BACKGROUND
Bladder hypertrophy as a consequence of partial outlet obstruction has been linked to degenerative changes causing impairment of detrusor function. Data from my initial study suggest that diet-induced metabolic phenotypes have an influence on the course and severity of hypertrophy in bladder outlet obstruction (BOO). This diet-induced hypertrophy in BOO was also seen to increase smooth muscle/collagen ratio (SM/C), and decrease detrusor muscle contractility. The resultant effect of all these is an impairment of bladder functions in Wistar rats, with and without obstruction of the bladder. These effects were linked in our study to the changes induced in Insulin-like Growth Factor-I (IGF-I) concentrations in response to various dietary feeding in Wistar rats. Several other receptors, signalling pathways and growth factors have been implicated in the hypertrophic response to stretch of bladder wall in obstruction. These include Epidermal Growth Factor (EGF) (Vinter-Jensen et al., 1996), Basic fibroblast growth factor (bFGF) (Nguyen et al., 2000), and Heparin-binding EGF-like growth factor (HB-EGF) (Chen et al., 1994). Also, changes in myosin isoform expression pattern have been suggested as responsible for a slower, more economical bladder muscle in BOO (Sjuve et al., 1996) and a decrease in SM2/SM1 ratio has been reported in the obstructed urinary bladder of rats (Malmqvist et al., 1991). There is also an increase in intermediate filaments in the hypertrophying urinary bladder of experimental animals and in humans, where the amount of the intermediate filament protein desmin increases relative to other contractile and cytoskeletal proteins (Malmqvist et al., 1991). Vimentin in the urinary bladder has been reported to increase also in hypertrophy (Malmqvist et al., 1991).
AIM
The aim of the present study is to determine the influence of diet on other factors implicated in hypertrophy of the detrusor muscle in both normal and bladders with obstruction. The study would also investigate the effects of these diets on factors involved in detrusor mechanics and blood flow in both normal and obstructed rats’ bladders.
OBJECTIVES
To achieve the above aim, the following variables will be assessed in rats with normal or obstructed bladders:
- Epidermal Growth Factor (EGF)
- Basic fibroblast growth factor (bFGF)
- Heparin-binding EGF-like growth factor (HB-EGF)
- SM2/SM1 ratio (SM=smooth muscle myosin sub-type)
- Changes in Desmin and Vimentin (intermediate filaments reported to increase in BOO) concentration.
METHODS
80 male Wistar rats will be procured from the Central Animal House of the Department of Physiology, University of Ibadan and used in this study. The animals will be housed in cages and acclimatized for two weeks prior to the commencement of the experiment. Animals will then be divided into eight groups namely: Sham-operated control (Fed on standard rats’ feeds), BOO control (surgically induced BOO animals fed on standard rats’ feeds), High Carbohydrate Diet (HCD), HCD with BOO), High Fat Diet (HFD), HFD with BOO, High Protein Diet (HPD), and HPD with BOO. Rats will be fed for 8 weeks, prior to experimental BOO surgery, on the diets based on their grouping. After induction of obstruction, animals will then be fed for a further 4 weeks and which they will be euthanized and bladders excised.
Bladder detrusor muscle will be excised and homogenised. Enzyme-linked immunosorbent assay (ELISA) would be used to assay for EGF, bFGF, and HB-EGF. Rat ELISA kits for each of the proteins will be purchased and used for these, following manufacturers’ protocols. SM1 and SM2 expression will be determined using Polymerase Chain Reaction (PCR) technique following established methods (Koi et al 2007; Chua et al., 2009). Desmin and Vimentin will also be assayed using ELISA technique.
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