The rise of the plasma lipid concentration elicited by dietary sodium chloride restriction in Wistar rats is due to an impairment of the plasma triacylglycerol removal rate

Studies in humans have indicated that dietary salt restriction raises plasma levels of total cholesterol (TC) and triacylglycerols (TAG). In order to explain the mechanisms involved, a rat experimental model was developed consisting of chronic feeding ad libitum isocaloric diets with variable sodium chloride contents. Rates of synthesis of plasma TAG were measured either as the increase of plasma TAG after blocking its removal from plasma by the intra-arterial pulse infusion of Triton-WR 1339, or as the plasma rate of incorporation of [(14)C]-oleic acid [(14)C]-TAG. Plasma TAG removal rate was determined by the intra-arterial pulse infusion of a lipid emulsion. Severe salt restriction increased the plasma concentrations of TAG (71%) and of TC (10%). This result was not due to modification of the rate of synthesis of plasma TAG but was attributed to a 55% slower rate of removal of the TAG-containing lipoproteins. An increased plasma non-esterified fatty acid concentration, probably due to a salt restriction-related insulin resistance, may have impaired the activity of the enzyme lipoprotein lipase.

Effects of apolipoprotein B-100 on the metabolism of a lipid microemulsion model in rats

In previous studies, it was shown that lipid microemulsions resembling LDL (LDE) but not containing protein, acquire apolipoprotein E when injected into the bloodstream and bind to LDL receptors (LDLR) using this protein as ligand. Aiming to evaluate the effects of apolipoprotein (apo) B-100 on the catabolism of these microemulsions, LDE with incorporated apo B-100 (LDE-apoB) and native LDL, all labeled with radioactive lipids were studied after intraarterial injection into Wistar rats. Plasma decay curves of the labels were determined in samples collected over 10 h and tissue uptake was assayed from organs excised from the animals sacrificed 24 h after injection. LDE-apo B had a fractional clearance rate (FCR) similar to native LDL (0.40 and 0.33, respectively) but both had FCR pronouncedly smaller than LDE (0.56, P<0.01). Liver was the main uptake site for LDE, LDE-apoB, and native LDL, but LDE-apoB and native LDL had lower hepatic uptake rates than LDE. Pre-treatment of the rats with 17alpha-ethinylestradiol, known to upregulate LDLR, accelerated the removal from plasma of both LDE and LDE-apoB, but the effect was greater upon LDE than LDE-apoB. These differences in metabolic behavior documented in vivo can be interpreted by the lower affinity of LDLR for apo B-100 than for apo E, demonstrated in in vitro studies. Therefore, our study shows in vivo that, in comparison with apo E, apo B is a less efficient ligand to remove lipid particles such as microemulsions or lipoproteins from the intravascular compartment.

Plasma kinetic behavior in hyperlipidemic subjects of a lipidic microemulsion that binds to low density lipoprotein receptors

It was previously reported that a protein-free microemulsion (LDE) with structure roughly resembling that of the lipid portion of low density lipoprotein (LDL) was presumably taken up by LDL receptors when injected into the bloodstream. In contact with plasma, LDE acquires apolipoproteins (apo) including apo E that would be the ligand for receptor binding. Currently, apo were associated to LDE by incubation with high density lipoprotein (HDL). LDE-apo uptake by mononuclear cells showed a saturation kinetics, with an apparent K(m) of 13.1 ng protein/mL. LDE-apo is able to displace LDL uptake by mononuclear cells with a Ki of 11.5 ng protein/mL. LDE without apo is, however, unable to displace LDL. The uptake of 14C-HDL is not dislocated by increasing amounts of LDE-apo, indicating that HDL and LDE-apo do not bind to the same receptor sites. In human hyperlipidemias, LDE labeled with 14C-cholesteryl ester behaved kinetically as expected for native LDL. LDE plasma disappearance curve obtained from eight hypercholesterolemic patients was markedly slower than that from 10 control normolipidemic subjects [fractional clearance rate (FCR) = 0.02 +/- 0.01 and 0.12 +/- 0.04 h-1, respectively; P < 0.0001]. On the other hand, in four severely hypertriglyceridemic patients, LDE FCR was not significantly different from the controls (0.07 +/- 0.03 h-1). These results suggest that LDE can be a useful device to study lipoprotein metabolism.

