Effect of simulated ascent to 3500 meter on neuro-endocrine functions.

Ascent to extreme High Altitude (HA) is in steps and it entails acclimatization at moderately HA locations. In terms of acclimatization, it is pertinent to understand the physiological changes, which occur on immediate ascent to moderate HA. The study aimed to evaluate the effect of ascent to 3500 m on neuro-endocrine responses in the first hour of induction. The plasma levels of catecholamines and cortisol were measured before and after one hour of ascent to high altitude. The peripheral oxygen saturation (SpO2), Galvanic Skin Resistance (GSR), Heart Rate (HR) and Blood Pressure (BP) were simultaneously monitored. The plasma epinephrine, norepinephrine, dopamine and cortisol were increased after one-hour exposure to 3500 m altitude as compared to before exposure. The SpO2 showed a significant decrease during and after high altitude induction. The heart rate and diastolic BP increased at 3500 m whereas the GSR did not show significant changes. There are changes in neuroendocrine responses, which reflect a sympathetic over activity in the first hour of exposure to 3500 m.

Circadian rhythmicity of growth hormone at high altitude in man.

Circulatory levels of growth hormone (GH) were estimated at 0600 h, 1200 h, 1800 h and 2400 h in each of 10 subjects of sea level residents (SLR) in New Delhi (226 m) and in high altitude natives (HAN) settled at an altitude of 3650 m. Both in SLR and HAN the GH secretion showed an identical pattern, the values were lowest at 0600 h and highest at 2400 h. Nevertheless, in HAN the GH levels at different timings of the day were found to be significantly higher than in SLR.

A study of pituitary-thyroid function during exercise in man.

Exercise induced modulations in circulatory T4, T3 and TSH were monitored in 14 healthy euthyroid male volunteers undergoing exercise on a bicycle ergometer at 750 KPM for 20 minutes. TSH response to 100 micrograms TRH was also studied in 4 exercising and 4 resting subjects. Serial blood samples were obtained before, during and after the exercise. Serum T4 exhibited a significant decrease (P less than 0.05) from 9.6 +/- 0.49 microgram/dl (mean +/- SE) to 8.3 +/- 0.47 microgram/dl at 20 min after the termination of the exercise, whereas a significant decrease (P less than 0.01) in T3 levels from 158 +/- 9 ng/dl to 144 +/- 8.2 ng/dl was recorded at 40 min after the termination of the exercise. The basal TSH levels as well as the sensitivity of the pituitary thyroid axis, monitored as overall TSH response, reflected by the sum of TSH values at different time intervals and the maximum rise over the basal levels (delta TSH) remained unaltered after exercise. These observations suggest that hormone secretion by the thyroid and its responsiveness to endogenous TSH are maintained after exercise. The decrease in circulatory T4 and T3 could be due to an increase in degradation of the hormones or may reflect a generalized adaptation phenomenon. The exact mechanism and significance of these alterations remains to be elucidated.

Plasma insulin, growth hormone, and blood sugar during exercise in man.

Alterations in plasma immunoreactive insulin (IRI), human growth hormone (hGH) and blood glucose were studied in five male volunteers undergoing exercise for 20 min on a bicycle ergometer at 750 kpm/min. Plasma IRI and hGH levels before exercise were 4.42 +/- 1.35 micro U/ml (mean +/- SE) and 1.94 +/- 0.88 ng/ml respectively. A significant decrease (p less than 0.01) in plasma IRI was observed at 20 min postexercise and remained at lower levels upto 80 min of observations. hGH levels showed significant increase (p less than 0.05) to a mean value of 7.46 +/- 0.71 ng/ml at 20 min of exercise with a peak value of 16.0 +/- 5.04 ng/ml at 20 min postexercise. Sixty min after termination of exercise, hGH levels returned to pre-exercise values. Blood glucose rose progressively with the increase in the duration of exercise and peak levels were recorded at 20 min of exercise. Sixty min after termination of exercise, blood glucose levels returned to pre-exercise values. These observations suggest that exercise stress can lead to a physiological situation in which circulating insulin and glucose are not exclusively dependent on each other.