Niels Haugaard

The Functional Effect of Mild Outlet Obstruction on the Rabbit Urinary Bladder

Bladder outlet obstruction has been the subject of numerous studies. In previous studies on severe obstruction, the initial response of the bladder has been to produce an acute overdistension of the bladder resulting in severe tissue damage and functional disorders. This is quite different from the slow onset of outlet obstruction seen in association with benign prostatic hypertrophy (BPH). The present study describes the functional effect of mild outlet obstruction created in a rabbit model, and compares it to a previously described model of severe obstruction. Mild bladder outlet obstruction was created by placing a silicon sleeve (inner circumference 30 mm.) around the bladder neck of mature male NZW rabbits. Individual groups of rabbits were studied at one, seven, and 14 days following the creation of the outlet obstruction. The following studies were performed on each group of rabbits: in vivo and in vitro cystometry, field stimulation and cholinergic stimulation using the in vitro whole bladder model. In addition, the tissue concentration of ATP (adenosine triphosphate) and CP (creatine phosphate) and the muscarinic receptor density were determined. The obstructed bladders showed no significant cystometric difference at one day, but revealed a marked decrease of compliance and capacity at one and two weeks. Unlike the response to severe outlet obstruction, there was no initial acute overdistension of the bladder wall. Although the ability of the obstructed bladders to generate intravesical pressure in response to both field stimulation and bethanechol did not decrease, the ability of both forms of stimulation to empty the obstructed bladders was markedly impaired. The response to field stimulation was reduced to a significantly greater extent than the response to bethanechol, indicating neuronal damage. The muscarinic receptor number per bladder was increased above control at all time periods. The intracellular concentration of ATP and CP in the obstructed bladders was similar to that of control. Our present model of mild obstruction was not accompanied by a massive increase in tissue mass nor was there an overdistension of the detrusor; thus, this model would be a more suitable model for the study of clinical outlet obstruction.

Stimulation of glucose utilization by thioctic acid in rat diaphragm incubated in vitro

Abstract In rat diaphragm incubated in vitro thioctic acid increased the utilization of glucose. Time studies showed that, in contrast to the stimulatory effect of insulin on glucose uptake, the action of thioctic acid became apparent only after prolonged incubation. Thioctic acid did not interfere with the action of insulin and its effect was additive to that of insulin.

The role of sulfhydryl groups in oxidative phosphorylation and ion transport by rat liver mitochondria

Abstract The influence of the sulfhydryl reagent 5,5′-dithio-bis-(2-nitrobenzoic acid) (DNTB) on metabolism of liver mitochondria was studied under different experimental conditions. 1. 1. DTNB prevented the stimulation of respiration produced by ADP and inorganic phosphate in the presence of glutamate or succinate but had little effect on 2,4-dinitrophenol-stimulated respiration. 2. 2. The formation of ATP from ADP and phosphate was depressed by DTNB. The inhibition could be reversed by dithiothreitol. 3. 3. The increase in mitochondrial oxygen uptake produced by calcium and phosphate was depressed by DTNB. 4. 4. The uptake of calcium by mitochondria in the presence of ATP and glumate was only partially inhibited by DTNB. In contrast, the stimulatory effect of inorganic phosphate on calcium transport was completely prevented. 5. 5. In the presence of glutamate and no added ATP the uptake of calcium was associated with an entrance of phosphate. DTNB almost abolished the uptake of phosphate and inhibited calcium uptake by about 60%. The decrease in calcium uptake produced by DTNB was equal, mole for mole, to the decrease in phosphate uptake. 6. 6. DTNB completely prevented the extrusion of calcium exhibited by calcium-loaded mitochondria incubated in the presence of inorganic phosphate and a low concentration of magnesium. 7. 7. N-Ethylmaleimide had effects similar to DTNB but in addition severely inhibited 2,4-dinitrophenol-stimulated respiration with glutamate as substrate. 8. 8. It was concluded that a reactive site involving a sulfhydryl group is intimately involved in either the entrance of inorganic phosphate into the mitochondrion or in the formation of a phosphorylated intermediate essential for oxidative phosphorylation and ion transport.

