Dr. Jibachha Sah,M.V.Sc( Veterinary pharmacology, TU,Nepal),posted lecturer notes on AUTONOMIC AND SYSTEMIC PHARMACOLOGY for B.V.Sc & A.H. 6 th semester veterinary students of College of veterinary science,Nepal Polytechnique Institute, Bharatpur, Bhojard, Chitwan, Nepal.I hope this lecture notes may be beneficial for other Nepalese veterinary students. Please send your comment and suggestion .Email:jibachhashah@gmail.com,moble,00977-9845024121

1. Vasodilators and
Antihypertensive agents
Dr.Jibachha Sah
M.V.Sc (Pharmacology)
College of Veterinary Science, NPI,
Bhojard, Chitwan

2. Vasodilators are medications that open (dilate) blood vessels. They affect the
muscles in the walls of arteries and veins, preventing the muscles from tightening
and the walls from narrowing.
Vasodilators
As a result, blood flows more easily through vessels. Heart doesn't have to pump as
hard, reducing blood pressure.

3. Classification of Vasodilators
1. Organic nitrates:
(i) Nitroglycerin (glyceryl trinitrate)
(ii) Amyl nitrite
(iii) Isosorbide di-nitrate
(iv) Erythrityl tetra nitrate
(v) Pentaerythritol tetra nitrate
2. Arterial Vasodilators:
(i) Hydralazine
(ii) Minoxidil
(iii) Diazoxide
3. Arterial and venous vasodilators:
(i) Sod. nitroprusside
(ii) Prazosin
(iii) Terazosin
(iv) Doxazosin

4. 1.Nitrates:
These drugs are mainly used to treat or prevent angina pectoris and acute as well
as chronic congestive heart failure (CHF).
The nitrates reduce the myocardial oxygen requirements by decreasing both
preload and afterload of heart. They dilate arteries and thereby reduce mean
systemic arterial pressure. Thus, afterload of the heart is reduced.

5. 2.Arteriolar Vasodilators:
These drugs are commonly used as antihypertensive agents.
(i) Hydralazine
They produce reflex sympathomimetic action resulting in increased cardiac output, heart
rate and renin secretion.
It is used in moderate to severe hypertension, acute and chronic CHF.
(ii) Minoxidil
It is a pro-drug which is metabolized by hepatic sulfotransferase to the active minoxidil N-O
sulphate. This minoxidil sulphate activates the ATP-dependent K+ channel to open, resulting
in K+ efflux. It causes hyperpolarization and relaxation of smooth muscle of blood vessels.
(iii) Diazoxide
It is one of the two important antihypertensive drugs (another is Sod. nitroprusside) used
for hypertensive emergencies. For this purpose, it is given, through i.v. route only.

6. 3. Arterial and venous vasodilators
Sodium Nitroprusside:
It is clinically used in hypertensive emergency through i.v. infusion with sterile 5%
dextrose.
Prazosin, Terazosin and Doxazosin:
They are selective α1 adrenoceptor blockers and dilate both the arteries and veins,
resulting in decreased peripheral vascular registance and blood pressure.

7. Uses for vasodilators
●High blood pressure
● High blood pressure during pregnancy or whelping (preeclampsia or eclampsia)
● Heart failure
● High blood pressure that affects the arteries in lungs (pulmonary hypertension)

10. Side effects and cautions
Direct vasodilators are strong medications that generally are used only when other
medications haven't controlled blood pressure adequately.
●Side effects include:
● Rapid heartbeat (tachycardia)
● Heart palpitations
● Fluid retention (edema)
● Nausea
● Vomiting
● Flushing
● Headache
● Excessive hair growth
● Joint pain
● Chest pain

11. Antihypertensive Drugs
Antihypertensives are a class of drugs that are used to treat hypertension (high blood
pressure).
Antihypertensives are a class of drugs that are used to treat hypertension (high blood
pressure).

12. Antihypertensive Drugs
Class Examples
Targeting renin–angiotensin system
Angiotensin-converting enzyme
inhibitors
Captopril, lisinopril, ramipril
Angiotensin receptor antagonists Candesartan, losartan, valsartan
Direct renin antagonists Aliskiren
Adrenoceptor antagonists
β-Blockers Atenolol, metoprolol, propranolol
α-Blockers
Doxazosin, labetalol (also a β-
blocker), phentolamine,
phenoxybenzamine
Classes and subclasses of antihypertensive medications with common examples

13. Calcium channel blockers
Phenylalkamines Verapamil
Dihydropyridines Amlodipine, nifedipine, nimodipine
Benzothiazepines Diltiazem

14. Vasodilators Hydralazine, minoxidil
Centrally acting agents Clonidine, methyldopa
Ganglion block Trimetaphan

15. (i) Diuretics
Thiazide Diuretics Loop Diuretics
Potassium-Sparing
Diuretics
CHLOROTHIAZIDE FUROSEMIDE SPIRONOLACTONE
HYDROCHLOROTHIAZIDE bumetanide amiloride
chlorthalidone ethacrynic acid triamterene
metolazone torsemide eplerenone
indapamide
hydroflumethiazide
Drugs that increase urine flow are called diuretics. Diuretics play an important role in
the management of high blood pressure. They are often used in combination with
other classes of antihypertensive drugs. These drugs are ion transport inhibitors in
the kidney,

16. Antihypertensive drugs have their primary action on systemic vascular resistance.
Some of these drugs produce vasodilation by interfering with sympathetic adrenergic
vascular tone (sympatholytics) or by blocking the formation of angiotensin II or its
vascular receptors.
Mechanism of action

17. Mechanism of action of the anti-hypertensive
drugs at different organs of the human body