Effects of antidepressants on receptor-activated and Ca2+-activated contractions of rabbit isolated aorta

Direct and indirect effects of psychopharmacological treatment on the cardiovascular system

Background Severe mental disorders, i.e. psychotic disorders, unipolar and bipolar disorders are associated with increased morbidity and mortality from cardiovascular and metabolic disorders. The underlying cause of this association is complex and comprises disorder specific alterations such as dysfunctions of immunological and hormonal systems, body-composition changes and health associated behaviors (smoking, sedentary lifestyle, alcohol intake and treatment compliance). Furthermore, some psychopharmacological drugs may exert unwanted side effects that impact the cardiovascular system. Methods This paper reviews studies concerning commonly used antidepressant and antipsychotics drugs with a particular focus on direct and indirect cardiovascular side effects. Results Newer antidepressant drugs have a favorable cardiovascular safety profile compared to tricyclic antidepressants. However, QTc prolongation, increased blood pressure and potentially higher risks of bleeding have been observed in some newer antidepressants. Some second generation (atypical) antipsychotics have raised concern because of indirect cardiovascular, metabolic side effects such as weight gain and disturbances in lipid and glucose metabolism. Conclusions Psychiatrists need to be aware of potential direct and indirect cardiovascular side effects and to include them in the risk/benefit assessment when choosing a specific individualized treatment.

Effects of amitriptyline, a tricyclic antidepressant, on smooth muscle reactivity in isolated rat trachea

PURPOSE

This study was designed to investigate the action of amitriptyline, a tricyclic antidepressant, on airway smooth muscle reactivity and its underlying mechanisms.

METHODS

In isolated rat trachea, isometric force was recorded to examine the effects of amitriptyline on the contractile response to acetylcholine (ACh), electrical field stimulation (EFS), calyculin A (a myosin light chain phosphatase inhibitor), and sphingosylphosphorylcholine (SPC; a Rhokinase activator). In addition, inositol monophosphate (IP1) accumulation was measured to examine its effects on inositol 1, 4, 5-trisphosphate (IP(3)) production during stimulation with ACh.

RESULTS

Amitriptyline inhibited the contractile responses to ACh, EFS, calyculin A, and SPC, with the concentrations of amitriptyline (mean +/- SD) required to exert 50% inhibition (IC(50)) being 4.3 +/- 1.3 microM, 3.2 +/- 1.6 microM, 256.4 +/- 106.4 microM, and 98.2 +/- 21.8 microM, respectively. In addition, amitriptyline (10 microM) eliminated the ACh (10 microM)-induced IP(1) accumulation.

CONCLUSION

The results suggest that amitriptyline does not influence tracheal smooth muscle reactivity at clinical concentrations (<1 microM), but attenuates the reactivity at supraclinical concentrations (> or =1 microM). The attenuated response to ACh brought about by amitriptyline is presumably due, at least in part, to the inhibition of phosphatidylinositol (PI) metabolism. The ability of amitriptyline to inhibit the calyculin Ainduced contraction suggests that amitriptyline also inhibits the Ca(2+)-calmodulin-myosin light chain pathway independently of the inhibition of PI metabolism. Finally, the difference between the IC(50) values for SPC-induced contraction and those for calyculin A-induced contraction suggests that amitriptyline may also inhibit the Rho-kinase pathway.

Serotonin reuptake inhibitor fluoxetine decreases arteriolar myogenic tone by reducing smooth muscle [Ca2+]i

Previous studies showed that the serotonin reuptake inhibitor (SSRI) antidepressant fluoxetine (Prozac) dilates skeletal muscle and cerebral arterioles independent of the endothelium. We hypothesized that fluoxetine affects the contractile activity of arteriolar smooth muscle by interfering with Ca2+ signaling pathways. The effects of fluoxetine on pressure-induced tone of isolated rat skeletal muscle arterioles (approximately 110 microm) were investigated by videomicroscopy. Changes in smooth muscle [Ca2+]i were measured simultaneously by the fura-2 ratiometric method. Elevation of intraluminal pressure (from 20 to 120 mm Hg) increased (by approximately 20%) the smooth muscle calcium fluorescence ratio (R(Ca)) and resulted in a significant myogenic constriction (approximately 40%). Fluoxetine and nifedipine significantly decreased R(Ca) (by approximately 30%) and abolished pressure-induced arteriolar tone (EC50, 3.1 x 10(-6) and 6.0 x 10(-9) M, respectively). Constrictions to the L-type Ca2+ channel opener Bay K 8644 also were inhibited and abolished by increasing doses of fluoxetine (3 x 10(-6) and 10(-5) M, respectively). In the presence of 10(-5) M fluoxetine, a concentration that elicited submaximal (approximately 80%) dilation, elevation of extracellular Ca2+ concentration (from 2.5 to 15 mM) normalized R(Ca) and restored arteriolar myogenic tone. Thus, fluoxetine reduces [Ca2+]i and tone of arteriolar smooth muscle, likely by interfering with Ca2+ entry. We speculate that the "calcium antagonist" effect of fluoxetine may be an additional element in the therapeutic actions of this drug.

Fluoxetine dilates isolated small cerebral arteries of rats and attenuates constrictions to serotonin, norepinephrine, and a voltage-dependent Ca(2+) channel opener

BACKGROUND AND PURPOSE

Recent clinical observations question that the antidepressant effect of fluoxetine (Prozac) can be explained solely with serotonin reuptake inhibition in the central nervous system. We hypothesized that fluoxetine affects the tone of vessels and thereby modulates cerebral blood flow.

METHODS

A small branch of rat anterior cerebral artery (195+/-15 microm in diameter at 80 mm Hg perfusion pressure) was isolated, cannulated, and pressurized (at 80 mm Hg), and changes in diameter were measured by videomicroscopy.

RESULTS

Fluoxetine dilated small cerebral arteries with an EC(50) of 7.7+/-1.0x10(-6) mol/L, a response that was not affected by removal of the endothelium or application of 4-aminopyridine (an inhibitor of aminopyridine-sensitive K(+) channels), glibenclamide (an inhibitor of ATP-sensitive K(+) channels), or tetraethylammonium (a nonspecific inhibitor of K(+) channels). The presence of fluoxetine (10(-6) to 3x10(-5) mol/L) significantly attenuated constrictions to serotonin (10(-9) to 10(-5) mol/L) and norepinephrine (10(-9) to 10(-5) mol/L). Increasing concentrations of Bay K 8644 (a voltage-dependent Ca(2+) channel opener, 10(-10) to 10(-6) mol/L) elicited constrictions, which were markedly reduced by 2x10(-6) and 10(-5) mol/L fluoxetine, whereas 3x10(-5) mol/L fluoxetine practically abolished the responses.

CONCLUSIONS

Fluoxetine elicits substantial dilation of isolated small cerebral arteries, a response that is not mediated by endothelium-derived dilator factors or activation of K(+) channels. The finding that fluoxetine inhibits constrictor responses to Ca(2+) channel opener, as well as serotonin and norepinephrine, suggests that fluoxetine interferes with the Ca(2+) signaling mechanisms in the vascular smooth muscle. We speculate that fluoxetine increases cerebral blood flow in vivo, which contributes to its previously described beneficial actions in the treatment of mental disorders.