Effects of hormones on the fast axoplasmic transport of substances in ventral horns of the spinal cord in rats of different ages.

Samples of 7-8 microl of aqueous solution of L-[(14C)]leucine (spec. act. 12543 MBq/mmol) were introduced in the zone of the ventral horn (L(5)-L(6)) of the spinal cord of adult (8-12 month) and old (26-28 month) male Wistar rats. The radioactivity of all 3-mm parts of the corresponding ventral roots was measured. Anabolic hormones (including sex steroids and small doses of thyroxine) increase the rate of axoplasmic transport of substances both in adult and old rats, while insulin accelerates the rate of axoplasmic transport in adult rats and has no effect in old animals. There is a more marked increase in the rate due to administration of estradiol dipropionate in old rats and due to testosterone propionate in adult animals. The catabolic hormone hydrocortisone slows down the flow. In old rats the effect of castration on the axoplasmic flow is weakened, while thyroidectomy induces no change. The data obtained revealed age-related change in hormonal regulation, being linked with hormonal effects upon protein biosynthesis in tissues of the zone of the ventral horns of the spinal cord. With aging, the effects of many hormonal systems on the axonal transport are weakened, which is one of the reasons for its slowdown in old age.