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Biomedical subjects

A R Khan

Publications and source records attributed to A R Khan.

At least 73 records · Page 4Linked to original sources
PubMed1987

Low potency of Ca antagonists in smooth muscle from different levels of the respiratory tract.

Respiratory smooth muscle at different levels of the respiratory tract was isolated from rabbit, rat and guinea-pig and incubated with the Ca antagonists, verapamil, D-600, felodipine, and nifedipine. There was no effect of the Ca antagonists when added on top of an already developed contraction. When added before the contractile agent at high concentrations (10-100 microM) the Ca antagonists reduced the contractions. Lanthanum (2 mM) was considerably more effective to prevent contractions than the Ca antagonists. Preparations from the trachea and bronchus responded in all animals, whereas the third generation bronchus from rat and guinea-pig failed to contract and that from rabbit showed very weak contractions. The failure to contract was not specific for the agonist, as depolarization with isotonic potassium solution (124 mM) did not evoke contractions either. Microscopic investigation showed well-developed smooth muscle in the trachea and main bronchus of the rat, whereas the muscle of the third generation bronchus was inhomogenous with scattered groups of muscle cells.

Animals↗
PubMed1987

Food and nutrition services in bone marrow transplant centers.

Nutrition care for bone marrow transplant recipients is recognized as vital for a successful transplant, yet little research has been done to determine the most effective foodservice methods. Many decisions regarding methods for the oral feeding of bone marrow transplant patients are based on tradition and/or individual judgments. This study surveyed marrow transplant centers to identify existing food and nutrition services that could be used as a basis for developing a foodservice protocol. A survey instrument was developed and sent to all chief dietitians (no. = 35) affiliated with transplantation centers in the United States. Four of the 30 respondents reported changing from the traditional sterile diet to either a low-bacteria or a modified house diet. Problems of limited availability of single-serve sterile foods, lack of standardization of recipes, and low patient acceptance of autoclaved sterile foods were reported as reasons for the move toward less stringent dietary procedures. The responses clearly indicate the need for additional research before a foodservice model can be established.

Bone Marrow Transplantation↗
PubMed1986

Influence of substance P on ciliary beat frequency in airway isolated preparations.

The neuropeptide substance P (SP), which is released from sensory C-fibres after stimulation by chemical irritants. accelerates mucociliary activity in rabbit maxillary sinus in vivo. In order to investigate the mechanism behind this finding, we recorded ciliary beat frequency (CBF) in vitro from various respiratory explants by a photoelectric technique. It was noticed that ciliated cells from the maxillary sinus displayed a higher beating frequency than cells from the trachea and the bronchus, in that order. SP 10(-10)-10(-4) M did not influence the CBF in explants from rabbit maxillary sinus, rabbit trachea and main bronchi, guinea-pig trachea and human adenoids. Neurokinin A (NKA) 10(-6)-10(-5) M, which is also thought to be released from sensory C-fibres, did not influence the CBF in guinea-pig trachea. Neither did the C-fibre stimulant capsaicin 10(-8)-10(-4) M increase CBF in explants from human adenoids. The present findings indicate that the mucociliary effect of SP in vivo is not mediated by an effect on the cilia themselves.

Animals↗
PubMed1986

Effects of toxin II from the sea anemone Anemonia sulcata on contractile and electrical responses of frog skeletal muscle fibres.

The effects of Anemonia sulcata toxin II (ATX-II) were studied on mechanical and electrical activities of frog muscle fibres isolated from semitendinosus or tibialis anterior muscles of Rana temporaria (2.8-7.7 degrees C). In concentrations ranging between 7.7 and 100 microM, ATX-II greatly potentiated the isometric twitch of single muscle fibres in a time-dependent manner. Increase in twitch amplitude by ATX-II was associated with an increase in time to peak tension and time from peak tension to half relaxation. ATX-II caused no change in maximum force production during fused tetanus, but the tension was maintained for several seconds after the cessation of stimulation. Such long tetanic contractions were also obtained in low-Na Ringer solution, but their duration was somewhat shorter. No specific action of ATX-II was detected on relaxation kinetics during a tetanus. The twitch potentiating effect of ATX-II was markedly increased by 3,4-diaminopyridine. Action potentials recorded from single muscle fibres in the presence of ATX-II showed a delayed onset of repolarization with a reduced rate of fall. In addition, ATX-II caused repetitive spontaneous firing of action potentials after the cessation of tetanic stimulation. ATX-II (3.3 - 10 microM) also increased action potential duration by reducing the rate of repolarization in surface fibres of formamide-treated sartorius or cutaneous pectoris muscles (20 degrees C) stimulated indirectly or directly. The potentiation of twitch force and the prolongation of contractions caused by tetanic stimulation can be attributed to the membrane action of ATX-II, which leads to prolongation of action potentials, to repetitive muscle firing and to the appearance of plateau potentials.

