Surgically induced urologic models in swine

The porcine urological system is similar anatomically and physiologically to that of humans. Swine have a true multirenculate, multipapillate kidney with a calyceal system like that of humans. The gross anatomic and histologic characteristics of the porcine and the human kidney are more similar than most other commonly used laboratory animals. The physiologic functions of the urinary system including urodynamic parameters are also similar to humans. Swine have been used extensively as models of urologic conditions in humans, most commonly in obstructive urologic syndromes. A large number of investigative procedures can be performed in one experiment both in acute and chronic models. Recently, a new technique of surgically induced antenatal lower urinary tract obstruction in swine has been developed.

Evaluation of renal function in normal and hydronephrotic kidneys in rats using gadolinium diethylenetetramine-pentaacetic acid enhanced dynamic magnetic resonance imaging

PURPOSE

Magnetic resonance imaging (MRI) is becoming established as a modality complementary to computerized tomography and ultrasound for evaluating kidney function. The evaluation of renal function during ureteral obstruction may be improved by contrast enhanced MRI. We evaluated dynamic changes in relative signal intensity in normal and hydronephrotic rat kidneys after intravenous injection of gadolinium (Gd) diethylenetetramine-pentaacetic acid (DTPA).

MATERIALS AND METHODS

Using Gd-DTPA enhanced dynamic MRI we evaluated 35, 1-year-old rats, including 10 with partial and complete unilateral ureteral obstruction, respectively, and 15 with sham operated nonobstructed kidneys. Partial obstruction was created in 2-day-old rats by embedding the left ureter into the psoas muscle. Complete obstruction was created 10 days before MRI by placing a ligature around the upper third of the left ureter. MRI was performed before and 0.1 to 60 minutes after and intravenous injection of Gd-DTPA. We calculated relative signal intensity per time interval in the renal cortex, medulla and pelvis.

RESULTS

Dynamic relative signal intensity patterns differed significantly among normal, and partially and completely obstructed kidneys. In normal kidneys signal intensity changes were divided into 3 phases after Gd-DTPA administration. During phase 1 rapid parenchymal uptake of Gd-DTPA within the initial minute after injection produced a rapid signal intensity decrease in the cortex, which achieved a minimum of 28% of pre-injection intensity. During phase 2 signal intensity decreased in the medulla and pelvis to a minimum of 18% and 22%, respectively, of pre-injection intensity within 5 minutes. During phase 3 significant relative signal intensity recovery began in the cortex at 7 minutes, and in the medulla and pelvis at 10 to 15 minutes, and lasted 30 to 60 minutes. In partially obstructed kidneys the 3 phases were significantly slower than in controls. In completely obstructed kidneys only phase 1 occurred within 60 minutes.

CONCLUSIONS

Gd-DTPA enhanced dynamic MRI provides useful information for distinguishing obstructed from nonobstructed and partially from completely obstructed kidneys.

Analysis of bladder related nerve cuff electrode recordings from preganglionic pelvic nerve and sacral roots in pigs

PURPOSE

Electrical stimulation of appropriate lower urinary tract (LUT) nerves may be used in bladder dysfunction to achieve continence and abolish hyper-reflexic detrusor contractions. It can also be used for consequent emptying of the bladder. To control the time course of the described functional phases, knowledge of bladder sensory information is needed. We investigated if the latter could be extracted from the LUT nerve activity.

MATERIALS AND METHODS

In acute experiments using 10 pigs, tripolar cuff electrodes were placed unilaterally around the pelvic nerve and the S3 and S2 roots. The cuff electrode signals, filling rate and the bladder and rectal pressures were recorded during slow and fast bladder fillings/emptyings.

RESULTS

Two pigs were excluded from the analysis because of no observed changes in the nerve signals in one animal, and because of electrical noise problems in the other animal. Fast bladder pressure increases resulted in a sudden pelvic nerve signal rise in 6 out of 7 pigs (3 out of 6 for the S3 nerve signal). Slow bladder pressure increase was reflected in the recorded nerve activity only in 3 out of 8 and in 3 out of 7 pigs for the pelvic and S3 cuff signals respectively. In 2 animals small spontaneous bladder contractions were clearly reflected in the pelvic nerve signal (contractions were observed only in 3 pigs). Except in one pig, there were no slow/fast bladder filling responses recorded in the S2 roots. It is shown that the recorded responses were afferent.

