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Biomedical subjects

H M Snyder

Publications and source records attributed to H M Snyder.

At least 91 records · Page 5Linked to original sources
PubMed1992

Variations in practice among urologists and nephrologists treating children with vesicoureteral reflux.

To analyze the current management recommendations among physicians treating children with vesicoureteral reflux, the American Urological Association Reflux Practice Guidelines Panel surveyed 100 pediatric urologists, 100 general urologists and 100 pediatric nephrologists by questionnaire, and received a 60% response. In the evaluation of a 4-year-old girl with bilateral grade 2 reflux general urologists were more likely than the other 2 groups to recommend cystoscopy and urethral dilation. At followup nuclear cystography was recommended by 76% of pediatric urologists, 48% of general urologists and 71% of pediatric nephrologists, while the latter 2 groups were less likely to recommend any subsequent upper tract evaluation. Pediatric urologists were significantly more likely to recommend antireflux surgery if the child had 1 breakthrough febrile urinary tract infection, poor compliance with medical management or persistent reflux at age 11 years. In a 6-year-old girl with unilateral grade 4 reflux and detrusor instability 44% of pediatric urologists recommended antimicrobial prophylaxis and anticholinergic therapy compared to 12% of general urologists and 6% of pediatric nephrologists. Antireflux surgery was recommended by 29% of pediatric urologists, 60% of general urologists and 59% of pediatric nephrologists. In older girls with persistent grade 2 or 3 reflux pediatric urologists were much more likely to recommend antireflux surgery. In contrast, they were less likely to recommend surgery in young girls and boys with newly diagnosed grade 4 reflux. These data demonstrate significant differences in therapeutic recommendations among pediatric urologists, general urologists and pediatric nephrologists, and suggest the need for outcomes research to determine the optimal management of children with vesicoureteral reflux.

Child↗
PubMed1992

Managing apparent ureteropelvic junction obstruction in the newborn.

A total of 97 newborns with apparent ureteropelvic junction obstruction was evaluated from mid 1984 to 1989. Evaluation and management are described. Of these patients 39 with an affected kidney showing good initial differential function (greater than 35%) by diethylenetriaminepentaacetic acid scan and 2 showing diminished function (less than 35%) were followed nonoperatively. Six patients (15%) eventually required pyeloplasty for diminishing function (4), urinary tract infections (1) or symptoms of colic (1). The 4 patients with diminishing function improved after pyeloplasty to at least the initial level. A total of 12 patients with good initial function (greater than 35%) of the affected kidney underwent early pyeloplasty (within 6 weeks of diagnosis). They were compared to the similar group of patients managed nonoperatively and followed by sequential renal scans. Eventual changes in percentage differential function in the nonoperative and early surgery groups were +2.8% and +4.1%, respectively. Changes in extraction factor were +0.8% (nonoperative group) and +0.9% (surgery group). No statistically significant difference was found. In the kidney with apparent ureteropelvic junction obstruction and good function, an initial nonoperative approach with sequential renal scan followup and pyeloplasty as needed appears to be reasonable and has resulted in no permanent loss of function.

Follow-Up Studies↗
PubMed1992

Meatal advancement and glanuloplasty hypospadias repair after 1,000 cases: avoidance of meatal stenosis and regression.

We first described the meatal advancement and glanuloplasty (MAGPI) procedure in 1981 as a technique to repair distal hypospadias. During the last 10 years our experience has increased to more than 1,000 cases. Case selection is critical to surgical outcome. Excessively thin or rigid ventral parameatal skin, or a meatus that is too proximal or too wide must be avoided. To prevent the ventral meatal wall from falling back and leaving a retrusive meatus, the glans wrap to support the advanced ventral urethral wall requires a solid approximation of glans tissue in 2 layers. Meatal stenosis may be avoided by an adequately deep dorsal Heineke-Mikulicz tissue rearrangement, making the incision from within the urethral meatus distally into the glanular urethral groove. The MAGPI procedure is routinely performed on an outpatient basis without urinary diversion. A review of our experience with 1,111 cases during a 12-year period reveals that a secondary procedure was required in only 1.2%. The overall success rate with the MAGPI procedure suggests that it should continue to be an important operation in the reconstruction of distal hypospadias.

