receptor up-regulation

Receptor up-regulation is the cell turning up its sensitivity by building more receptors. If a cell is being under-stimulated — for instance because a drug is constantly blocking the signal — it compensates by putting extra receptors on its surface, the way someone straining to hear turns up the volume. The cell tries to restore its normal level of signalling.

This adaptive change classically follows prolonged exposure to an antagonist or a sustained lack of the natural agonist. Over days to weeks the cell increases receptor production, so it now carries more receptors than before. The system has effectively recalibrated itself toward the chronic condition.

Up-regulation matters most when the drug is suddenly stopped. With many extra receptors waiting and the blockade lifted, the system can over-respond, producing rebound or withdrawal effects. This is why long-term beta-blockers should be tapered rather than stopped abruptly: the up-regulated receptors, suddenly exposed to the body's own adrenaline, can cause rebound tachycardia, hypertension or angina.