In vitro decrease of lyase activity in rat ovarian cells during incubation: effect of hCG

Area of Science:

• Biochemistry
• Endocrinology
• Cell Biology

Background:

• Ovarian cells possess C17-C20 lyase activity crucial for steroidogenesis.
• The regulation of this enzyme activity, particularly its spontaneous changes during incubation, is not fully understood.

Purpose of the Study:

• To investigate the mechanisms underlying the spontaneous decrease in C17-C20 lyase activity in ovarian cells.
• To determine the role of oxygen radicals, RNA, and protein synthesis in this decrease.
• To examine the effect of human chorionic gonadotropin (hCG) on C17-C20 lyase activity and its underlying mechanisms.

Main Methods:

• Dispersed ovarian cells from PMSG-pretreated immature rats were incubated in McCoy's 5a medium.
• C17-C20 lyase activity was measured in cell homogenates.
• The effects of N,N'-Diphenyl-p-phenylenediamine (DPPD), actinomycin D, cycloheximide, and hCG on enzyme activity were assessed.

Main Results:

• Spontaneous decrease in C17-C20 lyase activity occurred over time.
• DPPD and actinomycin D inhibited this spontaneous decrease, suggesting a role for oxygen radicals and de novo synthesis.
• Cycloheximide also protected the activity, further supporting the involvement of protein synthesis.
• hCG decreased lyase activity, an effect prevented by actinomycin D and cycloheximide, indicating RNA and protein synthesis involvement, but not oxygen radicals.
• Delta 5-3 beta-hydroxysteroid dehydrogenase activity remained largely unchanged.

Conclusions:

• The spontaneous decline in C17-C20 lyase activity is mediated by both oxygen radical damage and de novo RNA/protein synthesis.
• hCG-induced reduction in C17-C20 lyase activity involves de novo RNA and protein synthesis, independent of oxygen radicals.
• These findings align with the in vivo effects of hCG on ovarian lyase activity.