Reduced sympathetic outflow and adrenal secretory activity during a 40-day stay in the Antarctic

Human adaptation to unknown and extreme environments requires changes in the psychological and physical homeostasis. We previously reported a significant decrease of anterior pituitary and adrenal hormonal levels and a significant modification of psychophysiological correlates of stress, such as galvanic skin response, after exposure to Antarctica, suggesting a possible decrease of individual arousal. The latter was hypothesized to be correlated with a modification of autonomic balance, mainly represented by a possible reduction of adrenergic output. The aim of the present study was to assess the patterns of hormonal circadian rhythms and the autonomic nervous system balance by means of spectral analysis of heart rate variability (HRV). These parameters were evaluated during 3 sessions (baseline, session 1 and session 2), before, at the beginning and after a 40-day stay in Antarctica (Station of Terra Nova Bay; average temperature in the study period: -11 degrees C, 24 h of light, sea level). In each of the sessions, 6 healthy male subjects underwent a 24-h electrocardiogram and blood sampling (08.00, 12.00, 16.00, 20.00, 24.00 and 08.00 h) for hormonal determinations. The data showed a remarkable decrease of hormonal levels without significant changes in circadian rhythms. Spectral analysis of HRV showed an imbalance of the autonomic nervous system with a relative significant decrease of the low frequency band (0.1 Hz) in session 1 and 2 compared to baseline, which can be functionally interpreted as a relative decrement of the sympathetic component. In conclusion, the exposure to a cold and extreme environment seems to affect autonomic balance over a 40-day period. This is followed by a significant reduction of the anterior pituitary and adrenal hormonal secretory patterns with preserved hormonal circadian rhythms (within the same time period of 40 days). This pattern is suggestive of a trophotropic neurovegetative adaptive process.

Modified autonomic balance in offsprings of diabetics detected by spectral analysis of heart rate variability

This study was performed to evaluate the influence of family history for non-insulin-dependent diabetes mellitus (NIDDM) on autonomic balance. The latter was assessed by spectral analysis of heart rate variability (SA-HRV) and by analyzing the relative contribution of low-frequency (LF) and high-frequency (HF) components. Twenty glucose normotolerant offsprings of NIDDM parents and 20 controls underwent a 1-hour continuous electrocardiogram (ECG). LF and HF (mean +/- SEM in normalized units [NU]), respectively increased and decreased in offspring versus controls. The LF/HF ratio (mean +/- SEM) significantly increased (LF/HF = 3.25 +/- 0.7 v 1.45 +/- 0.5, P <.0001 offsprings v controls). To test a stimulated response, a passive tilting (+ 90 degrees ) after 30 minutes of bed rest (0 degrees ) was performed in a subsample of subjects (10 offsprings v 10 controls). During bed rest, we found significantly higher values of the LF/HF ratio in offsprings versus controls (1.93 +/- 0.3 v 1.08 +/- 0.2, P <.05), whereas in the head-up position, the LF/HF ratio value increased to the same levels in the 2 groups (6.48 +/- 1.3 v 6.89 +/- 1.4, not significant [NS]). NIDDM family history is characterized in the basal condition by an imbalance of the autonomic system, which, compared with controls, is expressed by a higher weight of sympathetic and a lower weight of parasympathetic components. No significant differences can be found under stimulated conditions.

Association of persistent bronchial hyperresponsiveness with beta2-adrenoceptor (ADRB2) haplotypes. A population study

Bronchial hyperresponsiveness (BHR) is a hallmark of asthma and represents a strong risk factor for the disease. However, not all asthmatics have BHR and it can be observed in normal subjects too, probably because of genetic predisposition. Increasing attention is being focused on the beta2-adrenoceptor gene (ADRB2), whose genetic variability at amino acids 16 and 27 has been shown to correlate with some clinical features of asthma, including airways reactivity. To verify whether ADRB2 gene polymorphisms can influence BHR at a broader level, we studied a large, highly homogeneous sample of individuals sharing race, gender, age, and current living environment. BHR was strictly defined as a constant positive response to serial methacholine challenge tests and an improved definition of genetic variability at the ADRB2 locus was used, by identifying the haplotypic combinations of polymorphisms 16 and 27. We observed that the ADRB2 haplotype with a Gly at position 16 and a Gln at position 27 is associated with BHR in our sample. The association persisted also after correction for potentially confounding variables such as specific and total IgE levels. This observation suggests therefore that ADRB2 gene can confer genetic susceptibility to BHR, rather than having only a disease-modifying effect in asthma.