Effects of Outlet Obstruction on Glucose Metabolism of the Rabbit Urinary Bladder

Bladder outlet obstruction has been shown to cause detrusor contractile dysfunction. To determine if alterations in bladder metabolism may in part underlie these functional defects, we investigated the effects of mild outlet obstruction on the glucose metabolism of the rabbit urinary bladder. Mild outlet obstruction was created in mature male rabbits by the surgical placement of a silicon sleeve around the bladder neck. Two weeks after surgery, the in vitro ability of the obstructed bladder tissues to metabolize glucose was compared to that of the controls. The results can be summarized as follows: 1) The bladder wet weight increased 2.3-fold following two weeks of obstruction. 2) Obstructed bladder tissues had a reduced glucose consumption as compared to the controls. 3) CO2 generation was significantly reduced by 31% in obstructed bladder tissues whereas lactate formation increased significantly by 22%. 4) Tissue concentrations of ATP, creatine phosphate, and glycogen before incubation showed no significant differences between control and obstructed bladder tissues. In summary, bladder tissues following two weeks obstruction showed a decrease in aerobic metabolism and an increase in anaerobic metabolism. Previous studies have indicated that the ability of the bladder to maintain a contraction and empty may be directly related to aerobic metabolism. Therefore, the decrease in aerobic metabolism (even in the presence of increased anaerobic metabolism) may in part explain the decreased ability of the obstructed bladder to empty.

The effect of phosphoenolypyruvate on calcium transport by mitochondria

Abstract Phosphoenolpyruvate was found to inhibit net uptake of Ca 2+ by rat heart and liver mitochondria. The main action of phosphoenolpyruvate is to increase the rate of efflux of mitochondrial Ca 2+ . The effect of phosphoenolpyruvate on mitochondrial Ca 2+ transport is antagonized by ATP and by atractylate and is observed when mitochondria are respiring in the presence of NAD-linked subtrates such as glutamate and pyruvate plus malate. In liver mitochondria phosphoenolpyruvate is also effective in the presence of succinate but not when rotenone is added. Glycolytic intermdiates other than phosphoenolpyruvate had little effect on mitochondrial Ca 2+ transport.

Effect of Partial Obstruction of the Rabbit Urinary Bladder on Malate Dehydrogenase and Citrate Synthase Activity

Previous studies have demonstrated that partial outlet obstruction in rabbits induced a significant decrease in oxidative metabolism in urinary bladder smooth muscle. The current experiments were designed to determine whether the decreased oxidative metabolism of obstructed bladder tissue is associated with alterations in the activities of specific mitochondrial enzymes. The activities of two important enzymes in the tricarboxylic acid cycle, malate dehydrogenase and citrate synthase, were measured in samples of bladder body and base from normal bladders and in bladders from rabbits in which partial outlet obstruction had been produced seven days prior to the experiments. The results can be summarized as follows: malate dehydrogenase activity was similar in bladder body and base isolated from control rabbits; and decreased by approximately 40% in both segments of the bladder isolated from obstructed rabbits. In contrast to malate dehydrogenase, citrate synthase activity was significantly higher in the bladder body than in the base of normal rabbits. Outlet obstruction caused about a 50% decrease in activity of this enzyme in the bladder body, but had no significant effect on citrate synthase activity of the bladder base. These findings demonstrate that the deficiency in bladder function following partial outlet obstruction is associated with a marked decrease in the activities of two essential enzymes in oxidative metabolism: malate dehydrogenase and citrate synthase. This decrease in enzyme activity is consistent with the previously observed decrease in oxidative metabolism and would be expected to lead to an inability of the tissue to supply sufficient metabolic energy for proper contractile function.

