Notes on Reproductive Cyclicity - Luteal Phase

Overview of the Luteal Phase

• Time Frame: From ovulation until luteolysis of the corpus luteum (CL).
• Dominant Hormone: Progesterone (P4).
• Stages: Two stages include Metestrus and Diestrus.

Antral Follicle and Luteinization

• Origin: Corpus luteum forms from the ovulatory follicle after ovulation, driven by LH.
• Process: Luteinization occurs, transforming follicular cells into luteal cells, essential for progesterone production.

Corpus Luteum (CL)

• Palpation: CL can be palpated in cattle, functionality assessed via ultrasonography.
• Cell Types: Large luteal cells (secretory) and small luteal cells (steroidogenic). P4 production is crucial for maintaining pregnancy.

Progesterone's Role

• Effects:
  • Endocrine Influence: High P4 inhibits cyclicity, reduces GnRH frequency, and prepares for the next cycle.
  • Target Tissues: Affects the hypothalamus, uterus, mammary glands, and muscular myometrium.

Luteolysis

• Definition: Decomposition of the corpus luteum to resume folliculogenesis.
• Hormonal Interaction: Involve oxytocin, progesterone, and PGF2α; essential for CL regression.
• Countercurrent Exchange: Efficient transport of PGF2α from the uterus to the CL.

Manipulating Estrous Cycles

• Exogenous P4: Used to synchronize estrus; controlled internal drug release (CIDR) devices provide an artificial CL effect.
• Synchronization Methods: Various methods exist (e.g., Ovsynch) to manage breeding times effectively.

Human Contraception Strategies

• P4 Administration: Various methods include oral pills, transdermal patches, and injections that suppress GnRH and cyclicity, mimicking luteal phase conditions.