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Biomedical subjects

M Akhtar

Publications and source records attributed to M Akhtar.

At least 559 records · Page 31Linked to original sources
PubMed1967

The transfer of hydrogen from C-24 to C-25 in ergosterol biosynthesis.

1. A convenient synthesis of 3-hydroxytrisnorlanost-8-en-24-al and its conversion into [24-(3)H]lanosterol and [26,27-(14)C(2)]lanosterol is described. 2. A method for the efficient incorporation of lanosterol into ergosterol by the whole cells of Saccharomyces cerevisiae is also described. 3. It is shown that in the biosynthesis of ergosterol from doubly labelled lanosterol the C-24 hydrogen atom of lanosterol is retained in ergosterol. 4. On the basis of unambiguous degradations it is shown that the C-alkylation step in ergosterol biosynthesis is accompanied by the migration of a hydrogen atom from C-24 to C-25. 5. The mechanism for the biosynthesis of the ergosterol side chain is presented. 6. Mechanisms of other C-alkylation reactions are also discussed.

Aldehydes↗
PubMed1967

The conversion of cholest-7-en-3beta-ol into cholesterol. General comments on the mechanism of the introduction of double bonds in enzymic reactions.

Convenient syntheses of 6beta-tritiated Delta(7)-cholestenol and 3alpha-tritiated Delta(7)-cholestene-3beta,5alpha-diol are described. It was shown that the conversion of 6beta-tritiated Delta(7)-cholestenol into cholesterol is accompanied by the complete retention of label. It was unambiguously established that the overall reaction leading to the introduction of the double bond in the 5,6-position in cholesterol occurs via a cis-elimination involving the 5alpha- and 6alpha-hydrogen atoms and that during this process the 6beta-hydrogen atom remains completely undisturbed. Metabolic studies with 3alpha-tritiated Delta(7)-cholestene-3beta,5alpha-diol revealed that under anaerobic conditions the compound is not converted into cholesterol. This observation, coupled with the previous work of Slaytor & Bloch (1965), is interpreted to exclude a hydroxylation-dehydration mechanism for the origin of the 5,6-double bond in cholesterol. It was also shown that under aerobic conditions 3alpha-tritiated Delta(7)-cholestene-3beta,5alpha-diol is efficiently converted into cholesterol and that this conversion occurs through the intermediacy of 7-dehydrocholesterol. Cumulative experimental evidence presented in this paper and elsewhere is used to suggest that the 5,6-double bond in cholesterol originates through an oxygen-dependent dehydrogenation process and a hypothetical mechanism for this and related reactions is outlined.

Journal Article↗
PubMedDate not supplied

Intracardiac rhabdomyosarcoma: transesophageal echocardiographic findings and diagnosis.

Transesophageal echocardiography (TEE) was performed on a 41-year-old woman who presented with a cerebrovascular accident. TEE confirmed the presence of a morphologically bizarre biatrial tumor with precarious, vigorous motion throughout the cardiac cycle. Surgical intervention was decided on, and the patient underwent cardiac surgery for tumor excision 16 hours after TEE. Intraoperative frozen section diagnosis was spindle cell sarcoma, and subsequent immunohistochemical analysis showed the tumor to be a rhabdomyosarcoma. The data are presented here, and the role of TEE to establish a preoperative diagnosis of intracardiac tumor is discussed.

Adult↗
PubMedDate not supplied

Effects of phenytoin on refractoriness and conduction in the human heart.

Using His bundle electrograms and the atrial (A2) and ventricular extrastimulus (V2) techniques, anterograde and retrograde refractory period studies were performed (in 9 and 12 patients, respectively) before and 10 min after intravenous infusion of phenytoin (DPH; mean plasma level, 17.3 micrograms/ml). DPH had no effect on the duration of the QRS complex or the H-V interval of the sinus beats; it had variable but insignificant effects on the sinus rates and the atrial, A-V nodal, and ventricular muscle refractoriness. With the use of the A2 technique, the effective refractory period (ERP) of the His-Purkinje system (HPS) could not be determined in any patient; the relative refractory period (RRP) of the HPS could be determined in 2/9 patients and shortened in both patients after DPH. With the use of the V2 technique, retrograde functional refractory period (FRP) and RRP of the HPS could be determined in all 12 patients and the retrograde ERP of the HPS in 7/12; DPH significantly shortened all these parameters (p less than 0.001, less than 0.001, and less than 0.005, respectively). Functional refractory period of the ventriculo-atrial conduction system (VACS) could be determined in 11/12 patients during control studies (the remaining one patient had complete ventriculo-atrial block). DPH significantly shortened the FRP of the VACS in those (4) patients (Group I) in whom it was determined primarily by the HPS (p less than 0.025), and had variable but insignificant effects on FRP of the VACS in the other seven patients (Group II) in whom it was determined almost exclusively by the A-V node. DPH significantly decreased the retrograde HPS conduction times of the premature impulses (V2H2 intervals) for the same coupling (V1V2) intervals (p less than 0.001). It is concluded that, in the human heart, DPH exerts its most important effects on the HPS where it significantly decreases refractoriness and enhances conduction of the premature impulses. This study also demonstrates that the V2 technique is far superior to the A2 technique for evaluating the effects of drugs on refractoriness and conduction in the HPS.

