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Biomedical subjects

J C Fenwick

Publications and source records attributed to J C Fenwick.

At least 37 records · Page 2Linked to original sources
PubMed1990

Pathologic dependence of oxygen consumption on oxygen delivery in acute respiratory failure secondary to AIDS-related Pneumocystis carinii pneumonia.

Oxygen consumption is pathologically dependent on oxygen delivery in ARDS and sepsis. We asked whether oxygen consumption is dependent on oxygen delivery in severe acute respiratory failure secondary to AIDS-related PCP. In five patients who had AIDS-related PCP, diffuse bilateral pulmonary infiltrates, no evidence of bacterial infection, and acute respiratory failure requiring mechanical ventilation with arterial oxygen tensions less than 75 mm Hg while breathing at least 50 percent oxygen, and PEEP greater than 10 cm H2O, we determined oxygen delivery and consumption by calculation from thermodilution cardiac output and arterial and mixed venous oxygen contents. Oxygen delivery was increased using transfusion of two units of packed red blood cells over one hour. Oxygen delivery increased 22 percent (638 +/- 204 to 778 +/- 201 ml/min.m2, p less than or equal to 0.006). Oxygen consumption increased 11 percent (134 +/- 34 to 149 +/- 29 ml/min.m2, p less than or equal to 0.02). The oxygen extraction ratio did not change. We conclude that similar to ARDS and sepsis, oxygen consumption may be pathologically dependent on oxygen delivery in patients who have severe acute respiratory failure secondary to AIDS-related PCP.

Acquired Immunodeficiency Syndrome↗
PubMed1989

The effect of eel calcitonin on calcium influx and plasma ion levels in axolotls, Ambystoma mexicanum.

Plasma total calcium and calcium influx, measured during 4-h 45Ca influx experiments, were lower in control axolotls, Ambystoma mexicanum, during August when compared to those in July. A single intraperitoneal injection of 10 micrograms of synthetic eel calcitonin significantly reduced the calcium influx rates during both months but the effect was greater in July (P less than 0.001) than in August (P less than 0.05). Plasma levels of calcium, sodium, potassium, and magnesium were not affected. In neotonous wholly aquatic amphibians, eel calcitonin may work in the same way as it does in fish by reducing the uptake of dissolved calcium from the ambient medium.

Ambystoma↗
PubMed1989

Calcitropic actions of prolactin in freshwater North American eel (Anguilla rostrata LeSueur).

In freshwater-acclimated American eels (Anguilla rostrata LeSueur), ovine prolactin and grafts of the part of the pituitary gland containing the prolactin cells induced hypercalcemia. The hypercalcemia was associated with increased uptake of calcium from the water (resulting from increased influx and decreased efflux) and with enhanced high-affinity Ca2+-adenosinetriphosphatase (ATPase) activity in the gills, the putative biochemical correlate of the branchial Ca2+ pump. Kinetic analyses of ATPase-mediated Ca2+ transport in plasma membrane vesicles of branchial epithelium provided evidence that prolactin enhanced the maximum velocity of the Ca2+ pump. Prolactin treatments raised plasma cortisol levels slightly but significantly in eels. However, cortisol per se was not hypercalcemic in eels and did not stimulate the branchial Ca2+ pump. We conclude that the hypercalcemic potency of prolactin in fish relates to its stimulatory action on active Ca2+ transport in the gills.

Adenosine Triphosphatases↗
PubMed1988

Effects of calcitonin on plasma calcium and phosphate in the mudskipper, Periophthalmodon schlosseri (Teleostei), in water and during exposure to air.

After 7 days in air on wet filter paper mudskippers had normal body weight and normal levels of plasma sodium, potassium, and phosphate. They were, however, significantly hypercalcemic. The hypercalcemia could be reduced by the daily intraperitoneal injection of synthetic eel calcitonin (1.67 microgram kg-1 day-1) and this effect was dose dependent with a maximal response at a dose of 3.33 micrograms kg-1 day-1. Calcitonin had no effect on plasma calcium levels of fish held in water but did induce significant hyperphosphatemia whether the fish were held in water or in air on wet filter paper with this effect being greater under the latter conditions. The hypocalcemic action of calcitonin was restricted to conditions under which the fish displayed patent hypercalcemia. Under no conditions did calcitonin produce significant hypocalcemia so it appears that the action of synthetic eel calcitonin in the mudskipper, Periophthalmodon schlosseri, is dependent upon the presence of excess plasma calcium and is thus more accurately described as being anti-hypercalcemic rather than hypocalcemic.

Animals↗
PubMed1988

Comparative biochemistry and physiology of teleocalcin from sockeye and coho salmon.

