Augmented glucoregulatory hormone concentrations during exhausting exercise in mildly iron-deficient rats
Zinker, B.A.; Dallman, P.R.; Brooks, G.A.
American Journal of Physiology 265(4 Pt 2): R863-R871
1993
ISSN/ISBN: 0002-9513 PMID: 8238458 Document Number: 414978
We hypothesized that augmented responses of glucoregulatory hormones in iron deficiency would enhance liver and muscle glycogenolysis, leading to increased gluconeogenic precursor (lactate) supply and upregulation of hepatic gluconeogenesis. Female weanling rats were randomly placed on either a mildly iron-deficient (-Fe; 15 mg Fe/kg diet) or an iron-insufficient (+Fe; 50 mg Fe/kg diet) diet for 4 wk and studied at rest 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 dietary iron deficiency. Arterial plasma epinephrine (Epi), norepinephrine (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 levels, Liver and kidney phosphoenolpyruvate carboxykinase (PEPCK) activities were similar in both groups. Maximum O-2 consumption was decreased (22%) in -Fe. Respiratory exchange ratio (CO-2 production/O-2 consumption) was unaffected at rest but increased at maximum O-2 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). During exercise, euglycemia was maintained in both groups, but blood lactate was elevated in -Fe. The mean net glycogen utilization during exercise was increased in liver (43%), soleus (33%), and superficial vastus medialis (106%) and decreased in the gastrocnemius (36%) in -Fe. Liver 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 exhaustion there was no difference between groups in either catecholamine. Though not measured during exercise, ACTH, insulin, and glucagon were similar between groups at exhaustion. Mild iron deficiency results in an elevated Epi response that is associated with an increased lactate supply and an augmented muscle and liver glycogenolysis. These adaptations in mild iron deficiency are associated with a shift toward carbohydrate utilization during exercise.