Evidence against VIP or substance P being the transmitter in non-cholinergic excitatory nerves supplying the guinea-pig bladder

Purinergic signalling in the urinary tract in health and disease

Purinergic signalling is involved in a number of physiological and pathophysiological activities in the lower urinary tract. In the bladder of laboratory animals there is parasympathetic excitatory cotransmission with the purinergic and cholinergic components being approximately equal, acting via P2X1 and muscarinic receptors, respectively. Purinergic mechanosensory transduction occurs where ATP, released from urothelial cells during distension of bladder and ureter, acts on P2X3 and P2X2/3 receptors on suburothelial sensory nerves to initiate the voiding reflex, via low threshold fibres, and nociception, via high threshold fibres. In human bladder the purinergic component of parasympathetic cotransmission is less than 3 %, but in pathological conditions, such as interstitial cystitis, obstructed and neuropathic bladder, the purinergic component is increased to 40 %. Other pathological conditions of the bladder have been shown to involve purinoceptor-mediated activities, including multiple sclerosis, ischaemia, diabetes, cancer and bacterial infections. In the ureter, P2X7 receptors have been implicated in inflammation and fibrosis. Purinergic therapeutic strategies are being explored that hopefully will be developed and bring benefit and relief to many patients with urinary tract disorders.

Capsaicin-induced bladder hyperactivity in normal conscious rats

Capsaicin, instilled intravesically in normal, unanesthetized rats induced a concentration-dependent bladder hyperactivity, which could be abolished by hexamethonium, given intra-arterially near the bladder, or by morphine administered intrathecally. The effect was reversible and could be repeated. The NK-2 receptor selective antagonist SR 48,968 and the nonselective NK receptor antagonist spantide, given intra-arterially near the bladder, which by themselves, in the concentrations used, did not affect cystometric parameters, both counteracted the capsaicin-induced hyperactivity, whereas the NK-1 receptor selective antagonist RP 67,580 failed to do so. Blockade of tachykinin receptors in the urinary bladder does not seem to produce changes of the micturition reflex associated with bladder filling in the conscious rat. However, tachykinins released from capsaicin-sensitive nerves by various stimuli may, through stimulation of NK-2 receptors, lower the threshold for initiation of the micturition reflex. In the rat, intravesical capsaicin may be a suitable model for studies of afferent activity caused by stimuli releasing peptides from sensory nerves in the bladder, thereby provoking bladder hyperactivity.

Localization of muscarinic receptors on somatostatin-like immunoreactive neurones of the newborn guinea pig urinary bladder in culture

Muscarinic receptors were localized on cells cultured from the detrusor muscle of the newborn guinea pig urinary bladder by autoradiography using the irreversible muscarinic antagonist [3H]propylbenzilylcholine mustard, before being immunostained with an antibody to somatostatin. Many mononucleate and binucleate intramural neurones immunoreactive for somatostatin were observed (60-75% of the total population), a subpopulation of which (40-60%) expressed muscarinic receptors. Autoradiographic grains were distributed over the whole cell body surface and the entire length of the neurites. An even distribution of silver grains was also seen on cultured smooth muscle cell surfaces, but not on other cell types present in the culture preparations. The demonstration of muscarinic receptors on specific neuropeptide-containing cells in culture is consistent with the existence of specialized cholinergic, intraganglionic circuits within the bladder wall, and suggests that somatostatin may also be involved in the integration and/or modulation of bladder function.

Release of purines and noradrenaline from the vascular adrenergic nerves by 5- and 6-hydroxydopamine

1. The in vitro effects of 6-hydroxydopamine (6-OHDA) and 5-hydroxydopamine (5-OHDA) on 3H-efflux from rabbit pulmonary artery after incubation with [3H]noradrenaline ([3H]NA) or [3H]adenosine were assessed. 2. 6-OHDA (100 microM) or 5-OHDA (100 microM) enhanced not only [3H]noradrenaline efflux, but also [3H]purines efflux. 3. Following Ca2+-removal, [3H]NA and [3H]purine effluxes evoked by these hydroxydopamines were moderately and considerably diminished, respectively. In addition, the 6-OHDA-evoked [3H]purine efflux was significantly decreased by W-7 (30 microM), a calmodulin inhibitor. 4. The 6-OHDA or 5-OHDA-evoked purine release was almost insensitive for prazosin (0.3 microM), indicating a neuronal release. 5. The peak [3H]purine efflux evoked by 6-OHDA or 5-OHDA occurred in the corresponding fraction number to that for the [3H]NA efflux. 6. These results suggest that 6-OHDA and 5-OHDA may expel NA together with purines from the amine stored sites (probably, in axoplasm) in the adrenergic nerves.