Differential blockade of alpha,beta-methylene-ATP, noradrenaline and electrically evoked contractions of the rat vas deferens

EFFECTS OF THE ANTIDEPRESSANT ST. JOHN′S WORT (HYPERICUM PERFORATUM) ON RAT AND HUMAN VAS DEFERENS CONTRACTILITY

PURPOSE

Since sexual dysfunction related to vas deferens smooth muscle contractility is a possible side effect of St. John's wort (SJW) (Hypericum perforatum) we evaluated the effect of this herbal antidepressant on rat and human vas deferens contractility.

MATERIALS AND METHODS

The effect of SJW was evaluated on contractions induced by electrical field stimulation or exogenous agonists (alpha,beta-methylene adenosine triphosphate and phenylephrine) in isolated rat and human vas deferens.

RESULTS

SJW (1 to 300 microM) decreased in a concentration dependent manner the amplitude of electrical field stimulation and agonist induced contractions with the same potency, suggesting direct inhibition of rat vas deferens smooth muscle. Of the chemical constituents of SJW tested hyperforin but not hypericin or the flavonoids quercitrin, rutin and kaempferol inhibited phenylephrine induced contractions. SJW and hyperforin also inhibited phenylephrine induced contractions in human vas deferens

CONCLUSIONS

The results of our study demonstrate that SJW directly inhibits rat and human vas deferens contractility. If confirmed in vivo, these results suggest that SJW might affect sexual function in humans. These results might explain delayed ejaculation described in patients receiving SJW.

Effect of in vivo and in vitro ethanol on adrenergic and purinergic responses of the bisected rat vas deferens to low and high frequency pulses

1. This study investigates the effect of acute in vivo and in vitro ethanol administration on the contractions evoked electrically and by exogenous noradrenaline and alpha,beta-methylene-ATP in the rat bisected vas deferens. 2. In vivo ethanol treatment (3 g kg(-1), i.p.) significantly potentiated the early purinergic (phase I) and the delayed adrenergic (phase II) phases evoked by single-pulse stimulation of the epididymal portion of the rat vas deferens, leaving unaffected both phases in the prostatic portion. In vitro 50 mM ethanol significantly depressed phase I leaving unaffected phase II in both portions from untreated rats. In vitro ethanol significantly depressed phase I in the epididymal portion from in vivo ethanol treated animals and potentiated phase II in both portions. 3. In vivo ethanol treatment (3.0 g kg(-1), i.p.) selectively impaired the response to noradrenaline only in the prostatic portion of rat vas deferens while it was devoid of any action on alpha,beta-methylene-ATP contractions. Ethanol 50 mM in vitro was devoid of any action on the response to exogenous noradrenaline and alpha,beta-methylene-ATP in both tissues. 4. In vivo ethanol treatment slightly but significantly increased the phasic response in the epididymal portion to trains of stimuli (2-30 Hz). In vitro 50 mM ethanol was ineffective against the phasic and tonic contractions elicited by the tetanus in both portions. 5. It is concluded that ethanol treatment affects purinergic and adrenergic pathways of transmission possibly leading to a disruption of physiological contractions necessary to seminal emission.

Differential effects of drugs interacting with autonomic transmitters on responses of rat vas deferens to field stimulation

1. Frequency-response curves (0.1-30 Hz) were obtained in the epididymal portion of rat vas deferens. At low frequencies (0.1-1 Hz), the parameters evaluated were the first twitch and the fourth twitch at each frequency. The responses to trains of stimuli at intermediate (2-5 Hz) and high (10-30 Hz) frequencies were biphasic consisting of phase I (the first rapid phase of tetanus) and of phase II (the secondary slowly developing one). 2. Prazosin inhibited the first and the fourth twitch but not when the frequency was < 1 Hz. Suramin inhibited the first twitch while substantially depressing the fourth one. The combination of prazosin and suramin almost completely abolished all the twitches evoked by a train of stimuli at low frequencies. Nifedipine left almost unaltered the first twitch while markedly depressing the fourth one, especially at relatively high frequency (1 Hz). Verapamil was devoid of any inhibitory action. Papaverine depressed the first twitch while only at the highest concentration used (1 x 10(-4) M) markedly inhibited the fourth one. Chloroethylclonidine (CEC) depressed the first twitch and increased the fourth. 3. When intermediate (2-5 Hz) and high (10-30 Hz) frequencies are considered, prazosin and suramin partially inhibited both phase I and phase II, while in combination they almost completely abolished both phases. Nifedipine and verapamil selectively suppressed phase II, leaving phase I unaffected. Papaverine completely abolished both phase I and phase II. CEC was able to completely abolish phase I but increased phase II. 4. These results suggest that the response to the first twitch of a train at low frequency is prevailingly noradrenergic, prazosin-sensitive, while when the twitches are close enough (i.e. at 1 Hz) a summation of stimuli takes place and a predominant purinergic component, both suramin- and nifedipine-sensitive, becomes evident. 5. At high frequencies, both phases are due to the concomitant release of noradrenaline and adenosine triphosphate (ATP). The noradrenergic component of phase I is nifedipine-insensitive and CEC-sensitive, resembling the pharmacological profile of the endogenously released noradrenaline by single pulse, while that of phase II, nifedipine-sensitive and CEC-insensitive, is similar to that produced by exogenously applied noradrenaline.