EXPERIMENTAL STUDIES ON THE NEUROGENIC BLADDER

XIX. The Morphological and Pharmacological Investigations on the Canine Posterior Urethra

Abstract

The histological, electrophysiological, and pharmacological observations were performed on the canine urethra (the posterior urethra in the male, and total urethra in the female), as well as the bladder neck and the bladder dome as the control, and the following results were obtained.
1. The canine urethra had the intrinsic smooh muscle with the construction of 2 layers (inner longitudinal and outer circular) just inside the mucosal layer. Besides it, the intrinsic urethral striated muscle with the construction of 3 layers (inner circular, middle longitudinal, and outer circular) was observed just outside the smooth muscle layers.
2. The intrinsic urethral striated muscle was observed to extend from the external sphincter region to the middle portion of the outer prostatic capsule in the male, but in the female, it was observed to extend from the external sphincter region to the slightly distal part of the midway of the urethra. This striated muscle gradually lost its 3 layers construction and tended to be thin in its proximal part, but in the distal part, it gradually increased its circular layers and tended to be thick.
3. The tissue strip in circular direction of the urethra with whole layer was suspended in the organ bath with Krebs solution at 38°C, and transmural electrostimulation (TMS) was done, and the contraction response was examined. Almost the same strip of the bladder neck and the bladder dome were used as the control. The tissue strips which were obtained from the distal part of the urethra, the midway of the urethra or just distal part from the apex of the prostate, and the bladder neck, showed somewhat different contraction response, which was assumed to be corresponded to the histological composition of the tissue, i. e., the ratio of the smooth muscle and the striated muscle.
4. With the same procedure, the effect of various drugs on the response of the tissue strip in the organ bath was observed. Acetylcholine and atropine for the cholinergic system, phenylephrine and phentolamine for the alpha-adrenergic system, isoproterenol and propranolol for the beta-adrenergic system, DMPP and hexamethonium for the ganglionic system, and Tetrodotoxin for the Na⁺-channel inhibitor, were used. The change of tonicity and contraction response to TMS was examined after administration of stimulant, blocker, stimulant after each blocker, or stimulant after Tetrodotoxin.
5. The response which was thought to reveal the existence of cholinergic system could be observed markedly in the bladder dome, and slightly in the bladder neck, but it could not be observed in the whole urethra.
6. The response which was thought to reveal the existence of the alpha-adrenergic system could be observed markedly in the proximal half of the urethra as well as the bladder neck, and slightly in the bladder dome, but it could not be observed in the distal half of the urethra.
7. The response which was thought to reveal the existence of the beta-adrenergic system could be observed in the whole urethra as well as the bladder neck and the bladder dome, as the inhibition of contraction response to TMS after administration of the beta-blocker. Howerer, the pattern of the response was somewhat different according to the locality.
8. The response which was thought to reveal the existence of the ganglionic system could be observed clearly in the proximal part of the urethra, the bladder neck, and the bladder dome with small difference in its response pattern
9. The administration of Tetrodotoxin could not affect the tonicity of each tissue strip used, but it could depress the contraction response of these tissue strips to TMS. The tonicity of the bladder dome increased by administration of acetylcholine after Tetrodotoxin, while the tonicity of the midurethra and the bladder neck increased by administration of alpha-stimulants after Tetrodotoxin.