Differential effects of hydrocortisone on sympathetic and hemodynamic responses to sympathoexcitatory manoeuvres in men.

Aim of the present study was to investigate the influence of hydrocortisone on muscle sympathetic nerve activity (MSNA) and hemodynamic parameters during different sympathoexcitatory manoeuvres in humans. The study focuses on the interaction of the hypothalamo-pituitary-adrenal system and the sympathetic nervous system. Hydrocortisone 100 mg or placebo was administered intravenously to eight young healthy subjects in a double-blind crossover design. After 6 h, blood pressure, heart rate and MSNA from the peroneal nerve were recorded at rest, during an arithmetic stress task, an apnea and a cold pressor test. Hydrocortisone treatment increased serum cortisol levels to the upper physiological range and suppressed basal levels of adrenocorticotropin. During mental stress, MSNA, heart rate and blood pressure levels were elevated independently of hydrocortisone pre-treatment. However, hydrocortisone induced a sustained increase in basal heart rate throughout the whole experiment. A stronger increase in diastolic blood pressure was observed during apnea and cold pressor test in the hydrocortisone experiments. MSNA or plasma catecholamines at rest or during the manoeuvres were not affected by hydrocortisone. The observed hydrocortisone effects may be due to an increased responsiveness of adrenergic receptors towards catecholamines or a central modulation of the baroreflex involving parasympathetic mechanisms. Further studies are needed to confirm that the increase in MSNA during mental stress does not depend on a concomitant activation of the hypothalamo-pituitary-adrenal system.

Effect of facial cooling and cold air inhalation on sympathetic nerve activity in men.

In nine healthy subjects, cold stimuli were administered to the forehead and hand, to the oral and nasal cavities via ice cubes and to the bronchial system via inhalation of cold air (-25 degrees C). Blood pressure, heart rate and muscle sympathetic nerve activity (MSNA) from the peroneal nerve were recorded. MSNA expressed as total activity increased during cold air inhalation, cooling of the forehead (P < 0.001, ANOVA), hand and mouth (P < or = 0.05), paralleled by a rise in blood pressure during cold air inhalation and cooling of the forehead and hand (P < 0.01). Cooling of the forehead provoked a faster increase of MSNA expressed as total activity (P < 0.05) and higher levels of diastolic blood pressure (P = 0.05) compared with cooling of the hand. Bradycardia was observed only during cooling of the nasal cavity (P < 0.001) and the forehead (P < 0.05). It is concluded that cooling of the skin and mucous membranes of the tracheobronchial tract elicits sympathetically mediated hemodynamic adaptations, probably via stimulation of cold-sensitive afferents.

Evidence for lower sympathetic nerve activity in young adults with low birth weight.

OBJECTIVE: A dysfunction of the sympathetic nervous system may contribute to the development of hypertension and obesity in subjects with low birth weight (LBW). The present study examines resting sympathetic nerve traffic and its baroreflex modulation to the muscle vascular bed in healthy LBW subjects. DESIGN: Case-control studies of 13 healthy LBW subjects (< 2500 g at term) aged 20-30 years and 13 normal birth weight subjects (NBW; 3200-3700 g) closely matched for age, gender and body mass index. METHODS: Muscle sympathetic nerve activity (MSNA) recordings from the superficial peroneal nerve, blood pressure and heart rate were obtained at rest, during an inspiratory apnoea and a cold pressor test. Baroreflex function was evaluated by short-term infusion of nitroprusside and phenylephrine, respectively, in nine subjects of each group. RESULTS: During resting conditions burst frequency was significantly lower in LBW subjects (LBW: 24.7 +/- 2.4; NBW: 34.4 +/- 2.1 bursts/min, P < 0.05). When normalized for the different baseline values, baroreflex-mediated changes in MSNA were similar in both groups. Maximal MSNA levels in response to inspiratory apnoea and the cold pressor test did not differ between the groups. Blood pressure and heart rate were similar in LBW and NBW subjects both at rest and during sympatho-excitatory manoeuvres. CONCLUSIONS: Subjects born too small for their gestational age show a significantly lower sympathetic nerve activity under baseline conditions. Given the different baseline values, the sympathetic response to haemodynamic alteration is not affected in LBW subjects, and maximal activation during non-haemodynamic sympatho-excitatory manoeuvres is preserved.