Search PubMed⌕ Search

Biomedical subjects

F H Epstein

Publications and source records attributed to F H Epstein.

At least 217 records · Page 12Linked to original sources
PubMed1979

Indirect evidence for enhancement of Na-K-ATPase activity with stimulation of rectal gland secretion.

The relation between active chloride secretion and Na-K-ATPase activity was studied in the isolated perfused rectal gland of Squalus acanthias stimulated by cAMP and theophylline. Ouabain inhibited both secretion and oxygen uptake in stimulated glands. Stimulation of chloride secretion by cAMP and theophylline resulted in a six- to sevenfold rise in ouabain-inhibitable oxygen consumption. Intracellular sodium concentration decreased while intracellular potassium rose. These findings suggest activation of Na-K-ATPase. On the other hand, the activity of Na-K-ATPase in whole homogenates of rectal gland tissue was not increased after cAMP stimulation of the perfused gland, nor was ouabain binding increased. Calculated intracellular chloride concentration fell after secretion was stimulated in a way consistent with an action of cAMP to increase luminal permeability to chloride.

Animals↗
PubMed1979

In vivo 24-hydroxylation of 25-hydroxyvitamin D3 in enterocolectomized rats.

To determine if the renal 25-hydroxyvitamin D3 24-hydroxylase is active in addition to the intestinal 25-hydroxyvitamin D3 24-hydroxylase in vivo in the rat, radiolabeled 25-hydroxyvitamin D3 was administrated to normocalcemic, vitamin D-replete, enterocolectomized rats. Substantial amounts of 24,25-dihydroxyvitamin D3 were detected and the identity of the isolated plasma 24,25-hydroxyvitamin D3 region in these animals were confirmed by coelution on high pressure liquid chromatography and periodate cleavage. This suggests that both intestinal and renal 25-hydroxyvitamin D3 24-hydroxylases are active in vivo in the rat.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗
PubMed1977

Cyclic AMP regulation of active chloride transport in the rectal gland of marine elasmobranchs.

Active transport of chloride in the salt secreting rectal gland of the dogfish Squalus acanthias is markedly stimulated by the addition of theophylline (0.01 to 5 mM) or dibutyryl cyclic AMP (0.05 mM) during in vitro perfusion. The effect occurs promptly and may persist for two hours. Specific hormonal effectors have not yet been identified. The isolated perfused rectal gland thus offers a unique opportunity to examine the cellular mechanisms of active chloride secretion.

Animals↗
PubMed1977

Preventive trials and the "diet-heart" question: wait for results or act now.

Is the relationship between coronary heart disease risk factors and the risk of disease causal? Direct evidence would have to come, of necessity, from preventive trials. However, the difficult nature of such trials carries the inherent danger of false negative results; even positive results may be open to challenge. With regard to demonstrating specifically a preventive effect of lowering serum lipid levels through nutritional changes alone, this evidence may never be forthcoming since ongoing trials intervene simultaneously on multiple factors; against this disadvantage, the strengths of such trials are reviewed. The view is stated and discussed that preventive action in the community is justified now, without waiting for the results of preventive trials, however important they will be eventually to help the development of optimally effective programs.

Arteriosclerosis↗
PubMed1977

Effect of catecholamines on tubular function in the isolated perfused rat kidney.

Addition of norepinephrine or epinephrine to the isolated rat kidney perfused at constant pressure resulted in an increase in sodium reabsorption and the excretion of a dilute urine with an increase in free water clearance. Vasopressin reversed the fall in urinary osmolarity but not the diminution in sodium excretion. The urinary changes produced by catecholamines were blocked by propranolol but not by phenoxybenzamine, suggesting that they were mediated, at least in part, by beta receptors. Similar though less pronounced changes in sodium excretion and urinary osmolarity were produced by isoproterenol and phenylephrine, while the combination of these drugs induced marked dilution of the urine. The results suggest that circulating catecholamines or adrenergic nerves innervating the kidney directly influence renal tubular function and might, therefore, participate in the regulation of sodium and water excretion by the kidneys.

Animals↗
PubMed1977

Mechanism of active chloride secretion by shark rectal gland: role of Na-K-ATPase in chloride transport.

The isolated rectal gland of Squalus acanthias was stimulated to secrete chloride against an electrical and a chemical gradient when perfused in vitro by theophylline and/or dibutyryl cyclic AMP. Chloride secretion was depressed by ouabain which inhibits Na-K-ATPase. Thiocyanate and furosemide also inhibited chloride secretion but ethoxzolamide, a carbonic anhydrase inhibitor, did not. Chloride transport was highly dependent on sodium concentration in the perfusate. The intracellular concentration of chloride averaged 70-80 meq/liter in intact glands, exceeding the level expected at electrochemical equilibrium and suggesting active transport of chloride into the cell. These features suggest a tentative hypothesis for chloride secretion by the rectal gland in which the uphill transport of chloride into the cytoplasm is coupled through a membrane carrier to the downhill movement of sodium along its electrochemical gradient. The latter is maintained by the Na-K-ATPase pump while chloride is extruded into the duct by electrical forces.

Adenosine Triphosphatases↗