Differential incorporation of fish-oil eicosapentaenoate and docosahexaenoate into lipids of lipoprotein fractions as related to their glyceryl esterification: a short-term (postprandial) and long-term study in healthy humans.

We investigated how the distribution of eicosapentaenoate (EPA, 20:5n-3) and docosahexaenoate (DHA, 22:6n-3) in the sn-2 and sn-1(3) positions of fish-oil triacylglycerols influenced their respective incorporation into triacylglycerol, cholesterol esters, and phospholipids of two lipoprotein fractions: low- and very-low-density lipoprotein (VL/LDL) and high-density lipoprotein (HDL). Nine healthy volunteers were studied over both a short-term (0-8 h) and a long-term (30 d) postprandial period of daily supplementation with 2 g EPA and 1.3 g DHA given as 11 g fish-oil triacylglycerol in which DHA was predominantly situated in the sn-2 position. Our results strongly suggest that the higher triacylglycerol incorporation of DHA and the higher metabolic availability of EPA compared with DHA for phospholipid accumulation (particularly in the short-term study) depend on their respective preferential sn-2/sn-1(3) positions in fish-oil triacylglycerol, emphasizing the important role of the triacylglycerol structure and its potential manipulation for modulating availability of either or both fatty acids.

Evidence for a short-term stimulatory effect of insulin on cholesterol synthesis in newly insulin-treated diabetic patients.

To gain further insight into the effects of insulin on cholesterol synthesis in humans, 19 newly insulin-treated diabetic patients were studied before any insulin treatment (study day 1) and after a few days of optimized glycemic control with a continuous intravenous insulin infusion (study day 2). The patients were divided into two groups according to their clinical characteristics and laboratory disorders. Groups I and II consisted, respectively, of 10 newly diagnosed type I diabetic patients and nine type II diabetic patients with secondary failure to oral antidiabetic drugs. Cholesterol synthesis was estimated from the determination of serum lathosterol, a metabolic precursor in the cholesterol pathway, and from the serum lathosterol to cholesterol ratio. Serum cholesterol (millimolar, mean +/- SEM) remained unchanged in both groups. After insulin therapy (study day 2), serum lathosterol (micromolar) and the serum lathosterol to cholesterol ratio (molar ratio x 10(3)) were significantly increased as compared with baseline (study day 1). Serum lathosterol levels were as follows: 9.9 +/- 2.0 versus 4.1 +/- 0.4 (P < .02) in group I, and 9.9 +/- 0.8 versus 5.7 +/- 0.7 (P < .005) in group II; serum lathosterol to cholesterol ratios were 2.10 +/- 0.39 versus 0.86 +/- 0.11 (P < .005) in group I, and 1.92 +/- 0.12 versus 0.98 +/- 0.10 (P < .001) in group II. The data indicate that in newly insulin-treated diabetic patients, short-term intensive insulin therapy has a stimulatory effect on cholesterol synthesis and even results in cholesterol overproduction.

Oxytocin receptors from LLC-PK1 cells: expression in Xenopus oocytes.

Two selective radioligands for oxytocin receptors, [3H]-[4-threonine,7-glycine]oxytocin [( 3H]-[Thr4,Gly7]OT) and 125I-[1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid), 2-(O-methyl)tyrosine, 4-threonine, 8-ornithine, 9-tyrosine amide]-oxytocin (125I-OTA), were used to characterize oxytocin receptors from two pig kidney-derived cell lines, LLC-PK1 and LLC-PK1L. [3H]-[Thr4,Gly7]OT and 125I-OTA bind with high affinity (mean Kd values of 14 and 0.06 nM, respectively) to the same population of sites on LLC-PK1 cell membranes [maximum binding (Bmax) of 100 fmol/mg membrane protein]. These sites had the expected ligand selectivity of oxytocin receptors. [3H]-[Thr4,Gly7]OT and 125I-OTA binding sites could be distinguished from V2 vasopressin receptors present on LLC-PK1 and LLC-PK1L cells on the basis of clearly different maximal capacities and ligand selectivities, different sensitivities to insulin and serum, and absence of heterologous downregulation. Oxytocin receptors from LLC-PK1 cells have no functional relationship with adenylate cyclase. [Thr4,Gly7]OT affected neither the basal adenosine 3',5'-cyclic monophosphate (cAMP) content nor the vasopressin-induced cAMP accumulation by LLC-PK1 cells. Xenopus laevis oocytes injected with LLC-PK1 cell mRNA responded to [Thr4,Gly7]OT by an increase in 45Ca2+ outflux; this effect is antagonized by a highly selective oxytocin antagonist.

