Stress, ACTH, salt intake and high blood pressure

The biopsychology of salt hunger and sodium deficiency

Sodium is a necessary dietary macromineral that tended to be sparsely distributed in mankind's environment in the past. Evolutionary selection pressure shaped physiological mechanisms including hormonal systems and neural circuits that serve to promote sodium ingestion. Sodium deficiency triggers the activation of these hormonal systems and neural circuits to engage motivational processes that elicit a craving for salty substances and a state of reward when salty foods are consumed. Sodium deficiency also appears to be associated with aversive psychological states including anhedonia, impaired cognition, and fatigue. Under certain circumstances the psychological processes that promote salt intake can become powerful enough to cause "salt gluttony," or salt intake far in excess of physiological need. The present review discusses three aspects of the biopsychology of salt hunger and sodium deficiency: (1) the psychological processes that promote salt intake during sodium deficiency, (2) the effects of sodium deficiency on mood and cognition, and (3) the sensitization of sodium appetite as a possible cause of salt gluttony.

Social adversity experience and blood pressure control following antihypertensive medication use in a community sample of older adults

BACKGROUND

Psychosocial stress is a risk factor for hypertension and has been shown to affect response to treatment for psychiatric illnesses.

PURPOSE

We investigate the relationship between a history of social adversity experience and blood pressure control following antihypertensive medication use.

METHODS

A total of 1,186 participants selected from the European Prospective Investigation into Cancer-Norfolk study (531 men and 655 women, aged 42 to 80 years) had attended two health checks at which blood pressure measurements were taken; were taking antihypertensive medication at the second, but not the first health check; and had completed a questionnaire assessment of their social and psychological circumstances which included details of traumatic experiences in childhood and of adverse life events, long-term difficulties, and perceived stress in adulthood.

RESULTS

Experience of recent loss events in adulthood was associated with a smaller reduction in systolic blood pressure after starting hypertension treatment (β = 1.78, 95 % confidence interval 0.15-3.40, per life event), independently of age, sex, preexisting health conditions, cigarette smoking history, alcohol consumption, physical activity, and obesity.

CONCLUSION

Results from this study suggest that stress caused by recent losses may be associated with reduced effectiveness of treatment for hypertension. Subject to replication, these findings may help determine the specific physiological mechanisms by which medication treatment effectiveness is affected by stress.

Functional correlates of activity in neurons projecting from the lamina terminalis to the ventrolateral periaqueductal gray

The lamina terminalis (LT) consists of the organum vasculosum of the LT (OVLT), the median preoptic nucleus (MnPO) and the subfornical organ (SFO). All subdivisions of the LT project to the ventrolateral periaqueductal gray (vlPAG). The LT and the vlPAG are implicated in several homeostatic and behavioral functions, including body fluid homeostasis, thermoregulation and the regulation of sleep and waking. By combining visualization of c-Fos protein and retrograde neuroanatomical tracer we have examined the functional correlates of LT-vlPAG projection neurons. Rats were injected with retrograde tracer into the vlPAG and, following a 1-week recovery period, they were subjected to either hypertonic saline administration (0.5 M NaCl, 1 mL/100 g i.p.), 24-h water deprivation, isoproterenol administration (increases circulating angiotensin II; 50 microg/kg s.c.), heat exposure (39 degrees C for 60 min) or permitted 180 min spontaneous sleep. Retrogradely labeled neurons from the vlPAG and double-labelled neurons were then identified and quantified throughout the LT. OVLT-vlPAG projection neurons were most responsive to hypertonic saline and water deprivation. SFO-vlPAG projection neurons were most active following isoproterenol administration, and MnPO-vlPAG projection neurons displayed significantly more Fos immunostaining following water deprivation, heat exposure and sleep. These results support the existence of functional subdivisions of LT-vlPAG-projecting neurons, and indicate three patterns of activity that correspond to thermal and sleep wake regulation, osmotic or hormonal stimuli.

Biobehavior of the human love of salt

We are beginning to understand why humans ingest so much salt. Here we address three issues: The first is whether our salt appetite is similar to that in animals, which we understand well. Our analysis suggests that this is doubtful, because of important differences between human and animal love of salt. The second issue then becomes how our predilection for salt is determined, for which we have a partial description, resting on development, conditioning, habit, and dietary culture. The last issue is the source of individual variation in salt avidity. We have partial answers to that too in the effects of perinatal sodium loss, sodium loss teaching us to seek salt, and gender. Other possibilities are suggested. From animal sodium appetite we humans may retain the lifelong enhancement of salt intake due to perinatal sodium loss, and a predisposition to learn the benefits of salt when in dire need. Nevertheless, human salt intake does not fit the biological model of a regulated sodium appetite. Indeed this archetypal 'wisdom of the body' fails us in all that has to do with behavioral regulation of this most basic need.

