Beta-endorphin in genetically hypoprolactinemic rat: IPL nude rat

Beta-endorphin has been reported to regulate not only stress- and suckling induced but also basal prolactin secretion. In the aim to better evaluate the endogenous beta-endorphin-prolactin interrelation, we measured beta-endorphin levels in a new rat strain, genetically hypoprolactinemic and characterized by a total lack of lactation : IPL nude rat.Beta-endorphin was measured using a specific anti-h-β endorphin in plasma and extracts of anterior and neurointermediate lobes of the pituitary, hypothalamus and brain. Pituitary extracts were also chromatographed on Sephadex G50 column. Results obtained showed that in IPL nude females on diestrus and males, the beta-endorphin contents of the neurointermediate lobe was significantly lower than in normal rats, while the values found in the other organs and plasma were similar. However, elution pattern of the anterior pituitary extract from male rats showed greater immunoactivity eluting as I¹²⁵ h-beta-endorphin than in normal rat; this was not the case for the female rat.These results are consistent with a differential regulation of beta-endorphin levels of anterior and neurointermediate lobe by catecholamines. Moreover they suggest that PRL secretion was more related to neurointermediate beta-endorphin.     

Metabolic clearance rate of rat prolactin in preweanling rat pups

The metabolic clearance rate (MCR) of immunoreactive rat prolactin (rPRL) was determined in urethane-anaesthetized 14 to 16-day-old rat pups using the constant infusion to equilibrium method. Two different doses of rPRL were used, 329 and 472 ng/min each at a volume of 0.0025 ml/min for 30 min. The MCR was 0.216 ml/min following infusion of 329 ng PRL/min dose and 0.337 ml/min following infusion of the 472-ng/min dose. When calculated on the basis of metabolic body weight the MCR of rPRL in rat pups was comparable to that of adult rats.     

Chromosomal nonhistone proteins of rat hepatomas and normal rat liver

Chromatin isolated from several well-differentiated rat hepatomas and regenerating liver contains more nonhistone proteins than chromatin of normal liver. Also there are several differences in the electrophoretic patterns of chromosomal nonhistone proteins between hepatomas and normal liver, but not between regenerating or fetal liver and normal liver.     

Inhibition of rat uterine contractions by rat and human CGRP

Effects of rat and human calcitonin gene-related peptide (r alpha CGRP and h beta CGRP, respectively) upon uterine contractile force were investigated using uterine horns from nonpregnant rats, r alpha CGRP and h beta CGRP were equipotent (pD2 = 8.85-9.09) in inhibiting spontaneous and electrically evoked uterine contractions. r alpha CGRP was relatively ineffective in inhibiting potassium-induced contractures of preparations from stilbestrol-pretreated rats. The use of selective antagonists established that r alpha CGRP did not release prostanoids, or release or act at receptors for catecholamines and histamine. The effects of the peptides were not significantly modulated by estrogen levels since pD2 values were similar (8.56-8.86) in field-stimulated preparations from rats in proestrus/estrus or metestrus/diestrus.     

Sialyl transferase activities of rat ascites hepatoma cells and rat liver

Sialyl transferase activities of the homogenate of rat ascites hepatome cells were compared with normal rat liver homogenate. The former had only 20% of the activity of the latter when an exogenous acceptor was added in the reaction mixture.Toward endogenous receptors, the activity of the hepatoma cell homogenate was 50% of that of the normal cell homogenate. A stimulation of the activity toward endogenous acceptors was observed when the homogenate of rat ascites hepatoma cells and that of rat liver were mixed. This stimulatory effect seems to be the consequence of utilization of acceptors from ascites hepatoma cells by the sialyl transferases of the rat liver.     

Depot iron in the rat liver after hypertransfusion with rat erythrocytes

In the rat liver the deposition of iron was measured after hypertransfusion with rat erythrocytes. The liver iron fractions were studied during four weeks after the hypertransfusions. In the first week the haemosiderin iron fraction increased together with the ferritin iron fraction. Most iron was deposited as ferritin iron. In the last week of the experiments, while the ferritin iron fraction still increased, the haemosiderin iron fraction decreased. At the same time plasma iron was utilized when erythropoiesis, which had been suppressed by the hypertransfusion, recommenced. It is suggest that, under these experimental conditions, liver haemosiderin iron is used in haemoglobin synthesis.     