4-Aminopyridine↗
PubMed1986

Ewing's sarcoma of the scapula with metastases to the lung and eye.

A small, round cell tumor of the left scapula was found in a 3-month-old female Caucasian child. The histology was consistent with Ewing's sarcoma. Subsequently, a solitary pulmonary metastasis was excised. Thirty-one months after diagnosis, the child presented with leukokoria and a solitary pleural metastasis. The histology of both was identical to that of the original scapular tumor. G-banded karyotypes of the pulmonary metastasis and the ocular tumor revealed the presence of a balanced translocation, 46,XX, t(11;22)(q24;q12), which supported the original diagnosis of Ewing's sarcoma.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1985

Fatigue in frog skeletal muscle fibres and effects of methylxanthine derivatives.

The influence of theophylline and the related drug caffeine on the mechanical performance of fatigued muscle fibre isolated from semitendinosus muscle of Rana temporaria (2.5-6.7 degrees C) was investigated. The fibre was stimulated supramaximally to produce I s fused tetani and 2 s and 10 s partially fused tetani at intervals of 10 min. Fatigue was produced by shortening the contraction interval to 15 and 30 s. This caused a 15-20% decline in the maximum tension during fused tetanus and a 40-50% decline during partially fused tetanus. Theophylline and caffeine (0.1-0.5 mM) did not change the maximum tension developed by the fatigued fibre during fused tetanization. Both drugs, however, markedly increased the tension output of the fatigued muscle fibre during partially fused tetanus. It was observed that the increase in partially fused tetanic tension by theophylline and caffeine was associated with an increase in the degree of fusion. This later effect was even more pronounced in the presence of diethyl-stilboestrol. It is concluded that these drugs may not reverse the metabolic changes caused by fatigue, since they are unnable to increase fused tetanic force of a fatigued muscle fibre. The increase in partially fused tetanic tension of a fatigued muscle fibre by these drugs is probably due to enhancement of the activator calcium release from the sarcoplasmic reticulum in response to stimulation.

Animals↗
PubMed1985

Role of different calcium pools in the contraction of respiratory smooth muscle.

Contractions were evoked in isolated strips of rat trachea by potassium and acetylcholine (ACh) respectively. Extracellular calcium (Ca) was removed by EGTA and Ca influx was inhibited by diethylstilboestrol (DES). Contractions evoked by potassium were completely inhibited in the presence of EGTA or DES. ACh-induced contractions were rapidly abolished by EGTA whereas DES did not completely block these responses when a high concentration of ACh (10(-4) M) was used. Repeated activation by ACh in the presence of DES displayed two different phases of the contractile response; one initial brief contraction that decreased only slowly in the presence of DES, and a second phase with sustained contraction that was more readily depressed by DES. It is suggested that the smooth muscle in rat trachea is activated by Ca originating both intra- and extracellularly. As EGTA almost immediately blocked even the initial contractile response, the intracellular store is apparently located in or very close to the plasma membrane.

Acetylcholine↗
PubMed1985

The influence of felodipine and diethyl-stilboestrol on [3H]noradrenaline release in the rat trachea.

The fractional release of [3H]noradrenaline was measured in rings from the rat trachea. Transmitter release was induced either by isotonic KCl (124 mM) or by 2.5 mM Ca added to a Ca-free depolarizing solution. Felodipine, a Ca antagonist (10(-4)M), had no effect on the basal release of [3H]NA whereas it reduced the overflow of transmitter caused by KCl or Ca. Diethyl-stilboestrol (25 microM), which also inhibits Ca influx in smooth muscle, had a stronger inhibitory effect than felodipine on [3H]NA release induced by high K and addition of Ca. Basal efflux of [3H]NA was increased by diethyl-stilboestrol. This increase also occurred in the absence of extracellular Ca.

