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G Recordati

Publications and source records attributed to G Recordati.

At least 19 recordsLinked to original sources
PubMed2004

A definition of internal constancy and homeostasis in the context of non-equilibrium thermodynamics.

The constancy of the internal environment, internal homeostasis, and its stability are necessary conditions for the survival of a biological system within its environment. These have never been clearly defined. For this purpose nonequilibrium thermodynamics is taken as a reference, and the essential principles of equilibrium, reversibility, stationary steady state and stability (Lyapounov, asymptotic, local and global), are briefly illustrated. On this basis, internal homeostasis describes a stationary state of nonequilibrium, the actual state of rest, X(t), resulting from the relation X(t) = Xs + x(t), between a time-independent steady state of reference (Xs), and time-dependent fluctuations of the state variables, x(t). In humans, two resting spontaneous homeostatic states are: (1) the conscious state of quiet wakefulness, during which time-dependent variables display bounded oscillations around the mean time-independent steady state level, this conscious state being thus stable in the sense of Lyapounov, and (2) the unconscious stable state of non-rapid eye movement sleep, in which the time-dependent variables would approach the lowest spontaneously attainable time-independent state asymptotically, sleep becoming a globally stable and attractive state. Exercise may be described as a non-resting, unstable active state far away from equilibrium and hibernation is a resting, time-independent steady state very near equilibrium. The range between sleep and exercise is neurohumorally regulated. For spontaneously stable states to occur, slowing of the metabolic rate, withdrawal of the sympathetic drive and reinforcement of the vagal tone to the heart and circulation are required, thus confirming that the parasympathetic division of the autonomic nervous system is the main controller of homeostasis.

Homeostasis↗
PubMed2000

Effects of a reversible 'nephrectomy' on renal sympathetic activity and blood pressure in the rat: evidence for an acute angiotensin-mediated hypertension.

OBJECTIVE: To verify whether the normal kidney exerts a supportive, facilitatory action on renal sympathetic nerve activity (RSNA), the effects of unilateral and bilateral nephrectomy on RSNA have been studied. METHODS: The RSNA, rectal temperature (T), rate of breathing (RB), arterial blood pressure (BP) and heart rate (HR) were continuously recorded in three groups of pentobarbital anaesthetized, spontaneously breathing Sprague-Dawley rats: group 1 (n = 5): both kidneys intact; group 2 (n = 5): left surgical nephrectomy; group 3 (n = 5): left surgical nephrectomy and functional exclusion of the right kidney (functional right nephrectomy, FRN), produced by a tight ligature of the renal hilum which was maintained for 3 h. In a fourth group (n = 7), in which nerve activity was not recorded, reopening of the right renal hilum was preceded or followed by intravenous administration of captopril (3 mg/kg). RESULTS: In groups 1 and 2 RSNA increased from 22.3 +/- 2.1 to 122.9 +/- 13.6 and from 26.7 +/- 1.2 to 93.2 +/- 14.0 impulses/s (mean +/- SEM), respectively, without concomitant changes in cardiovascular parameters. In group 3 RSNA decreased from 39.1 +/- 3.1 to 13.7 +/- 2.6 impulses/s during the 3 h of FRN. In group 3 the reopening of the right renal hilum was followed by a marked increase in BP and HR that was prevented or reversed by intravenous captopril in rats of group 4. CONCLUSIONS: The decrease in RSNA observed in rats during bilateral nephrectomy, in contrast to the increase observed in rats with one or both kidneys intact, suggests that the kidney as a whole exerts a supportive role on sympathetic nerve activity. The hypertension and tachycardia that follows the reopening of the right kidney hilum appears to be caused by the generation of endogenous angiotensin II; this is the first evidence of an acute angiotensin-mediated renal hypertension.

Acute Disease↗
PubMed1999

The contribution of the giraffe to hemodynamic knowledge: a unified physical principle for the circulation.

