SYMPATHOEXCITATION CANNOT ACCOUNT FOR GENDER DIFFERENCES IN EXERCISE-INDUCED ACUTE MOUNTAIN SICKNESS

Abstract

859 Exercise compared to rest during the first 6 hrs of altitude exposure caused more severe symptoms of acute mountain sickness (AMS) in men (Roach, ACSM 1999). However, in women taking oral contraceptives, exercise had no affect on AMS symptoms (Sandoval, MSSE, 29(5): S135, #778, 1997). We examined catecholamine and adrenocorticotropin hormone (ACTH) responses from these two studies in an attempt to explain the observed gender differences in the effects of exercise on AMS. At simulated altitude (429 mm Hg), we studied 13 subjects, 7 women (W) taking oral contraceptives and 6 men (M), on 2 occasions; once while resting (R), and once while performing 4, 30-min intermittent exercise bouts at 50% maximal altitude workload (EX). AMS symptom scores and plasma levels of norepinephrine (NE), epinephrine (E), and ACTH were measured at 0 and 9 hrs at altitude. Hormone values were log transformed to approximate a normal distribution. AMS scores in EX were significantly greater for M but not for W (p<0.05). At rest, NE and E were greater in M vs. W at 0 and 9 hrs (NE=2.6±0.05 and 2.7±0.03 vs. 2.5±0.08 and 2.6±0.06 in M vs. W for 0 and 9 hrs, respectively; E = 1.6±0.06 and 1.8±0.05 vs. 1.4±0.08 and 1.4±0.06, in M vs. W for 0 and 9 hrs, respectively; p<0.05). However, EX had no additional affect on NE or E. ACTH did not change over time at altitude, with exercise, or between genders. AMS scores were independent of NE, E, and ACTH. Despite the fact that M, but not W, experienced greater AMS during EX, gender differences in sympathoexcitation occurred independent of exercise and AMS scores. Thus, it is unlikely that sympathoexcitation can directly explain the increased incidence of AMS with EX in men. Further research is needed to clarify these observed gender differences in exercise-induced AMS and sympathoexcitation at simulated high altitude. Supported by NIH Training Grant HL07758