1. Activation of the sympathetic input to the urinary bladder by electrical stimulation of afferent fibres in the pelvic nerve evoked three responses: (1) an initial transient rise in intravesical pressure, (2) an inhibition of neurally evoked bladder contractions and (3) an inhibition of transmission in vesical parasympathetic ganglia. Similar responses were elicited by stimulation of the hypogastric nerve. 2. The reflex responses were observed in acute spinal preparations (T10‐T12) and in cats with intact spinal cords, but were abolished by bilateral transection of the hypogastric nerves. 3. The inhibition of bladder contractions was antagonized by the administration of propranolol (200‐400 mug, I.A.), a beta‐adrenergic blocking agent. The inhibition of ganglionic transmission was antagonized by dihydroergotamine (30‐75 mug, I.A.), an alpha‐adrenergic blocking agent. The initial rise in intravesical pressure was not antagonized by either agent. 4. Electrical stimulation of other afferents (carotid sinus nerve and sciatic nerve) did not consistently elicit responses in the urinary bladder. However, stimulation of these afferents as well as pelvic nerve afferents evoked reflex firing in nerve filaments on the surface of the urinary bladder. The firing was abolished by transection of the ipsilateral hypogastric nerve. 5. It is concluded that stimulation of vesical afferents activates a spinal sympathetic reflex which results in closing of the internal urethral sphincter and a depression of bladder activity. The latter occurs by a direct depression of detrusor smooth muscle as well as a block of the neural input to the bladder. This vesico‐sympathetic reflex represents a negative feed‐back mechanism which may have an important role in the maintenance of urinary continence.

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ANAPP3 produces a transient contraction of the urinary bladder of the cat similar to that produced by ATP and hypogastric nerve stimulation. 2 ANAPP3 partially antagonizes the inhibition of pelvic nerve-evoked bladder contractions induced by adenosine, possibly by blocking P1 receptors. 3 ANAPP3 antagonizes contractions of the cat urinary bladder induced by ATP, beta, gamma-methylene ATP, pelvic nerve stimulation and hypogastric nerve stimulation. 4 ANAPP3 produces no antagonism of either noradrenaline-induced inhibition of pelvic nerve-evoked bladder contractions or acetylcholine-induced bladder contractions, thereby substantiating the specificity of the effect of ANAPP3 against purines.

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