Tachykinin effects on bladder activity in conscious normal rats

Area of Science:

• Urology
• Neuropharmacology
• Physiology

Background:

• The role of tachykinins and their receptors in regulating bladder function is not fully elucidated.
• Neurokinin A (NKA), Substance P (SP), and Neurokinin B (NKB) are key tachykinins involved in various physiological processes.

Purpose of the Study:

• To investigate the role of NKA, SP, and NKB in initiating micturition and bladder contractility in rats.
• To determine the specific neurokinin (NK) receptor subtypes involved in these effects.

Main Methods:

• Intravesical and intra-arterial administration of NKA, SP, and NKB in normal, unanesthetized rats.
• Administration of selective NK1 and NK2 receptor antagonists (SR 48,968, MEN 10,627, RP 67,580, SR 140,333) to block receptor activity.
• Measurement of micturition initiation and intravesical pressure to assess bladder activity.

Main Results:

• Intravesical NKA, but not SP or NKB, stimulated micturition, an effect blocked by NK2 receptor antagonists.
• Intra-arterial NKA increased basal intravesical pressure, indicating direct detrusor smooth muscle contraction, an effect blocked by combined NK1 and NK2 antagonists.
• Intra-arterial NKB weakly stimulated micturition, while intra-arterial SP had minimal effects.

Conclusions:

• Intravesical NKA initiates micturition in rats via stimulation of urothelial NK2 receptors.
• Intra-arterial NKA induces bladder hyperactivity through the activation of both NK1 and NK2 receptors in the bladder.
• These findings highlight distinct receptor-mediated mechanisms for NKA in regulating bladder function depending on the route of administration.