Growth hormone deficiency and hyperthermia during exercise: a controlled study of sixteen GH-deficient patients

Sweat secretion is often disturbed in patients with GH secretory disorders. Hyperhidrosis is a classic feature of acromegaly, and it has recently been shown that GH-deficient patients exhibit decreased sweating capacity after pilocarpine stimulation of the skin. Thus, patients with GH-deficiency may be at risk for developing hyperthermia. To pursue this, we performed a controlled study on sweating and body temperature regulation during exercise in the heat in 16 GH-treated GH-deficient patients with normalized insulin-like growth factor-I and insulin-like growth factor/binding protein-3 serum levels [11 with multiple pituitary deficiency (MPD) and 5 with isolated GH deficiency] and in 10 healthy subjects as controls (CTs). Each subject exercised on a bicycle ergometer for 60 min at a workload corresponding to 45% of their individual maximal oxygen consumption (VO2max), in a room maintained at 35 C. GH serum concentrations increased significantly after approximately 10 min of exercise in the CTs (P < 0.001) but remained low in the patients. Body heat storage was significantly higher in the patients compared with the CTs [89 (SE +/- 10) watts (MPD) vs. 37 (SE +/- 8) watts (CTs), P < 0.001]. Consequently, the core temperatures of the patients increased significantly after exercise compared with those of the CTs [38.3 C (0.10 C) (MPD) and 38.1 C (0.06 C) (isolated GH deficiency) vs. 37.5 C (0.2 C) (CTs) (P < 0.004)]. Skin temperature increased significantly during exercise in the patients but remained unaltered in the CTs. Sweat secretion rates, as determined by the pilocarpine method, were significantly lower in the MPD patients [77 (SE +/- 10) mg/30 min] than in the CTs [115 (SE +/- 7) mg/30 min] (P < 0.005). Total body sweating was lower in the patients than in the CTs, although the difference did not reach statistical significance. Significantly reduced estimated evaporative heat loss was demonstrated in the patients compared with the CTs (P < 0.001). In conclusion, 1) decreased sweating, decreased sensitivity of the sweat gland, and impaired thermoregulation are part of the adult GH-deficiency syndrome, and 2) GH-deficient patients are at risk for developing hyperthermia during physical activity in hot environments.