AUGMENTED GLUCOREGULATORY HORMONE CONCENTRATIONS DURING EXHAUSTING EXERCISE IN MILDLY IRON-DEFICIENT RATS

We hypothesized that augmented responses of glucoregulatory hormones i n iron deficiency would enhance liver and muscle glycogenolysis, leadi ng to increased gluconeogenic precursor (lactate) supply and upregulat ion of hepatic gluconeogenesis. Female weanling rats were randomly pla ced on either a mildly iron-deficient (-Fe; 15 mg Fe/kg diet) or an ir on-sufficient (+Fe; 50 mg Fe/kg diet) diet for 4 wk and studied at res t and during exhaustive treadmill running. Hemoglobin was 9.0 +/- 0.2 and 13.1 +/- 0.3 g/dl in -Fe and +Fe, respectively, after 3.5 wk of di etary iron deficiency. Arterial plasma epinephrine (Epi), norepinephri ne (NE), adrenocorticotropic hormone (ACTH), corticosterone, insulin, and glucagon levels were similar at rest in both groups, as were liver , gastrocnemius, and superficial and deep vastus medialis glycogen lev els. Liver and kidney phosphoenolpyruvate carboxykinase (PEPCK) activi ties were similar in both groups. Maximum O2 consumption was decreased (22%) in -Fe. Respiratory exchange ratio (CO2 production/O2 consumpti on) was unaffected at rest but increased at maximum O2 consumption in -Fe. Time to exhaustion during a standardized running test (13.4 m/min , 0% grade) was decreased 45% in -Fe (63 +/- 5 vs. 116 +/- 10 min). Du ring exercise, euglycemia was maintained in both groups, but blood lac tate was elevated in -Fe. The mean net glycogen utilization during exe rcise was increased in liver (43%), soleus (33%), and superficial vast us medialis (106%) and decreased in the gastrocnemius (36%) in -Fe. Li ver and kidney PEPCK activities were increased similarly at exhaustion in both groups. There was a greater rate of rise in arterial Epi (220 % greater) and NE (130%) in -Fe during exercise; however, at exhaustio n there was no difference between groups in either catecholamine. Thou gh not measured during exercise, ACTH, insulin, and glucagon were simi lar between groups at exhaustion. Mild iron deficiency results in an e levated Epi response that is associated with an increased lactate supp ly and an augmented muscle and liver glycogenolysis. These adaptations in mild iron deficiency are associated with a shift toward carbohydra te utilization during exercise.