Pituitary-gonadal hormones during prolonged residency in Antarctica.

Plasma luteinizing hormone (LH), follicle stimulating hormone (FSH), prolactin (PRL) and testosterone levels were measured in nine eugonadal men in New Delhi and during the 1st week of different months of their stay at Dakshin Gangotri in Antarctica. During their 12-month stay in Antarctica, they were exposed to a severely cold climate, long polar nights and polar days, high wind velocity, increased amounts of solar and ultraviolet radiation and geomagnetism, as well as physical and social isolation. Plasma testosterone tended to increase in March, but a significant increase (P < 0.05) was not seen until April. The mean testosterone levels in May, June, September and November were also significantly higher than the March or New Delhi values. The absolute values of LH, FSH and PRL did not show any month-to-month changes in Antarctica. However, when the hormone levels were expressed as a percentage of the individual annual Antarctic mean, significant differences as a percentage of the individual annual Antarctic mean, significant differences were observed. The testosterone peak in April, May and June was associated with an increase in LH. The nadirs of testosterone, LH, FSH and PRL were seen in either July or August. FSH showed the highest values in March, whereas the highest PRL values were seen in November. These observations suggest the presence of circannual variations in gonadotropin, PRL and LH in Antarctica which are independent of polar days and polar nights. It appears that factors other than the duration of daylight might be involved in regulating these changes. The significance of maintenance of testosterone levels in the supra-physiological range in Antarctica remains unknown but may be important in acclimatization/habituation to the extreme polar cold by increasing basal metabolic rate, protein synthesis and erythropoiesis.

Plasma insulin and growth hormone during antarctic residence.

Circulatory levels of insulin and growth hormone (GH) were estimated in nine tropical euglycemic men in New Delhi and during the first week of every month of stay in Dakshin Gangotri, Antarctica. Prolonged residency in Antarctica did not alter GH levels because mean GH values during Austral summer and Austral winter were not significantly different from the New Delhi values. Compared with GH, the insulin levels during March, April, and June were found to be significantly lower than the New Delhi values. In Antarctica, the insulin levels in March, April, May, June, July, and August were also found to be significantly lower than the December values. This decline in insulin in Antarctica might be important in increasing substrate availability for heat production by facilitating lipolysis and hepatic glucose output.

Thyroid function during a prolonged stay in Antarctica.

Adaptation of the thyroid gland to the Antarctic environment was studied in nine healthy euthyroid tropical men of the Sixth Indian Antarctic Expedition during 1 year of their residence at polar latitudes. Circulatory concentrations of thyroid hormones, total T4 (TT4), total T3 (TT3), free T4 (FT4), free T3 (FT3), reverse T3 (rT3), thyroxine binding globulin (TBG), T3 uptake and thyroid stimulating hormone (TSH) were estimated in New Delhi and during the first week of each month of the stay in Antarctica. At the end of the Austral summer in March, the TT3 concentrations were found to be significantly lower (P < 0.01) compared to values recorded in New Delhi and showed a significant increase (P < 0.05) during the Austral winter in August. The mean TT3 concentrations from May to December were found to be significantly higher than the March or April values. Plasma TT4 and rT3 concentrations tended to decline in March but remained unaltered during the entire period in Antarctica. The FT4, FT3, TBG and T3 uptake did not show any appreciable change. Though, the TT3:TT4 ratio tended to decline in March and April suggesting decreased peripheral conversion of T4 to T3 as the possible mechanism for a decline in TT3 in March. physical exertion and prolonged exposure to extreme cold appeared to be the major contributory factors. The TSH concentration in March, April, November and December were found to be significantly higher than the New Delhi values. The morning as well as evening cortisol concentrations during the Austral winter were higher than the March values suggesting that cortisol rhythmicity was well maintained in Antarctica, albeit at a higher level. These observations indicated that the subtle changes in thyroid hormones during a prolonged stay at polar latitudes are related not only to the extreme cold but also to other factors such as physical activity, polar days and polar nights.