CONCLUSIONS

Cuff electrodes can be used to record bladder afferent information from the pelvic nerve and the sacral root S3 in pig. Pelvic nerve recordings were more selective than the sacral root recordings. Nerve activity increases were more distinct and repeatable during rapid bladder pressure changes and small spontaneous bladder contractions than during slow bladder fillings.

Fluid deprivation in enuresis--effect on urine output and plasma arginine vasopressin

Desmopressin responders tend to have a large volume of urine production at night, in contrast to desmopressin refractory patients who often produce normal volumes of urine. Controls and adolescent/adult primary monosymptomatic nocturnal enuretics were included in a study measuring urine volume and plasma vasopressin levels before and during a 24-hour water deprivation test. The results indicate a significantly higher urine production in desmopressin responders when compared with controls and non-responders. Before fluid deprivation, only the nocturnal polyuric patients showed a urine osmolality significantly lower than that of controls and desmopressin non-responders. A significant decrease in the clearance of osmols was evident in the desmopressin refractory group from day to night. All three groups showed a significant increase in plasma vasopressin during fluid deprivation, with polyuric, desmopressin-responding patients showing a lower increase that the non-responders and controls. Plasma vasopressin levels were normal in adolescent and adult enuretics regardless of their response to desmopressin. Moreover, response to fluid deprivation in both polyuric and enuretic patients resulted in a significant decrease in urine output from the first to the second night.

Definitions of subtypes of enuresis

Enuresis is a disease of complex pathogenicity. Most monosymptomatic bedwetters have either normal bladder function and capacity and large urine production at night-time, or slightly increased micturition frequency during the day, normal circadian rhythm and small bladder capacity at night-time. In some studies, patients who failed to become dry when using alarm treatment had normal bladder function and capacity with large urine production at night. This same group of patients showed an excellent response to desmopressin treatment. Recent studies have also looked at the possible relationship of natriuresis or calciuria in monosymptomatic enuresis. The molecular genetic aspects of enuresis are attracting increased attention. Studies have substantiated the involvement of numerous loci on certain chromosomes; in excess of 10 chromosomes are thought to be involved. Rare enuresis subtypes include night-time natriuretics with or without polyuria, calciuria and airway obstruction-induced bedwetting. The role of bladder dysfunction in monosymptomatic bedwetting remains undetermined.

Contralateral compensatory kidney growth in rats with partial unilateral ureteral obstruction monitored by magnetic resonance imaging

PURPOSE

We studied dynamic changes in total volume and renal vein blood flow in the kidneys contralateral to partial ureteral obstruction induced in newborn rats.

MATERIALS AND METHODS

Using magnetic resonance imaging we investigated changes in total kidney volume and renal vein blood flow in 20 rats with mild and 18 with severe partial ureteral obstruction that was induced on the left side 2 days after birth. A total of 15 sham operated control rats were also studied. Total kidney volume and renal vein blood flow were monitored sequentially every 2 to 6 weeks for a total of 24 weeks. Renal parenchymal volume measured in vivo by magnetic resonance imaging was compared with that measured in vitro at week 24.

RESULTS

Total volume and renal vein blood flow increased significantly in contralateral nonobstructed kidneys from week 14 and thereafter in rats with severe partial unilateral ureteral obstruction. At week 24 volume had increased by 22% and blood flow had increased by 25%. Volume and flow did not increase significantly in contralateral nonobstructed kidneys in rats with mild partial unilateral ureteral obstruction (p = 0.09). Before changes occurred in volume and blood flow in the contralateral nonobstructed kidneys, renal vein blood flow had decreased significantly from week 8 and thereafter in severely obstructed kidneys. In rats with mild partial unilateral ureteral obstruction renal vein blood flow decreased significantly in obstructed kidneys from week 18 and thereafter. Good correlation was noted between MRI in vivo and in vitro kidney volume measurements (r = 0.972, p <0.001).

CONCLUSIONS

A significant increase in total volume and renal vein blood flow in contralateral nonobstructed kidneys did not develop immediately after the onset of detectable functional deterioration in partially obstructed kidneys. Therefore, caution should be used when incorporating compensatory growth into surgical decision making.

