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Biomedical subjects

M H Weiss

Publications and source records attributed to M H Weiss.

At least 19 recordsLinked to original sources
PubMed1992

An in situ perfused guinea-pig eye model for blood-ocular transport studies: application to amino acids.

A technique for in situ vascular eye perfusion (VEP) in the guinea-pig has been developed for measurements of the blood-ocular transport kinetics of substrates under controlled conditions of arterial inflow. The blood-aqueous and blood-vitreous barriers remained intact to the vascular space marker [3H]dextran (MW 70 kDa) with the perfusion pressure maintained between 80 and 100 mmHg. Several 3H-, 14C- or 35S-labeled amino acids, and 3H- or 14C-labeled sucrose (extracellular space marker) were used to validate the VEP model for transport kinetic studies. Multiple time-point graphic analysis was used to estimate the compartmental unidirectional blood-ocular transport constants, K(in), within the 20 min period of the VEP experiment. Blood-to-aqueous humor K(in) values for [3H]serine, [14C]N-methyl-alpha-aminoisobutyric acid (MeAIB) and [3H] or ]14C]sucrose were 3.57 +/- 0.38, 1.21 +/- 0.13 and 1.13 +/- 0.17 microliters min-1 g-1, respectively. The respective blood-to-lens K(in) values for labeled serine, MeAIB and sucrose were 1.71 +/- 0.19, 0.09 +/- 0.03 and 0.03 +/- 0.002 microliters min-1 g-1. The uptake of newly secreted amino acids from the aqueous humor in the lens followed the order: [35S]methionine greater than [3H]serine greater than or equal to [35S]cysteine greater than or equal to [3H]alanine greater than [14C]cycloleucine greater than or equal to [14C]MeAIB greater than or equal to [3H] or [14C]sucrose. The data indicate lack of a rapid blood-to-lens uptake of two model amino acids defining the A and L amino acid carriers.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗
PubMed1992

Magnetic resonance imaging and pathological correlates of meningiomas.

We examined the relationships between specific magnetic resonance imaging features and certain gross and microscopic characteristics of meningiomas, including vascularity, gross texture (consistency), and venous sinus involvement. Magnetic resonance imaging scans, surgery reports, and the histopathological findings of tumors were examined retrospectively in 54 patients. Sinus involvement was accurately predicted on T1-weighted images in 9 of 10 cases (P = 0.001) and tumors with cystic changes in 3 of 3 cases. T1-weighted images were not useful for predicting vascularity unless actual flow voids could be visualized (five of six cases). There was no correlation between T1 signal intensity, tumor consistency, or histological findings. In tumors without detectable vascularity on T1-weighted images, hyperintensity relative to gray matter on T2-weighted images was correlated with increased vascularity (P = 0.004). Tumors with soft consistency (P = 0.007), cellular atypia, invasion, angioblastic, or melanocytic components were also hyperintense, compared with gray matter on T2-weighted images (P = 0.0266). Aggressive meningiomas were found to be more vascular (P = 0.045). No correlation was found between the degree of surrounding edema or contrast enhancement with histopathological findings, vascularity, or consistency.

Brain↗
PubMed1992

Surgery for recurrent and residual cholesteatoma.

One hundred twelve patients (116 ears) were treated for recurrent and residual cholesteatoma. A retrospective review revealed that 66% had undergone canal wall down mastoidectomy at the previous surgery. The surgical procedure at revision was selected on the basis of an intraoperative assessment of the extent of disease, and clinical prediction of eustachian tube function. The average period of follow-up was 3.4 years. Revision surgery was successful in providing the patient with a safe, dry ear in 105 (91%) of 116 cases. Surgical principles and hearing results are presented.

Adult↗
PubMed1991

Vasopressin uptake by hypothalamopituitary axis and pineal gland in guinea pigs.

