Follicular development and ovulation in hypothyroid rdw rats

Area of Science:

• Reproductive Endocrinology
• Thyroid Hormone Action
• Follicular Dynamics

Background:

• Spontaneously hypothyroid rats (rdw) exhibit infertility, impacting follicular development and ovulation.
• Thyroid hormones, like thyroxine (T4), play a crucial role in reproductive processes.
• Equine chorionic gonadotrophin (eCG) is a key gonadotropin used to stimulate follicular growth.

Purpose of the Study:

• To investigate the effects of thyroxine (T4) and equine chorionic gonadotrophin (eCG) on follicular development and ovulation in infertile, immature, hypothyroid rdw rats.
• To determine if T4 therapy can improve ovarian function and egg yield in this specific rat model.

Main Methods:

• Immature, spontaneously hypothyroid rdw rats were treated with T4 and/or eCG from postnatal day 21 to 29.
• Ovarian weight and follicular populations (healthy and atretic, by size) were assessed on day 30.
• Egg ovulation was quantified following gonadotropin treatment (hCG).

Main Results:

• T4 therapy increased ovarian weight and the number of healthy antral follicles (101-400 µm and >550 µm) in rdw rats, with or without eCG.
• T4 treatment did not alter atretic follicles but reduced large atretic follicles (>400 µm) when eCG was present.
• Significantly more eggs were ovulated (85±5) in rdw rats treated with both gonadotropins and T4 compared to gonadotropins alone (5±2).

Conclusions:

• Thyroxine (T4) treatment improves follicular development in the presence of eCG in hypothyroid rdw rats.
• T4 significantly increases the number of ovulated eggs following hCG treatment in this infertile rat model.
• T4 therapy represents a potential strategy to enhance reproductive outcomes in conditions of thyroid deficiency.