Pad testing in incontinent women: a review

This article reviews the literature on pad-weighing tests used for objectifying and quantifying incontinence in urinary incontinent women. The patients wear pads weighed before and after the test period. A weight gain is taken as a measure of the amount of urine loss. The tests are in principle of two different types: short-term office tests and long-term home tests, and measure different aspects of urinary control and dysfunction. Both have an inherent large intra- and interindividual variability. Pad weight gains obtained from patients referred for incontinence and those from self-reported continent controls overlap to a certain degree, and it is not possible to identify distinct numerical cut-off values separating continence from incontinence. This suggests that incontinence is a complex condition in which the amount of leakage, other sources of weight gain, and differences in the individual patients' personal characteristics influence the identification and quantification of the problem. In spite of the shortcomings the pad tests remain a valuable tool for both the clinician and the researcher. The home pad tests are superior to the office tests in terms of authenticity, and should be performed with a concomitant systematic registration of the participant's voidings, fluid intake and episodes of incontinence.

Nocturia and polyuria in men referred with lower urinary tract symptoms, assessed using a 7-day frequency-volume chart

OBJECTIVES

To investigate if a 7-day frequency-volume (FV) chart could identify nocturia on a polyuric basis in patients with lower urinary tract symptoms (LUTS) suggestive of benign prostatic hyperplasia (BPH).

PATIENTS AND METHODS

The study included 23 patients (mean age 62.8 years, range 42-78) with LUTS who were referred for the evaluation of potential BPH and 11 men (control subjects, mean age 63.3 years, range 58-69); all completed a 7-day FV chart investigation as outpatients.

RESULTS

Nocturia was associated with nocturnal polyuria in 10 of 23 patients with LUTS; these 10 patients had a diminished diurnal variation of urine production, whereas 13 patients had a diurnal variation in urine production comparable with that in controls with no nocturia. The degree of nocturia correlated positively with nocturnal urine production but showed no relationship with sleep duration. The nocturnal polyuria in these patients was associated with a higher 24-h urine production and seemed at least partly to be caused by a higher fluid intake during daytime.

CONCLUSION

Nocturia on a polyuric basis can be detected by using a FV chart. In these patients, a 3-day FV chart would be sufficient to detect nocturia on a polyuric basis and seems therefore to be a valuable tool in evaluating patients with LUTS referred for potential BPH.

Obstructive nephropathy: an update of the experimental research

Ureteral obstruction (UO) is one of the most common problems confronting the urologist. Although large amounts of animal and clinical research have been done, the pathophysiologic mechanisms accompanying UO are not fully elucidated. Most of our knowledge on UO has been derived from experimental studies in a variety of animal models. Both antenatal and postnatal UO models have been developed mainly by ligation of the ureter or by burying the ureter into the psoas muscle. Most experimental studies have focused on short-term complete ureteral obstruction. The long-term effects of partial ureteral obstruction have been less intensively studied. It is now clear that obstructive nephropathy is not a simple result of mechanical impairment to urine flow but a complex syndrome resulting in alterations of both glomerular hemodynamics and tubular function caused by the interaction of a variety of vasoactive factors and cytokines that are activated in response to UO. Leukocyte infiltration appears to play an important role in obstructive nephropathy suggesting that UO also has an immunological component. Growth factors such as platelet-derived growth factor, transforming growth factor-beta, epidermal growth factor and insulin-like growth factor I may all play a role in the development and progression of fibrotic and sclerotic changes in the obstructed kidney. At present, the selection of patients with congenital hydronephrosis for operative treatment is controversial. Studies in animals and patients have shown that partial unilateral UO does not always cause a loss of renal function or progression in urinary tract dilation during long-term follow-up. The implications of UO continue to raise many questions and further work is necessary to achieve a better understanding of the pathogenesis in obstructive nephropathy.

Prevalent urinary incontinence as a correlate of pregnancy, vaginal childbirth, and obstetric techniques

OBJECTIVES

This study examined the association between pregnancy, vaginal childbirth and obstetric techniques, and the prevalence of urinary incontinence among adult women aged 20 to 59 years.

