Load-Insensitive Measurements from an Isolated Perfused Biventricular Working Rat Heart

Corticotropin-releasing factor family peptide signaling in feline bladder urothelial cells

Corticotropin-releasing factor (CRF) plays a central role in the orchestration of behavioral and neuroendocrine responses to stress. The family of CRF-related peptides (CRF and paralogs: urocortin (Ucn)-I, -II, and -III) and associated receptors (CRFR1 and CRFR2) are also expressed in peripheral tissues such as the skin and gastrointestinal tract. Local signaling may exert multiple effects of stress-induced exacerbation of many complex syndromes, including psoriasis and visceral hypersensitivity. Interstitial cystitis/painful bladder syndrome (IC/PBS), a chronic visceral pain syndrome characterized by urinary frequency, urgency, and pelvic pain, is reported to be exacerbated by stress. Functional changes in the epithelial lining of the bladder, a vital blood-urine barrier called the urothelium, may play a role in IC/PBS. This study investigated the expression and functional activity of CRF-related peptides in the urothelium of normal cats and cats with feline interstitial cystitis (FIC), a chronic idiopathic cystitis exhibiting similarities to humans diagnosed with IC/PBS. Western blots analysis showed urothelial (UT) expression of CRFR1 and CRFR2. Enzyme immunoassay revealed release of endogenous ligands (CRF and Ucn) by UT cells in culture. Evidence of functional activation of CRFR1 and CRFR2 by receptor-selective agonists (CRF and UCN3 respectively) was shown by i) the measurement of ATP release using the luciferin-luciferase assay and ii) the use of membrane-impermeant fluorescent dyes (FM dyes) for fluorescence microscopy to assess membrane exocytotic responses in real time. Our findings show evidence of CRF-related peptide signaling in the urothelium. Differences in functional responses between FIC and normal UT indicate that this system is altered in IC/PBS.

NADH fluorescence imaging of isolated biventricular working rabbit hearts

Since its inception by Langendorff¹, the isolated perfused heart remains a prominent tool for studying cardiac physiology². However, it is not well-suited for studies of cardiac metabolism, which require the heart to perform work within the context of physiologic preload and afterload pressures. Neely introduced modifications to the Langendorff technique to establish appropriate left ventricular (LV) preload and afterload pressures³. The model is known as the isolated LV working heart model and has been used extensively to study LV performance and metabolism^4-6. This model, however, does not provide a properly loaded right ventricle (RV). Demmy et al. first reported a biventricular model as a modification of the LV working heart model^{7, 8}. They found that stroke volume, cardiac output, and pressure development improved in hearts converted from working LV mode to biventricular working mode⁸. A properly loaded RV also diminishes abnormal pressure gradients across the septum to improve septal function. Biventricular working hearts have been shown to maintain aortic output, pulmonary flow, mean aortic pressure, heart rate, and myocardial ATP levels for up to 3 hours⁸.

When studying the metabolic effects of myocardial injury, such as ischemia, it is often necessary to identify the location of the affected tissue. This can be done by imaging the fluorescence of NADH (the reduced form of nicotinamide adenine dinucleotide)^9-11, a coenzyme found in large quantities in the mitochondria. NADH fluorescence (fNADH) displays a near linearly inverse relationship with local oxygen concentration¹² and provides a measure of mitochondrial redox state¹³. fNADH imaging during hypoxic and ischemic conditions has been used as a dye-free method to identify hypoxic regions^{14, 15} and to monitor the progression of hypoxic conditions over time¹⁰.

The objective of the method is to monitor the mitochondrial redox state of biventricular working hearts during protocols that alter the rate of myocyte metabolism or induce hypoxia or create a combination of the two. Hearts from New Zealand white rabbits were connected to a biventricular working heart system (Hugo Sachs Elektronik) and perfused with modified Krebs-Henseleit solution¹⁶ at 37 °C. Aortic, LV, pulmonary artery, and left & right atrial pressures were recorded. Electrical activity was measured using a monophasic action potential electrode. To image fNADH, light from a mercury lamp was filtered (350±25 nm) and used to illuminate the epicardium. Emitted light was filtered (460±20 nm) and imaged using a CCD camera. Changes in the epicardial fNADH of biventricular working hearts during different pacing rates are presented. The combination of the heart model and fNADH imaging provides a new and valuable experimental tool for studying acute cardiac pathologies within the context of realistic physiological conditions.

