Effect of Postnatal Starvation on the 5α-Reductase Activity of the Brain and of the Isolated Myelin Membranes^*

Summary

The 5alpha-reductase, the enzyme which converts testosterone into its major “active” metabolite (dihydrotestosterone, DHT), has been found to be present in high concentration in brain structures particularly rich of myelin (white matter structures), as well as in myelin membranes. Previous ontogenetic observations seem to indicate that, during the process of myelinogenesis, the enzyme might be synthesized in the oligodendrocytes, and subsequently incorporated into the myelin membranes. It is well established that postnatal malnutrition produces a decreased formation of myelin, when starvation is performed from birth until to the 2nd or 3rd week of life ; on the contrary food deprivation does not produce any significant effect on myelin accumulation when performed after the 14th day of life.

The present experiments have been performed in the rat in order to study the effects of postnatal undernutrition (from birth to the 19th day of life: long malnutrition; and from the 14th to the 19th day of life: short malnutrition) on the 5alpha-reductase activity present in the following brain structures: cerebral cortex, hypothalamus, corpus callosum, pyramidal tract, as well as in isolated myelin membranes. Undernourished animals have been killed at 20 days of age. Normally nourished animals served as controls. Long undernutrition induced a statistically significant decrease of the formation of DHT in the corpus callosum and in the pyramidal tract vs controls. On the contrary, the nutritional deficiency did not decrease the 5alpha-reductase activity in the cerebral cortex and in the hypothalamus. Also the enzymatic activity measured in purified myelin membranes did not present any statistical significant variation in either group of starved animals when compared to that present in the myelin of normally fed controls. These data may indicate that postnatal starvation, from birth to the 19th day of life, does not directly influence the synthesis of the 5alpha-reductase, but produces its effects by decreasing the deposition of the myelin membranes in which the 5alpha-reductase appears to be located.

Key words

5alpha-reductase - Testosterone - Postnatal starvation - Myelin - White-matter - Gray-matter