reseptornivå

Reseptornivå refers to the density and functional availability of receptors on the surface of cells or within intracellular compartments. It determines how strongly a cell responds to a given ligand, such as a hormone, neurotransmitter, or drug. Higher receptor levels can increase sensitivity and maximal response, while lower levels can reduce both.

Receptornivå is dynamic. Cells regulate receptor numbers through synthesis and degradation, trafficking to and from the cell membrane, and post-translational modification. Chronic exposure to agonists often leads to downregulation or desensitization, reducing response over time; chronic exposure to antagonists can cause upregulation, increasing sensitivity. These processes contribute to tolerance, dependence, and withdrawal phenomena. The concept of receptor reserve or spare receptors explains why maximal effect may be achieved without full receptor occupancy.

Measurement and clinical relevance: Receptornivå can be estimated by binding assays, imaging, or measuring receptor protein or mRNA levels, but functional response may not directly reflect receptor number due to downstream signaling. Clinically, variations in receptor levels help explain differences in drug efficacy and side effects among individuals and tissues, and underpin strategies in dose optimization and drug development. Subtypes and tissue distribution add complexity, as different tissues may exhibit distinct receptor densities and regulatory mechanisms.

Examples illustrate the concept: in many tissues, beta-adrenergic receptors may downregulate with prolonged agonist exposure; opioid receptors can show tolerance via receptor desensitization; receptor upregulation can occur in response to antagonist therapy. Understanding reseptornivå is fundamental to pharmacodynamics and receptor pharmacology.