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I'm interested in the operation of various drugs as they related to the adrenergic response. I have no education in bio-chemistry past the high school level, but I like to understand the workings of drugs that I have been prescribed, and their overall effect on my body.
I was diagnosed with adult ADD a few years ago, and was prescribed Methylphenidate. Amongst the many affects of this drug, one of the strangest was that it completely cleared my nose if I had a cold. I discovered that because adrenaline causes the contraction of peripheral blood vessels, nasal blood vessels are strongly affected by sympathomimetic drugs. The amine that I've seen most commonly used for this effect is Pseudoephedrine.
The big question for me is about the source of the adrenergic reaction; is it because of a direct effect by the drug on the cellular tissues of the blood vessels, or by the operation of the drug on the adrenal glands. Is the drug mimicking the effects of adrenaline, or is it causing the release of adrenaline?
- Any adrenergic agonist affects the body by binding to adrenergic receptors on the post-neuroeffector junction, causing the target organ to which the junction is connected to act as if it had been stimulated by epinephrine, norepinephrine, or dopamine. Exactly what effect this has depends on how specifically the agonist binds with certain types of adrenergic receptors. The drug you refer to, methylphenidate, is a sympathomimetic, which means that it mimics the effects of the adrenergic hormones norepinephrine and epinephrine. Aramis1250 (talk) 14:51, 26 October 2008 (UTC)
Pseudoephedrine has been replaced in various cold preparations by Phenylephrine, which is described as an alpha adrenergic agonist. It is included in these preparations as a nasal decongestant. As the preparations are taken orally, and therefore distributed throughout the body, I imagine that Phenylephrine could activate the release of adrenaline from the adrenal glands. However, Phenylephrine is also used by optometrists to bring about another adrenergic effect - pupil dilation. In this role it is applied topically, so I assume it directly agonizes the adrenoceptors in the muscles of the iris.
Pseudoephedrine is also effective when used in nasal sprays, as is levo meth amphetamine when used as a broncho dilater in Vicks Inhalers. I assume that these two amines also have direct affect on the tissues without stimulating the adrenal glands. My questions are:
- Does this infer that Methylphenidate also binds directly to adrenoceptors?
- The Mehylphenidate page in Wikipedia indicates that Methylphenidate ingestion results in high serum levels of cortico-steroids. Does this mean that the drug works both directly as an adrenergic agonist and indirectly through its action on the adrenal glands?
- What is the method by which the nasal blood vessels contract? Is it through local action on neurons or by the binding of the drug with adrenoceptors on the surface on non-nuronal cells?
- If Methylphenidate and Meth Amphetamine work by blocking the reuptake of noradrenaline then why is this affect not mentioned when their mode of action on the CNS is discussed? Reports of CNS action focus on Dopamine active transport blockade.
- Has research to date really revealed much about all this stuff? When researching prescription drugs online the typical description of the drug's operation is "the method of action of this drug is not fully understood, but probably involves...". Drug descriptions in Wikipedia tend to be considerably more dogmatic, which makes me suspicious.
I'm sure I've said enough to reveal myself as a sincerely igonorant participant in this discussion. Please forgive my naivety!