The uptake of circulating arginine vasopressin (AVP) by the pituitary gland (anterior lobe), pineal gland, and hypothalamus (ventromedial part) was investigated in an isolated in situ perused brain of anesthetized guinea pig. Kinetic experiments revealed saturable AVP uptake in all studied regions with Km values of 0.79, 0.19, and 0.76 microM and maximum velocity values of 22, 2.1, and 1.6 pmol.min-1.g-1 for the pituitary gland, pineal gland, and hypothalamus, respectively. The nonsaturable components (diffusion constants) were not significantly different from zero. Peptide fragments, L-phenylalanine, and Bestatin (an aminopeptidase inhibitor) did not interfere with AVP uptake. However, uptake of AVP was strongly inhibited in the presence of the V1 antagonist [1-(beta-mercapto-beta-beta-cyclopentamethylenepropionic acid), 2-(O-methyl)tyrosine]AVP at 2.7 microM, and regional Ki values, assuming that the observed inhibitions were purely competitive, ranged between 0.32 and 2.23 microM. The V2 agonist 1-desamino-8-D-AVP at 2.7 microM produced only a weak inhibition of AVP uptake, and regional Ki values ranged between 9.56 and 21.3 microM. It is concluded that specific uptake mechanisms in the hypothalamopituitary axis and pineal gland are sensitive enough to detect blood-borne AVP under the physiological hormonal state. It is suggested that AVP binding in situ is primarily related to V1 receptors, which may be involved in mediating the central effects of this circulating peptide.

Animals↗
PubMed1991

Kinetics of circulating vasopressin uptake by choroid plexus.

Uptake of circulating arginine vasopressin (AVP) by choroid plexus was studied by means of the in situ brain perfusion technique in anesthetized guinea pig and by means of single-circulation paired-tracer dilution technique in isolated perfused sheep choroid plexus. Kinetic analysis revealed saturable AVP uptake with Michaelis constant (Km) values of 32 +/- 4 and 31 +/- 5 nM and maximal saturable influx rate (Vmax) of 0.45 +/- 0.06 and 12.1 +/- 0.67 pmol.min-1.g-1 in guinea pig and sheep choroid plexus, respectively. The peptide fragments AVP-(1-8) and [pGlu4,Cyt6]AVP-(4-9), the amino acids L-phenylalanine, L-tyrosine, and 2-aminobicyclo(2,2,1)heptane-2-carboxylic acid, and the aminopeptidase inhibitors Bestatin and bacitracin did not influence hormone kinetics. However, the V1 antagonist [(1-beta-mercapto-beta,beta-cyclo-pentamethylenepropionic acid)-O-methyl-Tyr2]AVP significantly inhibited AVP uptake with inhibitor constant (Ki) values of 0.19 +/- 0.03 (guinea pig) and 0.07 +/- 0.01 microM (sheep). The V2 agonist 1-desamino-8-D-AVP and pressinoic acid produced weak inhibitions only in guinea pig choroid plexus, and Ki/Km ratios indicated 220 and 310 times lower affinities than for AVP, respectively. It is suggested that the membrane mechanism responsible for AVP uptake in choroid plexus has a binding site with properties similar to those of V1 receptor.

Animals↗
PubMed1991

Choanal atresia and lymphedema.

The coexistence of bilateral bony choanal atresia and lower-extremity lymphedema was observed in a family with several consanguineous marriages. The combination of these two rare anomalies, in a hereditary form, has not been described before.

Abnormalities, Multiple↗
PubMed1991

Management of labyrinthine fistulas caused by cholesteatoma.

The surgical management of labyrinthine fistulas caused by cholesteatoma remains controversial. Forty cases (41 ears) of labyrinthine fistulas were reviewed. This represented 10% of our total series of cholesteatomas in adults and children (426 ears). Clinical presentation, extent of disease, results of fistula testing and audiometric studies, and radiographic findings were analyzed. A canal wall-down procedure was performed in all but one patient. Generally an attempt was made to completely remove the cholesteatoma, to graft the fistulous area, and to reconstruct the middle ear mechanism in one stage. The matrix was preserved in patients with large fistulas where the involved ear was the only hearing one, when the matrix was adherent to the underlying optic duct, and in selected elderly persons. Long-term followup did not reveal a significant difference in hearing, degree of vertigo, or incidence of recidivism when those patients in whom the matrix was removed were compared with those in whom the matrix was preserved. The importance of recognizing the presence of a labyrinthine fistula preoperatively is stressed, along with the need to be prepared for an unexpected fistula. Operative management is described.

Adolescent↗
PubMed1991

Treatment of unresectable meningiomas with the antiprogesterone agent mifepristone.