Follow-Up Studies↗
PubMed1992

cAMP-dependent protein kinase mediates hydrosmotic effect of vasopressin in collecting duct.

The role of adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase A (PKA) in mediating the hydrosmotic effect of vasopressin in in vitro microperfused rabbit cortical collecting ducts (CCDs) was examined. We measured PKA substrate phosphorylation and water permeability [hydraulic conductivity (Lp) = 10(-7) cm.atm-1.s-1], stimulated by substituted cAMP analogues selective for a unique cAMP binding site (site A or B) on PKA regulatory subunit (R). Synergy between site A- and site B-selective analogues suggests involvement of PKA, because both sites must be occupied for R to dissociate from the catalytic subunit (C), allowing phosphorylation to proceed. As single agents, the site B-selective analogues 8-(4-chlorophenylthio)-cAMP (8-CPT) and 8-thiomethyl-cAMP (8-SCH3) were at least two orders of magnitude more potent than the site A-selective analogues N6-monobutyryl-cAMP (N6-mono) or N6-benzoyl-cAMP (N6-benz). Combinations of subthreshold concentrations of two site A analogues (N6-mono+N6-benz) or two site B-selective analogues (8-CPT + 8-SCH3) failed to significantly increase protein phosphorylation or water permeability. In contrast, combination of a site A plus site B analogue synergistically stimulated both protein phosphorylation and Lp. Rp-cAMPS, an inhibitor of cAMP binding to PKA, reduced both vasopressin (41% inhibition)- and cAMP (56% inhibition)-stimulated water permeability. H-89 (50 microM), an inhibitor of PKA kinase activity, also blocked cAMP-stimulated water permeability (90% inhibition). These findings suggest that vasopressin-induced water permeability in the rabbit CCD is mediated by PKA.

Animals↗
PubMed1991

To circumcise or not.

The link to urinary tract infection during infancy has renewed the neonatal circumcision debate, with all of its emotional overtones. Proponents maintain that the intact prepuce invites bacterial colonization, and this in turn can lead to permanent renal damage. Opponents cite disadvantages and risks of the procedure. An effort is made to separate facts from assumptions.

Acquired Immunodeficiency Syndrome↗
PubMed1991

Early postnatal testicular maldevelopment in cryptorchidism.

It has been previously postulated that many cases of cryptorchidism are manifestations of a forme fruste of hypogonadotropic hypogonadism. In support of this theory the earliest postnatal histological abnormality in cryptorchid testes demonstrated by this morphometric study of semithin microscopic sections of testicular biopsies was hypoplasia of the Leydig cells, which was obvious from the first month of life. The second abnormality, defective transformation of gonocytes into adult dark spermatogonia, was significant from early in life. No reduction in the mean number of germ cells was detected in the first 7 months of life. The abnormal persistence of the untransformed gonocytes resulted in a total germ cell count that was similar to normal controls until the seventh month, when secondary degeneration of untransformed gonocytes led to a decrease in the total germ cell count. These findings are compatible with the hypothesis that the blunted neonatal surge of gonadotropins previously demonstrated in cryptorchid boys triggers a cascade of hormonal and secondary histological abnormalities that may culminate in a reduced fertility potential in adults. Early replacement hormonal therapy deserves further investigation as a rational approach to the treatment of germ cell maldevelopment and reduced fertility potential associated with cryptorchidism.

Biopsy↗
PubMed1991

Evidence in favor of the mechanical (intrauterine torsion) theory over the endocrinopathy (cryptorchidism) theory in the pathogenesis of testicular agenesis.

There are 2 competing theories regarding the pathogenesis of testicular agenesis--the endocrinopathy/cryptorchidism and the mechanical/intrauterine torsion theories. We compare the number of Leydig cells, total number of germ cells and the transformation of adult dark spermatogonia into primary spermatocytes in semithin sections of testicular biopsies from 59 contralateral descended testes of patients with testicular agenesis with those in the contralateral descended testes from 250 patients with unilateral cryptorchidism. The contralateral descended testes from boys with testicular agenesis demonstrated higher numbers of Leydig cells, higher numbers of total germ cells and a higher rate of transformation of adult dark spermatogonia into primary spermatocytes than did the contralateral descended testes from the patients with unilateral cryptorchidism. These findings favor the mechanical/intrauterine torsion theory over the endocrinopathy/cryptorchidism theory in the pathogenesis of testicular agenesis.