METHODS

A cross-sectional survey enrolled a random sample of 6240 women aged 20 to 59 years who were mailed a self-administered questionnaire focusing on urinary incontinence and other health variables. More than 75% of the women responded. The present analysis includes 4345 women who were not pregnant and did not experience a vaginal childbirth during 1994.

RESULTS

Multivariate prevalence odds ratios showed increases in relation to urinary incontinence during pregnancy, urinary incontinence immediately after a vaginal childbirth, and age of 30 years or more at the second vaginal childbirth. No multivariate associations were found for forceps delivery or vacuum extraction delivery, episiotomy, or perineal suturing.

CONCLUSION

Not only the process of childbirth itself but also processes during pregnancy seem to be strongly associated with prevalent urinary incontinence. Perineal suturing may be associated with prevalent urinary incontinence, whereas other obstetric techniques inspected do not seem to be so.

The efficacy of DDAVP is related to the circadian rhythm of urine output in patients with persisting nocturnal enuresis

OBJECTIVE

Desmopressin may be a useful treatment in some, but not all, patients with nocturnal enuresis. We have evaluated a relation between nocturnal urine output in patients with primary monosymptomatic nocturnal enuresis and the treatment response to synthetic vasopressin.

DESIGN

Adolescent or adult enuretics and normal subjects were enrolled in the study and admitted to hospital for a 24 hour investigation of the diurnal variation in urine output, plasma vasopressin (AVP) and plasma atrial natriuretic peptide (ANP). The enuretics were characterized prior to investigation as either 1-desamino-8-D-arginine vasopressin (DDAVP) responders or non-responders. During admission the fluid intake was restricted to 25 ml/kg per day.

PATIENTS

Twenty-four patients (15-37 years) with primary monosymptomatic nocturnal enuresis and 9 normal subjects (24-31 years).

MEASUREMENTS

Circulating levels of AVP, ANP, plasma electrolytes and plasma osmolality were measured (1400, 2000, 2300, 0200, 0500 and 0800 hours) together with urine volume, urine osmolality and urine electrolytes during daytime and nighttime. Tubular reabsorptive capacity for water, osmoles and creatinine were assessed as well as urinary and fractional excretion rates of sodium and potassium.

RESULTS

Controls and DDAVP non-responders had a significant decrease in urine output at night concomitant with a significant plasma AVP amplitude in peak/nadir values although both groups lacked a significant nocturnal increase in AVP. In contrast, in DDAVP responders there was no circadian variation in urine output and thus a nocturnal polyuria together with no oscillation in plasma AVP. The DDAVP responding group had a nocturnal urine production significantly larger than the two other groups. However, the mean 24 hour AVP levels were similar in all groups. The excessive urine production at night in DDAVP responders was accompanied by nocturnal natriuresis due to an increased fractional excretion of sodium. In contrast, nocturnal antidiuresis in controls and DDAVP non-responding enuretics coincided with diminished sodium excretion. Average ANP levels were elevated in both enuretic groups compared to normals, whereas a circadian variation was detected only in the latter.

CONCLUSION

It is concluded that DDAVP responsiveness is linked to the nocturnal urine production and that no pathophysiological role can be ascribed to AVP or ANP in DDAVP refractory adolescent and adult enuretics. Moreover, it is suggested that an abnormal tubular handling of sodium may contribute to the nocturnal polyuria seen in DDAVP responders.

In vivo measurement of T1 and T2 relaxivity in the kidney cortex of the pig--based on a two-compartment steady-state model

A two-compartment system for approximating five successive steady-state levels of gadopentetate dimeglumine (Gd-DTPA) concentration in pigs was developed. The method of calculating Gd-DTPA concentration was based on a simultaneous reference determination of 99mTc-DTPA. Experimental and theoretical results showed a steady state after 25 min. The nuclear magnetic resonance (NMR) relaxivities of Gd-DTPA were determined in vivo in pig kidneys during steady-state levels. T1 relaxivity (R1) and T2 relaxivity (R2) in the kidney cortex were found to be 1.1+/-0.03 and 2.0+/-0.2 (s(-1) mM(-1)), respectively. R1 and R2, in in vitro human plasma solutions at 25 degrees C were 5.3+/-0.02 and 5.8+/-0.06 s-1 mM-1 and at 37 degrees C 4.3+/-0.04 and 4.9+/-0.01 s(-1) mM(-1). Thus, the in vivo relaxivities were reduced 3.9 and 2.5 times for R1 and R2, respectively, compared to the in vitro relaxivities. This marked difference in relaxivities between tissue and plasma may be the result of the difference in steric relations. In plasma, the mobility and distribution of the Gd-DTPA complex are unrestricted, whereas they may be reduced in the tissues because of the close proximity to the cell wall, to the proteins and to other extracellular elements and compartments.