Plasma kinetics of a chylomicron-like emulsion in patients with coronary artery disease

Chylomicron catabolism in the bloodstream consists of lipolysis by lipoprotein lipase and uptake of remnants by the liver. In rats, triglyceride-rich emulsions can mimic chylomicron metabolism. To further validate this model in man, the emulsion was injected intravenously into fasting and into subjects previously fed a test fatty meal. The plasma kinetic curves of the emulsion 3H-triglyceride and 14C-cholesteryl ester were determined. The fractional clearance rate (FCR) of both labels was markedly reduced in the fed subjects (triglycerides: fed = 0.018 +/- 0.007; fasting = 0.105 +/- 0.013 min-1, P < 0.001; cholesteryl ester: fed = 0.016 +/- 0.001; fasting = 0.040 +/- 0.006 min-1; P < 0.05) indicating that the emulsion and chylomicrons generated from the testinal lipid absorption compete for the same catabolic processes, confirming the validity of the method. The emulsion was injected into 11 patients with CAD and into 11 controls. All had plasma cholesterol < 240 and triglycerides < 250 mg/dl. FCR of triglycerides was 5-fold smaller in CAD compared to controls (0.028 +/- 0.004 and 0.141 +/- 0.069 min-1, respectively, P < 0.01). FCR of cholesteryl ester was 4-fold smaller in CAD than in controls (0.015 +/- 0.004 and 0.056 +/- 0.067 min-1 respectively, P < 0.05). These results indicate that both chylomicron lipolysis and remnant removal are diminished in CAD.

Pharmacokinetic studies of 131I-stevioside and its metabolites

131I-STEVIOSIDE (1.10 MBq) was injected i.v in Wistar male rats, in distribution in the body and metabolism were studied. The highest concentration of radioactivity was observed in the liver and in the small intestine after 10 and 120 minutes, respectively. At 2 h after injection, the radioactivity eliminated in the bile was 52.0% of the original dose. The results of RP-HPLC analysis of the bile showed that stevioside was degraded in vivo and that steviol appeared as a major metabolite. However, in the urine; RP-HPLC analysis did not show the presence of steviol.

Metabolic behavior in rats of a nonprotein microemulsion resembling low-density lipoprotein

A protein-free microemulsion (LDE) with a lipid composition resembling that of low-density lipoprotein (LDL) was used in metabolic studies in rats to compare LDE with the native lipoprotein. LDE labeled with radioactive lipids was injected into the bloodstream of male Wistar rats, and plasma kinetics of the labeled lipids were followed on plasma samples collected at regular intervals for 12 h after injection. The 24-h LDE uptake by different tissues was also measured in tissue samples excised after the animals had been sacrificed. We found that LDE plasma kinetics were similar to those described for native LDL [fractional clearance rate (FCR) of cholesteryl ester, 0.42 +/- 0.11 h-1]. The major site for LDE uptake was the liver, and the tissue distribution of the LDE injected radioactivity was as one would expect for LDL. To test whether LDE was taken up by the specific LDL receptors, the LDE emulsion was injected into rats treated with 17 alpha-ethinylestradiol, which is known to increase the activity of these receptors; as expected, removal of LDE from the bloodstream increased (FCR = 0.90 +/- 0.35 h-1). On the other hand, saturation of the receptors that remove remnants by prior infusion of massive amounts of lymph chylomicrons did not change LDE plasma kinetics. These results indicate that LDE is cleared from plasma by B,E receptors and not by the E receptors that remove remnants. Incorporation of free cholesterol into LDE increased LDE plasma clearance. Incubation studies also showed that LDE incorporates a variety of apolipoproteins, including apo E, a ligand for recognition of lipoproteins by specific receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Characteristics of growth hormone binding to liver microsomes of pregnant women

