The visceral nervous system and its environments

Description of a large-scale study design to assess work-stress-disease associations for cardiovascular disease

We claim that a new level of studies is needed to answer a series of important questions about the expanding global chronic disease burden for cardiovascular disease (CVD) and for related conditions such as diabetes, metabolic syndrome, and obesity. These require a new study design structure, related to a new level of theory that goes beyond the current single-factor, a-theoretic epidemiological studies. This new platform for the design of large-scale Work/Stress/Disease studies would assess CVD-related disease mechanisms in a more general and dynamic form, based on the use of new tools for measuring autonomic functions in an occupational stress context and a new theory of disease causation. A sample outline is presented for such a study, based on Stress-Disequilibrium Theory (SDT) hypotheses, building on analytic tools developed for the assessment of stress-related exhaustion effects and chronic disease risks from Heart Rate Variability (HRV) research studies. The goal is to assess the associations between social organizational risks, particularly at work, and hypertension, metabolic syndrome, and diabetes II. The study design is multi-stage, spanning across several levels of disease-related de-regulation, and addressing co-morbidity of the conditions themselves. The study design is meant to span across a broad social population at all levels and would probably be multi-site, involving several countries, to yield the larger sample increased power for finding associations for work - physiological effects.

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.

A thermodynamic model of the sympathetic and parasympathetic nervous systems

In light of the nonequilibrium thermodynamics by I. Prigogine, the autonomic nervous system as a whole may be viewed as a dissipative structure progressively assembled in the course of evolution, plastically and rhythmically interfaced between forebrain, internal and external environments, to regulate energy, matter and information exchanges. In the present paper, this hypothesis is further pursued to verify whether the two main divisions of the autonomic nervous system, the sympathetic and parasympathetic systems, may support different types of exchange with the external environment. Previous data from hypothalamic stimulation experiments, studies of locus coeruleus function and available data on behavioral functional organization indicate that (1) tight engagement with the external environment, (2) high level of energy mobilization and utilization and (3) information mainly related to exteroceptive sensory stimulation characterize a behavioral prevalence of sympathoadrenal activation. On the other hand, (1) disengagement from the external environment, (2) low levels of internal energy and (3) dominance of proprioceptive information characterize a behavioral prevalence of vagal tone. Behavioral matter exchanges such as feeding, drinking, micturition and defecation are equally absent at the extreme of sympathoadrenal and vagally driven behaviors. The autonomic nervous system as a whole is genetically determined, but the sympathoadrenal system has been mainly designed to organize the visceral apparatus for an action to be performed by the biological system in the external environment and to deal with the novelty of task and of the environment, while the functional role of the parasympathetic is to prepare the visceral apparatus for an action to be performed by the biological system on itself, for recovery and self-protection (homeostasis), and is reinforced by repetition of phylo- and ontogenetically determined patterns. The available clinical data further support this interpretation indicating that an increased sympathetic and a decreased vagal tone may represent a consistent risk factor for cardiovascular diseases.

Factors influencing acute ischaemia-induced renal hypertension in rats

OBJECTIVE

To verify if the acute hypertension that occurs after reversal of complete renal ischaemia is related to the duration of ischaemia, is different in one-kidney (1K) and two-kidney (2K) rats, and is prevented by angiotensin receptor blockade.

METHODS

Four groups of Sprague-Dawley rats anaesthetized with pentobarbitone were studied before, during and after a reversible, complete renal ischaemia achieved by functional right nephrectomy.

RESULTS

In 1K rats (group 1, n = 21), reopening of right renal hilum after functional right nephrectomy of 180, 60 and 30 min was followed by peak increases in systolic blood pressure of 76.0 10.1 mmHg, 36.5 10.0 mmHg and 18.4 4.4 mmHg, respectively (mean SEM). In 2K rats (group 2, n = 21), functional right nephrectomy of 180, 60 and 30 min was followed by smaller increases in blood pressure of 49.8 7.6 mmHg, 5.9 3.3 mmHg and 8.3 2.1 mmHg, respectively. Plasma renin activity was directly related to the duration of functional right nephrectomy, and was greater in 1K rats. In group 3, irbesartan administered to 1K rats (n = 8) during functional right nephrectomy almost completely prevented the development of hypertension upon reopening. In group 4, labetalol injected intravenously in 1K rats (n = 3) did not prevent the blood pressure surge at reopening (49.2 8.5 mmHg).

CONCLUSIONS

An experimental acute renal hypertension may be elicited both in 1K and in 2K rats and for functional right nephrectomy of 30, 60 and 180 min duration. The increase in blood pressure is proportional to the duration of functional right nephrectomy and greater in 1K than in 2K rats. The experimental acute renal hypertension is due to acute release of renin and generation of endogenous angiotensin II, and is specifically prevented by the angiotensin II type 1 receptor blocker, irbesartan, but not by labetalol.