Biopsy↗
PubMed1991

The MAGPI hypospadias repair in 1111 patients.

The meatal advancement and glanduloplasty (MAGPI) procedure was first described in 1981 for the repair of distal hypospadias. In the past decade, our experience has grown to more than 1000 procedures. An excellent surgical result requires careful case selection, avoiding cases with thin or rigid ventral parameatal skin or a meatus too proximal or too wide. The glans wrap to support the advanced ventral urethral wall requires a solid tissue approximation in two layers to prevent a retrusive meatus. Meatal stenosis can be avoided by assuring an adequate dorsal Heineke-Mikulicz tissue rearrangement and making an incision from within the urethral meatus well distally into the urethral groove. The MAGPI procedure routinely is performed on an outpatient basis without any urinary diversion. Our experience in 1111 cases during 12 years has required a second procedure in 1.2% of cases. The overall success rate with the MAGPI procedure suggests that it should continue to be used in the repair of distal hypospadias.

Follow-Up Studies↗
PubMed1991

Clinical and pathologic spectrum of 46,XY gonadal dysgenesis: its relevance to the understanding of sex differentiation.

The condition termed "46,XY gonadal dysgenesis" is characterized by a 46,XY karyotype and incomplete testicular determination. It is likely the result of a mutation in the gene for the testicular determination factor or in another gene involved in the early stages of testicular differentiation. In view of the present interest in the identification of gene(s) initiating the differentiation of the embryonic gonads into testes, we have reviewed the phenotype of 15 patients with 46,XY gonadal dysgenesis to use this information for future molecular studies. Seven patients presented a complete form, 46,XY pure gonadal dysgenesis, including streak gonads, normal Müllerian structures, and normal female external genitalia. The structure of the streak gonads in these patients presented some variation. Eight patients presented an incomplete form, 46,XY partial gonadal dysgenesis, with ambiguous external genitalia and partial development of Müllerian and Wolffian structures. Among them, 3 had bilateral dysgenetic testes, and 4 had a streak gonad on one side with a contralateral dysgenetic testis. The streak gonads showed ovarian stroma with occasional primitive sex cords devoid of germ cells. However, a primordial follicle was observed in 1 streak gonad. The dysgenetic testes showed disorganized seminiferous tubules and ovarian stroma. In some patients, the ovarian stroma was intermixed with testicular tissue, while in others, distinct ovarian and testicular portions were present. In 1 patient, the dysgenetic testis contained a focus of well-differentiated ovarian tissue with primordial follicles. Our observations support the hypothesis that streak gonads in 46,XY pure gonadal dysgenesis arise from fetal ovaries and that dysgenetic testes in the partial form in 46,XY partial gonadal dysgenesis develop from ovotestis.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1991

Muscarinic receptor activation inhibits AVP-induced water flow in rabbit cortical collecting ducts.

We examined the effect of carbachol, an acetylcholine analogue, on hydraulic conductivity (Lp) response to 10 microU/ml arginine vasopressin (AVP) in rabbit cortical collecting duct (CCD). In CCDs in which water flow had been established with AVP, subsequent addition of carbachol caused Lp (X10(-7) cm.atm-1.s-1) to fall from 251 +/- 32 to 146 +/- 19. Carbachol washout resulted in recovery of Lp to 217 +/- 38. In CCDs in which water flow had been established using 10(-4) M 8-chlorophenylthioadenosine 3',5'-cyclic monophosphate (8-CPT-cAMP), addition of carbachol had no effect. These posttreatment studies suggest that carbachol's effects on modulating established water flow occur at a "pre-cAMP" step. With carbachol added first, AVP-induced Lp was reduced from 233 +/- 24 (controls) to 105 +/- 19 (carbachol-pretreated). Pretreatment with 10(-6) M atropine, a muscarinic receptor antagonist, totally reversed the inhibitory effect of carbachol, consistent with a receptor-mediated effect of carbachol. Carbachol pretreatment also inhibited 8-CPT-cAMP-induced Lp, indicating that carbachol's effects also occur at a "post-cAMP" step. Pretreatment with 10(-7) M staurosporine, a protein kinase C (PKC) inhibitor, reversed inhibitory effect of carbachol on AVP-induced Lp (193 +/- 26), suggesting that carbachol's effects are mediated by PKC. Intracellular calcium concentration [( Ca2+]i) was measured in fura-2-loaded CCDs. Carbachol also increased [Ca2+]i from 229 +/- 120 to 389 +/- 160 nM.(ABSTRACT TRUNCATED AT 250 WORDS)