Adult↗
PubMedDate not supplied

Database Conference January 27-30, 2000, Washington D.C.--Do existing databases answer clinical questions about geriatric cardiovascular disease and stroke?

EXECUTIVE SUMMARY: Most randomized, controlled trials evaluating the effectiveness of pharmaceutical, surgical, and device interventions for the prevention and treatment of cardiovascular disease have excluded patients over 75 years of age. Consequently, the use of these therapies in the older population is based on extrapolation of safety and effectiveness data obtained from younger patients. However, there are many registries and observational databases that contain large amounts of data on patients 75 years of age and older, as well as on younger patients. Although conclusions from such data are limited, it is possible to define the characteristics of patients who did well and those who did poorly. The goal of this conference was to convene the principal investigators of these databases, and others in the field of geriatric cardiology, to address questions relating to the safety and effectiveness of treatment interventions for several cardiovascular conditions in the elderly. Seven committees discussed the following topics: (I) Risk Factor Modification in the Elderly; (II) Chronic Heart Failure; (III) Chronic Coronary Artery Disease: Role of Revascularization; (IV) Acute Myocardial Infarction; (V) Valve Surgery in the Elderly; (VI) Electrophysiology, Pacemaker, and Automatic Internal Cardioverter Defibrillators Databases; (VII) Carotid Endarterectomy in the Elderly. The chairs of these committees were asked to invite principal investigators of key databases in each of these areas to discuss and prepare a written statement concerning the available safety and efficacy data regarding interventions for these conditions and to identify and prioritize areas for future study. The ultimate goal is to stimulate further collaborative outcomes research in the elderly so as to place the treatment of cardiovascular disease on a more scientific basis.

Aged↗
PubMedDate not supplied

Malignant rhabdoid tumor of the kidney presenting as intraocular metastasis.

A newborn infant presented with intraocular tumor that was clinically diagnosed as retinoblastoma and treated by exenteration of the globe. Within a few weeks however, a large abdominal mass was noted, which was found to involve the left kidney and right lobe of liver. Pathologic evaluation of the intraocular mass as well as fine-needle aspiration biopsy of the abdominal mass revealed features of malignant rhabdoid tumor. To our knowledge this is the first case of malignant rhabdoid tumor of the kidney with such an unusual clinical presentation.

Biopsy, Needle↗
PubMedDate not supplied

Fine needle aspiration biopsy in the diagnosis of tuberculosis.

Bacteriologic data and aspiration smears obtained by fine needle aspiration (FNA) biopsy for a series of 39 cases of tuberculosis were reviewed. Based on the morphologic features of the aspiration smears, the cases were divided into two groups: 18 cases in which distinct epithelioid granulomas were present and 21 in which no granulomas were found but large amounts of necrotic debris with variable numbers of polymorphonuclear cells, histiocytes and lymphocytes were present. Material from the FNA biopsy specimen was submitted for culture and fluorescence studies in 34 cases (15 with and 19 without granulomas). In the first group, auramine-rhodamine staining of smears was positive in 4 of 15 cases and Mycobacterium tuberculosis was isolated in 12 of 15 cases. In the second group, auramine-rhodamine staining was positive in 9 of 19 cases and culture was positive for M. tuberculosis in 16 of 19 cases. The results indicate that studying FNA smears by light microscopy and bacteriologic culture is an effective way of diagnosing tuberculosis.

Adult↗
PubMedDate not supplied

Morphologic spectrum of hepatocellular carcinoma in fine needle aspiration biopsies.

The light microscopic features of fine needle aspiration smears from 52 primary hepatocellular carcinomas were reviewed. Cytologic grading of these tumors, which indicated three grade I, 29 grade II and 20 grade III carcinomas, was compatible with grading done by histologic examination. In addition to the general cellular characteristics, other cytologic features observed in the smears included bile (48% of the cases), large cytoplasmic vacuoles (23%), small cytoplasmic vacuoles (46%), eosinophilic cytoplasmic inclusions (8%), basophilic cytoplasmic inclusions (48%) and intranuclear cytoplasmic inclusions (71%). The significance of these features is briefly discussed.

Biopsy, Needle↗
PubMedDate not supplied

Role of fine needle aspiration biopsy in the diagnosis and management of malacoplakia.

A case of malacoplakia of the colon and retroperitoneum is presented. The diagnosis was made by both endoscopic biopsy and fine needle aspiration biopsy (FNAB). The response to therapy was monitored by sequential FNAB. The initial biopsy revealed large numbers of bacilli within the histiocytes; these bacilli were markedly reduced in number during successful therapy but reappeared in large numbers when the disease relapsed. It is suggested that FNAB may play a role in both the diagnosis and management of patients with malacoplakia.

Biopsy, Needle↗