THE ADRENERGIC, CHOLINERGIC AND NANC NERVE-MEDIATED CONTRACTIONS OF THE FEMALE RABBIT BLADDER NECK AND PROXIMAL, MEDIAL AND DISTAL URETHRA

1 The nerve-mediated contraction of the female rabbit bladder neck and different portions of the urethra (proximal, medial and distal) was s tudied in vitro by electrical stimulation (50 V, 30 Hz, 0.05 ms width, trains of 5 s every 5 min) by use of a superfusion system. 2 The ampl itude (E-max) and the duration (D-max) of the stimulated contraction w ere studied in the four tissues. The E-max value was significantly hig her in distal urethra (2.07 +/- 0.15 g) compared to the bladder neck ( 1.08 +/- 0.10 g), proximal urethra (0.73 +/- 0.07 g) and medial urethr a (0.87 +/- 0.07 g). In contrast, the D-max value appeared slightly bu t significantly lower (P<0.05) in distal urethra (68.5 +/- 2.3 s) than in bladder neck (76.7 +/- 6.0 s), proximal urethra (84.5 +/- 5.0 s) a nd medial urethra (81.3 +/- 3.5 s). 3 Cocaine (1 mu M) significantly i ncreased the basal E-max values in medial and distal urethra and the b asal D-max values in the four tissues. 4 Prazosin (1 mu M) significant ly reduced E-max value in proximal, medial and distal urethra and D-ma x value in bladder neck and proximal urethra. Atropine (1 mu M) also s ignificantly reduced E-max values in bladder neck and proximal urethra and reduced D-max value in bladder neck, but not in other tissues. Yo himbine (0.1 mu M) was devoid of effect in the four tissues. 5 The ass ociation of prazosin (1 mu M) and atropine (1 mu M) did not modify the E-max and the D-max values of the electrically-induced contractions, except in proximal urethra and in bladder neck where an additive inhib itory effect ton E-max only) was observed compared to prazosin and atr opine alone. 6 The residual contractile response after combined treatm ent with prazosin and atropine was significantly diminished by tetrodo toxin (TTX; 1 mu M) but not completely abolished. These NANC contracti ons were insensitive to P2X-purinoceptor desensitization by continuous tissue perfusion with alpha,beta-methylene ATP (30 mu M). 7 These res ults demonstrate that bladder neck and proximal urethra are mainly inn ervated by the parasympathetic nervous system, whereas medial and dist al urethras are to a greater extent under the control of the sympathet ic innervation. The residual responses, insensitive to prazosin and at ropine, may indicate a NANC innervation in the four tissues. However, the nature of the NANC neurotransmitter remains to be identified.