Showing papers by "University of Buenos Aires published in 1974"

Effect of Gonadal Steroids on the Response to LH-RH in Intact and Castrated Male Rats*

Abstract: The effect of pretreatment with several sex steroids and some of their combinations was studied in intact and castrated male rats. The pretreatment of intact male rats with testosterone did not modify the FSH release but inhibited the LH release after the injection of LH-RH as compared with the oil-pretreatment control rats. Dihydrotestosterone significantly depressed LH release, but did not modify FSH release after the administration of LH-RH. This resulted in a change of the FSH/LH ratio in serum after LH-RH, as compared with the oil-treated rats. Estradiol significantly inhibited the FSH release, but augmented the LH release after administering LH-RH, also resulting in a change of the FSH/LH ratio as compared with control rats. 17-α-Hydroxyprogesterone and pregnandione did not modify the pituitary response to LH-RH. The combination of estradiol plus dihydrotestosterone depressed the pituitary response to LH-RH. Estradiol plus 17-α-hydroxyprogesterone slightly augmented, and estradiol plus pregnandione ...

Pseudotype formation between enveloped RNA and DNA viruses.

Abstract: ENVELOPED RNA viruses from different groups participate readily with each other in phenotypic mixing during maturation at the plasma membrane of host cells. These ‘pseudotypes’ with the envelope antigens of one virus and the genome of the other have been demonstrated for simian virus 5 and vesicular stomatitis virus (VSV)1, for avian or murine RNA tumour viruses and VSV2–4, and for fowl plague virus and VSV5. (An exception has been the lack of interaction between Sindbis virus and VSV6.) We have now found virions containing the RNA genomes of VSV in the envelope antigens of a DNA virus, herpes simplex virus (HSV). These interactions between genomes and antigens of unrelated groups may be part of a mechanism for viral pathogenesis and oncogenesis.

Blockage of cation permeability across the tight junctions of gallbladder and other leaky epithelia

Abstract: THE main route of passive ion permeability in gallbladder and other ‘leaky’ epithelia is through the so-called ‘tight’ junctions between cells, not through the cells themselves1. I report here that the protonated form of the organic base 2,4,6-triamino-pyrimidine (TAP), reversibly and specifically blocks cation permeation across this tight junction route in frog gallbladder and several other leaky epithelia. Since in these epithelia the tight junction permeability is mainly (or even completely) cationic, in principle on addition of TAP a low resistance, leaky epithelium can become a high resistance epithelium.

A kinetic study of the Na pump in red cells: its relevance to the mechanism of active transport.

Abstract: One of the possible approaches t o understand better the mechanism responsible of the active movements of Na or K catalyzed by the Na pump is t o look at the dependence of these movements with the concentration of cations in the intraor extracellular media. This sort of study has been greatly favored by the development of procedures that allow the intracellular composition of red cells to vary within a wide range.' The study of the kinetics of cation fluxes through the Na pump can be approached in two rather different ways. The first is t o look at the flux vs. cation concentration curves when cation concentration is varied at one of the surfaces and kept constant at the opposite surface of the cell membrane. From the shape of these curves we can obtain indirect information on the number of cation binding sites, their apparent affinities, their interactions, and the like.2y3 But, however useful these studies may be, they are hampered by the fact that almost always more than one kinetic scheme will fit the experimental results. The distinction between alternative models lies beyond the realm of kinetics and probably will become possible only when procedures t o measure the binding of cations t o purified ATPase preparations become available. Another way of using the kinetic approach to study the mechanism of the Na pump is to look at the effect that changes in the cation composition a t one of the surfaces of the cell membrane have on the shape of the curves relating cation flux with cation composition at the opposite surface of the cell membrane.4 We would like t o comment now on the results of experiments performed in human red cells in which the second approach was employed, and t o show that they place a set of rather stringent restrictions on the hypothetical schemes of the Na pump.

