Acta physiologica latino americana最新文献

The turnover and composition of normal and hyperlipemic (h.l.) low density lipoproteins (LDL) of rabbits, were studied. They were obtained by ultracentrifugation and labeled by Bolton and Hunter method. Normal and h.l. LDL labeled with 125I were injected directly and crossed to both groups of rabbits. Normal and h.l. LDL had a different protein/lipid ratio. The analysis of fractional catabolic rate of LDL and the half-life of the phases of rapid and slow decay, show that h.l. LDL had a fractional catabolic rate that is the half of normal LDL and an increased half life of the phases of rapid and slow decay. Apparently, two factors: a) defective LDL receptor in the h.l. rabbit and b) different physico-chemical properties between normal and h.l. LDL, would be the reason for this difference. Besides, when normal and h.l. 125I LDL were injected into h.l. and normal rabbit, respectively, LDL changed according to the injected rabbit, as can be deduced from the analysis of the half life of the phase of slow decay.

Glucose consumption by anaerobic glycolysis and the pentose pathway were studied in two Aymara populations living at different altitudes (3 600 m and 450 m). The measurements were made both with and without methylene blue. We observed a Pasteur effect for both pathways which may explain the increase in 2-3 DPG and ATP levels found in blood samples from people living at high altitudes. The results in the presence of methylene blue showed a reduced activity of the methaemoglobin reductase system in the high altitude group which may be partly responsible for their increased levels of methaemoglobin.

The present experiments were designed to analyze the effect of verapamil, nifedipine and isoproterenol on myocardial contractility (+dT/dtmax) and time to peak tension (TTP) and its dependence on extracellular calcium concentration (Ca2+). The experiments were performed on cat papillary muscles from reserpinized cats. At (Ca2+) 1.34 mM the negative inotropic effect of cumulative doses of verapamil and nifedipine and the positive inotropic effect of isoproterenol occurred associated with a significant and dose-dependent decrease in TTP. The decrease in TTP produced by calcium blockers was completely reversed by the addition of calcium in a close parallelism with the recovery in myocardial contractility: At (Ca2+) 1.34 mM; verapamil 10(-6)M significantly decreased TTP from 299 +/- 14 msec to 250 +/- 11 msec. At (Ca2+) 15 mM values for TTP were 285 +/- 7 msec (control) and 291 +/- 5 msec (verapamil). Nifedipine 5 X 10(-7) M decreased TTP from 343 +/- 20 msec to 246 +/- 4 msec (Ca 1.34 mM). Values of TTP at calcium 15 mM were 296 +/- 6 msec (control) and 300 +/- 17 msec (nifedipine). On the contrary, the significant decrease in TTP produced by isoproterenol 10(-5)M at (Ca2+) 1.34 from 266 +/- 14 msec to 222 +/- 14 msec was still present at (Ca2+) 15 mM: 233 +/- 8 msec (control) and 220 +/- 8 msec (isoproterenol). The results suggest that the decrease in TTP produced by calcium blockers and isoproterenol is mediated by different mechanisms.

When 3H-20-hydroxyecdysone was injected into Triatoma infestans during the fifth nymphal instar, it was converted to very polar metabolites (peak 1). The polar metabolites were glucuronoconjugates of 20-hydroxyecdysone. Acetylation of the conjugates followed by hydrolysis with glucuronidase gave a major labelled product: 20-hydroxyecdysone and minor peaks corresponding to a mixture of 20-hydroxyecdysone acetates. These results indicated that the 2,3,22,25-glucuronoconjugates of 20-hydroxyecdysone were the principal products in the inactivation process.

A group of male rabbits was starved for 7 days. Their blood samples were collected, before and after the starvation period. Six rabbits were slaughtered for the recovery of livers, while the rest were refed for the next 7 days, at the end of which their blood samples were collected and livers taken out for various analyses. After 7 days of starvation, the total leukocytic count, haemoglobin, bilirubin, proteins and glucose contents, and activities of alkaline phosphatase and glutamate pyruvate transaminase of blood serum decreased significantly, while its lactate dehydrogenase activity and cholesterol, total lipids and urea contents showed a significant increase. In liver, except for the bilirubin and glucose contents, all the biochemical components--RNA, DNA and total proteins included--showed highly elevated values. Refeeding of the starved rabbits tended to normalize most within 7 days. Although RNA, DNA, total proteins, cholesterol and urea contents did not reach the normal level in liver during this period, they were definitely less than those of the starved condition. The hepatic transaminases activities and lipid content in starved + refed livers were considerably decreased during the refeeding period. The histological parameters were slow to recover.

