Dopamine Agonists Both Stimulate And Inhibit Prolactin Release

PakPik

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Is this study relevant? This would imply dopamin agonists at sufficiently low doses may be giving a particular person an undesired effect, i.e, higher prolactin? Also, It would be interesting to know the concentration of bromocriptine in cacao (it is suggested it contains bromocriptine here, but not sure Cacao extends lifespan and keeps dopamine high | Ray Peat Forum).

Dopamine agonists both stimulate and inhibit prolactin release in GH4ZR7 cells

"Prolactin secretion from the anterior pituitary gland is regulated by multiple factors including prolactin-release inhibiting factors (PIFs) and prolactin releasing factors. PIFs, however, usually dominate to exert a tonic inhibition in the biological system, and the physiological PIF is believed to be dopamine. However, there is accumulating evidence that dopamine can not only inhibit but also stimulate prolactin release. Many investigators believe that this is achieved by activating inhibitory and stimulatory subtypes of dopamine receptors. "
"Although DA is established as the PIF, there is substantial evidence showing that DA, at much lower concentrations than those required for inhibition of prolactin secretion, stimulates prolactin release both in vitro (13–20) and in vivo (21). "
"...The significance of our study is not the different potencies of DA agonists but the demonstration that one subtype of D2 receptors can both stimulate and inhibit prolactin release depending on the concentrations of agonists."
"It is interesting to point out that the three dopamine D2 receptor agonists seem to have very different potencies regarding their stimulatory actions in GH4ZR7 cells. Dopamine, pomorphine and bromocriptine produced their peak stimulatory effects at 10^-8, 10^-10 and 10^-6 mol/l respectively. Regarding the inhibitory actions of the three DA agonists, on the other hand, our laboratory previously demonstrated that bromocriptine inhibited prolactin synthesis and release more potently than DA in primary cultured rat pituitary cells (36, 37), and Denef et al. (14) demonstrated earlier that apomorphine is more potent than DA in suppressing prolactin release in primary rat pituitary cultures. However, in this study we observed that their peak inhibitory actions were at similar concentrations, between 10^-4 and 10^-3 mol/l."
...
"Finally, the chemical nature of the physiological PRF is not yet established; several biologically active chemicals are considered to be PRFs (40). DA is the major PIF, but it may also play a role as a PRF since low concentrations of DA stimulate prolactin release."


Dopamine agonists both stimulate and inhibit prolactin release in GH4ZR7 cells
 
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nullredvector

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This would make sense in my experience as l-dopa gives me high prolactin symptoms. Same with tyrosine and even bromo maybe. Chocolate though seems to be very anti prolactin.
 

PakPik

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This would make sense in my experience as l-dopa gives me high prolactin symptoms. Same with tyrosine and even bromo maybe. Chocolate though seems to be very anti prolactin.
Wow, interesting. I appreciate your input.
 

GAF

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Ldopa/DA makes one sleepy quickly if taken before bed - prolactin release? But, libido up by the next morning - prolactin suppression?
 

haidut

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Maybe @haidut can help us out

These concentrations reported are very low. Picomolar concentrations of bromocriptine would be achieved by taking around 1/200 of a 2.5mg tablet. I am not sure if this is even high enough dose to be considered clinically relevant. At very low concentrations, the effects of many substances are unpredictable and hard to replicate. In physiological doses, all of these substances do inhibit prolactin. I guess the only analogy I can offer is very low dose progesterone being able to raise estrogen through conversion into the relevant pathways. But nobody would label progesterone estrogenic and in physiological doses it is the main endogenous estrogen antagonist in the body - both as estrogen "receptor" antagonist and aromatase inhibitor.
 

nullredvector

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Oh wow that's awesome, I didn't know that about low concentrations, it makes sense in my experience.

What kind of dose are we talking is physiological with progesterone/which would increase estrogen?

However I have tried really large doses of L-dopa any grams) and had it completely shutdown my libido.
 

haidut

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Oh wow that's awesome, I didn't know that about low concentrations, it makes sense in my experience.

What kind of dose are we talking is physiological with progesterone/which would increase estrogen?

However I have tried really large doses of L-dopa any grams) and had it completely shutdown my libido.

Physiological doses of progesterone (20mg - 30mg daily) have been shown to inhibit estrogen signalling and synthesis. Sub-physiological concentrations on the order of maybe 1mg and below can in theory raise estrogen by converting downstream. I am not aware of any direct studies that have used such low doses though.
 
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