Hemodynamics stands on three main physical principles: the hydrostatic pressure, firstly described by Stevino, the viscous flow pressure, described by Poiseuille and the total hydraulic energy, or Bernoulli's equation. However, neither of these physical principles gives a comprehensive description of the single pressure measurement in the cardiovascular system. Hence, all these principles should be used together to fully describe the physical forces acting in the circulation of blood. Experiments that measured the hydrostatic pressure in the jugular vein of the giraffe have shown that a few guidelines need to be followed to measure it correctly. Following these guidelines, it can be seen that hydrostatic and viscous flow pressures are strictly related to one another, and that this relationship is described in mathematical terms. In addition, it has been shown that hydrostatic and viscous pressures should be included in Bernoulli's principle, to give the combined Bernoulli-Poiseuille equation. This unified principle is helpful not only to measure correctly the pressure with a catheter connected to a pressure transducer, but also to give to the pressure measured in a patient with the mercury manometer, a strong connection with the description of the pressure as a physical force acting inside the circulation. In addition it provides a comprehensive view of the cardiovascular system as a closed hydrodynamic system, in which the heart is a pump, that does not normally work to overcome the force of gravity. The question at this point is: are there any pathophysiological conditions in which the heart needs to be confronted with the sudden appearance of the force of gravity inside the cardiovascular system?

Animals↗
PubMed1984

The functional role of the visceral nervous system. A critical evaluation of Cannon's "homeostatic" and "emergency" theories.

Cannon's view of the sympatico-adrenal system's functional role, the homeostatic concept and model, has been reexamined. The living being is an "open system" in which homeostasis, constancy of the internal psycho-chemical conditions, is essential for survival. This constancy is threatened by endangering stimuli. To safeguard it, physiological regulatory processes, work for stability, utility, and coordination: the body is wise. Along this teleological view, the sympathetic nervous system is the most important homeostatic agent. Sympathectomized animals, however, showed no evidence of instability of the fluid matrix. Cannon concluded that the sympathetic system is not essential for life and in emergency function is its main value for the individual. Homeostatic and emergency theory, when analyzed, reveal profoundly contradictory aspects. Emergency function cannot be interpreted homeostatically, because, in emergencies, is the sympathetic system which promotes changes, rather than resists them. Sympathectomized animals do not lack constancy of the fluid matrix; they lack rather the possibility to compensate, along patterns of responses, the internal organization of the visceral apparatus. In strong emotional reactions, moreover, it is the sympathetic system itself which may induce marked derangements in visceral function that damage the organism's stability. The a priori accepted view that all physiological regulatory processes, by necessity, work for the welfare of the body - the teleological explanation - masked the experimental evidence. The conclusion is drawn that homeostatic and emergency theories described only in part the functional role of the sympathetic nervous system in all its possible functional expressions.

Adrenal Medulla↗
PubMed1982

Renorenal reflexes in the rat elicited upon stimulation of renal chemoreceptors.

The effects of renal ischemia and backflow of non-diuretic urine into the renal pelvis on renal efferent sympathetic postganglionic nerve activity, femoral arterial pressure and heart rate were studied to verify whether stimulation of renal chemoreceptors elicits autonomic reflexes. In rats with intact spinal cord or spinal cord sectioned at the T6 level a brief activation of renal chemoreceptors produced excitatory ipsilateral and contralateral renorenal reflexes, whereas it only slightly and insignificantly altered arterial pressure and heart rate. These results indicate that stimulation of renal chemoreceptors elicits renorenal excitatory reflexes which might be integrated both at spinal and supraspinal levels.

Adrenergic Fibers↗
PubMed1981

Renal chemoreceptors.

