Mecamylamine

Mecamylamine hydrochloride (Inversine) is a secondary amine and can therefore easily penetrate cell membranes. Its absorption from the gastrointestinal tract is more complete than that of the quaternary ammonium compounds. Mecamylamine is well absorbed orally and crosses both the blood-brain and placental barriers; its distribution is not confined to the extracellular space. High concentrations of the drug accumulate in the liver and kidney, and it is excreted unchanged by the kidney. In contrast to most of the highly ionized ganglionic blocking agents, mecamy-lamine can produce central nervous system effects, including tremors, mental confusion, seizures, mania, and depression. The mechanism by which these central effects are produced is unclear. Mecamylamine is rarely used today as an antihypertensive drug because it blocks both parasympathetic and sympathetic ganglia.

^ Study Questions

During a laboratory demonstration to depict the complexity of neurotransmission in autonomic ganglia, Professor Smith sets up an anesthetized mammalian preparation in which she is recording postsynaptic events following the electrical stimulation of pregan-glionic sympathetic nerves. This demonstrates a complex action potential that consists of a fast EPSP followed by a slow IPSP followed by a slow EPSP and finally by a late very slow EPSP.

1. In Professor Smith's demonstration, the mediator of the fast EPSP is

(A) Dopamine

(B) Neuropeptide Y

(C) Serotonin

(D) Angiotensin

(E) Acetylcholine

2. In Professor Smith's demonstration, the slow EPSP and slow IPSP can both be blocked by prior administration of

(A) Prazosin

(B) Sumatriptan

(C) Atropine

(D) Losartan

(E) Chlorpromazine

3. In Professor Smith's demonstration, the receptor most likely mediating the slow EPSP is

(A) Nicotinic cholinergic

(B) Muscarinic cholinergic

(C) a-Adrenergic

(D) P2X Purinergic

(E) (3-Adrenergic

4. A patient you are treating in the hospital has a hypertensive emergency, with blood pressure of 210/140 mm Hg. Of the following drugs, which would be most effective intravenously?

(A) Hydralazine

(B) Hydrochlorothiazide

(C) Trimethaphan (d) Methyldopa (E) Spironolactone

5. Ganglionic blocking agents are rarely used because of the numerous side effects they may produce. One such side effect is

(A) Increased stimulation of the genital tract

(B) Urinary hesitation or urgency

(C) Vasoconstriction

(D) Increased cardiac output

(E) Mydriasis

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