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Biomedical subjects

A A Mohammed

Publications and source records attributed to A A Mohammed.

9 recordsLinked to original sources
PubMed2005

Force-frequency relation in frog-ventricle is dependent on the direction of sodium/calcium exchange in diastole.

AIM: Force of contraction increases with stimulus-frequency in mammalian and amphibian hearts under control conditions. Here, we have analysed the mechanism of the force-frequency relation (FFR) in frog-ventricle. METHODS: Circular strips of frog-ventricle were subjected to field-stimulation with frequencies in the range 0.03-0.2 Hz and force recorded on a chart-recorder. In another protocol, varying rest-periods were imposed while the preparation beat steadily at 0.2 Hz and the effect of rest on post-rest beat amplitude was noted. RESULTS: Under control conditions, a positive FFR and a rest-induced decay of contraction amplitude (RID) were seen in the frequency range 0.03-0.2 Hz. With cadmium, nifedipine, nickel (40 micromol L(-1)), ryanodine and adrenaline (all drugs at 10 micromol L(-1) concentration, except nickel), the positive FFR and RID seen under control conditions persisted. When the bathing solution contained ouabain (10 micromol L(-1)) or low external sodium (40 mmol L(-1)), or high external calcium (5 mmol L(-1)), the FFR turned negative in the frequency range stated above and there were rest-induced potentiations (RIP). CONCLUSION: When the conditions favour a net leak of calcium in diastole from intracellular stores via the calcium-extrusive mode of sodium-calcium exchanger (NCX), FFR is positive. An increase in frequency lessens the diastolic interval and therefore the diastolic calcium leak, thereby augmenting force. On the other hand, interventions which favour the calcium-acquisitive mode of NCX during diastole, changed the pattern of RID to RIP and converted FFR from positive to negative. With net diastolic calcium uptake, there is better store-filling and therefore higher force at lower frequencies.

Animals↗
PubMed2000

Concordant expression of Hirschsprung's disease in monozygous twins.

A monozygous pair of twins with long segment Hirschsprung's disease born to non consanguineous parents is presented. Mother's history was uneventful. In the absence of prenatal and postnatal illness, the concordant lesions in this pair could be attributed to genetic factors.

Barium Sulfate↗
PubMed1998

Factors affecting the outcome of foetal hydrocephaly.

In this study, the authors attempt to provide an account of the factors that affect the outcome of hydrocephaly in 26 foetuses. The hydrocephalus was related to a myelomeningocele in 35% of patients. Sixty-two percent of foetuses showed intra-uterine progression of their hydrocephalus and 50% were shunted postnatally. At a mean follow up of 2 years, the outcome was considered "fair" in 54% of patients. Our findings demonstrate that in foetal hydrocephaly a more favourable outcome is expected in patients with hydrocephalus which does not progress in utero, in whom the labour is not induced before 36 weeks of gestation, who are delivered vaginally weighing more than 2.5 kg and have a head circumference below the 95th centile and a CT cortical mantle thickness of 2 cm and more and who are treated by CSF shunting. The diagnosis of the foetal hydrocephaly at or before 28 weeks of gestation and the presence of a myelomeningocele did not affect the outcome significantly. Neurosurgeons are reminded to keep an open mind for infants with foetal hydrocephaly and to offer active treatment to patients with a potentially favourable outcome.

Birth Weight↗
PubMed1996

Multiloculated hydrocephalus related to cerebrospinal fluid shunt infection.

This study is an attempt to establish that CSF shunt infection has a role in the aetiology of multiloculated hydrocephalus. The authors carried out a review of 12 cases of multiloculated hydrocephalus who were treated at King Khalid University Hospital between 1988-1994. The multiloculation appears to have developed following the shunt infection in all cases. The hydrocephalus was related to an intraventricular haemorrhage (IVH) in 9 patients and was congenital in 2 patients and post-meningitic in 1 patient. The shunt infection was caused by a gram-negative organism in 8 patients and duration of external ventricular drainage ranged from 9-24 (median 13) days. The diagnosis of multiloculated hydrocephalus was made on average 2 months after the shunt infection. In three patients endoscopic fenestration of intraventricular septations was attempted but was effective in only one case. The other patients were managed by two shunts (9 patients) and three shunts (2 patients). At a mean follow-up of 15 months, the shunt revision rate of the patients was 0.4/year. One patient died of multiple brain abscesses and 6 patients remain severely disabled. The poor outcome may also be related to the original IVH as well as the multiloculated hydrocephalus. The study also shows that patients with post-haemorrhagic hydrocephalus, who develop a shunt infection due to gram-negative organisms and in whom the CSF fails to be cleared of the infection following 12 days of external drainage appear to be at risk of developing multiloculated hydrocephalus.

Adolescent↗
PubMed1996

Susceptibility of Brugia malayi and Onchocerca lienalis microfilariae to nitric oxide and hydrogen peroxide in cell-free culture and from IFN gamma-activated macrophages.

The susceptibility of Brugia malayi and Onchocerca lienalis microfilariae to H2O2 and NO either in cell-free culture or from IFN gamma-activated macrophages was examined. In cell-free culture, O. lienalis microfilariae were highly susceptible to H2O2 induced toxicity, exhibiting rapid reductions in motility and viability. The addition of exogenous catalase abrogated H2O2-induced killing. In contrast, B. malayi microfilariae were relatively resistant to H2O2, with concentrations as high as 50 microM having no effect on motility or viability. On exposure to NO, both species showed reductions in motility within 5-30 min, but longer was required to see effects on the viability of microfilariae. Parasites incubated with IFN gamma-activated macrophages also exhibited marked reductions in motility and viability. In cultures with B. malayi and activated macrophages, inhibition of these effects was achieved by the addition of either L-NMMA, to abolish NO production, or neutralizing anti-TNF alpha antibodies. Attempts to inhibit parasite killing by the addition of catalase to macrophage cultures were ineffective. The results of this study show that B. malayi and O. lienalis microfilariae have different susceptibility to H2O2, but are equally affected by exposure to NO. Moreover both species are killed by IFN gamma-activated macrophages and in the case of B. malayi, killing is dependent on the generation of NO via TNF alpha.

Animals↗