Patterns of apoptosis during degeneration of the pronephros and mesonephros.

Purpose: The adult mammalian kidney is preceded developmentally by 2 primitive kidneys. We determine whether apoptosis is involved in the regression of these primitive organs and document its temporospatial characteristics.

Materials And Methods: Timed pregnant rats were sacrificed at 11 to 16 days of gestation inclusively. The fetuses were histologically examined to determine the timing and pattern of apoptosis in the primitive kidneys, including pronephros and mesonephros.

Results: Apoptosis of the pronephros occurred primarily at 12 days of gestation. Apoptosis of the distal mesonephros occurred primarily at 13 days and was completed by 14, which left the proximal mesonephros a functioning kidney during the early period of development. The location and timing of apoptosis were consistent and specific.

Conclusions: Apoptosis appears to be an important mechanism of the normal regression of the primitive kidney and follows a strict temporospatial pattern.