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[Possible implication of TRH and dopamine in postnatal lactotropic hypoactivity in rats]
Insights
Young rat pituitary glands show increased prolactin (PRL) secretion with thyrotropin-releasing hormone (TRH), but dopamine (DA) significantly weakens this response, indicating complex hormonal regulation.
Area of Science:
- Endocrinology
- Neuroscience
- Developmental Biology
Background:
- Prolactin (PRL) secretion is crucial for lactation and is regulated by hypothalamic hormones.
- Thyrotropin-releasing hormone (TRH) stimulates PRL release, while dopamine (DA) inhibits it.
- Understanding the developmental changes in pituitary gland reactivity is essential for reproductive health.
Purpose of the Study:
- To investigate the in vitro response of immature and mature rat pituitary glands to TRH and DA.
- To elucidate the role of dopaminergic control in early postnatal PRL secretion regulation.
- To examine the factors influencing lactotroph sensitivity to TRH during early life.
Main Methods:
- Primary pituitary cell cultures from 6-day-old and adult rats.
- In vitro incubation of pituitary glands with varying concentrations of TRH and DA.
- Measurement of prolactin (PRL) secretion using established biochemical assays.
Main Results:
- Immature rat pituitary glands exhibited a proportionally greater increase in PRL secretion in response to TRH compared to adult glands.
- Dopamine (DA) significantly attenuated the TRH-stimulated PRL secretion in both young (60%) and adult (40%) pituitary glands.
- Basal PRL secretion was significantly lower in immature glands compared to mature glands.
Conclusions:
- The observed insensitivity to TRH in early postnatal life is not due to lactotroph failure but rather the influence of multiple regulatory factors.
- Dopaminergic control plays a critical role in modulating lactotroph responsiveness during the early postnatal period.
- These findings highlight the complex interplay of central and peripheral factors in regulating prolactin secretion during development.
Abstract:
Our results show that pituitary glands of young rats (6 days) incubated in vitro, increase their PRL secretion in presence of TRH, this responses is greater than that in adult glands. Indeed, in presence of TRH 10(-7) M, PRL basal secretion of immature glands passes from 478.70 +/- 67.25 to 952.78 +/- 67.02, versus 5333.29 +/- 75.456 and 6347.15 +/- 75.246 ng/mg protein at mature glands. The same dose of dopamine (DA), weakens the TRH stimulating effect by 60% and 40% respectively by young and adult pituitary glands. These results suggest that lactotroph insensitiveness to TRH injection observed during the first days of postnatal life at the rat, would not be explained by lactotroph failure, but by intervention of central and peripheral multiple modulator factors affecting lactotrophs reactivity, in particular the importance of dopaminergic control.