nifedipine q.

[HiddenTruth]

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Ok, this may be a stupid q., but I am kinda' stumped on this.
FA says nifedipine's effects are similar to nitrates. First off, nitrates are primarily venoselective, while dihydropyridines are more selective on the arterial system. SO, wouldn't that mean that nifedipine actually contributes to an increase in PL (because of arteriodilation; VC of arterioles certainly decreases PL)? While, nitrates actually decrease PL because of venodilation? I thought nifedipine's primary mechanism in reducing BP was basically due to decreasing AL. But, then I think it can increase PL also.

 

[idq1i]

Nifedipine is somewhat more selective for vsm of arterioles, whereas nitrates act on veins. Therefore, nifedipine is much less likely to decrease LVEDP and LVEDV (preload) than the nitrates.

Also, remember that dihydropyridines also have some cardioselectivity

 

[HiddenTruth]

Nifedipine is somewhat more selective for vsm of arterioles, whereas nitrates act on veins. Therefore, nifedipine is much less likely to decrease LVEDP and LVEDV (preload) than the nitrates.

Also, remember that dihydropyridines also have some cardioselectivity

Thanks, but you basically reiterated what I said. My question was, whether there is an actual INCREASE in PL rather than "much less likely to decrease" or no change.

And, actually I don't think it's "somewhat"...I think it's venodialtion effects are nonsignificant--therefore it's primarily arterioselective.

 

[idq1i]

Thanks, but you basically reiterated what I said. My question was, whether there is an actual INCREASE in PL rather than "much less likely to decrease" or no change.

And, actually I don't think it's "somewhat"...I think it's venodialtion effects are nonsignificant--therefore it's primarily arterioselective.

1 - There is decrease in preload due to the fact that blood is pooling peripherally. One of the minor complaints that pts have with CCBs is ankle edema. I don't understand what you are trying to say

2 - Beta blockers (and verapamil) are the drugs that increase preload

3 - Venodilation does in fact occur, arteriolar > venular. I don't know about the significance

 

[Idiopathic]

Its similar, in that CCB's decrease both arterial and venous smooth muscle tone. You will understand this clinically when you see your first patient on Norvasc with LE edema from the diminished vascular tone. Since nitrates dilate arterial smooth muscle at higher dosages (primarily venous, I agree), you could certainly say that their MOA are similar.

 

[HiddenTruth]

ok thanks--sorry, I don't know what I was thinking...i read somewhere that it was super arterioselective--and therefore vasodilating them would actually increase PL....but nevermind--thanks for your help.

 

[Ramoray]

not that this is really part of the question but dihydros do not really decreased the preload much at all and it is their arteriol dilating that make them usefull as anti hypertensives and antianginals. Remember that dihyrdos arteriol dilation reflexes increases sympth tone, which constricts veins and blood return to heart and thus preload. That is why orthostatic BP is not decreased with CCB but it is with nitro. So anyway preload doesnt increase but it definetly doesnt sig. decrease due to the compensatory constriction of veins. Of course CCBs do partially dilate viens at higher doses so this cancels some of they symp. compensatory action but if you are goingjust preload, nitro decrease preload, and CCBs decrease afterload and doesnt really effect preload, that is what you should take away from the two IMO.

 

[HiddenTruth]

not that this is really part of the question but dihydros do not really decreased the preload much at all and it is their arteriol dilating that make them usefull as anti hypertensives and antianginals. Remember that dihyrdos arteriol dilation reflexes increases sympth tone, which constricts veins and blood return to heart and thus preload. That is why orthostatic BP is not decreased with CCB but it is with nitro. So anyway preload doesnt increase but it definetly doesnt sig. decrease due to the compensatory constriction of veins. Of course CCBs do partially dilate viens at higher doses so this cancels some of they symp. compensatory action but if you are goingjust preload, nitro decrease preload, and CCBs decrease afterload and doesnt really effect preload, that is what you should take away from the two IMO.

makes sense, thanks ram!