Permeability response of cerebral and cutaneous blood vessels to vasoactive agents

Overview

Physiological barriers are semi-permeable cellular structures restricting drug diffusion into intracellular compartments and tissues. There are six types of physiological barriers: blood endothelial, cell membrane, blood-brain, blood-cerebrospinal fluid (CSF), blood-placenta, and blood-testis barriers.
The blood endothelial barrier is the most porous of these. It allows all small ionized, un-ionized, and lipophilic molecules to pass through the endothelial lining into the interstitial space...

Capillaries, a crucial constituent of the circulatory system, are diminutive vessels with a diameter between 5–10 micrometers, accommodating perfusion to the tissues through the phenomenon known as microcirculation. Through their permeable walls, consisting of an endothelial layer ensconced by a basement membrane and sporadically dispersed smooth muscle fibers, the exchange of substances between the blood and the interstitial fluid becomes plausible. Variance in wall composition exists, with...

Autoregulation mechanisms are characterized by their inherent capacity for self-regulation without necessitating specific nervous stimulation or endocrine control. These mechanisms facilitate the adjustment of blood flow and, therefore, perfusion specific to each tissue region. This self-regulation encompasses chemical signals and myogenic controls.
Chemical Signaling in Autoregulation
Chemical signaling operates at the precapillary sphincter level, inciting either contraction or relaxation.

Drug distribution in the body is intricately regulated by various physiological barriers that control the passage of substances. These include the capillary endothelial barrier, the blood-brain, blood-cerebrospinal fluid, blood-placental, and blood-testis barriers.
The capillary endothelial barrier allows only smaller molecules below 600 Da (Daltons) to pass through. It also restricts drugs like heparin that are bound to blood components, limiting their movement within the bloodstream.
The...

Drug distribution within the body is a complex process influenced by several factors, including perfusion rate, the rate at which the bloodstream transports drugs to tissue. This limitation becomes particularly significant when dealing with highly lipophilic drugs. In such cases, the rate at which the drug can move across membranes is crucial, and if the membrane is highly permeable to the drug, distribution becomes rate-limited by perfusion.
Perfusion rate-limited distribution relies on the...