Labelling of lipids by radioactive amino acids in the central nervous system

Involvement of sphingolipids in the endothelin-1 signal transduction mechanism in rat brain

In cerebral cortex, endothelin-1 (ET-1) evoked a decrease of 40% in sphingomyelin (SM) levels together with an increase in both ceramide and glycosphingolipid (GSL) levels (100 and 56% respectively). These facts indicate that ET-1 increases sphingomyelinase activity and, possibly, activates the synthesis of GSL. By contrast, in cerebellum ET-1 seems to activate the hydrolysis of both SM and GSL, since the peptide evoked a decrease (near 30%) of their levels concomitantly with an increased production of ceramides (200%). These ceramides are clearly different from those produced in cerebral cortex which come from the SM hydrolysis only. It is suggested that ETB receptor subtype is involved in these responses.

Increased dietary leucine changes the rhythm of prolactin secretion

As we have recently shown that prolactin secretion in vitro is regulated by extracellular leucine, we wanted to determine whether leucine had a similar regulatory action on prolactin secretion in the intact animal. Leucine was administered to cycling female rats by way of their drinking water (0.5%) for a period of 24 days. At daily intervals during this time, six control and six leucine-treated rats were killed and their trunk blood subsequently assayed for prolactin content. On days 7, 14, and 21 during this period, pituitaries from the sacrificed rats were fixed and processed for electron microscopy. Leucine treatment resulted in an alteration in the normal four-day cyclicity in serum prolactin levels and a stimulation of prolactin synthesis as evidenced by ultrastructural changes in the pituitary mammotrophs. In a parallel set of experiments, daily vaginal smears were taken from nonsynchronized animals for 24 days before and 24 days during leucine administration. Leucine treatment resulted in variable alterations in the estrus cycle depending upon the stage of the cycle when the leucine was first administered. The changes in serum prolactin and the disturbances of the estrus cycle in the leucine-treated animals persisted for approximately 20 of the 24 days. In a shorter control experiment (seven days), alanine treatment (0.5%) was found to have no effect on prolactin levels. It is concluded that a mild elevation in dietary leucine can affect prolactin synthesis and release and the normal progression of the estrus cycle.

Effects of branched-chain amino acids on beta-endorphin in the pituitary of the rat

Despite evidence that the branched-chain amino acids (BCAAs) influence brain metabolism and neurotransmitter synthesis, there is little information on the neuroendocrine effects of the BCAAs. We now report that administration of a mixture of the BCAAs 3 times daily for 12 days to Sprague-Dawley rats decreased the concentration of beta-endorphin immunoreactivity (BEI) in the neurointermediate lobe of the pituitary. In BCAA-treated rats, BEI was 21 +/- 4 compared to control levels of 57 +/- 12 (ng/microgram of protein). The BCAAs had no effect on the level of BEI in the adenohypophysis. These findings suggest that changes in availability of leucine, isoleucine, and valine mediate specific neuroendocrine responses to metabolic perturbations in the rat.

Distribution of radioactivity among total myelin protein amino acids following administration of labeled glycine, leucine, or methionine

This paper analyzes the distribution of radioactivity in the different amino acids of brain myelin protein for up to 6-7 weeks after an intracranial pulse administration of radioactive leucine, glycine, or methionine. Results show that there is no significant accumulation or reutilization of protein radioactivity in any form other than the one administered.

Lipogenesis in the developing brain: utilization of radioactive leucine, isoleucine, octanoic acid and beta-hydroxybutyric acid

Incorporation of radioactivity from intracranially injected radioactive leucine, isoleucine (ketogenic amino acids), octanoic acid and beta-hydroxybutyric acid into the brain lipids of 15 to 16 day-old rats was examined. The results showed that radioactivity from all the above precursors was incorporated into brain lipids. Radioactivity from injected isoleucine was incorporated into odd numbered fatty acids indicating an alternate pathway to alpha-oxidation for the biosynthesis of these fatty acids in the brain. For some as yet unclear reasons, a substantial portion of the radioactivity from injected octanoic acid was incorporated into free fatty acids. Utilization of these compounds for providing carbon for lipogenesis during development under unstressed normal conditions is discussed.

Lithium induced alterations in rat ganglionic lipids

Superior cervical ganglia from normal or lithium fed rats were incubated in vitro with [U-14C]pyruvic acid, in Krebs-Ringer solution with or without lithium ion. Acute lithium incubations were performed on ganglia from normal rats with 25 mEquiv./l of lithium ion, while chronic incubations were performed on ganglia from lithium fed rats with 0.5 mEquiv./l lithium in the bathing solution. Lipids were extracted, separated by thin layer chromatography and specific activities of individual lipids and their fatty acids determined. In control ganglia shinogolipids contained 60-70% of the lipid radioactivity, glycerophospholipids 20-30% and neutral lipids 10-25%. Phosphatidylcholine contained 65% of the glycerophospholipid label and 40% of the lipid phosphorus, while sphingomyelin contained 90% of the sphingolipid label and exhibited the highest specific activity over all. Cholesterol was the major neutral lipid. Niety-five per cent of the glycerophospholipid label and 4% of the sphingomyelin label was localized in the fatty acids. The lipid and fatty acid compositions of all ganglia were similar. However the lipid radioactivity in chronic ganglia was lower than in control, with the sphingolipids most affected. In 80 min stimulated chronic ganglia stearic and oleic acid, radioactivity was depressed with respect to both control fatty acids and to the [14C]palmitate of chronic tissues. In both chronic and acute lithium ganglia stimulated for 80 min, the specific activities of phosphatidylinositol were significantly lower than in control. In contrast to control, the labeling of sphingolipids in resting acute ganglia was higher than in stimulated tissues.

Leucine and D-3-hydroxybutyrate as lipid precursors in developing rat spinal cord and liver

By using a labelled ketone body, D-3-hydroxy[3-14C]butyrate, or a ketone-body precursor, L-[4,5-3H]leucine, preferential labelling of spinal-cord cholesterol was demonstrated. In contrast, the phospholipid fraction was more heavily labelled in the liver. In both tissues phosphatidylcholine was the major labelled complex lipid. Incorporation ob both substrates into total lipid, on a tissue-weight basis, was appreciably greater for spinal cord.