Effects of age and streptozotocin-induced diabetes on contents and effects of substance P and vasoactive intestinal polypeptide in the lower urinary tract of the rat

The neuropeptide substance P/neurokinin-1 receptor system and diabetes: From mechanism to therapy

Diabetes is a significant public health issue known as the world's fastest-growing disease condition. It is characterized by persistent hyperglycemia and subsequent chronic complications leading to organ dysfunction and, ultimately, the failure of target organs. Substance P (SP) is an undecapeptide that belongs to the family of tachykinin (TK) peptides. The SP-mediated activation of the neurokinin 1 receptor (NK1R) regulates many pathophysiological processes in the body. There is also a relation between the SP/NK1R system and diabetic processes. Importantly, deregulated expression of SP has been reported in diabetes and diabetes-associated chronic complications. SP can induce both diabetogenic and antidiabetogenic effects and thus affect the pathology of diabetes destructively or protectively. Here, we review the current knowledge of the functional relevance of the SP/NK1R system in diabetes pathogenesis and its exploitation for diabetes therapy. A comprehensive understanding of the role of the SP/NK1R system in diabetes is expected to shed further light on developing new therapeutic possibilities for diabetes and its associated chronic conditions.

The role of vasoactive intestinal polypeptide and pituitary adenylate cyclase-activating polypeptide in the neural pathways controlling the lower urinary tract

Vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are expressed in the neural pathways regulating the lower urinary tract. VIP-immunoreactivity (IR) is present in afferent and autonomic efferent neurons innervating the bladder and urethra, whereas PACAP-IR is present primarily in afferent neurons. Exogenously applied VIP relaxes bladder and urethral smooth muscle and excites parasympathetic neurons in bladder ganglia. PACAP relaxes bladder and urethral smooth muscle in some species (pig) but excites the smooth muscle in other species (mouse). Intrathecal administration of VIP in cats with an intact spinal cord suppresses reflex bladder activity, but intrathecal administration of VIP or PACAP in rats enhances bladder activity and suppresses urethral sphincter activity. PACAP has presynaptic facilitatory effects and direct excitatory effects on lumbosacral parasympathetic preganglionic neurons. Chronic spinal cord transection produces an expansion of VIP-IR (cats) and PACAP-IR (rats) in primary afferent axons in the lumbosacral spinal cord and unmasks spinal excitatory effects of VIP on bladder reflexes in cats. Intrathecal administration of PACAP6-38, a PAC1 receptor antagonist, reduces bladder hyperactivity in chronic spinal-cord-injured rats. These observations raise the possibility that VIP or PACAP have a role in the control of normal or abnormal voiding.

Smooth muscle of the bladder in the normal and the diseased state: pathophysiology, diagnosis and treatment

The smooth muscle of the normal bladder wall must have some specific properties. It must be very compliant and able to reorganise itself during filling and emptying to accommodate the change in volume without generating any intravesical pressure, but whilst maintaining the normal shape of the bladder. It must be capable of synchronous activation to generate intravesical pressure at any length to allow voiding. The cells achieve this through spontaneous electrical activity combined with poor electrical coupling between cells, and a dense excitatory innervation. In the diseased state, alterations of the smooth muscle may lead to failure to store or failure to empty properly. The diseased states discussed are bladder instability and diabetic neuropathy. Bladder instability is characterised urodynamically by uninhibitable rises in pressure during filling, and is seen idiopathically and in association with bladder outflow obstruction and neuropathy. In diabetic neuropathy, many of the smooth muscle changes are a consequence of diuresis, but there is evidence for alterations in the sensory arm of the micturition reflex. In the unstable bladder, additional alterations of the smooth muscle are seen, which are probably caused by the patchy denervation that occurs. The causes of this denervation are not fully established. Nonsurgical treatment of instability is not yet satisfactory; neuromodulation has some promise, but is expensive, and the mechanisms poorly understood. Pharmacological treatment is largely through muscarinic receptor blockade. Drugs to reduce the excitability of the smooth muscle are being sought, since they may represent a better pharmacological option.

Effect of substance P and capsaicin on stomach fundus and ileum of streptozotocin-diabetic rats

The in vitro responses of longitudinal preparations of rat stomach fundus and ileum to capsaicin at 1, 8, 4, 16 and 26 weeks and to substance P at 1 and 8 weeks from diabetes induction were studied. The results were compared with those obtained in age-matched control rats. The contractile responses to exogenous substance P and capsaicin were not affected in the stomach fundus from diabetic rats. Atropine (1 microM) did not antagonize the substance P-induced response whereas it inhibited about 90% of the capsaicin-induced response in controls and about 60% of the response in diabetic rats. At the resting tone, capsaicin induced a relaxation followed by a contraction in stomach fundus of control rats. Only a contraction was evoked in diabetic rats. In carbachol (0.05-0.1 microM) pre-stimulated strips, a complete restoration of the biphasic response was obtained in the diabetic state. The contractile response elicited by exogenous substance P was not significantly increased in the ileum preparations from diabetic rats; nevertheless the EC50 value for substance P was reduced 8 weeks after the onset of diabetes. The response elicited by capsaicin in the ileum of control rats was also biphasic. The capsaicin-induced contraction was greater in tissue from diabetic rats as compared with controls and relaxation was not evident. An age-related decrease of the contraction was also evident in both groups. Atropine (1 microM) partially antagonized the responses to substance P and capsaicin. The inhibition of the responses with atropine was more evident in control than in diabetic rats. These results suggest that the myogenic actions of several agonists in these two tissues are differently modified in experimental diabetes.

