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Functional development of the hypothalamic-adenohypophyseal-testicular (HAT) axis in the chick embryo
Insights
The male chick embryo
Area of Science:
- Reproductive Endocrinology
- Developmental Biology
- Avian Embryology
Background:
- The development of the reproductive axis in avian embryos is crucial for sexual differentiation and development.
- Understanding the timeline of the hypothalamic-adenohypophyseal-testicular axis functionality is key to comprehending embryonic development.
- Previous studies have suggested but not definitively proven the early functionality of this axis in chick embryos.
Purpose of the Study:
- To determine the functional status of the adenohypophyseal-testicular axis in chick embryos.
- To investigate the role of the pituitary gland and luteinizing hormone (LH) in regulating embryonic testosterone production.
- To establish the earliest time point at which the hypothalamic-adenohypophyseal-testicular complex is functional during incubation.
Main Methods:
- Surgical partial decapitation (hypophysectomy) was performed on male chick embryos at 33-38 hours of incubation.
- Plasma testosterone concentrations were measured using radioimmunoassay (RIA) throughout the incubation period (Days 7.5-17.5).
- Luteinizing hormone (LH) was administered via the chorioallantoic membrane (CAM), and pituitary tissue was transplanted to the CAM in some groups.
Main Results:
- Decapitated chick embryos exhibited significantly lower plasma testosterone levels compared to intact controls from Day 13.5 onwards.
- Administration of LH to decapitated embryos restored plasma testosterone to normal levels by Day 13.5.
- Combined LH and pituitary CAM transplants elevated plasma testosterone levels above normal by Day 15.5.
Conclusions:
- The adenohypophyseal-testicular axis is functional in the chick embryo by Day 13.5 of incubation.
- The pituitary gland, through LH, plays a critical role in stimulating testosterone production in the developing embryonic testes.
- Evidence suggests the hypothalamic-adenohypophyseal-testicular complex is functional by Day 13.5, indicating coordinated endocrine regulation.
Abstract:
Plasma testosterone concentrations in intact and surgically partially decapitated (hypothalamo-hypophyseoprivic) chick embryos were determined by radioimmunoassay for the incubation interval, Days 7.5-17.5. "Hypophysectomy" of male chick embryos at 33-38 hr of incubation resulted in plasma testosterone levels which were significantly lower than those of intact embryos on Days 13.5, 15.5, and 17.5. The addition of luteinizing hormone (LH) to the chorioallantoic membrane (CAM) of decapitated embryos increased plasma testosterone concentrations to normal levels by Day 13.5, while LH and pituitary transplants to the CAM elevated plasma testosterone to above normal values by Day 15.5. These observations, together with other findings, are interpreted as demonstrating that in the chick embryo the adenohypophyseal-testicular axis is functional by Day 13.5 of incubation. There are also indications that the hypothalamic-adenohypophyseal-testicular complex is functional at this same embryonic time.