Mucosa, mimics

The identification and characterization of cell culture systems (e.g., Caco-2-cells) that mimic in vivo biological barriers (e.g., intestinal mucosa) have afforded pharmaceutical scientists the opportunity to rapidly and efficiently assess the permeability of drugs through these barriers in vitro. The results generated from these types of in vitro studies are generally expressed as effective permeability coefficients (Pe). If Pe is properly corrected to account for the barrier effects of the filter (PF) and the aqueous boundary layer (PAbl) as previously described in Section II.C, the results provide the permeability coefficient for the cell monolayer... 

Sympathomimetics mimic the action of noradrenaline (norepinephrine), the principal neurotransmitter between the nerve endings of the sympathetic nervous system and the adrenergic receptors of the innervated tissues. They stimulate both alpha-adrenoceptors, causing constriction of smooth muscle and blood vessels, and beta-adrenoceptors, producing bronchodilatation. They are therefore useful in coughs where the tissues of the upper respiratory tract are congested, as they shrink swollen mucosa and open up the airways. 

True absorption, as the element fraction that is taken up by the intestinal mucosa and released into circulation, cannot be assessed by fecal balance techniques using a single oral isotopic label only. A second label needs to be administered intravenously to determine the fraction of absorbed element that re-enters the intestine by secretory pathways. Intravenous isotopic labels in metabolic studies are usually intended to mimic freshly absorbed element from the diet. This entails that labels must be injected slowly over several minutes about 1 h after test meal administration or, ideally, as an infusion over 20-30 min in physiological saline. 

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