ISOLATION OF HYDROPHOBIC PROTEINS BINDING NEUROTRANSMITTER AMINO ACIDS: γ‐AMINOBUTYRIC ACID RECEPTOR OF THE SHRIMP MUSCLE

Abstract: — The total lipid extract of shrimp muscle (Artemisia longinaris) was precipitated with ether. The supernatant containing 95 per cent of the phospholipids and 50 per cent of the protein showed binding for L-[14C]glutamatc in the first peak of protein. The sediment, redissolved in chloroform-methanol was chromatographed on a Sephadex LH-20 column. A single peak was eluted in the chloroform (20-40 ml) having no lipid phosphorous and high affinity binding for [14C]GABA. The saturation was achieved at 1 mole per 80.000 g protein and the curve revealed a single type of binding site. The purification achieved was of about 4000-fold. There was no binding of L-[14C]glulamate to the ether precipitate. The specificity of the binding of [14C]GABA was further supported by competition experiments with bicuculline. picro-toxin and muscimol. It is suggested that the hydrophobic protein isolated by us represents the GABA receptor. The findings presented in the two papers of the series suggest that the excitatory and inhibitory receptor from crustacean muscle can be separated as two different proteins.

Isolation of hydrophobic proteins binding neurotransmitter aminoacids. Glutamate receptor of the shrimp muscle.

Abstract: — –Muscle of shrimps (Artemisia longinaris) were extracted with chloroform-methanol (2:1, v/v) and the proteolipids were separated by column chromatography on Sephadex LH-20. Three peaks of protein were eluted with chloroform and one with chloroform-methanol (4:1, v/v). Only the first peak eluted between 16 and 26 ml of chloroform showed binding for l-(14C]-glutamate. The type of saturation curve obtained suggests the existence of single type of binding site. The saturation is reached at one mole of l-glutamate per 320,000 g protein and the purification achieved about 3200-fold. The protein binding-glutamate does not bind GABA, aspartate or glutamine. The binding of l-[14C]-glutamate was inhibited by dl-α -methyl glutamic acid and l-glutamic acid diethyl ester. The binding properties of this hydrophobic protein fraction suggest that it may represent the isolated glutamate receptor of the shrimp muscle.

Neonatal undernutrition and RNA synthesis in developing rat brain.

Abstract: —Underfeeding of newborn rats results in a decreased body and brain weight at 10, 20 and 30 days of age. The DNA and RNA content of the brain in these animals are similar to those of normal controls. The in vivo and in vitro synthesis of RNA in brain is significantly decreased in undernourished rats at 10 days of age when compared with controls. The metabolic transformation of 3H-orotic acid to nucleotides is also diminished. A short period of food rehabilitation produces -an improvement in the above mentioned alterations. However, a reduced incorporation of label into microsomal RNA persists even in the last condition. The results suggest that malnutrition, during the first days of life, alters the metabolism of cerebral RNA.

Serum levels of C1q, C1r and C1s in normal and pathologic sera.

Abstract: C1q, C1r and C1s protein concentrations were simultaneously assayed in sera of patients with systemic lupus erythematosus (SLE), rheumatoid arthritis, autoimmune hemolytic anemia, and viral hemorrhagic fever as well as in healthy adult control subjects. Correlation coefficients between the three subunits of C1 were calculated and the sequential evolution of C1q, C1r, and C1s levels was studied in patients with SLE. In the majority of cases there was a good correlation between C1q, C1r, and C1s; subunit levels increased or decreased in a coordinated fashion. A marked discrepancy between C1q, C1r, and C1s serum concentration was observed in 3 instances. Low C1q coexisted with extremely high C1r and C1s values. It appears that C1r and C1s are closely linked while C1q may vary in a more independent way.

