The in vitro action of polyamines on rat basilar and femoral artery contractile activity

Effects of Polyamines on Human Umbilical Artery Tone In Vitro

OBJECTIVE

Polyamines act as endogenous modulators of cell function and excitability. There are no data in relation to their effects on the human fetoplacental circulation. The aim of this study was to investigate the effects of the polyamines, spermine, and spermidine on human umbilical artery resistance in vitro.

METHODS

Isometric tension recordings were performed under physiologic conditions on human umbilical arterial rings (n = 12). The in vitro effects of spermine and spermidine (at concentrations ranging between 10(-9) M to 10(-3) M) were measured, and compared with those measured in vehicle control experiments. The maximal inhibition (MMI) at the highest concentration and the pD2 (-log EC50) values for each compound were calculated and compared.

RESULTS

Spermine and spermidine exerted a potent relaxant effect on human umbilical arterial tone in comparison to vehicle control experiments. The MMI +/- SEM for spermine was 18.41 +/- 1.437% (n = 6; P <.001) and for spermidine was 38.31 +/- 3.572% (n = 6; P <.001). There was no difference observed between the pD2 +/- SEM values for spermine (5.78 +/- 1.54; n = 6) and spermidine (6.27 +/-0.85; n = 6) (P = .517).

CONCLUSION

The polyamines spermine and spermidine exert a potent relaxant effect on human umbilical artery tone suggestive of an endogenous role for these compounds in vasomotor regulation of the fetoplacental circulation.

Spermine-induced negative inotropic effect in isolated rat heart, is mediated through the release of ATP

Putrescine, spermidine and spermine are natural compounds found in up to millimolar concentrations in eukaryotic and prokaryotic cells. At physiologic pH, the polyamines are protonated (+2, +3 and +4 charges), their polycationic properties lead to the assumption that they could affect physiological systems by binding to anionic sites of the cellular membrane and/or by modulating ion channels. At the cardiovascular level, their effects are not completely understood. However, these compounds may be able to exert the induction of synthesis and release of cellular mediators. In an attempt to explore this possibility, we used the isolated and perfused rat heart, Langendorff, model in order to evaluate the inotropic effects of these polyamines, putrescine, spermidine and spermine. Dose-response curves (0.1-0.6 mM) for putrescine, spermidine and spermine were constructed; with the finding that spermine had the largest negative effect. The obtained effects were not blocked by nitric oxide synthesis inhibitors (L-NAME), H(1) and H(2) receptor antagonists (Brompheniramine and Cimetidine) or by Glibenclamide, an antagonist of ATP-sensitive K(+) channels. We found that spermine-induced and increased ATP concentration in cardiac effluents. Reactive Blue, a P(2y) purinoreceptor antagonist and Aminophylline, an unspecific adenosine receptor antagonist, blocked the spermine-induced effects. These results showed that ATP, at least in part, is responsible of the spermine cardiovascular effects. Adenosine was shown to also play an important role on those effects.

A mechanism of vasodilatory action of polyamines and acetylpolyamines: possible involvement of their Ca2+ antagonistic properties

Polyamines, a class of low-molecular weight organic polycations, have been shown to produce relaxing effects in vascular smooth muscles, although the mechanism has not been carefully examined. In this study, the mechanism of vascular action of polyamines and their metabolites, acetylpolyamines, was pharmacologically examined in the rabbit isolated thoracic aorta focusing on an endothelium-dependent component of vasodilatation and Ca2+ influx through plasma membrane channels. Both polyamines and acetylpolyamines (except N1-acetylputrescine, which produced no response or very slight contraction) caused concentration-dependent relaxation in preconstricted aortic rings containing an intact endothelium. Aortic rings denuded of endothelium were also responsive to both polyamines and acetylpolyamines. Inhibitors of nitric oxide (reduced haemoglobin and Nomega-nitro-L-arginine methyl ester), vasodilator prostaglandins (indomethacin) and guanylyl cyclase (methylene blue) did not affect the relaxation induced by both polyamines and acetylpolyamines in either endothelium-intact or -denuded aortic rings. Both polyamines and acetylpolyamines inhibited the concentration-dependent contraction for phenylephrine and K+. The Ca2+ agonist Bay K 8644 induced concentration-dependent contraction in segments of rabbit aorta partially depolarized with 15 mM KCl, and both polyamines and acetylpolyamines relaxed the Bay K 8644-induced contraction in a concentration-dependent manner. Interestingly, both polyamines and acetylpolyamines also decreased contractions evoked by the Ca2+ ionophore A23187. The concentration-response curve to exogenous Ca2+ in K+-depolarization medium (K+ = 120 mM) was shifted to the right by both polyamines and acetylpolyamines. The response elicited by Ca2+ was increased by Bay K 8644 (10(-6) M), and this potentiation was also inhibited by both polyamines and acetylpolyamines. The results indicate that both polyamines and acetylpolyamines can induce vasorelaxation of rabbit thoracic aorta by an endothelium-independent mechanism in-vitro and relax vascular smooth muscle by acting at the plasma membrane level, decreasing the influx of Ca2+. Therefore, polyamines and acetylpolyamines may have Ca2+ antagonistic properties which may, in part, be involved in the mechanism of rabbit aortic vascular smooth muscle relaxation.