This study will describe the interplay between the gut hormones GIP and CCK and their regulation of blood flow to the large vessels in patients with Postural Orthostatic Tachycardia Syndrome (POTS) and GIP, CCK and GLP-1 in healthy. This is addressed by hormone infusions during MR-scans of the abdomen and intake of oral glucose.

Each participant will attend independent randomized experimental days with MR-scans during and intravenous infusions of hormones or placebo and ingestion of glucose or water. A continuous intravenous infusion of either GIP(3-30)NH2, CCK8- or saline for POTS-group or GIP(3-30)NH2, CCK-8, saline or exendin(9-39)NH2 in healthy is started while the participant lie in the scanner while scans, blood samples and questionnaires are repeated over the time course of 2 hours. At a specific timepoint the participants will ingest 75 g of glucose dissolved in 250 ml water.

Inclusion Criteria POTS patients:

• Previously diagnosed with POTS in tilt test or active stand-test (either newly diagnosed within last 3 months or in new tilt test/active stand test during screenings visit)
• Reproducible orthostatic intolerance with raise in HR on >30 bpm when standing within 10 minutes of change of supine to standing in age >19 years or >40 bpm in age 18-19 years.
• POTS symptoms/orthostatic intolerance
• Age 18-50
• Waist ratio <180 cm

Exclusion Criteria:

• Chronic illness
• Metallic implants
• Above 10 alcoholic drinks or week or substance abuse
• Other types of sinus tachycardia or heart disease
• Liverenzymes two times above normal values
• Decreased kidney function eGFR <90 or elevated kreatinkinasis
• Thyroid disease or TSH out of reference
• Uncontrollable low or high blood pressure
• Blood vessels that cannot be visualized on MR
• Any disease that might influence the health of the participant during the study or participants that receives medicine that cannot be paused for 36 hours

Inclusion Criteria:

• Age 18-50
• Waist ratio <180 cm
• Matched a POTS patient in age, sex and BMI

Exclusion Criteria:

• Chronic illness
• Metallic implants
• Above 10 alcoholic drinks or week or substance abuse
• POTS; other types of sinus tachycardia or heart disease
• Liverenzymes two times above normal values
• Decreased kidney function eGFR <90 or elevated kreatinkinasis
• Thyroid disease or TSH out of reference
• Uncontrollable low or high blood pressure, Orthostatic hypotension
• Blood vessels that cannot be visualized on MR
• Any disease that might influence the health of the participant during the study or participants that receives medicine that cannot be paused for 36 hours

Will share upon request

Data will be shared upon request after study completion

Qualified researchers can request access by submitting a proposal to the study sponsor. Data will be shared via a secure online repository upon approval of the request.