This is a comparative study of the glycoprotein hormone, teleocalcin, from the corpuscles of Stannius of sockeye (Oncorhynchus nerka) and coho (O. kisutch) salmon. Coho teleocalcin was purified by the same procedures used previously to obtain sockeye teleocalcin and was obtained in a comparable yield. Both salmon teleocalcins had the same molecular weight as estimated by sodium dodecyl sulfate-electrophoresis and both appeared to have the structure of disulfide-linked oligomers. The two hormones were similar on the basis of amino acid and carbohydrate composition and shared 95% homology in the first 40 residues on the N-terminal. The salmon teleocalcins also shared 80% homology with the predicted 1-40 N-terminal sequence from Australian eels (Anguilla australis). Both teleocalcins had potent inhibitory effects on gill calcium uptake in intact rainbow trout (Salmo gairdneri). However, these effects were observed only at the peak in the calcium uptake cycle that is displayed by this species. In North American eels (A. rostrata), the acute administration of both teleocalcins caused significant inhibition of gill calcium uptake without any concomitant changes in plasma calcium levels or other plasma electrolytes. In 4- and 7-day stanniectomy (STX) eels, the acute administration of coho teleocalcin significantly reduced or completely abolished the accelerated gill calcium transport that occurs postoperatively, with no concomitant changes in plasma electrolytes or post-STX hypercalcemia. These experiments provide further evidence that teleocalcin is a regulator of gill calcium transport and has no acute hypocalcemic effects in fish.

Amino Acid Sequence↗
PubMed1987

Anatomy of the reproductive tract of the female muskox (Ovibos moschatus).

Reproductive tracts from 23 female muskoxen were collected from the Canadian high arctic during annual native muskox hunts. Twenty tracts were collected during the late breeding season and the last third of pregnancy or anoestrus, with 3 additional specimens taken just before the breeding season in August. The non-gravid muskox uterus was very similar to that of sheep and goats except for two features found in parous muskoxen. The first was endometrial pigmentation found only in the caruncles and associated with a dense collection of lipofuscin granules in the endometrial stroma. The second was a prominent 5 mm deep band of muscular tissue protruding from the antimesometrial border of the uterine horns throughout most of their length. The pregnant uterus and the fetal membranes of the muskox resembled homologous structures in domestic ruminants. However, there was no morphological evidence of a corpus luteum during late pregnancy, apart from a luteal scar in the ovary ipsilateral to the pregnant horn. Of the 4 females collected at the end of the breeding season, 2 lactating females were apparently not cyclic while 2 others had more than one CL, suggesting that they had undergone at least 2 cycles without conceiving or remaining pregnant.

Animals↗
PubMed1986

Effects of ovine prolactin on calcium uptake and distribution in Oreochromis mossambicus.

Ovine prolactin stimulated the net uptake rate of Ca2+ from the water by 96%, produced frank hypercalcemia, and increased total bone calcium content in fed rapidly growing freshwater male tilapia, Oreochromis mossambicus. It did not, however, alter the size of the readily exchangeable bone calcium pool. The increase in calcium accumulation resulted from an increase in whole-body Ca2+ influx and a decrease in Ca2+ efflux. It is concluded that prolactin exerts an important control over Ca2+ exchange between the fish and its environment and that through its hypercalcemic action prolactin indirectly facilitates bone mineralization.

Animals↗
PubMed1985

Active Ca2+ transport in plasma membranes of branchial epithelium of the North-American eel, Anguilla rostrata LeSueur.

A branchial epithelial membrane fraction, more than 20-fold enriched in Na+/K+-ATPase activity when compared with the crude homogenate of the tissue, was obtained from adult freshwater American eels. In a membrane vesicle preparation that consisted of 33% inside-out, 23% right-side-out and 44% leaky vesicles, the accumulation of 45Ca2+ was stimulated by ATP, but not by ADP. Accumulation of 45Ca2+ was prevented when vesicles were pretreated with detergent or the Ca2+ ionophore A23187; Ca2+ efflux was observed when the ionophore was added to actively 45Ca2+-loading vesicles. Oxalate did not affect Ca2+ accumulation in these vesicles. Kinetic analysis of the Ca2+-transport process by an Eadie-Hofstee plot revealed that the process is homogeneous; its kinetic parameters are a K0.5 for Ca2+ of 0.053 microM and a Vmax of 2.25 nmol Ca2+/min.mg protein (at 37 degrees C). The calmodulin dependency of this Ca2+ transporting process was shown by the inhibitory action of calmodulin antagonists and by the stimulatory effect of calmodulin repletion after EGTA treatment of the membranes. We conclude that an ATP-energized Ca2+ pump is present in the plasma membranes of branchial epithelium, that resembles the Ca2+ pumps of e.g. mammalian intestinal or renal plasma membranes, and propose its involvement in branchial Ca2+-uptake from the water.