Alkaloids↗
PubMed1991

Developmental aspects of bladder contractile function: sensitivity to extracellular calcium.

The urinary bladders of 1-day and 1-week-old rabbits generate higher intravesical pressures in response to bethanechol and field stimulation than bladders isolated from mature 8-week-old rabbits. Yet the density of cholinergic receptors in the rabbit bladder does not change with maturation (1 day to 8 weeks). In an effort to better understand the molecular mechanisms by which newborn rabbit bladders generate greater pressures than the bladders of adult rabbits, we studied the effect of maturation on the relationship between extracellular calcium and contraction. Our results showed quite clearly that (1) at physiologic concentrations of calcium (2.5 mumol/l), isolated bladder strips of 1-day- and 1-week-old rabbits contracted in response to bethanechol to 98% of their maximal tension as opposed to 68% for their 8-week-old counterparts, (2) the ED50 (for calcium) for the 1-day and 1-week bladders was 0.4 mmol/l whereas the ED50 for the adult bladder strips was 2.2 mmol/l, and (3) the neonatal bladders demonstrated a much greater sensitivity to diltiazem than the adult bladders. The contractile response to calcium of the neonatal bladders was significantly inhibited by 1 mumol/l diltiazem whereas the 8-week-old bladders showed no inhibition at this concentration. In a second series of experiments, the effect of extracellular calcium on concentration was correlated with the intracellular concentration of free calcium using the calcium fluoride FURA-2 and surface spectrofluorometry. These studies confirmed that the increased contractile response of the neonatal bladder strips to calcium or cholinergic agonists was associated with an increase in the maximal intracellular free calcium concentration.

Animals↗
PubMed1990

Low transurethral incision of single system intravesical ureteroceles in children.

Single system intravesical ureteroceles in children usually result in various degrees of hydroureteronephrosis requiring surgical intervention to provide drainage, decompression and preservation of renal function. Our experience with 7 symptomatic single system ureteroceles in 5 children managed by low transverse endoscopic ureterocele incision is reviewed. After endoscopic incision, hydroureteronephrosis decreased in all patients. Vesicoureteral reflux after incision was noted in only 1 kidney. The technique of short (2 to 3 mm.) low transverse ureterocele incision is recommended for the initial management of single system ureteroceles to relieve obstruction. Preservation of the flap valve ureteral antireflux mechanism is possible in most children. The technique is simply performed, can be safely done in the youngest child and, in many, obviates the need for a further operation.

Adolescent↗
PubMed1990

Ontogeny of bladder function in the rabbit.

Although numerous experimental studies have addressed urinary bladder innervation, physiology and pharmacology, little information is available concerning the ontogeny of bladder function. The present study describes the developmental aspects of bladder mass, bladder capacity, pressure development and emptying in white New Zealand rabbits one day of age through maturity (11 to 15 weeks of age). The following studies were performed: Cystometry, pressure generation, rate of pressure generation, and emptying responses to field stimulation, cholinergic and purinergic stimulation using the in vitro whole bladder model. The results of these studies can be summarized as follows: 1) body weight and bladder weight increased in proportion to each other, bladder capacity increase proportionally with development until eight weeks of age, then increased substantially greater than body and bladder weight between eight and 11 to 15 weeks of age; 2) the ability to empty is similar for all ages; 3) pressure responsiveness to field stimulation, bethanechol, and ATP is greater at one day? of age, intermediate at one week of age, and similar for the other age groups; 4) The response to ATP (purinergic transmitter) is of an equal magnitude to the cholinergic response at one day, and reduces rapidly to approximately 45% of the cholinergic response by four weeks. Desensitization of the bladders to ATP reduced the response to field stimulation in the one day bladders to a significantly greater degree than the other age groups. These functional results indicate a marked alteration in cholinergic and purinergic response between the one day and the four week old rabbit bladders, with the response of the one week old bladders in between. The responses of the four, eight, and 11 to 15 week bladders was similar for equal volumes even though the bladder mass increased over threefold. This indicates that the ability of the bladder to generate pressure (during development) is not directly related to bladder mass.