A study of the renal receptors and types of stimuli which give origin to supraspinal and spinal-mediated autonomic reflexes is presented. Multiunit and single unit recordings from the afferent renal nerves of male Sprague-Dawley rats have revealed two groups of renal chemosensitive receptors (chemoreceptors). These we have called renal R1 and R2 "chemoceptive" receptors. R1 receptors do not have a resting discharge but are activated after 38.7 +/- 3.3 (S.E) sec (n = 40) of complete renal ischemia (occlusion of the renal artery). Other activating stimuli are associated with a marked impairment in renal blood flow (prolonged occlusion of the renal vein and the hypotension of systemic asphyxia or hemorrhage). Their discharge is characterized by trains of impulses which cease abruptly upon re-entry of blood into the kidney. They are not responsive to increases or decreases in renal perfusion pressure or to increases in renal venous or ureteral pressure. In contrast, R2 receptors have a resting discharge and respond vigorously to backflow of normal urine (nondiuretic) into the renal pelvis. The results of the backflow into the pelvis of different test solutions (diuretic and nondiuretic urine, 1 M urea, 1 M mannitol and solutions of NaCl and KCl) indicate that this response is dependent upon the composition of the fluid bathing the renal pelvis rather than the increase in pelvic pressure or pelvic distension. The resting discharge rate is highest in nondiuretic conditions and declines substantially after diuresis is induced by extracellular volume expansion. R2 receptors are also activated by renal ischemia produced by clamping the renal artery. It is concluded that these two groups of afferent sensory units are renal chemosensitive receptors, (chemoreceptors) which respond to the chemical environment of renal interstitium.

Afferent Pathways↗
PubMed1981

Excitatory effect of converting enzyme inhibitors on efferent sympathetic postganglionic nerve activity to the kidney in the rat.

1. Experiments were designed to evaluate the effect of converting enzyme inhibitors on autonomic nervous system function in the rat. 2. Arterial blood pressure, heart rate, efferent postganglionic sympathetic activity and afferent nerve activity from the right renal nerves were recorded in anaesthetized, spontaneously breathing, non diuretic rats, either with an intact spinal cord or with a spinal cord transected at the T6 level, before, during and after intravenous injections of 0.5--1.0 mg/kg of teprotide or captopril. 3. After injection of drugs, efferent sympathetic nerve activity markedly increased and reached its peak value 4 min later, both in rats with an intact spinal cord (101 +/- 21% mean +/- SE, above the control discharge) and with a spinal cord transected at the T6 level (166 +/- 41%, above the control). 4. Afferent activity from the renal nerve, on the other hand, did not consistently change during converting enzyme blockade. 5. The results indicate that the efferent sympathetic excitation cannot be due either to a baroreceptor or to a renorenal reflex. This excitation might be responsible, at least in part, for the increase in renin secretion which follows the blockade of angiotensin-converting enzyme.

Adrenergic Fibers↗
PubMed1980

Reno-renal and reno-adrenal reflexes in the rat.

1. Experiments were carried out to investigate whether the activation of renal chemoceptive receptors by natural stimuli might induce reflex alterations of efferent postganglionic activity to the ipsilateral kidney and preganglionic activity to the ipsilateral adrenal. 2. In anaesthetized rats with intact nervous system back-flow of urine and occlusion of the renal artery were accompanied by increments in efferent sympathetic activity both to the kidney and adrenal without concomitant changes in heart rate and blood pressure. 3. Greater excitatory responses in nerve activity to the same test stimuli were observed in rats with the spinal cord cut at C 1. 4. These results indicate that the natural activation of renal chemoceptive receptors might induce reno-renal and reno-adrenal excitatory reflexes which are likely to be integrated at spinal and supraspinal levels.

Adrenal Glands↗
PubMed1976

Reflex sympathetic tachycardia during intravenous infusions in chronic spinal cats.