Experimental partial unilateral ureter obstruction. I. Pressure flow relationship in a rat model with mild and severe acute ureter obstruction

PURPOSE

To create an animal model with mild and severe partial unilateral ureter obstruction in young rats using a modified Ulm and Miller technique and to characterize the model by acute renal pelvic pressure measurements.

MATERIAL AND METHODS

During anesthesia the upper fourth (n = 15) or the upper two-thirds of the left ureter (n = 15) was embedded into the psoas muscle causing either a mild or severe partial obstruction. Sham-operated control rats were prepared in parallel (n = 20). The baseline pelvic pressure, the perfusion pelvic pressure (perfusion rates: 0.2 to 1.0 ml. per minute) and peristaltic waves were recorded after a resting period.

RESULTS

Mean baseline pelvic pressure and perfusion pelvic pressure were significantly higher in obstructed kidneys than in non-obstructed kidneys, and significantly higher in severely obstructed kidneys than in mildly obstructed kidneys (p < 0.05). A fair linear relationship existed between the increase in pelvic pressure and the increase in perfusion rates in all groups. In the severely obstructed kidneys, baseline pelvic pressure was 16.9 +/- 2.3 cm. H2O and the perfusion pelvic pressure increased significantly from 41.7 +/- 3.3 cm. H2O to 68.6 +/- 6.3 cm. H2O. The pelvic peristaltic amplitude increased significantly following the increase in perfusion rate and there was a significant difference in the amplitude between severely obstructed and non-obstructed kidneys when the perfusion rate exceeded 0.4 ml. per minute (p < 0.05).

CONCLUSION

Embedding either the upper fourth or the upper two-thirds of the ureter into the psoas muscle produced a mild or a severe partial obstruction. In the latter model a significant increase in pelvic pressure and amplitude was observed, indicating the existence of severe obstruction.

No relationship between subjective assessment of urinary incontinence and pad test weight gain in a random population sample of menopausal women

PURPOSE

We studied the association between urinary incontinence and pad weight gain during a 24-hour pad test in healthy menopausal women.

MATERIALS AND METHODS

Menopausal women 45 to 58 years old were randomly sampled from the national register. Information on self-reported urinary incontinence was collected at patient interview using a structured questionnaire. A 24-hour home pad test was performed and episodes of urinary incontinence during the pad test were noted.

RESULTS

A total of 144 women 45 to 57 years old (mean age 50) were included in the study. At the interview 99 subjects (69%) reported urinary continence and 45 (31%) reported incontinence. Of the continence group 78 women (80%) performed the pad test and the mean weight gain was 3.1 gm. (range 0 to 9). Of the incontinence group 38 women (84%) performed the pad test and the mean weight gain was 3.3 gm. (range 0 to 8, not significant). Of the 38 women in the incontinence group 16 reported 1 or more episodes of urinary incontinence, whereas the remaining 22 reported no incontinence during the pad test. There was no difference in pad weight gain between these 2 groups (mean gain 3.3 gm., range 0 to 8).

CONCLUSIONS

The subjective assessment of urinary incontinence was frequent but it was not associated with the objective findings of the 24-hour pad test.

Colorectal function in patients with spinal cord lesions

PURPOSE

This study was designed to describe the frequency and severity of colorectal problems among patients with spinal cord lesions and to determine whether these problems are associated with age, gender, time since the lesion, and level and severity of the lesion.

PATIENTS AND METHODS

A detailed questionnaire describing colorectal and bladder function was sent to all 589 members of The Danish Paraplegic Association; 424 responded (72 percent).

