Norepinephrine kinetics in the rat with tail-suspension-induced central hypervolemia, as a model of cardio-vascular deconditioning.

Tail-suspension (TS) in the rat represents an interesting experimental condition to mimic, on Earth, the microgravity-induced cardiovascular deconditioning although the rat's profile of response is partially different from human's. To investigate underlying pathophysiological mechanisms, we have speculated on a decreased activity of the sympathetic system, (sigma S) triggered by the increase of the central venous pressure (CVP) induced by TS. Thus a decreased activity of the sigma S could account, at least partly, for the deconditioning of the cardiovascular system.

Adrenaline hypothesis: effect of formoterol on noradrenaline release.

1 Originally, the so-called 'adrenaline hypothesis' related the release of noradrenaline (NA) to stimulation of presynaptic beta2-receptors in nerve endings; now it confers a possible role to adrenaline taken up then released by nerves endings. It represents a potentially useful therapeutic pathway. The present study aims to investigate the effects of formoterol, a highly selective beta2-adrenoceptor agonist.

Norepinephrine kinetics in freely moving rats.

Norepinephrine (NE) kinetics were investigated in freely moving (FM) and minimally stressed (MS) rats with the isotope dilution technique. 1) The mean NE spillover rate (NE-SOR) was 79 +/- 6 ng. kg(-1).

Sympathetic activity in the rat: effects of anaesthesia on noradrenaline kinetics.

Noradrenaline (NA) kinetics represent an effective tool for evaluating the activity of the sympathetic system: thus plasma NA concentration, spillover rate (SOR) and metabolic clearance rate (MC) were measured in the rat. The dilution technique was adapted and validated: pithing that caused mechanical destruction of the spinal cord was shown to reduce drastically NA-SOR and plasma NA concentration with no effect on NA-MC. NA-SOR and plasma NA concentration were restored within their normal limits when 2.

Further study on the carotid baroreflex system in the cardiovascular deconditioning induced by head-down tilt.

Hypothesis: The responses of the carotid baroreflex and of the peripheral sympathetic system to stimulations induced by either lower body negative pressure (LBNP -40 mmHg) or cold pressor test were investigated in eight volunteers before and after 48 h in the -6 degrees head-down tilt (HDT).

Methods: Geometry (diastolic diameter and pulsatile distention) and dynamics (cross-sectional compliance and tangential tension) of the bulb and the common carotid artery were investigated using ultrasonic devices, echotracking and aplanation tonometry. The activity of the sympathetic system was evaluated through measurements of plasma concentrations of catecholamines (CAs) and 3,4-dihydroxyphenyl glycol (DHPG).