Phosphoinositide (PI) hydrolysis by phospholipase C is accelerated by heat-stable (ST) E. coli enterotoxin in rat intestine

Abstract A partially purified E. coli heat-stable (ST) enterotoxin stimulated the phosphoinositide (PI)-specific phospholipase C (PLC) activity of the rat intestine. The effect of ST on PI-specific PLC was significant compared with the control. The importance of PI-specific phospholipase C as a potential agent to promote calcium translocation across the plasma membrane, was discussed in this communication.     

The renin-angiotensin-aldosterone system in Cushing's syndrome and pheochromocytoma

We investigated the status of the renin-angiotensin-aldosterone axis in 5 patients with Cushing's syndrome and 7 patients with pheochromocytoma. In most of the patients with Cushing's syndrome no significant abnormalities of the renin-angiotensin-aldosterone system could be detected. In 4 out of 7 patients with pheochromocytoma, plasma renin activity remained high after saline suppression and decreased into the normal range in all 4 patients after removal of pheochromocytoma. These results imply that the postulated mineralocorticoid excess was not present in the patients with Cushing's syndrome studied. In pheochromocytoma, high levels of plasma catecholamines contribute to a high renin state which may have pathophysiologic implications.     

Stimulation of calcium pump activity in heart sarcolemma by timolol

The effects of beta-adrenergic blocking agents, timolol and atenolol (1-1000 microM), were studied on rat heart sarcolemmal ATPase and Ca2+ binding activities. Timolol, unlike atenolol, increased both Ca2+-stimulated ATPase and ATP-dependent Ca2+ binding; the maximal effects were seen at 1 microM concentration of timolol. Both timolol and atenolol did not alter the sarcolemmal Mg2+ ATPase and nonspecific Ca2+ binding activities. Sarcolemmal Ca2+-stimulated ATPase was also activated by concanavalin A (6-66 micrograms/mL) which is known to alter membrane fluidity; however, Mg2+ ATPase was unaffected by this agent. These results indicate that timolol may stimulate Ca2+ pump activity in heart sarcolemma by changing membrane fluidity in a manner similar to that of concanavalin A.     

Studies on the metabolism of beta-carotene and apo-beta-carotenoids in rats and chickens.

(1)The relative abilities of the various fractions of rat and chicken liver to oxidize and reduce retinal and 8'-and 12'-apo-beta-carotenal were investigatjed and it has been shown that, while retinal is exclusely oxidized by the soluble fraction, the apocarotenals are mostly oxidized by the particulate fractions of the homogenate. (2) Addition of NAD+ or NADP+ markedly activated the oxidation of the apocarotenals, but not of retinal by the particulate fractions. (3) Considerable amounts of retinal and 8'-, 10'- and 12'-apo-beta-carotenal were isolated from the intestine of chickens fed beta-carotene and these apocarotenoids were conclusively identified. (4) Significant amounts of 8'-, 10'- and 12'-apo-beta-carotenoic acids were isolated from the intestine of rats given 8'-apo-beta-carotenal and these apocarotenoic acids were also conclusively identified. (5) In the light of these observations it is suggested that during conversion to vitamin A, the beta-carotene molecule is simultaneously attacked by the dioxygenase at several double bonds, the primary attack being at the central double bond and a tentative scheme for the mechanism of conversion is proposed.     

A novel thrombin enhancement factor in human plasma

A protein has been isolated from human plasma by gel filtration followed by affinity chromatography with a derivative of wheat germ agglutinin and ion exchange chromatography. This protein showed one peak in high performance liquid chromatography but in gel electrophoresis, in the presence of sodium dodecyl sulfate and β-mercaptoethanol, revealed two major components of 74 kDa and 55 kDa. These results indicate that the protein probably exists as a complex of the two polypeptides. This protein complex enhanced platelet aggregation by thrombin while aggregation induced by ADP was not significantly affected. Similarly, the rate of thrombin action on fibrinogen and N-benzoylarginine ethyl ester as measured in a spectrophotometer was increased in the presence of this plasma protein. These results suggest the presence of a protein complex in human plasma which can directly interact with thrombin and enhance its reactivity.     

(Ca2+ + Mg2+) ATPase activity in kidney basolateral membrane in diabetes: role of atrial natriuretic peptide

Summary The (Ca²⁺ + Mg²⁺) ATPase which serves as a Ca²⁺ pump in the kidney basolateral membranes is essential to the maintenance of an intracellular Ca²⁺ concentration optimal for kidney function. Since atrial natriuretic peptide (ANP) is known to participate in the Ca²⁺ homeostasis mechanism, altered levels of ANP in diabetes may vary the pump activity and consequently the kidney function. In order to examine the modulatory role of ANP on (Ca²⁺ + Mg²⁺) ATPase in short- (6 weeks) and long-term (6 months) diabetes, rats were injected with streptozotocin (65 mg/kg body wt, i.v.). At 6 weeks, the plasma ANP was decreased whereas, ANP-receptor binding in the kidney basolateral membrane was increased. In contrast, there was an increased plasma ANP and decreased ANP receptor binding at 6 months. Insulin treatment to diabetic animals normalized these parameters. The (Ca²⁺ + Mg²⁺) ATPase activity was unchanged both at 6 weeks and 6 months. Our results demonstrate that the unchanged Ca²⁺ pump activity in short-term and long-term diabetes serves to maintain the Ca²⁺ homeostasis in the kidney cells and thus may maintain the hyperfiltration state in diabetes. Unaltered (Ca²⁺ + Mg²⁺) ATPase is achieved by the initial up-regulation and subsequent down-regulation of the ANP receptors.     

Glycosaminoglycans in human fetal liver in relation to water and electrolytes

The acidic mucoPolysaccharides secreted into the extracellular sPace are thought to Play many imPortant functions amongst which are binding of water and electrolytes on the Polyanionic glycosaminoglycans. Characteristically these comPonents undergo continuous changes during growth and develoPment of the fetuses. RelationshiPs of the concentrations of glycosaminoglycans to the water and PrinciPal electrolytes at different Periods of gestation were studied in human fetuses. It was found that during growth of the human fetuses there was a Progressive decrease in water, thiocyanate sPace, total sodium content and glycosaminoglycans. However the decrease of glycosaminoglycans was greater than the rate of decrease of the other constituents. Hence mucoPolysaccharides were thought to Play more imPortant roles than just binding of water and cations.