Adenosine Triphosphate↗
PubMed1985

Whole-body calcium flux rates in cichlid teleost fish Oreochromis mossambicus adapted to freshwater.

Radiotracer techniques were used to measure influx and efflux rates of Ca2+ in freshwater-adapted Oreochromis mossambicus. The influx rate of Ca2+ is related to body weight (W) as Fin = 50W0.805 nmol Ca2+/h. For a 20-g fish the calculated influx rate was 558 nmol Ca2+/h, and this was attributed largely to extraintestinal uptake since the drinking rate was estimated to be only 28 microliter water/h, which corresponds to an intake of 22.4 nmol Ca2+/h. The Ca2+ efflux rate was calculated using the initial rate of appearance of radiotracer in the ambient water and the specific activity of plasma Ca2+. Tracer efflux rates were constant over 6-8 h, which indicated that there was no substantial loss of tracer in either the urine or the feces because this would have resulted in random bursts of tracer loss. Efflux rates then primarily represent integumentary and presumably branchial efflux rates. The efflux rate of Ca2+ is related to body weight as Fout = 30W0.563 nmol Ca2+/h, which means an efflux rate of 162 nmol Ca2+/h for a 20-g fish. The net whole-body Ca2+ influx, calculated as Fnet = Fin - Fout, was 396 nmol/h for a 20-g fish, which proves that the ambient water is an important source of Ca2+.

Adaptation, Physiological↗
PubMed1984

Effect of various vitamin D analogs on plasma calcium and phosphorus and intestinal calcium absorption in fed and unfed American eels, Anguilla rostrata.

Injection of about 1 ng/g body wt per day of either vitamin D3 or 1,25-(OH)2-vitamin D3 for 7 days induces hypercalcemia and hyperphosphatemia in fed American eels, Anguilla rostrata, but only hyperphosphatemia in unfed eels. These same analogs also stimulated the uptake of 45Ca from intestinal sacs in situ. The vitamin D3 appeared to be relatively more effective than the 1,25-(OH)2D3 metabolite and chlorpromazine inhibited the effect of vitamin D3 on intestinal calcium uptake. 7-Dehydrocholesterol, vitamin D2, and 24,25-(OH)2D3 did not stimulate hypercalcemia, hyperphosphatemia, or intestinal calcium uptake.

24,25-Dihydroxyvitamin D 3↗
PubMed1984

Ca2+-dependent phosphatase and Ca2+-dependent ATPase activities in plasma membranes of eel gill epithelium--III. Stimulation of branchial high-affinity Ca2+-ATPase activity during prolactin-induced hypercalcemia in American eels.

Infusions of ovine prolactin for 10 days induced hypercalcemia in unfed American eels, Anguilla rostrata LeSueur, that tentatively was related to stimulation of branchial Ca2+-uptake mechanisms. Analysis of ATPase activities in the plasma membranes of the branchial epithelium in prolactin treated eels showed a specific stimulation of high-affinity Ca2+-ATPase. The results of this study form further evidence that the high-affinity Ca2+-ATPase activity represents the Ca2+-pump of the branchial epithelium.

Animals↗
PubMed1983

Ca2+-dependent phosphatase and ATPase activities in eel gill plasma membranes--I. Identification of Ca2+-activated ATPase activities with non-specific phosphatase activities.

The characteristics of Ca2+-activated ATPase activities previously often postulated as components for the calcium transporting system in fish gills do not fulfil the requirements of a transport Ca2+-ATPase. The chelation of Ca2+- or Mg2+-ions is a prerequisite for the adenosinephosphate esters to serve as substrate for gill plasma membrane phosphatases. Ca2+-activated ATP hydrolysis results from the activity of a heterogeneous pool of phosphatases located in the plasma membranes of the branchial epithelium, as is concluded from substrate specificity tests and the effects of various inhibitors on these hydrolytic activities. In the present study only non-specific phosphatases could be shown.

Adenine Nucleotides↗
PubMed1977

Relationship between net 45calcium influx across a perfused isolated eel gill and the development of post-stanniectomy hypercalcemia.

The net 45calcium influx was measured in perfused isolated individual hemibranchs taken from Anguilla rostrata L. at various intervals following the surgical removal of the Corpuscles of Stannius. Total plasma calcium concentrations were recorded at the same time. A relationship between the development of post-stanniectomy hypercalcemia and the net rate of 45calcium uptake in the isolated gills is suggested. The net influx of 45calcium increased rapidly during the first week, peaked at two weeks and dropped back to control levels at three weeks. Plasma calcium levels followed the same trend over the first two weeks but continued to rise through the third week before dropping slightly during the fourth week. We conclude that the corpuscles of Stannius play some role in controlling the branchial uptake of calcium and that the gills are of primary importance in the appearance of post-stanniectomy hypercalcemia.

Animals↗