REFLEX CONTROL OF GLUCOREGULATORY EXERCISE RESPONSES BY GROUP-III ANDGROUP-IV MUSCLE AFFERENTS

Group III and IV muscle afferents are active during exercise and relay information from mechano- and metaboreceptors in muscle. We hypothesi zed that these afferents participate in the regulation of endocrine an d metabolic adjustments to exercise. Muscle branches of the femoral ne rves were electrically stimulated in 10 anesthetized and paralyzed cat s at 3, 20, and 140 times motor threshold, for 10 min at each intensit y, recruiting group III afferents at 20 times motor threshold and grou p III and IV afferents at 140 times motor threshold. Six cats were not stimulated but were otherwise treated as stimulated cats. [3-H-3]gluc ose was infused intravenously, and arterial blood was sampled for anal ysis of substrates and hormones. Three times motor threshold stimulati on induced no changes in measured metabolic parameters. Twenty times m otor threshold stimulation elicited increases (P < 0.05 vs. control) i n glucose production (8.2 +/- 1.8 mu mol.min(-1).kg(-1)) and plasma gl ucose (0.29 +/- 0.07 mmol/l) and adrenocorticotropic hormone (ACTH; 35 +/- 12 pg/ml). Stimulation at 140 times motor threshold elicited incr eases (P < 0.05 vs. control) in glucose production (10.2 +/- 5.4 mu mo l.min(-1).kg(-1)), plasma glucose (0.53 +/- 0.10 mmol/l), ACTH (94 +/- 28 pg/ml), beta-endorphin (17 +/- 6 pg/ml), and Met-enkephalin (15 +/ - 2 pg/ml) and decreases (P < 0.05 vs. control) in insulin (0.65 +/- 0 .14 mu U/ml). Glycerol and glucagon did not change with stimulations. The findings provide evidence for a reflex control from muscle of horm one secretion and mobilization of glucose during exercise.