Effects of gender on neuroendocrine and metabolic counterregulatory responses to exercise in normal man

Significant, sexual dimorphisms exist in counterregulatory responses to com monly occurring stresses, such as hypoglycemia, fasting, and cognitive test ing. The question of whether counterregulatory responses differ during exer cise in healthy men and women remains controversial. The aim of this study was to determine whether a sexual dimorphism exists in neuroendocrine, meta bolic, or cardiovascular responses to prolonged moderate exercise. Sixteen healthy (eight men and eight women) subjects matched for age (28 +/- 2 yr), body mass index (22 +/- 1 kg/m(2)), nutrient intake, and spectrum of physi cal fitness were studied in a randomized fashion during 90 min of exercise on a cycle ergometer at 80% of their anaerobic threshold (congruent to 50% VO2 max). Respiratory quotient and oxygen consumption relative to body weig ht were identical in men and women. Glycemia was equated (5.3 +/- 0.2 mmol/ L) during exercise via an exogenous glucose infusion. Gender had significan t effects on counterregulatory responses during exercise. Arterialized epin ephrine (1.05 +/- 0.2 vs. 0.45 +/- 0.04 nmol/L), norepinephrine (9.2 +/- 1. 1 us. 5.8 +/- 1.1 nmol/L), and pancreatic polypeptide (52 +/- 6 vs. 37 +/- 6 pmol/L) were significantly (P < 0.01) increased in men compared to women, respectively. Plasma glucagon, cortisol, and GH levels responded similarly in men and women. Insulin values were higher at baseline in men and fell b y a greater amount to reach similar levels during exercise compared to thos e in women. Endogenous glucose production, measured with [3(-3)H] glucose w as similar in men and women. Carbohydrate oxidation was significantly incre ased in men relative to women (21.2 +/- 2 us. 15.6 +/- 2 mg/kg fat free mas s min; P < 0.05). Despite reduced sympathetic nervous system (SNS) drive, l ipolytic responses were increased in women. Arterialized blood glycerol (21 5 +/- 30 vs. 140 +/- 20 mu mol/L), beta-hydroxybutyrate (54 +/- 9 vs. 25 +/ - 10 mu mol/L), and plasma nonesterified fatty acids (720 +/- 56 vs. 469 +/ - 103 mu mol/L) were significantly (P < 0.01) increased in women. In keepin g with increased SNS activity, systolic blood pressure and mean arterial pr essure were significantly increased (P < 0.01) in men. In summary, this study demonstrates that a significant sexual dimorphism ex ists in neuroendocrine, metabolic, and cardiovascular counterregulatory res ponses to prolonged moderate exercise in man. We conclude that during exerc ise, men have increased autonomic nervous system (epinephrine, norepinephri ne, pancreatic polypeptide), cardiovascular (systolic, mean arterial pressu re) and certain metabolic (carbohydrate oxidation) counterregulatory respon ses, but that women have increased lipolytic (glycerol, nonesterified fatty acids) and ketogenic (beta-hydroxybutyrate) responses. Women may compensat e for diminished SNS activity during exercise by increased lipolytic respon ses.