The presence of two fractions with affinity for 1-14C palmitic acid was demonstrated in the 105,000 x g supernatant of rat liver homogenate by Sephadex G-75 gel filtration. The lowest molecular weight fraction was identified as fatty acid binding protein as judged by its relative elution volume in Sephadex G-75, its binding characteristics to sulfobromophthalein and palmitic acid binding inhibition by flavaspidic acid. Discontinuous sucrose gradient was used to study palmitic acid exchange from these cytosolic fractions to microsomes and mitochondria. Both fractions from rat liver were more effective than albumin in the exchange of palmitic acid to particulate material. Palmitic acid was exchanged from fatty acid binding protein to liposomes. This and perhaps other cytosolic protein/s participate in cellular fatty acid transport.

Binding of cortisol and corticosterone by serum proteins is well established, but discrepancies exist regarding aldosterone. We have observed that approximately 1% of 3H-aldosterone incubated with rat serum was bound in a time-dependent process, although it was not competed by a large excess of non-radioactive aldosterone, assessed by Florisil separation or gel filtration on Sephadex G-50 columns. After electrophoresis on cellulose acetate of rat serum incubated with 3H-aldosterone, specific or non-specific binding to protein fractions was not obtained. Further, a 10 000-fold molar excess of aldosterone (10 microM) displaced only 34% of the bound 3H-aldosterone to rat serum, preventing the calculation of the IC50 value. Increasing concentrations of aldosterone (3-83 nM) did not displace 3H-corticosterone bound in rat serum to presumably corticosterone binding globulin (CBG). In contrast, inhibition of this binding by 3-83 nM corticosterone was concentration dependent, showing an IC50 value of 10(-8) M. In normal human serum, binding of 3H-aldosterone demonstrated competition by a 100 and 1 000-fold excess of aldosterone. Displacement curves of 3H corticosterone bound to human serum by 1.7-75 nM corticosterone or 0.05-8.8 microM aldosterone yielded IC50 values in the range of 10(-8) M for corticosterone and 10(-6) M for aldosterone. With horse serum, aldosterone's binding affinity was three orders of magnitude lower than that of corticosterone. These studies suggest that in the rat aldosterone was loosely and weakly bound to a high capacity binder, possibly albumin. In agreement with the work of others, in humans aldosterone may be bound to both CBG and albumin. The current data do not substantiate for the presence of specific aldosterone binding proteins in serum.

The effects of cyproterone and of tamoxifen citrate upon the hair waves were studied in normal and castrated C57 mice. Cyproterone (1 mg/day) had no effect upon the hair waves in normal male mice and produced a slight inhibition of the diffuse growth induced by their castration. Tamoxifen citrate (1 mg/day) had no effect upon the hair waves in normal female mice and produced a marked inhibition (0.2 to 1 mg/day) upon the diffuse hair growth induced by their castration. The differences between the effects of castration and the effect of these drugs can be explained in the case of cyproterone by a slight agonistic androgenic effect and in the case of tamoxifen citrate by a marked agonistic estrogenic effect upon the hair follicles in mice.

An evaluation was made on the growth of Sarcoma 180 (S 180) in normal and splenectomized BALB/c mice which had been immunized 40 days before the tumor challenge with BCG, either intradermally or in diffusion chambers placed in the peritoneal cavity. Immunization with intradermal BCG did not modify the growth of subcutaneous S 180, whereas it provided significant protection when the tumor was inoculated with BCG. Previous treatment with BCG in diffusion chambers had no effect on the development of S 180, but significantly decreased the percentage of survival of mice inoculated with S 180 mixed with BCG, as compared to the homologous group immunized with intradermal BCG. Splenectomy performed before the challenge with S 180, enabled 56% of mice lacking previous immunization to survive and increased this percentage to 100% when the tumor was inoculated mixed with BCG. As for splenectomized mice immunized with BCG within diffusion chambers and challenged with S 180, there was 90% of survival and 69% in those challenged with S 180 mixed with BCG. These results would suggest that the action of BCG on the growth of S 180 differs according to whether the mycobacteria are in direct contact with the host or exert their effect by means of soluble antigens capable of passing through the millipore filter of the diffusion chambers. These effects would be conditioned by the immunological state of the host.