Activation of these receptors causes adenylyl cyclase to convert ATP to cAMP, beginning the signalling cascade that ends with the inhibition of myosin phosphorylation and lowering the intracellular concentration of calcium ions (myosin phosphorylation and calcium ions are necessary for muscle contractions). The increase in cAMP also inhibits inflammatory cells in the airway, such as basophils, eosinophils, and most especially mast cells, from releasing inflammatory mediators and cytokines. Salbutamol and other β2 receptor agonists also increase the conductance of channels sensitive to calcium and potassium ions, leading to hyperpolarization and relaxation of bronchial smooth muscles.Salbutamol is either filtered out by the kidneys directly or is first metabolized into the 4′-O-sulfate, which is excreted in the urine. Chemistry
Salbutamol is sold as a racemic mixture. The (R)-(−)-enantiomer (CIP nomenclature) is shown in the image at right (top), and is responsible for the pharmacologic activity; the (S)-(+)-enantiomer (bottom) blocks metabolic pathways associated with elimination of itself and of the pharmacologically active enantiomer (R). The slower metabolism of the (S)-(+)-enantiomer also causes it to accumulate in the lungs, which can cause airway hyperreactivity and inflammation. Potential formulation of the R form as an enantiopure drug is complicated by the fact that the stereochemistry is not stable, but rather the compound undergoes racemization within a few days to weeks, depending on pH.
Fat is then gradually lost in is the limbs and trunk. Fat may accumulate around the face and between the shoulder blades. Insulin resistance is common. Other conditions associated with this condition include acanthosis nigricans, fatty liver, hypertriglyceridemia and polycystic ovary syndrome in women. There is an increased risk of coronary heart disease. Cardiomyopathy and muscular dystrophy may occur rarely. Xanthoma and nail changes may occur. Type 3 is due to mutations in the PPARG gene. It is rare with approximately 30 cases reported to date. It is similar to type 2 but tends to be milder. Type 4 is due to mutations in the PLIN1 gene. It is rare with only a small number of cases reported. Fat loss tends to affect the lower limbs and buttocks. Insulin resistance and hypertriglyceridemia occur. Calf muscular hypertrophy may occur. Type 5 is due to mutations in the AKT2 gene. It has been reported in four patients all members of the same family. Fat loss affects the upper and lower limbs. The patients also had hypertension, insulin resistance and hypertriglyceridemia. Type 6 due to mutations in the  CIDEC gene. It is inherited in an autosomal recessive fashion and has been reported in only one patient to date. Features included  fat loss, severe insulin resistance, fatty liver, acanthosis nigricans and diabetes. Another gene that has been associated with this condition is AGPAT2. Diagnosis
Treatment
Prevalence
This not known with certainty but is estimated to be about one per million. It appears to be more common in females than males.