The reflex tachycardia elicited by rapid intravenous infusions of a blood substitute was studied in 21 chronic cats with spinal sections at C8. All animals could breath spontaneously. The day after section the average resting heart rate (HR) and arterial pressure (AP) were 109 beats/min and 98/67 mmHg, respectively. Vagal blockade with atropine (0.5-0.7 mg/kg iv) was performed prior to each infusion, increasing the average HR To 127 beats/min. In 39 infusions in 21 cats the average increase in HR was 10 beats/min (range from -6 to +22 beats/min). A tachycardia was observed in all but five trials, four of which were obtained in two cats that subsequently responded with a tachycardia. In seven animals the neural circuit mediating the response was partially or totally interrupted by section of several thoracic dorsal roots (T1-T4 or T1-T6) and of the spinal cord at the inferior level of these sections (between T6 and T7). The tachycardia response was progressively reduced and finally abolished by these procedures. These experiments indicate that spinal neural mechanisms are likely to contribute to the phenomenon first described by Bainbridge.

Animals↗
PubMed1976

Mechanical stimuli exciting type A atrial vagal receptors in the cat.

The activity of type A right atrial vagal receptors was recorded from the right cervical vagus in cats anesthetized with sodium pentobarbital, immobilized with gallamine, and with their chests open. Nerve impulses initiated by receptor activation were recorded simultaneously with instantaneous right atrial pressure and dimensional changes under various hemodynamic conditions. Atrial volume changes induced by infusion of saline, bleeding, and occlusion of the inferior vena cava did not alter consistently the systolic activity of the receptors. Electrical stimulation of the right stellate ganglion significantly increased the frequency of discharge during systole, whereas electrical stimulation of the left thoracic vagus significantly reduced the frequency of discharge. These inotropic interventions produced similar effects when the heart was paced at a fixed rate. Pacing the right atrial appendage increased the systolic discharge of the receptors only when at high rates the atrium contracted against closed atrioventricular valves. To investigate the influence of tonic efferent sympathetic activity on spontaneous receptor discharge, three receptors were studied before and after bilateral surgical stellectomy, and in cats with their chest closed three receptors were studied before and after infusion of propranolol. Both of these interventions markedly reduced the systolic activity. In addition to having effects on systolic activity, injection of saline, vagal stimulation, and sympathetic "denervation" always activated the receptors during filling. Our results indicate that: (1) the systolic discharge of type A receptors is a function of the active tension developed by atrial muscle during contraction; and (2) the pattern of discharge of the receptors during the atrial cycle depends on both the degree of atrial distention and the state and extent of contraction.

Animals↗
PubMed1975

Spinal sympathetic reflexes in the cat and the pathogenesis of arterial hypertension.

1. In vagotomized anaesthetized cats with both common carotid arteries occluded, stretch of the thoracic aorta induced reflex increases in arterial blood pressure, heart rate and left ventricular dP/dtmax. Similar responses were obtained in cats with spinal transection at the level of the first cervical nerve roots. 2. The hypothesis is advanced that sympathetic excitatory reflexes may contribute to the maintenance of hypertension through positive feedback.

Animals↗
PubMed1975

Response of type B atrial vagal receptors to changes in wall tension during atrial filling.

In anesthetized curarized cats with their chests open, we recorded the activity of type B right atrial vagal stretch receptors, right atrial pressure, and instantaneous dimensional changes of the right atrium. The nervous activity was analyzed during alterations in atrial dynamics produced by acute volume loading of the right atrium under control conditions and during sympathetic and vagal stimulations. Our results demonstrated that the mean frequency of discharge in the burst was dependent on the absolute tension and the rate of change in tension developed in atrial muscles during filling. The responses of different receptors to changes in atrial dynamics were qualitatively similar but characteristic for each receptor studied. In some experiments nervous activity was recorded after the cats had been killed: static and dynamic changes in atrial tension were then produced by injecting blood into the right atrium. Under these conditions dynamic stimuli always activated the receptors at tensions below the threshold for static stimuli. During dynamic stimuli the instantaneous firing rate was always higher than it was during static stimuli applied at the same level of tension. This study indicates that the nervous activity of type B atrial vagal receptors is closely dependent on static and dynamic changes in atrial wall tension.

Animals↗