Mechanism of the activation of arachidonic acid release by oxysterols in NRK 49F cells: role of calcium.

We previously demonstrated that oxysterols added to the culture medium of NRK 49F cells labelled with [14C] arachidonic acid potentiated arachidonic acid (AA) release and prostaglandin (PG) E2 biosynthesis induced by the activation of these cells with fetal calf serum (FCS). In the absence of FCS, oxysterols had no effect on AA release. As phospholipase (Plase) A2 activity is Ca2(+)-dependent, we investigated whether oxysterol potentiating effect on AA release was related to an effect of these compounds on cell Ca2+ concentration. In this paper, we show that the intensity of potentiation by oxysterol varies with the external cell Ca2+ concentration; when external Ca2+ is chelated by EGTA, the oxysterol effect persists, though it is decreased. The Ca2+ channel inhibitor nifedipine does not decrease the potentiating effect of 25-OH cholesterol, indicating that, if oxysterol favours Ca2+ entry into the cell, the nifedipine inhibited channel is not involved. At the usual concentration (5 micrograms/ml), oxysterols are not able to increase, immediately or after a short time of contact (90 min) the concentration of intracellular free Ca2+ ([Ca2+])i measured by fluorescence of Quin-2; at very high concentration of oxysterol (25 micrograms/ml), [Ca2+]i only slightly increases (+30%). The liberation of AA induced by cell activation with the Ca2+ ionophore ionomycin is also potentiated by 25-OH cholesterol. All these observations are not in favour of a proper effect of oxysterols on cell Ca2+ level.

Hemodynamic and coagulation responses to 1-desamino[8-D-arginine] vasopressin in patients with congenital nephrogenic diabetes insipidus.

The antidiuretic hormone arginine vasopressin interacts with two types of receptors: V1, which mediates the effects of vasopressin on vascular smooth muscle, and V2, which mediates the antidiuretic effects on renal tubules. Resistance of the renal tubules to arginine vasopressin and to the antidiuretic V2-specific agonist 1-desamino[8-D-arginine] vasopressin (dDAVP) occurs in congenital nephrogenic diabetes insipidus, a rare X-linked disease, although the V1-receptor responses remain intact. The extrarenal actions of dDAVP in normal persons are a decrease in blood pressure, an increase in plasma renin activity, and stimulation of the release of factor VIIIc and von Willebrand factor. We measured the response of mean arterial pressure, pulse rate, plasma renin activity, factor VIIIc, and von Willebrand factor to an infusion of dDAVP (0.3 microgram per kilogram of body weight) in seven male patients with congenital nephrogenic diabetes insipidus, six obligatory carriers of the gene for nephrogenic diabetes insipidus, five patients with central diabetes insipidus, and four normal subjects. In the normal subjects and the patients with central diabetes insipidus, dDAVP decreased mean arterial pressure (by 10 to 15 percent) and increased pulse rate (by 20 to 25 percent), renin activity (by 65 percent), and the release of coagulation factors (twofold to threefold) (all changes were significant, P less than 0.01). None of these changes were observed in the patients with congenital nephrogenic diabetes insipidus, and minimal responses were observed in the obligatory carriers. These results confirm the existence of extrarenal vasopressin V2-like receptors, which may be defective in patients with congenital nephrogenic diabetes insipidus.

Human platelet fraction arginine-vasopressin. Potential physiological role.