RESULTS

Only 19 percent felt a normal desire to defecate, whereas the remaining patients felt no desire to defecate (38 percent) or a combination of abdominal discomfort (37 percent) and headache, physical uneasiness, and perspiration (25 percent). Digital stimulation of the anal canal before defecation or digital evacuation of the rectum was used regularly by 65 percent of patients. Fecal incontinence was experienced by 75 percent of patients; however, most patients only had a few episodes of fecal incontinence each month (15 percent) or each year (56 percent). Overall, 39 percent of patients reported that colorectal dysfunction caused some or major restrictions on social activities or on their quality of life, and 30 percent regarded colorectal complaints to be worse than both bladder and sexual dysfunction. The severity of most symptoms was significantly correlated with the severity of the lesion, and the self-reported impact on social activities or quality of life was significantly more severe among women than men.

CONCLUSION

Colorectal dysfunction is very common among spinal cord-injured patients, often causing restriction on social activities and quality of life. Therefore, these problems deserve more attention in the treatment of spinal cord-injured patients.

Single dose imipramine reduces nocturnal urine output in patients with nocturnal enuresis and nocturnal polyuria

PURPOSE

We investigated the effect of imipramine on nocturnal urine output in patients with nocturnal enuresis.

MATERIALS AND METHODS

There were 15 monosymptomatic enuretic patients 15 to 37 years and 8 control subjects 25 to 32 years old. We measured nocturnal urine output, urine osmolality, creatinine clearance, osmolal clearance, free water clearance, excretion of solutes, fractional excretion of sodium, fractional excretion of potassium and plasma vasopressin with and without a single oral dose of imipramine (1 mg./kg. of body weight) taken at 8 p.m.

RESULTS

Baseline studies showed significantly larger and less concentrated nocturnal urine among enuretics compared with controls. We observed a marked antidiuretic effect of imipramine in 6 enuretics with severe nocturnal polyuria. The imipramine induced decrease in urine output was accompanied by reduced osmolal clearance. Approximately a third of the observed decrease in solute excretion was attributed to lower excretion of sodium and potassium. The remaining two-thirds were most likely caused by an increased tubular reabsorption of urea, which may be secondary to a sympathomimetic effect of imipramine tubules, possibly because of altered adrenal medullary function with an increase in proximal tubular sodium and water reabsorption. The resultant lower tubular flow rate facilitates tubular reabsorption of urea in the distal part of the nephron.

CONCLUSIONS

Imipramine has a vasopressin independent antidiuretic effect if nocturnal polyuria is present. The antidiuretic effect of imipramine can be attributed primarily to increased alpha-adrenergic stimulation in the proximal tubules with a secondary increased urea and water reabsorption more distally in the nephron.

Downregulation of aquaporin-2 parallels changes in renal water excretion in unilateral ureteral obstruction

In bilateral ureteral obstruction, both aquaporin-2 (AQP2) levels and urinary concentrating capacity are markedly reduced. However, the mechanisms involved in AQP2 downregulation are unknown. In rats with unilateral ureteral obstruction (UUO) the relative role of intrarenal and systemic factors can be evaluated. Semiquantitative immunoblotting revealed a marked decrease in AQP2 in obstructed kidneys to 23 +/- 7% (n = 9) of sham levels. This downregulation persisted 24 h after release of UUO. Furthermore, there was a significant but less extensive downregulation of AQP2 in the nonobstructed kidneys to 75 +/- 7% (n = 9) of sham levels. Consistent with impairment of collecting duct water reabsorption, free water clearance was greatly elevated in the obstructed kidneys (-2 +/- 1 microliter-min-1.kg-1, determined immediately after release) and only moderately elevated in nonobstructed kidneys (-44 +/- 5 microliters.min-1.kg-1) compared with sham-operated controls (-59 +/- 3 microliters.min-1.kg-1). Also AQP2 mRNA levels were reduced in obstructed kidneys. Immunocytochemistry confirmed the marked decrease in AQP2 expression in obstructed kidneys. In nonobstructed kidneys AQP2 was predominantly found in intracellular vesicles, which together with the reduced expression and elevated free water clearance strongly suggests a role of AQP2 in the observed compensatory diuresis from nonobstructed kidneys. The much lower AQP2 protein and mRNA levels in obstructed vs. nonobstructed kidneys are consistent with intrarenal factors playing a major role for downregulation of AQP2.