Hormonal responses to surgical stress

Trial watch: beta-blockers in cancer therapy

Compelling evidence supports the hypothesis that stress negatively impacts cancer development and prognosis. Irrespective of its physical, biological or psychological source, stress triggers a physiological response that is mediated by the hypothalamic-pituitary-adrenal axis and the sympathetic adrenal medullary axis. The resulting release of glucocorticoids and catecholamines into the systemic circulation leads to neuroendocrine and metabolic adaptations that can affect immune homeostasis and immunosurveillance, thus impairing the detection and eradication of malignant cells. Moreover, catecholamines directly act on β-adrenoreceptors present on tumor cells, thereby stimulating survival, proliferation, and migration of nascent neoplasms. Numerous preclinical studies have shown that blocking adrenergic receptors slows tumor growth, suggesting potential clinical benefits of using β-blockers in cancer therapy. Much of these positive effects of β-blockade are mediated by improved immunosurveillance. The present trial watch summarizes current knowledge from preclinical and clinical studies investigating the anticancer effects of β-blockers either as standalone agents or in combination with conventional antineoplastic treatments or immunotherapy.

Stress hormones and immune function

Over the past 20 years we have demonstrated both in animal models and in human studies that stress increases neuroendocrine hormones, particularly glucocorticoids and catecholamines but to some extent also prolactin, growth hormone and nerve growth factor. We have also shown that stress, through the action of these stress hormones, has detrimental effects on immune function, including reduced NK cell activity, lymphocyte populations, lymphocyte proliferation, antibody production and reactivation of latent viral infections. Such effects on the immune system have severe consequences on health which include, but are not limited to, delayed wound healing, impaired responses to vaccination and development and progression of cancer. These data provide scientific evidence of the effects of stress on immune function and implications for health.

Cortisol responses to immobilization with Telazol or ketamine in baboons (Papio cynocephalus/anubis) and rhesus macaques (Macaca mulatta)

Little is known about the influence of Telazol on cortisol or of anesthetic agents on immunological measures, and reports of ketamine's effect on cortisol are inconsistent. We measured effects of Telazol, ketamine and blood sampling on cortisol in male rhesus macaques and male savannah baboons. We also obtained leukocyte counts in the macaques. In macaques, Telazol reduced cortisol in the morning but not in the afternoon; ketamine had no effect on cortisol in these animals. In baboons, cortisol changed little post-Telazol but increased post-ketamine. In macaques, lymphocyte numbers decreased following afternoon injection of Telazol, ketamine or saline. The injection and blood sampling process increased cortisol levels in monkeys not trained to extend an arm but exerted no effect on cortisol in trained macaques. Thus, the animals' physiological responses to blood sampling and immobilization are influenced by such variables as anesthetic agent, species, time of day, and familiarity with the blood sampling process.

Reciprocal interactions between the neuroendocrine and immune systems during inflammation

The neuroendocrine and immune responses to inflammatory stress represent important integrated physiologic circuits for the regulation of inflammation whose basis has been reviewed. Proinflammatory cytokines such as IL-1 beta, TNF alpha, and IL-6 released from inflammatory foci initiate a local inflammatory response and travel by way of the blood-stream to the central nervous system, where they trigger a variety of neuroendocrine counterregulatory mechanisms. There is an important NEI loop. Stimulatory signals are received by the neural systems from inflammatory foci and are transduced by the hypothalamus, thereby initiating a complex hormonal and cytokine cascade of reactions aimed at modulating inflammation and returning the organism to normal physiologic homeostasis once the trigger has been neutralized. Conversely, a number of mechanisms that modulate the anti-inflammatory activity of the neuroendocrine responses to inflammation are also activated. Defects in the neuroendocrine-immune interactions can profoundly affect the susceptibility to developing chronic inflammatory disease and influencing survival after bacterial infections. The NEI loop has important pathophysiologic implications for disease processes.

Response of fecal cortisol to stress in captive chimpanzees (Pan troglodytes)

This study examined whether fecal cortisol could be used as an index of stress responses. The stress responsiveness of fecal cortisol was tested with a stressor known to stimulate adrenal activity, the stress of anesthesia. Daily fecal and urine samples were collected from four captive chimpanzees (Pan troglodytes) before and after anesthetizations with Telazol/Ketasat. Tests of assay validity indicated that cortisol was measurable in chimpanzee fecal extracts. Fecal cortisol concentrations were significantly elevated 2 days after anesthetization, with elevations in seven of the eight treatments. The posttreatment peak was significantly greater than baseline values in three of the four subjects. Both fecal concentrations and proportionate increases in responses to stress were significantly correlated with the corresponding values in urinary cortisol, confirming the stressfulness of these procedures and the stress responsiveness of fecal cortisol. These findings provide evidence for the application of fecal cortisol as a noninvasive index of physiologic stress in nonhuman primates.

