Effects of prostaglandin A2 on Na+, K+-ATPase activity in basolateral plasma membrane of rat intestine in vitro

Renal sodium handling and stimulation of medullary Na-K-ATPase during blockade of prostaglandin synthesis

The effect of suppression of prostaglandin synthesis on renal sodium handling and microsomal Na-K ATPase was studied in control and indomethacin treated intact rats maintained on a normal sodium diet (series A) and chronically salt loaded (series B). Indomethacin administration resulted in a decreased GFR and a significantly depressed urinary excretion and an increased fractional reabsorption of sodium in animals fed the normal sodium diet or chronically salt loaded. In rats maintained on a normal Na diet, the activity of the renal medullary Na-K ATPase after indomethacin was 206.3 +/- 6.4 ug Pi/mg protein, i.e. significantly higher as compared with the enzyme activity in the medullary renal fraction from control animals in which it averaged 148 +/- 7.79 ug Pi/mg protein (p less than 0.001). While after chronic salt load a similar increment in the activity of renal medullary Na-K ATPase was observed, no additional stimulation was elicited by subsequent indomethacin administration. The addition of exogenous PGE2, 0.1 mM to microsomal fractions obtained from kidneys of normal rats, was associated with a moderate suppression of the medullary Na-K-ATPase activity, from a basal level of 170 +/- 16 to 151.3 +/- 13 umol Pi/mg protein/hr (p less than 0.005). In isolated segments of medullary thick ascending limb of Henle's loop (MTAL) addition of PGE2 to the incubation medium resulted in a significant inhibition of Na-K ATPase from 37.2 +/- 2 to 21.25 +/- 1.17 x 10(-11) mol/mm/min (p less than 0.0001). These findings suggest that the increased renal Na reabsorption after inhibition of PG synthesis might be related, at least partly, to stimulation of medullary Na-K ATPase. In parallel, the reported natriuretic effect of prostaglandins might imply a direct inhibitory effect of these mediators on renal Na-K ATPase.

The effects of enprostil and RS-86505-007 on in-vitro intestinal permeability of rabbit and monkey

Enprostil is a prostaglandin E2 analogue characterized as a racemic mixture of four stereoisomers. Enprostil and a single isomer, RS-86505-007, were evaluated for their effects on the permeability of actively and passively transported compounds in segments of small intestine from rabbits and monkeys. Consistent with human in-vivo studies, which have demonstrated decreases in absorption of D-xylose, both compounds inhibited D-glucose transport. The passively transported compounds mannitol and progesterone were also less permeable in this model in the presence of enprostil or RS-86505-007. In contrast to the concentration-dependent inhibition displayed by ouabain, RS-86505-007 had no effect on purified Na+K(+)-ATPase. It is suggested that an effect of a general nature, possibly an increase in the barrier properties at the intestinal surface, may explain the transport inhibition. Of two other enprostil isomers, RS-86812-007 inhibited D-glucose transport in rabbit small intestine, while RS-86505-008 had no effect. The prostaglandin E1 analogue misoprostol was ineffective in monkey and poorly effective in rabbit. This suggests that the inhibition of D-glucose transport by enprostil and its active stereoisomers is mediated through some structurally specific receptor interaction.

Na,K-ATPase activity in rectal mucosa of children with ulcerative colitis and Crohn's disease

Mucosal Na,K-ATPase activity was studied in rectal biopsy specimens from 19 children with ulcerative colitis (UC) (mean age, 13 years) and 4 children with Crohn's colitis (mean age, 14 years) and compared with biopsy specimens from 12 control children (mean age, 12 years). The Na,K-ATPase activity was significantly decreased in UC with severe rectal inflammation compared with UC in remission or with children with unspecific symptoms and normal mucosa (p less than 0.001, respectively). A higher enzyme activity was shown with age in the group with normal rectal mucosa and no evidence of inflammatory bowel disease (n = 17). The decreased Na,K-ATPase in UC with severe rectal inflammation might contribute to the diarrhoea by impairment of sodium transport.

Circulating digitalis-like factors

The ability of extracts of mammalian plasma and tissue to mimic the biologic activities of the digitalis glycosides has suggested the existence of endogenous regulators for Na, K ATPase. Purification of plasma extracts has identified several classes of circulating lipids with digitalis-like activity including free fatty acids, lysophospholipids, and arachidonic acid metabolites of the lipoxygenase pathway. Circulating steroids with digitalis-like activity include dehydroepiandrosterone sulfate and hydrocortisone. Evidence for other, more unique compounds has also been published although their structure has not yet been determined. Analysis of tissue suggests that hypothalamus contains a unique, low molecular digitalis-like factor (DLF) which also circulates in plasma. Some studies suggest that the hypothalamic factor is also present in other parts of the brain and in the adrenal. Some of these endogenous DLF may function as modulators of cardiovascular function by regulating renal sodium excretion and peripheral vascular resistance in both physiological and pathophysiological situations.

