Oral receptors

Nonspecific immunosuppressive therapy in an adult patient is usually through cyclosporin (35), started intravenously at the time of transplantation, and given orally once feeding is tolerated. Typically, methylprednisone is started also at the time of transplantation, then reduced to a maintenance dose. A athioprine (31) may also be used in conjunction with the prednisone to achieve adequate immunosuppression. Whereas the objective of immunosuppression is to protect the transplant, general or excessive immunosuppression may lead to undesirable compHcations, eg, opportunistic infections and potential malignancies. These adverse effects could be avoided if selective immunosuppression could be achieved. Suspected rejection episodes are treated with intravenous corticosteroids. Steroid-resistant rejection may be treated with monoclonal antibodies (78,79) such as Muromonab-CD3, specific for the T3-receptor on human T-ceUs. Alternatively, antithymocyte globulin (ATG) may be used against both B- and T-ceUs. 

DuP 753 is an orally active AT receptor antagonist and as of this writing is in clinical trials as an antihypertensive (see Cardiovascularagents). AT-11 antagonists affect the brain RAS system to enhance ACh release offering the possibiUty that these agents may function as cognition enhancers. 

Ro 46-2005 (140) and SB 209670 (141) are the first synthetic orally active endothelin receptor antagonists. The ET receptor is a third ET receptor. 

Ephedrine, which is not a catecholamine, has weak oral activity as a bronchodilator and although it has some direct action at adrenergic receptors, its predominant mode of action is by displacing norepinephrine from storage vesicules. 2"Agonists which are in use or are under investigation are the result of quests for improved selectivity, retention of potency, oral activity, and longer duration of action. 

Because of the widespread nature of adrenoceptors, nonselective P-agonists can produce many undesirable side effects. Therefore, before adrenergic agonists could become widely used in the treatment of asthma, some selectivity in action was needed. Whereas epinephrine and ephedrine have significant agonist activity at both a and P adrenoceptors, isoproterenol is a selective agonist at the P receptor (39). However, isoproterenol does not distinguish between the P and receptors and it is not active orally. 

The hydantoin moiety has been utilized as a biostere for the peptide linkage, transforming a peptide lead into an orally available drug candidate. Therefore, an Arg-Gly-Asp-Ser tetrapeptide (18) lead structure was modified to a non-peptide RGD mimetic as an orally active fibrinogen receptor antagonist 19. ° ... 

Fenoldopam (76) is an antihypertensive renal vasodilator apparently operating through the dopamine system. It is conceptually similar to trepipam. Fenoldopam is superior to dopamine itself because of its oral activity and selectivity for dopamine D-1 receptors (D-2 receptors are as.sociated with emesis). It is synthesized by reduction of 3,4-dimethoxyphenylacetonitrile (70) to dimethoxyphenethylamine (71). Attack of diis last on 4-methoxystyrene oxide (72) leads to the product of attack on the epoxide on the less hindered side (73). Ring closure with strong acid leads to substituted benzazepine 74. O-Dealkylation is accomplished with boron tribromide and the catechol moiety is oxidized to the ortho-quinone 75. Treatment with 9NHC1 results in conjugate (1,6) chloride addition and the formation of fenoldopam (76) [20,21]. 

Intravenous and Oral Platelet Ub/fi3 Receptor Antagonists Potential Clinical Utilities... 

Also, the outcome covers a large spectrum. Autoantibodies can specifically block an important protein (such as the gastric intrinsic factor required for the uptake of orally taken vitamin B12), or the receptor for —> acetylcholine (as in myasthenia gravis), but also can... 

Metabolic Syndrome Insulin Receptor Glucose Transporters ATP-dependent K+ Channel Oral Antidiabetic Drugs... 

Inhibition of V2 vasopressin receptors causes an increase in urine volume primarily by reducing the re-absoiption of water along the collecting duct, an aquaretic effect that is fundamentally different from the natriuretic actions discussed so far. Nevertheless, some of the conditions calling for the use of natriuretic intervention are identical to those in which the administration of a new class of orally active nonpeptide V2 antagonists may be useful (tolvaptan, lixivaptan, and others). 

Several steroidal and non-steroidal glucocorticoid receptor selective dissociated agonists are in development by many pharmaceutical companies and some are now in clinical development. This suggests that the development of dissociated glucocorticoids with a greater margin of safety is possible and may even lead to the development of oral compounds that do not have significant adverse effects. 

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