The tolerance of the organic nitrate is due to
One of the important limitation of the nitrovasodilators is their tolerance. Organic nitrates when used for long period develop tolerance towards their vasodilatory effects. Neither metabolism nor clearance is responsible for tolerance. Organic nitrates not act on any receptor but act by release of nitric oxide which increases cGMP. The tolerance is may be due to decreased release of nitric oxide from organic nitrates due to depletion of thiol groups in the tissues or due to any alteration in cGMP activity. The tolerance can be prevented by nitrate-free intervals. Hence long acting organic nitrates should be give 12-hour nitrate free interval to restore their activity.
The drug indicated to for cerebral vasospasm
Amlodipine is long acting vasodilator used in treatment of hypertension. Nimodipine is selective for cerebral blood vessels and indicated for cerebral vasospasm.
Calcium channel blockers are contraindicated in
(A) Heart failure
(D) None of the above
Calcium channel blockers can act on L-type calcium channels which are present on heart and smooth muscle. Verapamil acts on heart and nifedipine acts on smooth muscle. So they decrease heart rate and produce vasodilation respectively. At the same time, as they block calcium channels, decrease the contractility of the heart which is more pronounced with verapamil. Hence CCBs are contraindicated in heart failure.
The important effect of natriuretic peptides in heart failure is
(A) Increasing Na+ excretion in kidney
(B) Release of aldosterone
(C) Release of antidiuretic hormone
(D) Release of endothelin
Natriuretic peptides are released in heart failure as a compensatory mechanism and cause dilatation of afferent arterioles leading to increased excretion of sodium and water.
The drug that is used for stable angina in patients for whom -blockers are contra indicated is
Ivabradine is a new drug that blocks sodium-potassium channels in pacemaker potential thereby decreases automaticity. Hence it can be used instead of betablockers.