Medicine

Reverse triiodothyronine (reverse T3, or rT3) is a molecule which is an isomer of triiodothyronine (T3). It is derived from thyroxine (T4) through the use of deiodinase.rT3, unlike T3, does not stimulate thyroid hormone receptors. However, rT3 nonetheless binds to these receptors, thereby blocking the action of T3. Under stress conditions, the adrenal glands produce excess amounts of cortisol. Cortisol inhibits the conversion of T4 to T3, thus shunting T4 conversion from T3 towards rT3. Consequently, there is a widespread shutdown in T3 binding across the body. This condition is termed Reverse T3 Dominance. It results in reduced body temperature,

In pharmacology, the term mechanism of action (MOA) refers to the specific biochemical interaction through which a drug substance produces its pharmacological effect. A mechanism of action usually includes mention of the specific molecular targets to which the drug binds, such as an enzyme or receptor. For example, the mechanism of action of aspirin involved irreversible inhibition of the enzyme cyclooxygenase, which suppresses the production of prostaglandins and thromboxanes thereby reducing pain and inflammation.

The mechanism of action of progestin only contraceptives depends on the progestin activity and dose.[2] Intermediate dose progestin-only contraceptives, like Implanon (and the progestin-only pill Cerazette) allow some follicular development but inhibit ovulation in almost all cycles as the primary mechanism of action. Ovulation was not observed in studies of Implanon in the first two years of use and only rarely in the third year with no pregnancies. A secondary mechanism of action is the progestogenic increase in cervical mucus viscosity which inhibits sperm penetration.[3] Hormonal contraceptives also have effects on the endometrium that theoretically could affect implantation, however no

Macbecins mechanism of action is in part due to heat shock protein Hsp90 protein inhibition.[3]

Macbecins mechanism of action is in part due to heat shock protein Hsp90 protein inhibition.[3]

Proxymetacaine is believed to act as an antagonist on voltage-gated sodium channels to affect the permeability of neuronal membranes; how this inhibits pain sensations and the exact mechanism of action of proxymetacaine are, however, unknown.

Idraparinux selectively blocks coagulation factor Xa.[2] See Heparin: Mechanism of anticoagulant action for a comparison of the mechanism of heparin, low-molecular-weight heparins, fondaparinux and idraparinux.

Similar to Methylphenidate, the mechanism of action of Pemoline is to inhibit the reuptake of Dopamine and to increase the release of Dopamine and Norepinephrine in the central nervous system.

The mechanism of action of ergotamine is complex.[2] The molecule shares structural similarity with neurotransmitters such as serotonin, dopamine, and adrenaline and can thus bind to several receptors acting as an agonist. The anti-migraine effect is due to constriction of the intercranial extracerebral blood vessels through the 5-HT1B receptor, and by inhibiting trigeminal neurotransmission by 5-HT1D receptors. Ergotamine also has effects on the dopamine and noradrenaline receptors. It is its action on the D2 dopamine and 5-HT1A receptors that can cause some side effects. [3]

The T3 (and T4) bind to nuclear receptors, thyroid receptors. However, T3 (and T4) are not very lipophilic and as a result, are unable to pass through the phospholipid bilayers. They therefore have specific transport proteins on the cell membranes of the effector organs which allow the T3 and T4 to pass into the cells. The thyroid receptors bind to response elements in gene promoters and thus enabling them to activate or inhibit transcription. The sensitivity of a tissue to T3 is modulated through the thyroid receptors.

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