Cerebral mechanisms and voiding function

Some of the most recent work investigating the cerebral mechanisms involved in bladder control has been very helpful in adding to our understanding of bladder dysfunction. The group behind this work, from London, presents a mini-review which will help to update our knowledge in this area. Authors from Australia present a review describing the interactions between bone and prostate cancer cells in metastatic disease. This area has generated much interest and is something for which we should develop a full understanding, to optimise our treatments for this condition.

Quantitative immunohistochemical study of the innervation of the guinea-pig lower urinary tract

OBJECTIVE

To study the innervation of the different muscle systems of the guinea-pig lower urinary tract, using immunohistochemical and enzyme histochemical methods.

MATERIALS AND METHODS

Serial cryostat sections of both genders (four guinea-pigs each) were quantitatively analysed for cholinergic, adrenergic and peptidergic nerve fibre density using specific antibodies or enzyme histochemical labelling. Smooth muscle cell nuclei and varicosities or sectioned nerves were counted in detrusor, internal vesical sphincter (VS), ventral longitudinal musculature (VLM), and dorsal longitudinal musculature (DLM), and the ratios of nerves/nucleus (for detrusor, VLM and DLM) were evaluated statistically. The striated and the smooth external sphincter were examined qualitatively.

RESULTS

Detrusor, VS, VLM and DLM had significantly different innervation patterns. In detrusor muscle parasympathetic nerve fibres dominated, while the VS and the urethral muscles had a major sympathetic nerve supply. Neuropeptide Y-positive nerve fibres were abundant in all of the muscles.

CONCLUSIONS

Smooth muscles of the lower urinary tract of the guinea-pig are distinct muscular units with distinct innervation patterns. Although there are no corresponding studies in humans the general innervation seems to be equivalent in human and guinea-pig, qualifying the guinea-pig for comparative urological studies.

Pharmacology of the lower urinary tract

The functions of the lower urinary tract, to store and periodically release urine, are dependent on the activity of smooth and striated muscles in the urinary bladder, urethra, and external urethral sphincter. This activity is in turn controlled by neural circuits in the brain, spinal cord, and peripheral ganglia. Various neurotransmitters, including acetylcholine, norepinephrine, dopamine, serotonin, excitatory and inhibitory amino acids, adenosine triphosphate, nitric oxide, and neuropeptides, have been implicated in the neural regulation of the lower urinary tract. Injuries or diseases of the nervous system, as well as drugs and disorders of the peripheral organs, can produce voiding dysfunctions such as urinary frequency, urgency, and incontinence or inefficient voiding and urinary retention. This chapter will review recent advances in our understanding of the pathophysiology of voiding disorders and the targets for drug therapy.

Laboratory confirmation of clinical heart allograft preservation variability

BACKGROUND

Previously, we reported survival differences from the national heart transplant registry favoring centers that used intracellular organ preservation solutions. To eliminate center selection bias, we tested some of these solutions in a biventricular working rat heart model to determine their relative efficacy.

METHODS

Using 103 Sprague-Dawley rat hearts perfused with modified Krebs-Henseleit buffer, both ventricles functioned with adjustable independent preload and afterload and their pressure-length loops generated load-insensitive measurements of cardiac performance. After 15 minutes of stable function, each heart sustained 180 minutes of cold (4 degrees C) ischemia after a 5-minute perfusion by University of Missouri (UMC), Plegisol, Collins, University of Wisconsin, Custodiol, or Roe solutions. Eighty-two hearts were reperfused and the remainder were used for ATP analyses.

RESULTS

Although the extracellular solution Plegisol showed good recovery of traditional hemodynamic values, including developed pressure and cardiac output, intracellular solutions like Roe had superior preservation of load-insensitive indices such as preload recruitable stroke work: Roe (intracellular) 103%+/-13%; Custodiol (intracellular) 96%+/-9%; UW (intracellular) 69%+/-12%; Collins (intracellular) 68%+/-9%; Plegisol (extracellular) 68%+/-7%; and University of Missouri (extracellular) 56%+/-10% (p = 0.04). Furthermore, recovery with intracellular solutions tended to be gradual but more progressive after ischemia in contrast to an early plateau shown by extracellular (p < 0.001). Right ventricular recovery and ATP measurements were similar between groups.

CONCLUSIONS

These data support the superiority of certain intracellular preservation solutions and provide evidence that optimal heart organ protection may be difficult to judge clinically using hemodynamic values routinely available to the heart transplant surgeon. Care should be taken to verify the performance of some solutions used in heart organ transplantation.