed to a reduction in sympathetic nervous system activity (Lansberg and Young 1979;Jung et al 1979;Andersson et al 1991), although this is not a consistent viewpoint (Andersson et al 1988;Chan et al 2007;Messaoudi et al 1998). For example, it has been reported that the reduction in blood pressure during 8 days of semi-starvation was not accompanied by a decrease in sympathetic nerve activity (Messaoudi et al 1998), with no change in heart rate or urinary catecholamine excretion observed.…”