The purpose of this study is to assess the effect of C21 on forearm blood flow by use of strain-gauge venous occlusion plethysmography.

Subject will be screened for eligibility. Eligible subjects will receive ascending doses of C21 (3, 10, 30, 100, and 200 µg/min through local intra-arterial infusions for 5 min/dose. Forearm blood flow measurements will be performed in both arms during the last 2 minutes of each dose.

Infusions of sodium nitroprusside will be performed as a positive control using the same methodology.

Inclusion Criteria:

1. Willing and able to give written informed consent for participation in the study and to comply with study requirements.
2. Healthy male subject aged 18-45 years
3. Body mass index ≥ 18.5 and ≤ 30.0 kg/m2.
4. Wlling to use condom or be vasectomised or practice sexual abstinence
5. Clinically normal medical history, physical findings, vital signs, ECG and laboratory values

Exclusion Criteria:

1. History of any clinically significant disease or disorder which may either put the subject at risk because of participation in the study, or influence the results or the subject's ability to participate in the study.
2. History of thrombotic disease, vascular disorder, or severe bleeding disease.
3. Poor brachial artery access.
4. Any clinically significant illness, medical/surgical procedure, or trauma within 4 weeks of baseline
5. Malignancy within the past 5 years with the exception of basal cell or squamous epithelial carcinomas of the skin that have been resected with no evidence of metastatic disease for 3 years.
6. Any planned major surgery within the duration of the study.
7. Any positive result on screening for serum hepatitis B surface antigen, hepatitis C antibody and human immunodeficiency virus (HIV).
8. Abnormal vital signs
9. Prolonged QT interval, cardiac arrhythmias or any clinically significant abnormalities in the resting ECG
10. History of severe allergy/hypersensitivity or ongoing allergy/hypersensitivity or history of hypersensitivity to drugs with a similar chemical structure or class to the IMPs, including any of the excipients of the IMPs.
11. Regular use of any prescribed or non-prescribed medication including antacids, analgesics, herbal remedies, vitamins, and minerals
12. Regular use of non-steroidal anti-inflammatory drugs or acetylsalicylic acid
13. Vaccination within 1 week prior to dosing or plans to receive any vaccine during the study conduct.
14. Planned treatment or treatment with another investigational drug within 3 months
15. Current regular smokers or users of nicotine products.
16. History of alcohol abuse
17. Presence or history of drug abuse
18. Positive screen for drugs of abuse or alcohol at screening
19. History of, or current use of, anabolic steroids.
20. Inability to refrain from consuming caffeine-containing beverages during Day 1
21. Plasma donation within 1 month of screening or blood donation (or corresponding blood loss) during the 3 months prior to screening.
22. Investigator considers the subject unlikely to comply with study procedures, restrictions and requirements.

Adverse events were recorded from trial start until end-of-trial contact (follow-up), 7 days after trial start

Adverse events were recorded from trial start until end-of-trial contact (follow-up),