Animals↗
PubMed1984

Comparative studies on Ca2+- and Mg2+-binding of sarcoplasmic reticulum and chromaffin granule membranes.

The binding of calcium and magnesium ions to sarcoplasmic reticulum (SR) and chromaffin granule membranes was comparatively studied. The SR membranes are equipped with equal quantities of binding sites for both calcium and magnesium ions. The binding sites in presence of ATP combine specifically with calcium ions, while in the absence of ATP the binding sites react unspecifically with both ions. The trace amount of magnesium present in the SR membranes preparations is sufficient to drive ATP dependent calcium accumulation. Magnesium binding, however, is not affected by ATP. The chromaffin granule membranes bind calcium and magnesium in the same concentration range as observed for the SR membranes. Magnesium binding, however, is two times higher than that of calcium binding. In the absence of ATP, calcium and magnesium ions mutually compete. In the presence of ATP, magnesium binding values increase 3-5-fold, while the calcium binding isotherm remains unchanged. The appreciable contribution of the lipid phase to ions binding has been investigated, but was found to be of minor importance in this study.

Adenosine Triphosphate↗
PubMed1984

In vitro release of salicylic acid from lanolin alcohols-ethylcellulose films.

Lanolin alcohols-ethylcellulose films were investigated as a potential drug delivery system for the controlled release of salicylic acid. The effects of changes in film composition, drug concentration, drug solubility, and stirrer speed on the in vitro release of salicylic acid have been examined. The drug release has been found to obey a diffusion-controlled matrix model and square root of time release profile both in the suspension and solution cases.

Alcohols↗
PubMed1984

The effect of the immunomodulator corynebacterium parvum on hemisplenectomized mice.

The immunomodulator Corynebacterium parvum stimulates the reticuloendothelial system and causes splenic hypertrophy. The ability of C parvum to stimulate splenic regeneration in hemisplenectomized mice and decrease susceptibility to intranasal pneumococcal challenge was studied. Mice were divided into two groups, control sham-operated (n = 48) and hemisplenectomized (n = 47) animals. Ten days later, each group was divided into two subgroups, those injected with C parvum (700 mcg IVP) and those injected with an equivalent volume of saline. The animals were challenged with Streptococcus pneumoniae, which was injected into one nostril three weeks postoperatively, and mortality was assessed. Four and one-half weeks postoperatively, splenic tissue was removed, measured, weighed, and submitted for histologic examination. The number of spleen cells per gram of tissue was assessed. Treatment with C parvum resulted in a significant increase in the splenic weight in both hemisplenectomized and control animals compared to similar saline-injected mice (P less than 0.001). The percentage increase in spleen weight of hemisplenectomized mice (106%) was significantly greater than that for control animals (56%; P less than 0.01). There was no significant difference among experimental groups in the number of spleen cells per gram of splenic tissue or in the histologic characteristics, indicating that C parvum stimulated relatively normal splenic growth. Survival following pneumococcal challenge was significantly increased for hemisplenectomized mice by C parvum treatment to a level that did not significantly differ from control mice. This study demonstrates that in mice the deficits related to resistance to infection and spleen size following hemisplenectomy are significantly improved by treatment with C parvum.

Adjuvants, Immunologic↗
PubMed1983

Diazepam, a highly effective twitch potentiator in isolated muscle fibres of the frog.

The contractile effects of diazepam (10-200 microM) were studied on twitch and tetanus responses of isolated fibres of the semitendinosus muscle of Rana temporaria (3.5-5.0 degrees C). Diazepam (100-200 microM) enhanced the twitch amplitude to 95-100% of maximum tetanic force and increased the rate of rise of force, the time to peak twitch force and the total duration of the relaxation phase. The maximum tetanic output was unaffected by diazepam but the drug increased the rate of rise of the tetanic force and delayed the onset of force decay after the last stimulus. However, the kinetics of relaxation was unaffected by the drug. Diazepam had no effect on either threshold, submaximum or maximum contracture responses to caffeine and to increased potassium concentration. Diazepam in concentrations producing full twitch potentiation caused only a moderate (ca 30%) increase in action potential duration. The results are in line with the idea that 1: diazepam enhances the twitch response by increasing the rate of release of activator calcium without affecting the rate of calcium resequestration and 2: diazepam acts by modulating a mechanism in the excitation-contraction coupling that responds specifically to membrane excitation.

Action Potentials↗