Hypoglycemia, an Old Tool for New Findings in the Adrenomedullary Hormonal System in Patients with Rheumatic Diseases

Adrenomedullary response to hypoglycemia in first-degree relatives of patients with rheumatoid arthritis

Our recent studies showed blunted adrenomedullary responses to insulin-induced hypoglycemia in premenopausal females with rheumatoid arthritis (RA) and systemic sclerosis, suggesting dysregulation of the adrenomedullary hormonal system (AMHS). Since no relationship has been found between degree of AMHS dysfunction and clinical or inflammatory parameters in those patients, we hypothesize the presence of an inherited perturbation of the AMHS. To test this hypothesis, we evaluated adrenomedullary responses to insulin-induced hypoglycemia (0.1 IU/kg) in premenopausal female subjects: 17 glucocorticoid-naïve RA patients, 15 healthy first-degree family members (FDR), and 18 age- and body mass index-matched healthy controls. Our results demonstrate that when compared to controls, RA patients had lower baseline epinephrine levels (P= 0.01) and lower area under response curve (AUC) levels of norepinephrine (P < 0.001) and epinephrine (P < 0.003). In contrast, FDR had lower (P= 0.001) AUC levels of norepinephrine compared to controls and higher (P= 0.033) AUC levels of epinephrine compared to RA patients. There were no significant differences in epinephrine response between FDR and controls. Although we found lower norepinephrine responses to hypoglycemia in FDR of RA patients, adrenomedullary responses to hypoglycemia does not appear to be altered to the degree found in RA patients.

Heart rate variability and catecholamines during hypoglycemia and orthostasis

The low frequency component of heart rate variability (HRV) is believed to be affected by sympathetic activity, but an evidence for this suggestion remains controversial. This study analyzed association between HRV and plasma catecholamines in response to two distinct conditions activating sympathetic nervous system. Changes in HRV were analysed from ECG recording and plasma norepinephrine and epinephrine levels were measured in response to head-up tilt (60 degrees, 10 min) in 14 healthy volunteers (6 males, mean age 27.2+/-0.8) and in response to insulin-induced hypoglycemia (0.1 IU per kg, i.v. bolus) in 11 healthy volunteers (5 males, mean age 26.6+/-0.9 yr). Normalized low frequency power, low/high frequency ratio, plasma catecholamines increased, whereas normalized high frequency power decreased in response to head-up tilt or hypoglycemia. When analyzed individual time points of orthostatic test, plasma epinephrine correlated positively with low/high frequency ratio and negatively with normalized high frequency at the 3rd min of the head-up tilt. When all data at different time points were pooled significant correlations were found between catecholamines and normalized low frequency power and low/high frequency ratio. In insulin-induced hypoglycemia test plasma epinephrine correlated negatively with normalized high frequency power at the 30th minute. When all data measured at different time points were pooled no significant correlation was found between plasma catecholamines and HRV parameters. In conclusion, the present study shows an increase in low frequency component of HRV in response to orthostasis or hypoglycemia with significant, however inconsistent association to changes in plasma catecholamines.