Worsening Postural Tachycardia Syndrome Is Associated With Increased Glucose-Dependent Insulinotropic Polypeptide Secretion

BACKGROUND

Postural tachycardia syndrome (POTS) is characterized by excessive upright tachycardia and disabling presyncopal symptoms, which are exacerbated after consuming a high-carbohydrate meal; it is unknown, however, what is the precise underlying mechanism. We seek to investigate the effect of glucose intake on orthostatic hemodynamic changes and gastrointestinal hormone secretion in POTS.

METHODS

Prospective, case-control study, 12 women with POTS who reported a postprandial worsening of their POTS symptoms and 13 age-matched female controls received 75-g oral glucose and 20 mg/kg acetaminophen to assess nutrient absorption. Hemodynamic, gastrointestinal hormone and acetaminophen levels were measured for up to 120 minutes postingestion while supine and standing.

RESULTS

Patients with POTS had significant orthostatic tachycardia, 48.7±11.2 versus 23.3±8.1 bpm, P=0.012 and elevated upright norepinephrine levels, 835.2±368.4 versus 356.9±156.7 pg/mL, P=0.004. After oral glucose, upright heart rate significantly increased in POTS, 21.2±11.9% versus 6.0±19.9%, P=0.033 with a concomitant decline in upright stroke volume, -10.3±11.90% versus 3.3±13.7%, P=0.027; total peripheral resistance, blood pressure and cardiac output remained unaltered. Acetaminophen rate of appearance was similar between groups (P=0.707), indicating comparable nutrient absorption rates. POTS had increased plasma levels of C-peptide (P=0.001), GIP (glucose-dependent insulinotropic polypeptide; P=0.001), peptide YY (P=0.016), and pancreatic polypeptide (P=0.04) following glucose consumption, but only GIP had a time-dependent association with the worsening upright tachycardia and stroke volume fall.

CONCLUSIONS

The glucose-induced worsening orthostatic tachycardia in POTS was associated with a decline in SV; these changes occurred while GIP, a splanchnic vasodilator, was maximally elevated.

Abstract P3011: Role of CD36 in Insulin Mediated Microvascular Vasodilation in African Americans

CD36 is a membrane protein involved in fatty acids uptake that is expressed in the endothelium, which has been associated with endothelial dysfunction in African Americans (AA). One in four AA is G-allele carriers for coding CD36 SNP rs3211938, which results in ~50% reduction in its expression. We reported that potentiating nitric oxide action (NO) with sildenafil restored endothelial dysfunction in conduit arteries in G-allele carriers. In this study, we tested the hypothesis that in G-allele carriers, sildenafil would improve insulin-induced microvascular recruitment (MBV) in response to fat infusion. We recruited 25 healthy AA (17 non-carriers [ages 34 ± 7.4] and eight G-allele carriers [42 ± 7.4 yrs]). Subjects underwent three visits: Visit 1: Saline infusion and hyperinsulinemic euglycemic clamp (HIE clamp). Visit 2: Lipid infusion and HIE clamp and Visit 3: Lipid infusion and HIE clamp after a four-week sildenafil treatment (60 mg/day). During each visit, the subjects underwent an assessment of MBV at baseline (bsl), after 3-hour insulin (Ins) infusion (40mu/m 2 /min) and after Ins and L-arginine (10mg/kg/min) for 30 min. infusion (Ins+L-arg). Ins+L-arg (saline day) increased the % change in MBV in both groups. However, this increase was less in carriers as compared to non-carriers (13.6±42.4 and 38.9±74.4), Fig. A. Intralipid (IL) infusion increased MBV but only in non-carriers, Fig. B . Treatment with sildenafil in the presence of IL infusion induced a decline in MBV in G-allele carriers Fig. C . In conclusion, healthy AAs with CD36 deficiency had a poor insulin-induced microvascular recruitment and appeared to be worsened by potentiating NO function with sildenafil.