1. IL-6: Heart rate variability (HRV) is in inverse relationship with IL-6: Relationship between Heart Rate Variability, Interleukin-6, and Soluble Tissue Factor in Healthy Subjects: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8/
  2. D-dimer: D-dimer is in inverse relationship with endothelial progenitor cells and edothelial progenitor cells are positively associated with HRV or parasympathetic tone at least in patients with hypertension. : Lower Levels of Circulating Endothelial Progenitor Cells Are Associated with Increased Recurrence after Unprovoked Venous Thrombosis: https://ashpublications.org/blood/article/128/22/3805/97010/Lower-Levels-of-Circulating-Endothelial-Progenitor
    Sympathetic Predominance Is Associated With Impaired Endothelial Progenitor Cells and Tunneling Nanotubes in Controlled-Hypertensive Patients: https://pubmed.ncbi.nlm.nih.gov/24858852/
  3. Lymphopenia: Under certain condition lymphocytes (CD4+, CD8+ etc.) are positively associated with HRV or parasympathetic tone and C-peptide increases parasympathetic tone and HRV: Leukocyte Populations are Associated with Heart Rate Variability After a Triathlon: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5187961/
    Stress Determined Through Heart Rate Variability Predicts Immune Function: https://pubmed.ncbi.nlm.nih.gov/31408866/

Proinsulin C Peptide Obviates Sympathetically Mediated Suppression of Splenic Lymphocyte Activity in Rats: https://pubmed.ncbi.nlm.nih.gov/11151760/

C-peptide Improves Autonomic Nerve Function in IDDM Patients: https://pubmed.ncbi.nlm.nih.gov/8781764/

Proinsulin C-peptide Activates Vagus Efferent Output in Rats: https://pubmed.ncbi.nlm.nih.gov/16005542/
Intranasal Administration of Proinsulin C-Peptide Enhances the Stimulating Effect of Insulin on Insulin System Activity in the Hypothalamus of Diabetic Rats: https://pubmed.ncbi.nlm.nih.gov/31346872/