The response on glucoregulatory hormones of in vivo whole body hyperthermia

Abstract

This study was designed to examine the effects of in vivo hyperthermia on the circulating concentrations of a number of glucoregulatory hormones potentially involved in immunomodulation. Eight healthy male volunteers were immersed for 2 h in a hot water bath (water temperature 39.5°C) (WI) during which period their rectal temperature rose to 39.5°C. In a control study the subjects were immersed in thermoneutral water (water temperature 34.5°C). Blood samples were collected before, at body temperature 38°C (42.5 (30-52), (median and range), minutes of hot WI), 39°C (72.5 (58-97) minutes of hot WI), and 39-5°C (at the end of 2 h of hot WI), as well as 1 and 2 h after cessation of 2 h of hot WI. In the control experiment blood samples were collected at identical time points. The growth hormone concentrations were elevated already at 38°C to 24-2 (3.9-550) mU/1 and peaked at 39°C to 48-4 (20-8-81-5) mU/1 compared to 0.3 (0.3-9.0) mU/1 at baseline; at 39-5°C the concentration declined to 31.6 (130-480) mU/1 and further to 7.4 (0.8-17.3) mU/1 1 h after ending hot WI. The β-endorphin levels were augmented at 39°C and 39-5°, to 80 (3-4-27-8) pmol/1 and 8.1 (31.44-6) pmol/1, respectively, from 2-2 (0.7-5.6) pmol/1 at baseline. Glucagon levels raised from 230 (12.0-32.0) pmol/1 to 32.0 (24.0-52.0) pmol/1 at 39°C, and to 38.5 (26.0-57.0) pmol/1 at 39.5°C. Insulin levels remained unchanged. Plasma glucose increased from 4.75 (4.2-7.6) mmol/1 to 5.20 (4.6-5.6) mmol/1 alone after 90 min of WI (temperature 39-39-5°C). It is concluded that in vivo whole body WI hyperthermia increases the circulating levels of several essential glucoregulatory hormones.

Key Words:

• Hyperthermia
• growth hormone
• β-endorphins
• insulin
• glucagon