Receptor Site Sensitivity describes the affinity and responsiveness of cellular receptors to their specific circulating ligands, such as hormones or neurotransmitters, quantified by the concentration required to elicit a measurable biological response (EC50). In endocrinology, alterations in sensitivity, either up-regulation or down-regulation, dictate the overall effectiveness of hormone signaling pathways within target tissues. This concept is central to understanding conditions like insulin resistance.
Origin
This terminology arises from pharmacology and receptor theory, combining “Receptor Site,” the specific molecular binding location, with “Sensitivity,” which measures the biological impact of that binding event. It quantifies the efficiency of signal transduction initiated by hormone-receptor interaction.
Mechanism
Sensitivity is modulated by factors affecting receptor number, conformation, and the efficiency of downstream intracellular signaling molecules. For example, chronic high levels of a ligand can lead to receptor internalization and degradation, effectively decreasing sensitivity, a process known as down-regulation. Prolonged absence of a ligand can increase the number of available receptors, enhancing sensitivity. This dynamic equilibrium fine-tunes the tissue’s response to fluctuating systemic hormone concentrations.
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