This trial plans to learn more about the effects of a medication, semaglutide, on cardiovascular function, kidney function, and insulin sensitivity in adults with type 1 diabetes. This medication has been effective in reducing cardiovascular disease and diabetic kidney disease and improving glucose control and BMI in adults with type 2 diabetes. This study aims to look at how well the medication works in people with type 1 diabetes. Semaglutide is not approved by the FDA to be used in this way. These procedures are considered to be experimental.

Inclusion Criteria:

• Age 18-49 years
• 1) T1D diagnosis defined as positive T1D-associated antibody(ies) or 2) a clinical diagnosis of T1D plus insulin requirement since diagnosis
• Insulin pump or automated insulin delivery systems
• Estimated glomerular filtration rate (eGFR) ≥ 45 ml/min/1.73m2
• Stable doses of drugs altering cardiovascular and renal function (e.g., Angiotensin-Converting Enzyme Inhibitor (ACEi), Angiotensin Receptor Blocker (ARB), statins, diuretics)
• BMI 20-45 kg/m2
• Adequate contraceptive method for females

Exclusion Criteria:

• HbA1c >9%, recent diabetic ketoacidosis (DKA) or hospitalization
• Major congenital heart disease, anemia, severe non-proliferative retinopathy, proliferative retinopathy
• History/family history of medullary thyroid carcinoma, multiple endocrine neoplasia type 2 (MEN2), pancreatitis
• Current/planned pregnancy or nursing
• Uncontrolled thyroid disease or hypertension (HTN) (≥ 160/100 mm Hg despite optimal therapy)
• Use of other non-insulin diabetes medications, insulin sensitizing medications, or systemic steroids in past 3 months
• Use of atypical antipsychotics
• Significant systemic illness such as cancer
• Shellfish/iodine allergy (only exclusionary to iohexol clearance procedure)
• MRI or PAH contraindications (only exclusionary to MRI and PAH procedures), GLP-1RA allergy