Clinical Research Directory

Inclusion Criteria: * Male, age 18-65 years * Willing and able to provide informed consent and follow all study procedures, including providing sperm specimens 3 months apart. * Type 1 or type 2 diabetes diagnosis confirmed by an endocrinologist (for participants in the diabetes groups) * HbA1c \> 7% (for participants in the diabetes groups) * Overweight (BMI \> 25 kg/m2) (for all groups, to ensure groups are similar) Exclusion Criteria: * Chronic kidney disease stage 4 or 5 (including end-stage renal disease); * Hepatic disease, including serum alanine transaminase (ALT) or aspartate aminotransferase (AST) greater than or equal to 3 times the upper limit of normal; hepatic synthetic insufficiency as defined as serum albumin \< 3.0 g/dL; or serum bilirubin \> 2.0; * Severe diabetic retinopathy; * Congestive heart failure, New York Heart Association (NYHA) class II, III or IV; * History of myocardial infarction, unstable angina or revascularization within the past 6 months; * Active genitourinary infection; * Testicular volume \<12 mL (assessed using Prader orchidometer); * Hypogonadism, defined as total testosterone \<250 ng/dl; * Hyperprolactinemia, defined as prolactin \>18 ng/ml; * Hyperestrogenism, defined as estradiol \>42 pg/ml; * Cryptorchidism; * Cigarette smoking; * Active alcohol abuse or substance abuse; * Cancer (except localized non-melanoma skin cancers) or use of chemotherapy agents within 5 years; * Use of nitrates or guanylate cyclase stimulators; * Use of steroid hormones (including testosterone), other than inhalers for reactive airway disease