Magnetic Resonance Imaging for Assessment of Vena Caval Tumor Thrombi: Comparative Study With Venacavography and Computerized Tomography

To improve the quality of bladder contractions induced by parasympathetic stimulation and to facilitate the init iat ion of voiding, we investigated the effect of sympathetic stimulation on the parasympathetic innervation of the bladder i n 12 dogs. For the sympathetic system, the lumbar sympathetic trunks were electrically stimulated; for the parasympathetic system, either the pelvic nerve or the ventral root of S 2 was stimulated. W i t h voltages at or just above the threshold for achieving a measurable effect on bladder pressure, stimulation of the sympathetic system or the pelvic nerve alone did not lead to voiding, and sacral root stimulation alone elicited voiding in only 7.4 per cent of stimulations. However, when the same stimulus parameters were used for synchronous stimulation, the voiding process was facilitated when sympathetic stimulation was begun five to 10 seconds before parasympathetic stimulation. When the pelvic nerve was used, voiding resulted i n 77.7 per cent of stimulations and the bladder was emptied by a mean of 68.7 per cent; w i th S 2 ventral root stimulation, voiding resulted in 83.3 per cent of stimulations and the bladder was emptied by 59.7 per cent. The facilitory effect of sympathetic stimulation was not abolished when the sympathetic trunks were cut centrally to the point of stimulation, but was absent when the hypogastric nerves were transected. We feel that sympathetic stimulation modulates the parasympathetic innervation of the bladder. (J. Urol, 144: 1252-1257, 1990) Many studies have been undertaken t o elucidate the role o f the sympathetic nervous system i n bladder and urethral funct i o n , but t h e q u e s t i o n o f h o w t h e a u t o n o m i c n e r v o u s s y s t e m initiates voiding remains unclear. The sympathetic nervous system exhibits its action on smooth muscle cells through two different types o f adrenergic receptors. Stimulation o f alphaadrenergic receptors generally results in excitation, producing a contraction o f the smooth muscles, whereas stimulation o f the beta-receptors results in an inhibitory o r muscle-relaxing effect. Previous studies1 have shown that adrenergic receptors are present throughout the bladder: beta-adrenergic receptors predominate in the body and dome; and alpha-adrenergic r e ceptors in the base and bladder neck. In the urethra, alpha receptors predominate.2 The effects of sympathetic stimulation on bladder function can be summarized. Its most powerful effect is a direct inhibition, mediated by beta-adrenergic receptors, of bladder smooth muscle cells.3 A less powerful, alpha-receptor-mediated inhibition of the parasympathetic transmission in bladder ganglia has been described in the cat, although this inhibition varied among animals in the series and among different postganglionic fibers in the same animal, and was apparent only when the excitatory input to the parasympathetic ganglia was at a low level.3 In contrast, others have claimed a consistent, marked facilitation of the parasympathetic postganglionic potential in the same species.4 Histochemical5 ,6 and ultrastructural evidence6 for a sympathetic action on the parasympathetic bladder ganglia is now well established. During hypogastric nerve stimulation, an initial contractile A c c e p t e d for publ icat ion J u n e 6, 1990. * R e q u e s t s for repr ints : D e p t . of Urology , U C S F S c h o o l of M e d i c i n e , S a n F r a n c i s c o , C A 94143. D r . B o s c h w a s the recipient of a grant from the S o p h i a F o u n d a t i o n for M e d i c a l R e s e a r c h , T h e N e t h e r l a n d s . bladder response followed by relaxation was found in the cat 3 , 7 , 8 and dog. 9 1 1 This response was elicited whether the pelvic nerves w e r e i n t a c t o r t r a n s e c t e d . T h e r e l a x a t i o n p h a s e w a s a b o l i s h e d by ß-blockers.3,10 The initial bladder contraction was not blocked by phentolamine8'12 (or was so only partially 1 0) and was inconsistently influenced by phenoxybenzamine. 3 , 7 , 8 , 1 1 1 3 This initial contractile response is not confined to the bladder base11 and is not in accord with the prevailing theories of facilitation of storage by the sympathetic system. Pharmacologic studies have ascribed its origin variously: mediated via the parasympathetic postganglionic pathway,8 non-adrenergic,10 and possibly alpha-adrenergic, but mediated by receptors that must have pharmacologic characteristics different from those involved in ganglionic transmission.3 Apart from the initial non-reflexive contractile response, singular responses in the trigonal area have been noted. These probably represent a threshold effect or a greater preponderance of adrenergic receptor sites.11 Also, a forceful excitation at multiple points in the bladder wall has been obtained, possibly due to a secondary alpha-adrenergic positive feedback mechanism that excites parasympathetic neurons in the sacral spinal cord.11 In agreement with these findings, electrophysiologic studies have shown that hypogastric nerve stimulation often elicits reflex firing in the parasympathetic fibers to the bladder—an effect that can be abolished by transection of the pelvic nerves.3 On anatomical grounds, Feher et al. 1 4 have argued that bladder contractions are initiated in the trigone, as its innervation is three times greater than that of the dome. Furthermore, they argue that local nerve processes and numerous nexal (desmosome-like) contacts between smooth muscle cells have a role in the activation of other parts of the bladder wall. Thus, evidence exists for a modulatory role of the sympathetic nervous system