Bladder Function in Experimental Outlet Obstruction: Pharmacologic Responses to Alterations in Innervation, Energetics, Calcium Mobilization, and Genetics

The two functions of the urinary bladder is to store urine at low intravesical pressures, and to periodically expel the urine through a coordinated contraction of the bladder and relaxation of the urethra. To a large extent, urinary bladder function depends upon the underlying structure of the organ as a whole, particularly on the inter-relationships among the smooth muscle, connective tissue, and neuronal elements. An alteration in the ratio of connective tissue to smooth muscle, for example, can significantly alter compliance and functional capacity, structurally impairing the bladders ability to empty efficiently and fully. Thus, a change in structural compartmentation can affect bladder function independent of autonomic receptor density, response to receptor stimulation, and the contractile capabilities of the smooth muscle elements. Similarly, a selective alteration in either the afferent or efferent innervation of the bladder or urethra can induce significant alterations in the structural interrelationships between smooth muscle and connective elements. In addition, the bladder responds rapidly to alterations in urine volume and urethral resistance with marked changes in bladder and urethral structure and function, and these changes are under the controls of specific genes that are known to control cellular growth, hypertrophy, and hyperplasia. A knowledge of the mechanisms that control the response to specific forms of stress may lead to novel therapies for specific disease states.

COMPARATIVE RESPONSE OF RABBIT BLADDER SMOOTH MUSCLE AND MUCOSA TO ANOXIA

Recent studies indicate that the mucosa of the urinary bladder plays a major role in the maintenance of normal bladder function. Previous studies have demonstrated that rabbit bladder mucosa has higher rates of basal glycolysis and oxidative phosphorylation than that of bladder smooth muscle. The current study compares the response of rabbit bladder mucosa and smooth muscle compartments to anoxia. The results demonstrate that the rate of high energy phosphate degradation of the mucosa is significantly greater than the rate of high energy phosphate degradation of the smooth muscle. The implication is that the mucosa would be significantly more sensitive to ischemia than the smooth muscle of the bladder. This hypothesis may be extremely relevant to conditions such as interstitial cystitis and recurrent urinary bladder infections, in which ischemia has been implicated in their etiology.

Effects of Dichloroacetate on Brain Pyruvate Dehydrogenase

Abstract: The action of dichloroacetate (DCA) on pyruvate dehydrogenase (PDH) activity of rat brain has been studied in vitro and in vivo. In a crude brain mitochondrial fraction, DCA inhibits PDH kinase and in rat brain slices this compound increases PDH activity and stimulates glucose oxidation. In the whole animal, intraperitoneal injection of DCA causes activation of brain PDH, indicating that this inhibitor crosses the blood‐brain barrier. The same treatment with DCA also produced a large increase in heart PDH activity. Further studies of the effects of DCA on the CNS should lead to results of considerable importance.

Actions of lithium ions and insulin on glucose utilization, glycogen synthesis and glycogen synthase in the isolated rat diaphragm☆

Abstract The effects of lithium ions and insulin on carbohydrate metabolism of the isolated rat diaphragm were studied and compared. Like insulin, lithium ions caused a conversion of glycogen synthase D to the more active I form of the enzyme. Maximal activation of the enzyme was produced by about 5 mM LiCl. Lithium ions markedly increased glucose utilization and glycogen synthesis by the diaphragm, but the action of this ion appears to be exerted by a mechanism different from that of insulin, since the effects of maximal concentrations of the two agents are additive. In their action on glucose metabolism, lithium ions had a unique ability to direct the glucose taken up by the cell toward glycogen. Insulin and lithium ions had opposite effects on the tissue content of glucose 6-phosphate; insulin increased the tissue level of this metabolite, whereas lithium ions decreased it. ATP and creatine phosphate concentrations were not affected by insulin or lithium ions. The effects of lithium ions on carbohydrate metabolism are exerted at relatively low concentrations of Li, and our results indicate that significant alterations of carbohydrate metabolism may occur when therapeutic or toxic amounts of lithium salts are ingested by man.