Brain serotonin depletion enhances the sodium appetite induced by sodium depletion or beta-adrenergic stimulation

We investigate the influence of brain serotonin depletion on the sodium appetite. Rats depleted of serotonin through the systemic administration of p-chlorophenylalanine (300 mg/kg, ip, for 2 days) showed an intense natriorexigenic response induced by sodium depletion (furosemide, 20 mg/kg, sc, 24 h before water and 1.8% NaCl presentation). Intake of 1.8% NaCl was always higher than that observed for the control group (12.9 ± 1.4 and 21.4 ± 3.0 mL vs 5.7 ± 1.2 and 12.7 ± 1.6 mL, 30 and 300 min after water and saline presentation). After 24 h, the natriorexigenic response continued to be significantly higher compared to control (33.6±5.1 vs 21.9±3.6 mL,P <0.05). Fourteen days after p-chlorophenylalanine administration, 1.8% NaCl intake did not differ from controls. Serotonin-depleted rats expressed an early natriorexigenic response after isoproterenol administration on the third day after the first injection of p-chlorophenylalanine. An increase in 1.8% NaCl intake was first observed at 120 min (1.9 ± 0.2 vs 0.45 ± 0.3 mL,P <0.05) and remained high up to the end of the 24-h observation period (17.3±3.2 vs 1.1±0.5 mL,P <0.05). After 7 and 14 days, the natriorexigenic response became comparable to that of control animals. Present results show that brain serotonin depletion exaggerates the sodium appetite induced by the paradigm of sodium depletion or after beta-adrenergic stimulation.

Role of the central nucleus of the amygdala and bed nucleus of the stria terminalis in experimentally-induced salt appetite

The contributions of the central nucleus of the amygdala (CeA) and the bed nucleus of the stria terminalis (BST) to salt appetite were evaluated with two treatments which induce sodium chloride (NaCl) ingestion. Cumulative 3 h intakes of 2% NaCl after sodium depletion using furosemide, or subcutaneous (s.c.) injections of yohimbine (YOH), were measured in male, Sprague-Dawley rats both before and after electrolytic lesions of the CeA or the BST. Before surgery, sham-lesion and lesion groups drank equivalent amounts of 2% NaCl in response to furosemide depletion and YOH treatment. After surgery, rats with sham lesions increased their intakes of 2% NaCl following YOH while rats with CeA or BST lesions showed significant decreases. Rats with CeA or BST lesions also showed significant decreases in their intake of 2% NaCl after furosemide depletion, while intakes of the sham lesion groups remained unchanged. Lesions of either nucleus virtually eliminated 24 h need-free salt intake. Before and after surgery, all groups drank equivalent amounts of water in response to s.c. angiotensin II and to s.c. hypertonic saline, indicating the lesions specifically affected salt appetite. The results indicate that the CeA and the BST may be important sites for processing inputs mediating salt appetite.

Effects of cortisol on blood pressure and salt preference in normal humans

1. Adrenocorticotrophic hormone (ACTH) and corticosteroids stimulate salt appetite in laboratory animals. The hypothesis tested was that cortisol administration increases salt preference in humans. 2. Sodium taste studies (detection and recognition thresholds, taste intensity and preference tests) were conducted before, during and after cortisol administration (200 mg/day for 5 days) in normal men on a free diet. 3. Cortisol significantly increased systolic blood pressure (SBP), 113 +/- 3 - 130 +/- 4 mmHg, P < 0.05; diastolic blood pressure (DBP), 65 +/- 3 - 81 +/- 2 mmHg, P < 0.05; mean arterial pressure (MAP), 81 +/- 2 - 97 +/- 3 mmHg, P < 0.05; and bodyweight, 72.9 +/- 3.0 - 75.4 +/- 3.3 kg, P < 0.05. 4. Salt detection and recognition thresholds, taste intensity and preference for sodium chloride were unchanged following cortisol.

Stress, salt and hypertension

Reasons are given why calcium, obesity and genetics cannot be considered primary factors in the etiology of essential hypertension. This leaves the major protagonists as salt and neuroendocrine responses to the emotions aroused by the social environment. Most essential hypertension is renin dependent and associated with the physiological changes induced by arousal of the defence response. The psychosocial stimulation associated with this arousal induces an increase in salt appetite. This makes the salt consumption of society a measure of the social stress to which it is exposed. Primitive people whose blood pressure remains normal throughout their lives may lack modern societies' physically protective achievements but their religiously prescribed social solidarity may protect them from psychosocial stress. Our chronic suppression of awareness of emotional arousal together with loss of the ritualized support of affiliative behavior may result in repressed emotional responses which find somatic expression in diseases such as essential hypertension. Hypertensiologist George Pickering proposed that the primitive's ritual and taboo (the equivalent in our society might be the Alcoholic's Anonymous belief in a 'Higher Power') protect them from much anger and despair. He gave this precedence over salt as the primary factor in essential hypertension. New evidence supports this. Despite a high salt diet the blood pressure of socially adjusted rodents remains normal throughout their lifespan. On the other hand, the hypertension that develops when they are psychosocially stimulated is not abated by a low salt diet. In humans, the blood pressure of cloistered, secluded Italian nuns on a high salt diet has remained normal for 20 years while that of nearby village women has risen at a startling 2 mmHg/annum during the same period. On the other hand, in rapidly changing Malawi mature adult, rural and urban blood pressures are rising fast despite a low salt intake. Thus the evidence today argues that the most important factor in the etiology of essential hypertension is not salt but psychosocial stimulation.