Temporal relationships between stress protein induction, progesterone withdrawal, and apoptosis in corpora lutea of ewes treated with prostaglandin F2 alpha.

Immunofluorescent staining was used to detect in situ alterations in inducible heat shock (stress) protein (HSP)-70 production and DNA fragmentation (indicative of apoptotic cell death) in luteal tissues obtained from sheep after in vivo administration of a luteolytic dose of PGF2 alpha. Accumulation of HSP-70 was localized to PG-sensitive (i.e., large) luteal cells. Cytoplasmic HSP-70 increased within 2 h after treatment. Luteal concentrations of progesterone decreased precipitously thereafter. Expression of HSP-70 diminished by 16 h. An increase in immunostained digoxigenin-labeled DNA was not detected until the onset of structural involution at 16 h; both large and small steroidogenic cells were affected. It is suggested that HSP-70 induction by PGF2 alpha is a prelude to steroid depletion and active apoptotic death of luteal cells.