CRH-deficient mice have a normal anorectic response to chronic stress

Many studies have implicated corticotropin-releasing hormone (CRH) as a mediator of stress-induced decreases in food intake. However, urocortin, sauvagine, and urotensin, other members of the family of CRH-like molecules, have also been shown to be potent inhibitors of food intake. This raises the possibility that a CRH-related molecule might also be responsible for stress-induced anorexia. We therefore examined the effects of three chronic stressors, repetitive daily restraint, turpentine abscess, and surgical stress, upon food intake in wildtype and CRH-deficient mice created by targeted inactivation of the CRH gene. We have found that both genotypes have similar basal food intake which initially decreases to the same degree following initiation of each stress paradigm. Food intake also recovers following the same time course and to the same degree in both genotypes. Therefore, CRH is not necessary for decreases in food-intake induced by the chronic stressors examined in this study.

Mivazerol prevents the tachycardia caused by emergence from halothane anesthesia partly through activation of spinal alpha 2-adrenoceptors

BACKGROUND

Mivazerol (MIV) is an alpha 2-adrenoceptor agonist designed to prevent adverse cardiac outcome in perioperative patients. The present study was undertaken to determine whether the hyperdynamic state observed at emergence from halothane (HAL) anesthesia in rats could be modulated by MIV and to explore the mode of action of MIV under such conditions.

METHODS

Male Sprague Dawley rats were anesthetized with 1% HAL and assisted for respiration (N2O-O2: 70-30%). MIV 2.2-15.3 micrograms.kg-1.h-1 i.v. was infused 30 min before withdrawal of anesthesia and compared for heart rate (HR) and systolic arterial blood pressure (SAP) to control animals treated with saline. In some experiments, animals were pretreated with intrathecal pertussis toxin (T2 level, 0.5 microgram, 7 d), or i.v. rauwolscine (0.34 mg/kg, 5 min) or were bilaterally stellectomized (30 min) prior to withdrawal of HAL.

RESULTS

Increases in HR (65 bpm, +20%) and in SAP (25 mmHg, +26%) were observed immediately upon discontinuation of HAL and remained constant for at least 30 min. The increase in HR was abolished by removal of the stellate ganglia. MIV dose-dependently inhibited the increase in HR from 4.8 micrograms.kg-1.h-1 (68% reduction, P < 0.05) without affecting HR or SAP during anesthesia. Inhibition of HR increase was of 98% at 15.3 micrograms.kg-1.h-1. This effect was abolished by rauwolscine, and partially (50%) inhibited by pertussis toxin pre-treatment.

CONCLUSION

These results demonstrate that withdrawal of HAL anesthesia in the rat produces a sustained increase in HR due to activation of the sympathetic system and that MIV inhibits this tachycardia via activation of alpha 2-adrenoceptors located at least in part in the spinal cord.

Neuroendocrine immune responses to inflammation: the concept of the neuroendocrine immune loop

The neuroendocrine and immune responses to inflammatory stress represents an integrated circuit whose basis is reviewed in this chapter. Pro-inflammatory cytokines such as IL-1 beta, TNF-alpha and IL-6 released from inflammatory foci initiate local anti-inflammatory mechanisms and travel via the blood stream to the brain where they trigger a variety of neuroendocrine counter-regulatory mechanisms. There is therefore an important neuroendocrine-immune loop in which stimulatory signals are received by the neural systems from inflammatory foci. These signals are transduced by the hypothalamus which initiates a complex hormonal cascade reaction aimed at modulating inflammation and returning the organism to normal physiological homeostasis once the trigger has been neutralized. Abnormalities in this cross-talk can profoundly influence the susceptibility to developing chronic inflammatory disease. Thus, in conclusion, the neuroendocrine-immune loop has important pathophysiological implications for disease processes.

The neuroendocrine immunology of rheumatoid arthritis

Rheumatoid arthritis patients have defective neuroendocrine-immune responses to the stress of inflammation, and currently available data shows that this contributes to the pathophysiology of the disease. The advances in neuroendocrine immunology have improved our understanding of the pathophysiological mechanisms involved in RA. These observations raise important therapeutic questions which are certainly worth further investigation as they may open up novel avenues for the management of the disease.

Acute response of human muscle protein to catabolic hormones

OBJECTIVE

The purpose of this study was to determine the acute in vivo response of human muscle protein to stress.

SUMMARY BACKGROUND DATA

Prior animal and human in vitro studies have suggested that physiologic stress increases muscle protein turnover. In contrast, recent publications using a polyribosomal methodology have demonstrated a reduction in human muscle protein synthesis in vivo after surgery.

METHODS

Five healthy volunteers were given a stable isotopic infusion of 1,2(13)C leucine that allowed for determination of the fractional rate of muscle protein synthesis by measuring the rate of incorporation of 13C label into vastus lateralis muscle biopsies. Simultaneous infusion of 15N lysine and quantitation of leg blood flow by indocyanine green dye dilution allowed for estimation of leg muscle protein breakdown rate (Lys Ra) and synthesis rate (Lys Rd). These measurements were performed before and then at the conclusion of a 4-hour femoral arterial infusion of the catabolic hormones epinephrine, cortisol, and glucagon.

RESULTS

The catabolic hormone infusion elicited a significant (65%) increase in the leg muscle protein breakdown rate and a significant but less marked increase in the rate of muscle protein synthesis, as assessed by both an increase in the fractional rate of muscle protein synthesis of 48.5% and in lysine uptake within the leg of 32%.

CONCLUSIONS

This study conclusively demonstrates that a hormonally induced stress results in a net catabolism of human muscle protein by increasing the rate of protein breakdown in excess of an increased protein synthetic rate.