Effect of simulated microgravity on endocrine response to insulin-induced hypoglycemia in physically fit men.
Adaptation to microgravity is associated with alteration in some endocrine functions. In the present longitudinal study, the counterregulatory hormonal response to insulin-induced hypoglycemia (ITT, 0.1 IU/kg short acting insulin i. v.) was evaluated under simulated microgravity conditions in 15 physically fit subjects. ITT was performed at the beginning of the investigation, and again after completion of 6 weeks of endurance training and after a subsequent period of 4 days of head-down bed rest at a backward tilt of 6 degrees from the horizontal. Endurance training showed a significant increase in maximal aerobic capacity in previously well-trained subjects (increase by 12 %), as well as on attenuation of counterregulatory response of epinephrine to hypoglycemia. After 4 days of bed rest, basal concentrations of plasma norepinephrine was diminished (p < 0.002) and plasma renin activity was enhanced (p < 0.02). After bed rest, decreased responses of the two catecholamines (norepinephrine, p < 0.001; epinephrine, p < 0.001), growth hormone (p < 0.001), and cortisol (p < 0.05) were observed. Response of plasma renin activity after bed rest was increased (p < 0.01). This longitudinal study indicated that 4 days of bed rest in endurance-trained subjects induced increased response of PRA to hypoglycemia and attenuation of other counterregulatory neuroendocrine responses.
Ksinantova
L
L
Institute of Experimental Endocrinology, Slovak Academy of Sciences, Bratislava, Slovak Republic. ueenksin@savba.sk
Koska
J
J
Kvetnansky
R
R
Marko
M
M
Hamar
D
D
Vigas
M
M
D000328:Adult; D001510:Bed Rest / Q000009:adverse effects; D001786:Blood Glucose / Q000378:metabolism; D006728:Hormones / Q000097:blood*; D006801:Humans; D007003:Hypoglycemia / Q000097:blood* / Q000139:chemically induced; D007328:Insulin; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology; D010809:Physical Fitness / Q000502:physiology*; D018474:Weightlessness Simulation / Q000009:adverse effects*
D001786:Blood Glucose; D006728:Hormones; D007328:Insulin