The effect of suppression of prostaglandin synthesis on renal function in rats with intact and reduced renal mass

The present study was undertaken to assess the role of prostaglandin system in the compensatory response to reduced nephron population, respective to renal function and electrolyte excretion. Intact and 5/6 nephrectomized rats were divided in 4 groups: 1) rats pretreated with indomethacin, 2) rats pretreated with the vehicle of indomethacin, 3) rats pretreated with sulindac, and 4) rats pretreated with the vehicle of sulindac. In normal rats, indomethacin administration resulted in a mild decrease in creatinine clearance and a significant reduction of the urinary Na excretion. In the rats with reduced renal mass treated with indomethacin, the creatinine clearance did not differ from that in the control group. The 24 h urinary sodium excretion and the fractional excretion of sodium, however, were significantly lower in the indomethacin treated animals than in the control rats. No change in the creatinine clearance or in the sodium excretion was observed in all groups pretreated with sulindac. The urinary PGE2 and thromboxane excretion was significantly lower in the indomethacin treated intact rats and the rats with reduced renal mass. Sulindac induced a slight decrease in urinary excretion of PGE2 in intact rats. No significant change in urinary excretion of PGE2 or thromboxane was seen after sulindac in the rats with reduced renal mass. The antinatriuretic effect of indomethacin was dissociated from changes in urine flow in all groups of animals, suggesting that the increase in Na reabsorption took place in a water impermeable segment of nephron. These results suggest that the compensatory increase in urinary Na excretion per nephron in rats with reduced nephron population at least partly depends on an intact prostaglandin synthesis.

Prostaglandin A2 receptor in rat intestinal basolateral plasma membranes

The specific prostaglandin A2 receptor was presented in rat intestinal basolateral plasma membrane. The dissociation constant was 4.39 X 10(-8) M and the value of the binding capacity was 3.33 pmol/mg protein. [3H]prostaglandin A2 binding was specifically inhibited by Na+ or ATP. The inhibition manners of Na+ and ATP for [3H]prostaglandin A2 binding were of a competitive and noncompetitive type, respectively.

Phospholipid composition and metabolism of crustacean gills as related to changes in environmental salinities: relationship between Na+-K+-ATPase activity and phospholipids

The phospholipid composition and metabolism are studied in crustacean gills. It is reported that branchiae are rich in PC, PE and DPG and abundant in long chain polyunsaturated fatty acids (20:4 omega 6 and 20:5 omega 3 acids). The pathways of phospholipids synthesis appear similar to those described for vertebrates. It is demonstrated that there exist significant differences in the level of phosphatides between the anterior and posterior gills of Eriocheir sinensis. No matter what the salinity, the three more posterior located gills of Chinese crabs are shown to contain much more unsaturated phospholipids (PE and DPG). This is particularly true when animals are acclimated to dilute media. Moreover, lipids of posterior gills appear more fluid than the anterior ones as reported by the values of the degree of fluorescence polarization and the index of unsaturation of fatty acids. It is suggested that these lipid changes may indicate the existence of a functional difference between the various branchiae of euryhaline Eriocheir sinensis with respect to their ability to transport salt. It is shown that the renewal of DPG and PS is increased in posterior gills isolated from freshwater Chinese crabs. It is postulated that the enhanced formation of DPG in posterior gills is an indicator of an increased synthesis of mitochondria having as principal function to produce the necessary energy for the Na+ uptake. An attempt is made to correlate the PS metabolism and the Na+-K+-ATPase activity which is particularly located in the mitochondrial fractions of the three pairs of posterior gills.

Effect of prostaglandin A2 on Na+-K+-ATPase in basolateral plasma membrane of rat intestine in vitro inhibition of activation of K+-dependent p-nitrophenylphosphatase by Na+ and ATP

1. The activation of K+-dependent p-nitrophenylphosphatase (EC 3.6.1.7) by both Na+ and ATP in rat intestinal basolateral plasma membrane is inhibited by prostaglandin A2. 2. The drug's inhibition of the activation of the enzyme by both Na+ and ATP is due to a decrease in the affinity of the enzyme for Na+ and in the Vmax of the enzyme. 3. The Ki values for this drug for Na+ and ATP in the activation of the enzyme were 45 and 70 microM, respectively.

Inhibitory effect of prostaglandin A2 on Na+-K+-ATPase activity in synaptic plasma membrane of rat brain in vitro

1. The Na+-K+-ATPase activity in the synaptic plasma membrane of rat brain was inhibited by PGA2 in vitro. 2. PGA2 concentration required for 50% inhibition was 8.91 x 10(-5) M. 3. Inhibition mode of PGA2 for both ATP and Mg2+ was uncompetitive type. 4. PGA2 was competitive and noncompetitive with Na+ and K+, respectively. 5. The Ki values for PGA2 inhibition for ATP. Na+, K+ and Mg2+ were 6.0 x 10(-5), 2.7 x 10(-5), 10.8 x 10(-5) and 0.6 x 10(-5) M, respectively.