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Changes in uptake of 3H-progesterone by female rat brain and pituitary from birth to sexual maturity
Insights
Newborn rats show high progesterone uptake in the brain and pituitary. This uptake sharply decreases after the first week, suggesting developmental changes in hormone binding and plasma levels.
Area of Science:
- Neuroendocrinology
- Developmental Biology
- Pharmacology
Background:
- Progesterone plays a crucial role in reproductive functions and neurodevelopment.
- Understanding progesterone uptake dynamics in the developing brain is essential for comprehending its physiological effects.
Purpose of the Study:
- To investigate the developmental changes in 3H-progesterone uptake in the brain, pituitary, and skeletal muscle of female rats from birth to sexual maturity.
- To determine the timing of specific progesterone binding in the hypothalamus and pituitary.
Main Methods:
- Comparison of 3H-progesterone uptake across various tissues (brain regions, pituitary, skeletal muscle) at different ages (newborn to 50 days).
- Intraperitoneal injection of 3H-progesterone followed by radioactivity measurement at 1 hour post-injection.
- Calculation of tissue-to-cerebellar cortex radioactivity ratios to assess specific binding.
Main Results:
- High progesterone uptake was observed in all investigated tissues of newborn and 5-day-old rats, decreasing sharply thereafter.
- Pituitary consistently showed higher uptake than other tissues.
- Specific binding, indicated by increased tissue/cortex ratios, appeared in the posterior hypothalamus at 50 days, while the pituitary exhibited this from birth.
Conclusions:
- The initial high progesterone uptake in young rats is likely due to high plasma concentrations.
- The decrease in uptake during the first two weeks reflects declining plasma radioactivity.
- Specific progesterone binding capacity emerges in the hypothalamus with sexual maturity, whereas it is present in the pituitary from birth.
Abstract:
3H-progesterone uptake by various parts of the brain, pituitary and skeletal muscle was compared in newborn, 5-, 10-, 15-, 20-, 25- and 50-day old female rats at 1 hr after a single intraperitoneal injection of 50 muCi/100g body weight. High uptake values in newborn animals and in those aged 5 days were found in all tissues investigated. A sharp decrease in accumulation was observed from birth and/or 5th day of life. The uptake by pituitary was persistantly higher than those by other tissues investigated. The ratio of the concentration of radioactivity between the tissues and the cerebellar cortex increased significantly only in the posterior hypothalamus of adult females (at the age of 50 days). In the pituitary the ratio tissue/cortex was already significantly higher in newborns. The high level of brain radioactivity in the youngest animals is probably a manifestation of high plasma concentrations of tritiated progesterone. The striking decrease in uptake of radioactivity by the brain and pituitary during the first two weeks of life most likely reflects the decrease in level of plasma radioactivity, as shown indirectly by the concomitant decrease in labelled progesterone uptake by the skeletal muscle. The increase in tissue/cortex ratio in the posterior hypothalamus with attainment of sexual maturity suggests the first appearance of specific binding capacity for progesterone which is assumed to be present in the pituitary already from birth.