Polyamines and amino acid incorporation in vitro into microsomes of rat cerebral cortex

Modulation of protein synthesis in a cell-free system derived from rat brain by corticotropin (ACTH), magnesium, and spermine

Modulation of protein synthesis by fragments of the ACTH molecule has been studied in a cell-free system obtained from subcortical brain tissue of rats. Both the activity of the protein-synthesizing system and its sensitivity to ACTH-like peptides appeared to be highly dependent on the Mg2+ and spermine concentrations. At optimal Mg2+ concentrations (4 mM) the peptide sequences ACTH(1-24) and (11-24) were both inhibitory, the latter being the more active. The inhibitory effect was reduced or abolished at higher (suboptimal) concMg2+ concentrations. Spermine, like ACTH, inhibited protein synthesis at the optimal Mg2+ concentration. However, at lower Mg2+ concentrations spermine had a stimulatory effect and maximal activity was obtained at 0.75-1.0 mM Mg2+. In the presence of spermine (60 microM) and Mg2+ (0.75 mM), a half-maximal inhibition of protein synthesis was obtained with a peptide concentration of 5 microM. A structure-activity study showed that the peptides ACTH(7-16)-NH2, (11-24), (5-18, 17Lys 18Lys)-NH2 and (15-24) were active in inhibiting protein synthesis, whereas the fragments ACTH(1-16)-NH2 and (17-24) were inactive. The results are discussed in terms of an interaction between ACTH, Mg2+, and spermine, and intracellular processes involved in protein synthesis.

Effects of insulin on cultured rat brain cells: stimulation of ornithine decarboxylase activity

Growth-promoting peptide hormones, including growth hormone and insulin, stimulate rat brain ornithine decarboxylase (ODC; EC 4.1.1.17) activity in vivo (Roger et al., 1974; Roger and Fellows, 1980). To determine if this is a result of a direct action on brain, we have investigated the effect of peptide hormones in primary cell cultures of brain from fetal rats of 20 days gestational age. Significant stimulation of ODC activity was observed 4 h after administration of porcine insulin and bovine growth hormone. On a molar basis, growth hormone was less potent than insulin. By contrast, glucagon, enkephalin, and angiotensin II did not stimulate ODC in this system. At 25 ng/ml, insulin stimulated ODC activity approximately threefold, with maximum stimulation of five- to sevenfold reached at 1 microgram/ml. After a 1-h lag, insulin-stimulated ODC activity increased to a maximum between 5 h and 8 h and returned to basal levels by 24 h. The apparent Km of ODC, 5.66 +/- 1.16 microM, was not significantly altered by insulin treatment, nor was any enzyme activator found in mediating insulin actions. Additional evidence suggests that insulin stimulation of ODC activity involves both de novo synthesis of the enzyme and a prolongation of ODC half-life by 50%. These findings, implicating insulin as a regulator of ODC activity in brain cells, suggest the possible involvement of insulin or an insulin-like peptide in the control of growth and development of the CNS.

Effect of polyamines on cell-free protein synthesizing systems from rat cerebral cortex, cerebellum and liver

The naturally occurring polyamines spermine and spermidine stimulate in low concentrations the amino acid-incorporating activity of cell-free systems from cerebral cortex, cerebellum and liver from the rat to a significant degree, but in high concentrations they have strong inhibiting effects on these systems. Maximal polyamine stimulation is observed with suboptimal Mg2+ concentrations in the reaction mixtures; increasing Mg2+ to 15 mM results in an inhibition of cell-free protein synthesis by polyamines even at low concentrations. The stimulating effect of spermine and spermidine involves a facilitated binding of template RNA and aminoacylated tRNA to the ribosomes. In contrast, the aminoacylation of tRNA is not influenced. These data indicate that spermine as well as spermidine have regulatory functions during the translational process in cerebral cortex, cerebellum and liver. They seem to interact with ribosomal functions and to cause a shift in the optimal Mg2+ concentration required for the synthesis of brain and liver proteins.

Polyamines and their biosynthetic decarboxylases in various tissues of the young rat during recovery from undernutrition

1. Weanling male and female rats were undernourished for 4 weeks and then rehabilitated by allowing ad libitum feeding. 2. During rehabilitation polyamine-biosynthetic enzymes were examined in the liver, spleen and quadriceps and gastrocnemius muscles. 3. During the first few hours of rehabilitiation there was a marked increase in liver weight, accompanied by a very marked increase in ornithine decarboxylase activity. Increases in the activity of this enzyme in other tissues did not occur until between 2 and 7 days of rehabilitation, at which time there were further increases in enzyme activity in the liver. 4. S-Adenosylmethionine decarboxylase activity also showed marked fluctuations in activity in all the tissues examined. 5. Hepatic putrescine and spermidine concentrations also varied during rehabilitation, but permine concentration remained relatively constant. Both spermine and spermidine were at normal concentrations in the liver from the 10th days of rehabilitation onwards. 6. In all of the tissues examined there were marked sex differences in the parameters studied, particularly in splenic and muscular ornithine decarboxylase activity. 7. In the tissues of the male rats, changes in polyamine synthesis paralled changes in nucleic acid and protein synthesis.

The effect of chronic self-administration of d-amphetamine on food intake, locomotor activity, and C14-leucine incorporation into cerebral cortex protein

Rats had free access to 0.02% d-amphetamine solution instead of water for 23 days. The daily amphetamine consumption was found to increase from 16 mg/kg on day 1 up to 47 mg/kg on day 23. Tolerance to the anorexic effect of the drug was apparent on day 11. The initial depression in body weight persisted throughout the experiment. The hyperactivity of rats remained at the same level despite the daily increase in amphetamine intake. The incorporation of C14-leucine into cerebral cortex proteins was initially increased and returned to control level after 2 weeks of treatment. No direct correlation between hyperactivity and brain cortex protein synthesis was observed.

Ornithine decarboxylase activity in relation to DNA synthesis in mouse interfollicular epidermis and hair follicles

The relationship between ornithine decarboxylase (L-ornithine carboxylyase, EC 4.1.1.17) activity and DNA synthetic activity was studied in mouse epidermis. Interfollicular epidermis and hair follicles were investigated separately. It was found that, in hair follicles, the variations of DNA replicative activity, which are reflected in the cyclic growth of hair, are paralleled by corresponding changes in ornithine decarboxylase activity. In both interfollicular epidermis and hair follicles, stimulation of DNA synthetic activity by plucking of hair induced a rapid and marked increase in ornithine decarboxylase activity. The relationship of steady-state and induced ornithine decarboxylase activity to DNA synthetic activity was compared in hair follicles and interfollicular epidermis. A correlation between the activity of this enzyme and DNA replication was found thereby in each of these tissues.