The possibility that meningioma growth may be related to female sex hormone levels is suggested by several lines of evidence. Meningiomas are twice as common in women as in men, have been observed to wax and wane with pregnancy, and are positively associated with breast cancer. A physiological explanation for these phenomena is provided by the finding of steroid hormone receptors in meningiomas. However, unlike breast cancer, meningiomas are much more commonly positive for progesterone receptors than for estrogen receptors. The authors initiated a study on long-term oral therapy of unresectable meningiomas with the antiprogesterone mifepristone (RU486). Fourteen patients received mifepristone in daily doses of 200 mg for periods ranging from 2 to 31+ months (greater than or equal to 6 months in 12 patients). Five patients have shown signs of objective response (reduced tumor measurement on computerized tomography scan or magnetic resonance image, or improved visual field examination). Three have also experienced subjective improvement (improved extraocular muscle function or relief from headache). The side effects of long-term mifepristone therapy have been mild. Fatigue was noted in 11 of the 14 patients. Other side effects included hot flashes in five patients, gynecomastia in three, partial alopecia in two, and cessation of menses in two. Long-term therapy with mifepristone is a new therapeutic option that may have efficacy in cases of unresectable benign meningioma.

Adult↗
PubMed1991

Sixth nerve schwannomas. Report of two cases.

Two cases of sixth cranial nerve schwannoma are presented with a review of four other cases from the literature. The clinical spectrum, neuroradiological findings, and surgical outcome of the six cases are discussed. There are two distinct clinical presentations for sixth cranial nerve schwannomas. Type I sixth nerve schwannomas present with sixth nerve palsy and diplopia and arise from the cavernous sinus. In contrast, type II sixth nerve schwannomas have a more severe presentation with obstructive hydrocephalus, raised intracranial pressure, sixth nerve palsy, and diplopia. This type arises along the course of the sixth cranial nerve in the prepontine area. Cavernous sinus involvement in either type may preclude total surgical excision and indicate an increase possibility for recurrence.

Abducens Nerve↗
PubMed1991

Compulsive polydipsia following meningioma resection: an epileptic phenomenon? Case report.

The authors report the case of an individual who developed compulsive polydipsia following resection of a left sphenoidal ridge meningioma. The episodic, stereotyped nature of his symptoms, response to treatment, and electroencephalographic and magnetic resonance imaging findings are all highly consistent with temporal lobe-onset epilepsy. The pathophysiology of this underrecognized phenomenon is discussed.

Adult↗
PubMed1991

Monostotic fibrous dysplasia of the clivus. Case report.

A case report of monostotic fibrous dysplasia of the clivus in a postadolescent woman is described. Although fibrous dysplasia of craniofacial structures is well documented, involvement of the clivus has not been reported. Diagnosis by clinical, radiographic, and histopathological features is detailed. Implications for the role of surgery and management are discussed.

Adult↗
PubMed1991

Recidivism in congenital cholesteatoma surgery.

Forty-four cases of congenital cholesteatoma in the pediatric age group have been treated surgically. There have been three residual cholesteatomas, which were localized to the anterior aspect of the malleus and were easily excised. Two cases of postero-superior retraction pockets developed post-operatively, and these were treated by conventional tympanomastoid surgery with excision of the retraction pocket and grafting. All five of the patients with recidivism have experienced no further difficulty.

Child, Preschool↗
PubMed1990

Lack of efficacy of megestrol acetate in the treatment of unresectable meningioma.

The detection of hormone receptors on meningiomas raises the possibility of hormonal manipulation as a form of therapy. Since progesterone receptors are found on meningiomas more frequently and in greater amounts than estrogen receptors, manipulation of progesterone levels would be most promising. A trial of the oral progesterone agonist megestrol acetate for the treatment of unresectable meningioma was therefore performed. Megestrol acetate was administered at a dose of 40 mg four times daily which could be escalated to 80 mg four times daily. Nine patients (six meningothelial, two fibrous, and one anaplastic meningiomas) were treated for 1 to 12 months. No tumor responses were seen. However three patients required discontinuation of therapy due to deteriorating vision within 2 1/2 months. The major systemic toxicity of megestrol acetate was weight gain with a median weight gain of 14 kg for patients treated for at least 6 months. Due to the lack of efficacy and the significant toxicity noted, megestrol acetate is not recommended for the treatment of meningioma. However clinical trials of progesterone antagonists would still be of interest.

Adult↗