Circadian growth hormone and prolactin blood concentration during a self-limited viral infection and artificial hyperthermia in man

Growth hormone and prolactin blood concentrations were measured in five human volunteers over 28-hour periods including 24 hourly samples (0800 to 0800 hours) followed by an oral glucose tolerance test (0800 to 1100 hours) both preexposure and during the peak febrile phase of a self-limited viral infection, Sandfly fever. Several months after recovery, three of the subjects were studied for 24-hour periods while they sat in a tub of water at 41°C for 2 hours from 1300 to 1500 hours. During all studies, mealtimes (0800 hours, 1130 hours, 1630 hours) and dark phase (2300 to 700 hours) were fixed. Growth-hormone concentrations were strikingly elevated throughout the 24-hour study done during the febrile period of Sandfly fever infection (P < .01) except for the period of normal nocturnal release when they were not significantly different from the baseline study. No additional nocturnal surge was noted above the already elevated growth-hormone values during the viral-induced fever. Growth-hormone values tended to decline slowly during the night but increased considerably during the glucose-tolerance test the following morning. These changes were similar to responses previously reported in patients with cases of malnutrition. A clear-cut increase in growth-hormone concentrations (P < .001) was also seen during a brief 2-hour period of artificial hyperthermia, suggesting that elevated body temperature alone may explain part of the increase in growth-hormone values seen during the fever of infection. A nocturnal surge of growth hormone was still seen in the artificial hyperthermia study, albeit somewhat delayed. In contrast to growth hormone, prolactin concentrations were unchanged during Sandfly fever infection even during the glucose-tolerance test. Prolactin values were also unchanged during the brief period of artificial hyperthermia, even though simultaneous growth-hormone concentrations rose significantly. In conclusion, growth-hormone but not prolactin levels increased during the fever of infection and artificial hyperthermia. Since nitrogen loss has been documented in both of these situations, we assume that these increased concentrations of growth hormone are ineffective in maintaining normal nitrogen balance. This suggests a block in growth-hormone effectiveness during the fever of an infection and during artificial hyperthermia.