Adenosine Triphosphate↗
PubMed1990

Traumatic rupture of the corpus cavernosum: evaluation and management.

Rupture of the corpus cavernosum is a rare but probably under-reported entity. It truly represents a urological emergency and current recommendations are for early surgical intervention. We review 5 cases with evaluation, treatment and followup. Delays in treatment lead to long-term complications, such as erectile dysfunction and penile curvature.

Adult↗
PubMed1990

Preservation of the urethral plate in hypospadias repair: extended applications and further experience with the onlay island flap urethroplasty.

The onlay island flap urethroplasty, a variant of the transverse preputial (tubularized) island flap, was originally described for repair of anterior hypospadias. However, many cases of mid and proximal hypospadias have a well developed urethral plate and exhibit little or no chordee after release of skin tethering. Patients with this combination of findings are ideal candidates for onlay island flap urethroplasty regardless of initial meatal position. During the last 5 years the onlay island flap has been used for repair of mid to posterior hypospadias in 31 patients (38% of the cases). These are variants that formerly would have required more extensive urethroplasty. Because of the technical advantages of the onlay island flap this alteration in technique selection has resulted in fewer complications. When applied to mid and posterior hypospadias the onlay island flap maintained a significantly lower complication rate (10%) compared to other standard techniques. Preservation of the urethral plate in hypospadias repair is a principle with significant implications to an extended variety of hypospadias.

Humans↗
PubMed1990

Development factors in the contractile response of the rabbit bladder to both autonomic and non-autonomic agents.

Previous work in this laboratory has demonstrated that the bladders of 1-day-old and 1-week-old rabbits generate higher pressures in whole-bladder preparations than bladders from mature 8-week-old rabbits. In addition, the density of cholinergic receptors does not change during this maturation period. The present study was designed to determine if the increased responsiveness of the neonatal bladder was specific for cholinergic stimulation. Using bladder strips, we have demonstrated that the newborn bladders generated much greater tension in response to ATP, serotonin, histamine, and substance P. The response of the 1-day-old bladder smooth muscle to these contractile agents was at least double the response of the 8-week-old bladders. However, the response of all age groups to bethanechol was approximately the same, and the response to KCl was only 40% greater in the 1-day-old bladders as compared to the adult. These current studies indicate that the newborn bladder responds to a variety of nonadrenergic, noncholinergic agonists to a significantly higher degree than the adult bladder, and that maturation is accompanied by substantial changes in the pharmacology of the bladder.

Adenosine Triphosphate↗
PubMed1990

Effect of pregnancy on rabbit urinary bladder physiology. 1. Effects of extracellular calcium.

Recent advances in imaging technology have allowed for the diagnosis of many congenital urologic abnormalities through the use of antenatal ultrasonography. There is controversy in the literature as to whether antenatally detected dilatations of the urinary tract are always secondary to obstruction or if in select cases the dilatations are physiologic in nature and will spontaneously regress. Benign dilatations of the fetal urinary tract are postulated to be secondary to the increased fetal diuresis and a more compliant fetal urinary tract. No one has investigated the possibility that such dilatations might be a consequence of the hormonal changes seen with pregnancy. In this study we present evidence for a change in bladder function with pregnancy. A summary of our results shows that in the presence of bethanechol, strips from the urinary bladders of pregnant rabbits generate 50% less tension in response to calcium than those from nonpregnant rabbits. Such a suppression in smooth muscle function might also help explain the benign dilatations of the upper urinary tract which are seen frequently during pregnancy.

Animals↗