Specific binding of hGH to liver microsomes of nonpregnant women and men is low, usually 10% of less in RRA. In pregnant women, however, we found that this binding is 10 times higher. The binding reaction shared the properties common to receptor systems: time, temperature and cation dependence, saturability and reversibility, hGH specific binding without cations was 10 times lower. The cross-reactions of hPRL and human placental lactogen with hGH were 0.49 +/- 0.16% and 0.10 +/- 0.05%, respectively. 125I-hPRL and 125I-human placental lactogen binding to microsomes of two controls and two pregnant women were very low and poorly reproducible. The Scatchard analysis revealed two hGH binding sites, one with an association constant (KA) of 2.7 +/- 0.1 x 10(10) M-1, and the other with a KA of 1.5 +/- 0.1 x 10(9) M-1. In one nonpregnant woman, we found a single hGH binding site with a KA of 1.5 x 10(9) M-1, confirming results previously reported in the literature. A hGH RRA was set up with microsomes of pregnant women. Acromegalic sera produced curves parallel to the hGH standard and pituitary dwarf serum had no 125I-hGH displacing activity. Sera of pregnant women produced curves divergent to the hGH standard and showed a 125I-hGH displacing activity 20 to 40 times higher than could be predicted by hGH levels determined by RIA. Cord sera and sera from puerperal women had similar hGH levels as determined by either RRA or RIA (r = 0.93, P less than 0.001, slope = 0.85, n = 25). Our results show the existence of specific GH receptors and serum factor(s) with high 125I-hGH displacing activity from these receptors in pregnancy. These findings must be related to several metabolic changes of pregnancy, such as glucose intolerance, hyperinsulinemia, increased lipolysis, and ketogenesis.

Development of an homologous radioimmunoassay for the synthetic amino terminal (1-34) fragment of human parathyroid hormone using egg yolk-obtained antibodies

An homologous radioimmunoassay for the synthetic 1-34 amino terminal fragment of human parathyroid hormone (hPTH) was developed using antibodies obtained from yolk of eggs layed by an immunized chicken. The 125I labelled 1-34 hPTH peptide was purified by cation-exchange chromatography which provided a highly stable preparation. The specificity of the assay showed a cross-reactivity of 50% with the 1-34 hPTH (code 81/574) preparation and 27% with the 1-84 hPTH (code 79/500) preparation, when compared with the 1-34 hPTH from Bachem that was used for immunization and labelling. The minimal detectable dose of the assay was 10 pmol/l; in 69 healthy controls the values obtained ranged from less than 10 to 28 pmol/l and in 14 patients with surgically proven primary hyperparathyroidism from 10 to 519 pmol/l.

Periodic remission in Cushing's disease with paradoxical dexamethasone response: an expression of periodic hormonogenesis

A patient with Cushing's disease due to a chromophobe adenoma was studied for 243 days before pituitary surgery and evidence for periodicity in cortisol steroid production was found with cycles occurring every 85.8 days (peak-to-peak length), associated with laboratory remissions and paradoxical response to dexamethasone. The autonomy of ACTH secretion was suggested by the nonresponsiveness to repeated lysine-vasopressin stimulation tests and lack of increase in urinary 170HCS following metyrapone. A distinct response of the hyperplastic glands (as demonstrated by percutaneous adrenal venography) was obtained on several B1-24 corticotropin stimulation. The patient's hypercortisolism disappeared following removal of the chromophobe adenoma through transphenoidal hypophysectomy.

Comparison of plasma progesterone assay in women by competitive protein binding (CPB) and radioimmunoassay (RIA)

Plasma progesterone levels during the follicular and luteal phases were compared when measured simultaneously by competitive protein binding (using guinea pig sera as binding agent) and radioimmunoassay (antiserum against progesterone-11-alpha-succinyl bovine serum albumin in rabbits), the values obtained were significantly different within each technique, depending on whether previous thin-layer chromatographic purification of the extracts was employed or not. No significant differences were noticed between CPB and RIA when the chromatographic step was used, but when it was omitted, CPB was greater than RIA at the follicular but not at the luteal phase.