Stress, hypoglycemia, and the autonomic nervous system

TL;DR

This review argues that experimentally induced mild-to-moderate hypoglycemia is a paradigmatic physiological stress model for studying autonomic, neuroendocrine, and immune responses. It summarizes evidence that acute and antecedent hypoglycemia impair cardiovascular autonomic function and counterregulation, with some effects persisting after euglycemia is restored.

Key findings

• Hypoglycemia activates the HPA axis, sympathoadrenal system, and immune/inflammatory responses; counterregulatory increases in glucagon, epinephrine, growth hormone, and cortisol restore glucose. Acute hypoglycemia increases inflammatory markers—most consistently IL-6—prolongs QTc, and impairs cardiac-vagal baroreflex sensitivity.
• In 17 healthy volunteers exposed to experimental hypoglycemia for 120 min, cardiac-vagal baroreflex sensitivity was significantly decreased, the blood pressure threshold for baroreflex activation increased, and maximum R-R interval responses decreased.
• Antecedent hypoglycemia produces hypoglycemia-associated autonomic failure (HAAF), including blunted hormonal and sympathoadrenal responses and hypoglycemia unawareness, which can increase severe hypoglycemia risk six-fold; HAAF can be reversed by strict avoidance of hypoglycemia for 2–3 weeks.
• After euglycemia is restored, antecedent hypoglycemia attenuates cardiac-vagal baroreflex, vascular sympathetic baroreflex (MSNA response to transient hypotension), and catecholamine response to lower body negative pressure for at least 16 h; prothrombotic effects have been shown to persist at least 7 days. In ACCORD, >10,000 patients with T2DM were randomized, and the trial was stopped early for increased mortality in the strict glycemic control arm, with post-hoc analysis associating hypoglycemia with mortality in both groups.

Methods

• Narrative review synthesizing experimental human studies of hypoglycemic stress, including hyperinsulinemic clamps (euglycemic, hypoglycemic, and stepped), modified Oxford baroreflex testing, muscle sympathetic nerve activity (MSNA), lower body negative pressure, ACTH infusion, and inflammatory/coagulation markers.
• No new primary data are reported; the review cites studies including 17 healthy volunteers, ACCORD with >10,000 T2DM participants, and other T1DM/T2DM and healthy-volunteer cohorts.
• Main analysis is qualitative synthesis of cited literature rather than systematic review or meta-analysis.

Limitations

• Stated: the mechanisms mediating HAAF are not fully delineated; it is not known when the vascular-sympathetic baroreflex decrease first occurs or how long these impairments persist.
• Evident: as a narrative review, it lacks a systematic search strategy or quantitative synthesis, and it relies on cited studies with heterogeneity—for example, the text notes heterogeneity in studies of inflammatory and immune markers affected by hypoglycemia.