Roles for α1-adrenoceptors during contractions by electrical field stimulation in mouse vas deferens

Abstract

We have investigated the relative roles of α₁-adrenoceptors and purinoceptors in contractions to low and high frequency stimulation of the mouse vas deferens, in terms of the time course of responses. In separate experiments, isometric contractile responses were obtained to 10 pulses at 1 Hz and 40 pulses at 10 Hz. Responses to 1 Hz stimulation consisted of a series of discrete peaks. The α_1A-adrenoceptor antagonist RS100329 (10^-9M-10^-7M) significantly reduced the response to the first pulse, the α_1D-adrenoceptor antagonist BMY7378 (10^-7M-10^-6M) significantly reduced the response to the first two pulses, and the non-selective α₁-adrenoceptor antagonist prazosin (10^-8M) reduced the response to the first 4 pulses at 1 Hz. Responses to 10 Hz stimulation consisted of an early peak response and a maintained plateau response. RS100329 significantly reduced the peak response but did not significantly affect the plateau response. Prazosin, significantly reduced both the peak and plateau responses. The α_1A-adrenoceptor antagonist RS17053 in high concentrations reduced mainly the plateau response leaving a clear early peak response. The plateau response of contraction was almost abolished by the purinoceptor antagonist suramin. These results suggest that there is a relatively minor early α_1D-adrenoceptor and a larger early α_1A-adrenoceptor component to stimulationevoked contractions of mouse vas deferens, but the major α₁-adrenoceptor component is revealed by prazosin to be α_1B-adrenoceptor mediated. α_1B-Adrenoceptor activation probably facilitates contractions mediated by other α₁-adrenoceptors and by purinoceptors. These results suggest that combined non-selective α₁-adrenoceptor blockade, particularly α_1B-adrenoceptor blockade, in addition to P2X1-purinoceptor blockade is useful in reducing male fertility.

Keywords: Adrenergic; Fertility; Muscle; Neuromuscular junction; Vas deferens; smooth.

Fig. 1. Effects of vehicle and antagonists on isometric contractions of mouse vas deferens produced by 10 pulses at 1 Hz, expressed as tension in grams.

(A) Original recording of isometric contractions obtained to field stimulation in mouse vas deferens with 10 pulses at 1 Hz. The vertical axis shows tension in grams. The horizontal axis shows pulse number at 1 Hz and the time between each pulse is 1 sec. The response to the first pulse is clearly shown. (B–E) The effects of (B) vehicle (veh) (4 additions), (C) BMY7378 (BMY) (10 nM–10 µM), (D) RS100329 (1 nM–1 µM) and (E) prazosin (praz) (1 nM–1 µM) on isometric contractions to each pulse of 10 pulse field stimulation at 1 Hz in mouse vas deferens, expressed as absolute tension in grams. Values are presented as mean ± SEM from 6 experiments. Statistical tests were carried out on data expressed as a percentage of control (see ).

Fig. 2. Effects of vehicle and antagonists on isometric contractions of mouse vas deferens produced by 10 pulses at 1 Hz, expressed as % of control.

The effects of (A) vehicle (veh) (4 additions), (B) BMY7378 (BMY) (10 nM–10 µM), (C) RS100329 (1 nM–1 µM) and (D) prazosin (praz) (1 nM–1 µM) on isometric contractions to each pulse of 10 pulse field stimulation at 1 Hz in mouse vas deferens, expressed as % of control response (see for responses expressed as absolute tension). Values are presented as mean ± SEM from 6 experiments. Responses in the presence of antagonist were compared with the effects of respective vehicle by 2 way analysis of variance and Bonferroni post-hoc test. Asterisks denote effects of antagonist significantly different from the effects of vehicle in response to a given pulse, and are colour coded to match the antagonist concentration symbol colour: *p < 0.05; **p < 0.01; ***p < 0.001.

Fig. 3. Effects of vehicle and antagonists on isometric contractions of mouse vas deferens produced by 40 pulses at 10 Hz, expressed as tension in grams.

(A) Original recordings of isometric contraction obtained to field stimulation in mouse vas deferens with 40 pulses at 10 Hz. The vertical axis shows tension in grams. The horizontal axis shows time in sec, with stimulation at 10 Hz beginning at time zero and ending at 4 sec. (B–G) The effects of (B) vehicle (veh) (4 additions), (C) BMY7378 (BMY) (10 nM–1 µM), (D) RS100329 (0.1 nM–100 nM), (E) prazosin (praz) (1 nM–1 µM) and (F) RS17053 (100 nM–10 µM) on isometric contractions to field stimulation with 40 pulses at 10 Hz in mouse vas deferens, expressed as absolute tension in grams. In (G) responses in the presence suramin (sur) 100 µM and nifedipine (nif) 100 µM are shown. Values are presented as mean ± SEM from 6 experiments, except for suramin and nifedipine, where n = 5, and RS17053, where n = 4. Statistical tests were carried out on data expressed as a percentage of control (see ).

Fig. 4. Effects of vehicle and antagonists on isometric contractions of mouse vas deferens produced by 40 pulses at 10 Hz, expressed as % of control.

The effects of (A) vehicle (veh) (4 additions), (B) BMY7378 (BMY) (10 nM–1 µM), (C) RS100329 (0.1 nM–100 nM), (D) prazosin (praz) (1 nM–1 µM) and (E) RS17053 (100 nM–10 µM) on isometric contractions to field stimulation with 40 pulses at 10 Hz in mouse vas deferens, expressed as a percentage of the respective control response (see for responses expressed as absolute tension). Values are presented as mean ± SEM from 6 experiments, except for (E), where n = 4. Responses in the presence of antagonist were compared with the effects of respective vehicle by 2 way analysis of variance and Bonferroni post-hoc test. Asterisks denote effects of antagonist significantly different from the effects of vehicle at a given time point, and are colour coded to match the antagonist concentration symbol colour: *p < 0.05; **p < 0.01; ***p < 0.001.