Specific saturable binding of rat high-density lipoproteins to rat kidney membranes

The binding of rat 125I-labelled high-density lipoprotein (HDL) to rat kidney membranes was studied using HDL fractions varying in their apolipoprotein E content. The apolipoprotein E/apolipoprotein A-I ratio (g/g) in the HDL fractions ranged from essentially 0 to 1.5. All these HDL preparations showed the same binding characteristics. The saturation curves, measured at 0 degrees C in the presence of 2% bovine serum albumin, consisted of two components: low-affinity non-saturable binding and high-affinity binding (Kd about 40 micrograms of HDL protein/ml). Scatchard analyses of the high-affinity binding suggest a single class of non-interacting binding sites. These sites could be purified together with the plasma membrane marker enzyme 5'-nucleotidase. The binding of rat HDL to rat kidney membranes was not sensitive to high concentrations of EDTA, relatively insensitive to pronase treatment and influenced by temperature. The specific binding of rat HDL was highest at acid pH and showed an additional optimum at pH 7.5. On a total protein basis unlabelled rat VLDL competed as effectively as unlabelled rat HDL for binding of 125I-labelled rat HDL to partially purified kidney membranes. Rat LDL, purified by chromatography on concanavalin A columns and human LDL did not compete. Unlabelled human HDL was a much weaker competitor than unlabelled rat HDL and the maximal specific binding of 125I-labelled human HDL was only 10% of the value for 125I-labelled rat HDL.     

Metabolic fate of rat and human lipoprotein apoproteins in the rat

The fate of (125)I-labeled apolipoproteins was studied in vivo in rats that had received intravenous injections of (125)I-labeled rat HDL and (125)I-labeled human HDL, LDL, and VLDL. Plasma decay curves of rat and human HDL were exponential with similar half-lives in the circulation (11-12 hr). After injection, low molecular weight apolipoproteins (apoLP-alanine of human HDL and fraction HS-3 of rat HDL) were found to redistribute to other lipoproteins, predominantly VLDL. Decay curves of individual HDL proteins were constructed after lipoprotein fractionation, delipidation, and polyacrylamide gel electrophoresis. It was found that the half-lives of the different HDL apoproteins were not identical. A major rat HDL protein (52% of total counts) had a circulating half-life (t((1/2))) of 12.5 hr. Two others had a t((1/2)) of 8-9 hr while the t((1/2)) of several others was 11-12 hr. The t((1/2)) of three well-characterized human HDL apoproteins, apoLP-glutamine I, apoLP-glutamine II, and apoLP-alanine, were 13.5, 9.0, and 15.0 hr, respectively. The fate of (125)I-labeled human VLDL and LDL apoproteins in rats was similar to that described previously in humans. After injection of (125)I-labeled human VLDL into rats, apoLP-glutamic acid and apoLP-alanine rapidly transferred to rat HDL and were lost thereafter from the circulation from both VLDL and HDL. The apoLDL moiety of human VLDL moved metabolically to the LDL density range (d = 1.019-1.063) through a lipoprotein of intermediate density (d = 1.006-1.019).     

Comparative studies on oestrogen-induced rat uterus peroxidase and rat eosinophil peroxidase

Rat eosinophil peroxidase and rat uterine peroxidase II showed similar electrophoretic mobilities, molecular weights, specific activities and spectral properties and could be purified by essentially identical techniques. Antibodies raised against the uterine enzyme strongly inhibited the eosinophil enzyme. It is suggested that rat eosinophil peroxidase and rat uterine peroxidase II may well be one and the same enzyme.     

Stereospecificity of monoacylglycerol acyltransferase activity from rat intestine and suckling rat liver

The stereospecificity of monoacylglycerol acyltransferase from rat intestinal mucosa and suckling rat liver microsomes was examined using sn-1,2-diacylglycerol kinase from Escherichia coli. With 2-monooleoyl glycerol and palmitoyl-CoA, 88 and 87.9% of the diacylglycerol synthesized by the intestinal mucosa and suckling liver, respectively, was demonstrated to be the sn-1,2-isomer. Analysis of similar preparations of these diacylglycerol products by gas-liquid chromatography-mass spectrometry indicated that most of the remaining diacylglycerol was the 1,3-isomer that probably arose via acyl-migration. These results indicate that monoacylglycerol acyltransferase is stereospecific. Measurement of acyltransferase activities in microsomes using 1- and 2-monoacyl- and monoalkylglycerols as substrates indicated that the monoacylglycerol acyltransferases from suckling liver and intestinal mucosa have different substrate specificities.