Lactose, a disaccharide molecule found in milk and dairy products, cannot be directly absorbed through the wall of the small intestine into the bloodstream, so, in the absence of lactase, passes intact into the colon. Bacteria in the colon can metabolise lactose, and the resulting fermentation produces copious amounts of gas (a mixture of hydrogen, carbon dioxide, and methane) that causes the various abdominal symptoms. The unabsorbed sugars and fermentation products also raise the osmotic pressure of the colon, causing an increased flow of water into the bowels (diarrhea).Lactose intolerance in infants (congenital lactase deficiency) is caused by mutations in the LCT gene. The LCT gene provides the instructions for making lactase. Mutations are believed to interfere with the function of lactase, causing affected infants to have a severely impaired ability to digest lactose in breast milk or formula. Lactose intolerance in adulthood is a result of gradually decreasing activity (expression) of the LCT gene after infancy, which occurs in most humans. The specific DNA sequence in the MCM6 gene helps control whether the LCT gene is turned on or off. At least several thousand years ago, some humans developed a mutation in the MCM6 gene that keeps the LCT gene turned on even after breast feeding is stopped. Populations that are lactose intolerant lack this mutation. The LCT and MCM6 genes are both located on the long arm (q) of chromosome 2 in region 21. The locus can be expressed as 2q21. The lactase deficiency also could be linked to certain heritages and varies widely.
At higher doses however, maprotiline increases serotonergic transmission and increases the level of serotonin available. Pharmacokinetics
After oral use absorption is good. It binds to plasma proteins 80–90%. Maximal plasma concentration is reached 6 hours after use. The mean time to peak is 12 hours. The terminal half-life of averages 51 hours. Chemistry
Maprotiline is a tetracyclic compound and is grouped with the TeCAs. Its chemical name is N-methyl-9,10-ethanoanthracen-9(10H)-propylamine. The drug has a dibenzobicyclo[2.2.2]octadiene (9,10-dihydro-9,10-ethanoanthracene) ring system; that is, a tricyclic anthracene ring system with an ethylene bridge across the central ring. This results in it having a unique three-dimensional central ring (a bicyclo[2.2.2]octane or 1,4-endoethylenecyclohexane ring) and being a tetracyclic rather than a tricyclic compound. However, it could also or alternatively be considered to be a tricyclic and hence a TCA. In addition to its heterocyclic ring system, maprotiline has an alkylamine side chain attached similarly to other TCAs (but notably unlike other TeCAs). In terms of the side chain, it is a secondary amine, and its chemical structure, aside from the ethylene link in the central ring, is similar to that of secondary amine TCAs like nortriptyline and protriptyline. In accordance, the pharmacology of maprotiline is very similar to that of secondary amine TCAs.Maprotiline is very similar in structure to the anxiolytic, sedative, and muscle relaxant drug benzoctamine (Tacitin). The only structural difference between the two compounds is in the length of their side chain. However, this modification results in considerable differences in their pharmacological and therapeutic effects.