Age-dependent mechanism in guinea pig bronchoconstriction induced by exsanguination

Age-related mechanism in exsanguination-induced bronchoconstriction (EIB) was studied in guinea pigs. We used a total of 36 guinea pigs divided into three age categories (immature, adolescent, and mature). Each age category was separated into two groups: control and catalase (CAT). CAT is an antioxidant. Both saline (the control group) and CAT were instilled intratracheally 30 min before exsanguination. The animals were anesthetized, sternotomized and exsanguinated. Maximal expiratory flow (Vmax) was measured both before and 1-30 min after exsanguination. In the control group, exsanguination caused gradual decreases in both total lung capacity (TLC) and Vmax at 50% baseline TLC, and an increase in minimal lung volume, indicating EIB. EIB occurred faster in the immature than in the adolescent and mature guinea pigs, and it was significantly ameliorated by CAT. In 36 additional animals tested before exsanguination, there was no age-related change in either airway neutral endopeptidase (NEP) activity or lung tissue substance P level. Thirty minutes after exsanguination in the control groups, airway NEP activity decreased significantly in all age categories, while lung tissue substance P level increased significantly only in the immature category. CAT prevented most of these NEP and substance P changes. These data suggest that exsanguination increases production of oxygen radicals, which inactivate NEP and enhance breakdown of substance P precursor; the increased tachykinin levels induce EIB. Furthermore, our data indicate that this chain reaction is age-dependent, with a faster and more severe reaction in immature guinea pigs.

Effect of substance P and capsaicin on urinary bladder of diabetic rats and the role of the epithelium

The in vitro responses of rat urinary bladder, to substance P and capsaicin were studied at 1, 4, 16, and 26 weeks of diabetes induction by streptozotocin. We also studied the role of epithelium in these responses. The results were compared with those obtained in age-matched control rats. The bladder contractile response to exogenous substance P was similar in both groups at all stages (1-26 weeks) studied, whereas the bladder response to capsaicin gradually decreased with the progression of diabetes. Atropine did not inhibit these responses whereas indomethacin slightly reduced substance P- but not capsaicin-induced responses in control and diabetic rats. The removal of epithelium slightly increased the substance P- and capsaicin-induced responses in control tissue; these responses were significantly reduced in tissue excised from diabetic rats. Our results indicate that, in rat urinary bladder, diabetes (1) provokes an impairment of capsaicin-sensitive sensory fibers but not of the cholinergic system even at an early stage (4 weeks) of the disease, (2) has no effect on the sensitivity of smooth muscle cells to substance P, (3) stimulates the release of epithelial contracting factors, partially non-prostanoic. Furthermore epithelium removal impairs acetylcholine-induced contraction in bladder excised from diabetic rats but not in controls.

Alterations in neural pathways to the urinary bladder of the rat in response to streptozotocin-induced diabetes

Voiding dysfunction in diabetics has been attributed to a variety of causes including an axonopathy in autonomic pathways to the urinary bladder. The present study was undertaken to determine whether changes occurred in afferent and efferent neurons supplying bladders of streptozotocin (STZ)-induced diabetic rats. Nine weeks after STZ treatment, the mean cross-sectional area for retrogradely labeled (Fluoro-Gold) bladder neurons in the major pelvic ganglion (MPG) was greater in diabetics (364 microns 2) than controls (300 microns 2). The number of labeled neurons was similar in these groups. In contrast, mean cross-sectional areas of bladder afferent neurons labeled with WGA-HRP in the L6 and S1 dorsal root ganglia (DRG) were smaller (393 microns 2) in diabetics than in normal rats (528 microns 2). In addition, very few DRG neurons were labeled in STZ-treated rats and transganglionic labeling of bladder afferent projections in the L6 and S1 spinal cord with WGA-HRP was sparse. Radioimmunoassay studies revealed that substance P was reduced by 70% in the MPG and by 40% in L6 DRG, yet this peptide was unchanged in the bladders of diabetic rats. The amounts of VIP in the MPG and DRG of diabetics and controls were similar, while VIP in the bladder was increased in diabetics. These observations indicate that both afferent and efferent neurons innervating the urinary bladder are altered in the STZ-induced diabetic rat. In addition, axonal transport in visceral afferent pathways may be disrupted.