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    • Implicit in this concept is the

    2023-02-01

    Implicit in this concept is the idea that the β-adrenoceptors in the detrusor would be activated by adrenergic nerves of the sympathetic system: sympathetic activity promoting relaxation and enhancing bladder capacity. However, it has been demonstrated that there is only a sparse adrenergic innervation of the detrusor in both rat and human (Gosling et al., 1999; Watanabe and Yamamoto, 1979). Thus, the nature of any physiological activation of β-adrenoceptors in the bladder wall is not fully understood. Recent observations have led to the suggestion that the organization of the contractile elements of the bladder wall might be more complex than previously thought (Gillespie, 2004; Vahabi and Drake, 2015). In vitro data suggests that rather than being inactive until stimulated, the smooth muscle in the bladder wall is involved in generating complex intrinsic micro-contractile activity (Gillespie et al., 2015a). Such activity influences the compliance of the bladder wall, but it is also thought to be related to complex non-voiding contractile activity seen in vivo, that may be part of a motor-sensory system involved in the detection of bladder volume (Gillespie, 2004). The micro-contractile activity may be generated within the smooth muscle cells themselves but it is now likely that a network of interstitial cells is involved in the generation and modulation of this complex activity (Gillespie et al., 2015a; Gillespie et al., 2015c; Hashitani, 2006; Hashitani et al., 2004; Persyn et al., 2016). In isolated rat bladder strips, it has been reported that isoprenaline reduces this intrinsic micro-contractile activity (Gillespie et al., 2015a; Gillespie et al., 2015b). Using selective adrenergic receptor antagonists, it has been suggested that this inhibition is primarily via a β1-adrenoceptor mechanism (Gillespie et al., 2015b).
    Materials and methods
    Results In all bladder studies, Angiotensin Fragment 1-7 acetate to tyrosine hydroxylase (TH), a key element on the synthesis of noradrenaline, and to vesicular mono-amine transporter (vmat), the transporter responsible for the storage of mono-amines into synaptic vesicles, identified nerve fibers within the bladder wall. It is more than likely that these TH immunoreactive (TH-IR) and vmat immunoreactive (vmat-IR) fibers identify adrenergic nerves. However, Fig. 1 shows that the number of TH-IR fibers in the bladder wall is low and that few fibers are to be found within or between the muscle bundles of the lateral wall (Fig. 1A), or towards the base (Fig. 1B and C). Fibers, when present, tend to run singly within muscle bundles, or in small groups between the bundles (Fig. 1F and G). In contrast, TH-IR nerves were readily found associated with blood vessels, primarily in the lamina propria (Fig. 1A–E). It was only in the bladder neck, in close proximity to the urethra, that a dense adrenergic innervation was found (Fig. 1D). Thus, in the main body of the bladder there appears to be a minimal adrenergic input to the detrusor. Towards the bladder base, muscle bundles were found occasionally with a dense innervation of TH-IR or vmat-IR fibers (Fig. 2A and B (*)). Such innervated bundles were found adjacent to bundles with no TH-IR or vmat-IR (+). The incidence of these densely innervated muscle bundles was low but this punctate innervation was seen in all bladders examined (n=11). Fig. 2B illustrates that there appears to be a population of cells lying between the muscle bundles that are vmat-IR (o). These cells are not nerve fibers and nuclei are readily seen in the cell bodies. Examination of the same section stained to identify TH-IR failed to show a significant or detectable staining in these cells. These vmat-IR cells were more abundant in the lateral wall near the base. Fig. 2C shows a further example of these cells (o) and a muscle bundle with TH-IR and vmat-IR nerve fibers. The cells have a stellate appearance and are typically found singly. No innervation of these vmat-IR cells by vmat or TH fibers was noted.