Rat kidney sialidase levels have been reported to be markedly altered in pathological
states such as diabetes. This was associated with a modification of sialic acid levels.
Therefore, it was interesting to study the variations of kidney sialidase and sialyltransferase
activities and sialic acid content according to sex and age. This was carried out from birth to
210 days of age. The substrates used were sialyla(2-3)[^3H]-lactitol for sialidase activity, asialofetuin
and [^14C]-CMPNeu5Ac for sialyltransferase activity. In males sialidase activity
increased until 32 days then slightly declined. In females, the activity increased and leveled
off at 135 days of age. Higher sialidase activity was observed in females than in males from
56 days of age. Gonadectomy had no effect on this activity. In both sexes, sialyltransferase
activity decreased markedly with age. This activity was higher in females than in males,
whereas sialic acid levels varied only moderately with age and were slightly higher in
females.