Arginine-vasopressin (AVP) immunoreactivity (Ir) has been found to be elevated in platelet-rich plasma. PlatAVP was defined as platelet-rich plasma Ir minus platelet-poor plasma Ir (Pavp). PlatAVP, Pavp, and synthetic AVP were found to have identical retention time on high performance liquid chromatography analysis and similar mobility on thin-layer chromatography. During a standard osmotic suppression-stimulation test, Pavp increased with plasma osmolality (Posm, mosmol/kg H2O); Pavp (pg/ml) = 0.98 (Posm -274.4), r = 0.57, P less than 0.001, n = 65; but PlatAVP was not significantly correlated with Posm and remained at 5 pg/ml. This PlatAVP concentration was estimated to represent a true intraplatelet AVP concentration of 0.4 to 3.7 X 10(-9) M. Binding studies on intact human platelets demonstrated specific binding sites for [3H]AVP (n = 16; BMax = 98 +/- 30 binding sites/platelet; Kd = 0.72 +/- 0.24 nM). This in vitro affinity association constant (Kd) was close to the estimated in vivo intraplatelet AVP concentration. Measurement of PlatAVP could estimate vasopressin bound to a specific platelet receptor.

Chronic renal and neurohumoral effects of the calcium entry blocker nisoldipine in patients with congestive heart failure.

Nisoldipine, a calcium entry blocker, was given to 10 patients with congestive heart failure. During a 2 month follow-up period, 7 of the 10 patients were readmitted with pulmonary edema; daily furosemide doses were increased (128 +/- 87 to 192 +/- 135 mg/day, p less than 0.01), and plasma creatinine increased (1.5 +/- 0.5 to 1.8 +/- 0.6 mg/dl, p less than 0.05) (all values mean +/- SD). Despite this unfavorable clinical course, nisoldipine caused some beneficial chronic (1 month) hemodynamic effects. It decreased systemic vascular resistance (from 1,781 +/- 229 to 1,306 +/- 345 dynes X s X cm-5, p less than 0.01), decreased mean arterial pressure (from 88 +/- 0 to 74 +/- 4 mm Hg, p less than 0.001) and increased stroke volume index (from 27 +/- 6 to 33 +/- 9 ml/min per m2, p less than 0.02). Heart rate, pulmonary capillary wedge pressure and stroke work index did not change. However, nisoldipine's chronic renal and neurohumoral effects were not as favorable. These were assessed during a 5 hour water load (15 ml/kg body weight of 5% dextrose in water) and compared with the effects of a water load before therapy. Nisoldipine did not change creatinine clearance or sodium excretion, but decreased water excretion (from 58 +/- 35 to 46 +/- 40% of water load in 5 hours). Over this 5 hour study, mean plasma vasopressin was also higher with nisoldipine (1.9 +/- 2.3 versus 2.7 +/- 3.2 pg/ml, p less than 0.05), but mean plasma aldosterone was lower (67 +/- 31 to 47 +/- 27 mg/dl, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Sodium and water excretion abnormalities in congestive heart failure. Determinant factors and clinical implications.

The renal hemodynamic and neurohumoral determinants of sodium and water excretion abnormalities were studied in 66 patients with severe chronic congestive heart failure. Abnormalities were not closely related to any one variable but were the result of the convergence of a number of determinants. The most important determinants for sodium excretion were activation of the renin-angiotensin system and ventricular function; and the most important for water excretion were plasma vasopressin, plasma norepinephrine, and renal and ventricular functions. In a subgroup of patients, neurohumoral overactivation led to severe sodium and water excretion abnormalities and to increased furosemide requirements. A 17-month follow-up of all 66 patients showed a less favorable clinical course for this subgroup even when compared with hemodynamically matched patients.

A specific antibody to vasopressin in a man with concomitant resistance to treatment with Pitressin.

A 26-year-old man with complete neurogenic diabetes insipidus since age nine was initially treated with vasopressin (Pitressin Tannate in oil). At age 13, its dosages were progressively increased to control the patient's polyuria; minor allergic symptoms occurred after every such treatment. We incubated serial dilutions of the patient's plasma with 125I-labeled arginine-vasopressin and obtained a 50% specific binding for the plasma at a final dilution of 625-fold. Cross-reactivity studies showed that lysine-vasopressin was better recognized by the antibody than arginine-vasopressin. These results were attributed to large concentrations of lysine-vasopressin (pork vasopressin) in the Pitressin.