Effect of Chronic ACE and DPP4 Inhibition on Blood Pressure

In this study the investigators will test the hypothesis that dipeptidyl peptidase IV (DPP4) inhibition attenuates the antihypertensive effect of angiotensin-converting enzyme (ACE) inhibition but not angiotensin receptor blockade or calcium channel blockade. The investigators further hypothesize that this effect is mediated by substance P.

The use of dipeptidyl peptidase IV (DPP4) inhibitors for the treatment of type 2 diabetes (T2DM) is growing rapidly. The majority of patients with T2DM are also taking ACE inhibitors or angiotensin receptor blockers (ARBs) in order to reduce cardiovascular and renal morbidity and mortality. DPP4 and ACE inhibitors share the common vasoactive substrate substance P. Substance P acts as a vasodilator but also activates the sympathetic nervous system. Understanding the interactive effects of DPP4 and ACE inhibitors on blood pressure and neurohumoral activation has important implications for the millions of patients with T2DM who take these drugs concurrently.

Eligibility Criteria:
Inclusion Criteria:

Age 18 to 80 years old

For female subjects the following conditions must be met:

Postmenopausal status for at least 1 year, or Status-post surgical sterilization, or If of childbearing potential, utilization of barrier methods of birth control and willingness to undergo urine β-HCG testing prior to drug treatment and on every study day

T2DM, as defined by 1 or more of the following at the time of screening visit:

* Hgb A1C ≥6.5%, or
* Fasting plasma glucose ≥126mg/dL, or
* 2-hour plasma glucose ≥200 mg/dL following 75gr oral glucose load

Hypertension, as defined by:

* Seated SBP ≥130 mm Hg on three occasions documented in medical record, or
* Seated DBP ≥80 mm Hg on three occasions documented in medical record, or
* Treatment with antihypertensive medications for a minimum of 6 months

Exclusion Criteria:

* Type 1 diabetes
* Poorly controlled T2DM, defined as Hgb A1C\>8.7%
* Use of anti-diabetic medications other than metformin for at least 12 months prior to initiation of the study
* Secondary hypertension
* Subjects who have participated in a weight-reduction program during the last 6 months and whose weight has increased or decreased more than 5 kg over the preceding 6 months
* Pregnancy
* Breast-feeding
* Treatment with drugs primarily metabolized through CYP3A4 (e.g. cisapride, pimozide)
* Clinically significant gastrointestinal impairment that could interfere with drug absorption
* Cardiovascular disease such as myocardial infarction within 6 months prior to enrollment, presence of angina pectoris, significant arrhythmia, congestive heart failure (LV hypertrophy and diastolic dysfunction acceptable), deep vein thrombosis, pulmonary embolism, second- or third-degree AV block, mitral valve stenosis, or hypertrophic cardiomyopathy
* Impaired hepatic function (aspartate amino transaminase \[AST\] and/or alanine amino transaminase \[ALT\] \>3 x upper limit of normal range)
* Impaired renal function (eGFR\< 50mL/min/1.73m2 as determined by the MDRD equation)
* History or presence of immunological or hematological disorders.
* History of pancreatitis or know pancreatic lesion
* History of angioedema while taking an ACE inhibitor
* Hematocrit \<35%
* Treatment with anticoagulants
* Diagnosis of asthma requiring use of inhaled β-2 agonist more than 1 time per week
* Any underlying or acute disease requiring regular medication which could possibly pose a threat to the subject or make implementation of the protocol or interpretation of the study results difficult
* Treatment with systemic glucocorticoids within the last 6 months
* Treatment with lithium salts
* Treatment with any investigational drug in the 1 month preceding the study
* Mental conditions rendering the subject unable to understand the nature, scope, or possible consequences of the study
* Inability to comply with the protocol, e.g., uncooperative attitude, inability to return for follow-up visits, and unlikelihood of completing the study