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Osmoregulatory effects of prolactin and growth hormone in embryonic chicks
Insights
Bovine prolactin (PRL) significantly reduced sodium and chloride levels in chick embryo allantoic fluid, suggesting sequestering in extracellular fluid. Ovine growth hormone (GH) had a lesser effect on sodium levels.
Area of Science:
- Developmental biology
- Endocrinology
- Comparative physiology
Background:
- Hormonal regulation of embryonic development is crucial for physiological adaptation.
- Prolactin (PRL) and growth hormone (GH) are key endocrine factors influencing growth and metabolism.
- Ionic and osmotic balance are critical for embryonic survival and development.
Purpose of the Study:
- To investigate the effects of bovine prolactin (PRL) and ovine growth hormone (GH) on ion and fluid balance in developing White Leghorn chick embryos.
- To determine the impact of these hormones on electrolyte concentrations ([Na+], [Cl-]) and osmolarity in various embryonic fluid compartments.
Main Methods:
- Intact White Leghorn chick embryos were treated daily with bovine PRL or ovine GH (4-10 µg/g embryo wet wt) from Day 6 to Day 13.
- Control embryos received avian saline.
- Allantoic, amniotic, and plasma samples were collected on Days 10, 12, and 14 for electrolyte and osmolarity analysis; embryo weight, hematocrit, and allantoic volume were also measured.
Main Results:
- PRL treatment led to significantly lower allantoic fluid [Na+] and [Cl-] on Days 10, 12, and 14, with reduced allantoic osmolarity and increased plasma osmolarity on Day 14.
- GH treatment resulted in significantly reduced allantoic [Na+] on Days 10 and 14, with no other significant effects.
- PRL did not affect allantoic volume, amniotic fluid parameters, plasma [Na+] or [Cl-], hematocrit, or embryo wet weight.
Conclusions:
- Bovine prolactin significantly alters ion and osmotic balance in the chick embryo allantoic compartment, indicating a potential role in fluid sequestration.
- The observed decrease in allantoic sodium due to PRL is substantial, equivalent to 10% of total egg sodium, suggesting a significant physiological impact.
- Findings suggest that PRL may induce an expanded extracellular fluid volume in the embryo, a phenomenon observed in other embryonic vertebrates.
Abstract:
Intact White Leghorn chick embryos were treated daily (on Days 6-13) with bovine prolactin (PRL) or ovine growth hormone (GH) at doses of 4-10 micrograms/g embryo wet wt. A control group received an equal volume of avian saline. [Na+] and [Cl-] were determined in allantoic fluid samples taken on Days 10, 12, and 14, and in amniotic fluid and blood plasma on Day 14. Allantoic fluid, amniotic fluid, and plasma osmolarities, embryo wet weight, hematocrit, and allantoic fluid volume were also determined on Day 14. PRL-treated embryos showed significantly lower allantoic [Na+] and [Cl-] compared to controls at Days 10, 12, and 14. Allantoic fluid osmolarity was reduced, and plasma osmolarity increased, at Day 14 in PRL-treated embryos. By contrast, PRL had no effect on allantoic volume, amniotic fluid [Na+], [Cl-], or osmolarity, plasma [Na+] or [Cl-], hematocrit, or embryo wet weight. GH-treated embryos showed significantly reduced allantoic [Na+] at both Days 10 and 14, but no other treatment effect. Calculations show that the decrease in total allantoic Na+ seen in PRL-treated embryos is equivalent in magnitude to 10% of the total egg Na+. Results from studies on embryonic amphibians and mammals suggest that this sodium is likely to be sequestered in an expanded extracellular volume.