Cardiac and endocrine medication review

Correct answer: B. Competitive inhibition of β1 receptors

• A. Increased nitric oxide release describes nitrates such as nitroglycerin, used for angina rather than routine hypertension, and hydralazine.
• B. CORRECT. Metoprolol is a CARDIOSELECTIVE beta-blocker. It competitively antagonises β1 receptors, which are concentrated in the heart and in the juxtaglomerular apparatus. The result is reduced heart rate and contractility, so cardiac output falls, and reduced renin release, so the renin-angiotensin-aldosterone system is dampened. Both lower blood pressure.
• C. β2 receptors sit in bronchial and vascular smooth muscle. BLOCKING them causes bronchoconstriction — which is precisely why non-selective agents such as propranolol are avoided in asthma, and why cardioselective metoprolol is preferred.
• D. Calcium channel blockade describes amlodipine, nifedipine, diltiazem and verapamil. The dihydropyridines are the ones associated with gingival enlargement.

Note: Dental relevance: with NON-selective beta-blockers, epinephrine can produce unopposed α stimulation with a hypertensive surge and reflex bradycardia. Limit the vasoconstrictor dose and aspirate carefully. NSAIDs also blunt the antihypertensive effect of beta-blockers over time.

Correct answer: C. Thyroid follicular cells

• A. Parafollicular or C cells produce CALCITONIN, which lowers serum calcium by inhibiting osteoclastic resorption. They are also the cell of origin of medullary thyroid carcinoma.
• B. Parietal cells of the renal glomerulus line Bowman's capsule and have no endocrine secretory role. Gastric parietal cells secrete hydrochloric acid and intrinsic factor.
• C. CORRECT. Levothyroxine is synthetic T4. THYROID FOLLICULAR CELLS synthesise thyroglobulin, iodinate it, and release T4 and T3 into the circulation. T4 is the main secretory product and is converted peripherally to the more active T3. Follicular cells are also the cells that concentrate iodide, which is the basis of radioiodine therapy and imaging.
• D. Chief cells occur in two places, neither of which is the thyroid: gastric chief cells secrete pepsinogen, and PARATHYROID chief cells secrete parathyroid hormone — the direct antagonist of calcitonin.

Note: Untreated or under-treated hypothyroidism matters dentally: these patients are sensitive to CNS depressants, so sedatives and opioids should be dosed cautiously, and severe untreated disease carries a risk of myxoedema coma under stress.