Expression of mRNA encoding insulin-like growth factor binding protein-2 (IGFBP-2) during induced and natural regression of equine corpora lutea.

This research article investigates the role of insulin-like growth factor binding protein-2 (IGFBP-2) in luteolysis, the degradation of the corpus luteum, in horses. The study finds evidence of increased potential for IGFBP-2 production in the early stages of natural luteolysis, which may assist in inhibiting progesterone production, but doesn’t deem IGFBP-2 to be a mediator in luteolysis triggered by a pharmacological dose.

Understanding the Context

• The research focuses on the role of insulin-like growth factor binding proteins (IGFBP), specifically IGFBP-2 and its impact on luteal function—the performance of the corpus luteum. Corpus luteum is an endocrine structure that forms in an ovary after an ovum is released from the follicle during ovulation and which secretes progesterone.
• The insulin-like growth factors (IGF) I and II are known to play an important role in luteal function. However, IGFBP-2 and -3 are capable of inhibiting the binding of IGF and lowering progesterone levels.

Research Methods

• The researchers collected corpora lutea (plural of corpus luteum) from female horses at different stages of the luteal phase: mid-luteal (day 10), early regression (day 14), and late regression (day 17). Two additional collections were done 12 and 36 hours after injecting the animals with cloprostenol, a synthetic form of the hormone prostaglandin F2α commonly used to induce luteolysis.

Insights and Findings

• The level of mRNA coding for P450scc, a key enzyme involved in steroidogenesis, decreases significantly during early natural regression and 12 hours after administering cloprostenol.
• On the other hand, the level of mRNA coding for IGFBP-2 significantly increases between mid-diestrus and during both early and late regression as well as 36 hours after the cloprostenol injection.

Conclusions

• The researchers deduce that the observed increased capability of producing IGFBP-2 in the early phases of natural luteolysis appears to restrict IGF-I within the corpus luteum, aiding in the inhibition of progesterone production.
• Despite this, the delay in the spike in IGFBP-2 mRNA following cloprostenol administration, along with the rapid decrease in P450scc mRNA suggests the luteolysis, brought on by this pharmacological intervention, may not involve IGFBP-2.