Effect of sulpiride on prolactin release by rat pituitaries in vitro

Abstract: La sulpiride stimule la liberation de la prolactine de l'hypophise apres 4 h d'incubation. L'addition d'extraits hypothalamiques l'inhibe, mais la sulpiride ajoutee en meme temps aux extraits hypothalamiques permet l'inversion de cet effet d'inhibition. Il semble evident que la sulpiride peut modifier la liberation de la prolactine en agissant directement sur l'hypophise du rat, in vitro.

Luteinizing Hormone Releasing Hormone-Biosynthesis by Rat Hypothalamus in Vitro. Influence of Castration

Abstract: Summary The biosynthesis of the luteinizing hormone releasing hormone (LRH) from3H-tyrosine by rat hypothalamus in vitro has been studied in normal and castrated male rats. After 1 hour of incubation with 3H-Tyr the hypothalamic extracts were chromatographed on Sephadex G-25. Fractions with LRH activity determined by in vivo assays, eluted from this column were passed through a CM-Sephadex C-25 column with a gradient of ammonium acetate 50 mM, pH 5.0–200 mM pH 7.0. Radioactivity which emerged in the fraction with LRH activity was considered as 3H-Tyr incorporated into peptides with LRH activity and this incorporation is higher in castrated than in normal rats.

Two novel metabolites of Aspergillus fonsecaeus.

Abstract: DelAspergillus fonsecaeus (N. R. R. L. 67, O 16-1) se han aislado dos nuevos pigmentos que fueron identificados como monometil eteres de la fonsecina y de la rubrofusarina, respectivamente.

Sequential renal lipid changes in weanling rats fed a choline-deficient diet.

Abstract: To clarify conflictive aspects related to the possible pathogenic role of renal lipid changes in the usually fatal renal necrosis occurring in choline-deficient rats, a severely hypolipotropic basal diet that induces renal necrosis was fed ad libitum to male rats for 5 days. Control rats were pair-fed the same basal diet supplemented with choline. Renal lipid changes were sequentially studied at days 2, 4, and 5, and the values of these determinations were expressed using different base parameters to facilitate adequate interpretation. Since at day 5 almost 50% of the choline-deficient rats had renal necrosis, the data obtained at this time were separated into those preceding and those accompanying necrosis. The analyses of the results obtained under these conditions suggested that the most significant prenecrotic lipid change is a decrease in the renal content of phospholipids occurring shortly before necrosis (day 5). At this time the levels of sphingomyelin in the nonnecrotic kidneys of choline-deficient rats were signifi cantly higher than those of the control rats while the levels of phosphatidylinositol were significantly lower. It is concluded that contrary to recent proposals, the possibility still exists that a renal phospholipid deficit and/or other more subtle changes in the indi vidual renal phospholipids may play a role in the pathogenesis of this condition. J. Nutr. 104: 1496-1502, 1974.

Development of a method to test anti-LH-RH activity in rats.

Abstract: A method for testing anti-LH-RH activity wasdevised. The substance to be investigated was infused for 2 h i.e. in ovariectomized, estrogen- and progesterone-pretreated rats, followed by an acute injec

Direct estimation of lightness of surface colors

Abstract: Achromatic and chromatic lightness and darkness of an array of 104 reflecting surfaces were scaled by the method of magnitude estimation. Samples subtended a visual angle of 4° and were viewed under both artificial light and daylight. The dominant wavelengths of the chromatic samples were blue 470, green 553, yellow 574, and red 622 nm. For each hue, the subjective attributes of both lightness and darkness were judged at five levels of colorimetric purity Pc. Both lightness and darkness increased as a power function of the luminous reflectance of the neutral grays and the pigmented surfaces. The lowest exponents, from 0.5 to 0.74, were found among the most and the least saturated samples. Exponents of about 1.0 were obtained for both lightness and darkness functions for the neutral grays, for two Pc levels of red, for one Pc level of green, and one of blue, under both artificial light and daylight. For the yellows, the exponents were close to 1.0 at all purity levels under daylight only. All other samples gave exponents less than one.