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Increased plasma prolactin levels in ovariectomized thyroidectomized rats treated with estrogen
1Institute of Physiology, National Yang-Ming Medical College, Taipei, Taiwan, Republic of China.
Endocrinology
|June 1, 1990
Summary
Hypothyroidism in female rats increases prolactin (PRL) secretion, particularly when estrogen is present. This is due to heightened pituitary gland responsiveness to thyrotropin-releasing hormone (TRH), not dopamine.
Area of Science:
- Endocrinology
- Reproductive Biology
Background:
- Thyrotropin-releasing hormone (TRH) stimulates prolactin (PRL) and thyroid-stimulating hormone (TSH) secretion.
- Hyperprolactinemia is common in hypothyroid women, but experimental findings vary by sex and treatment.
Purpose of the Study:
- To investigate the physiological control of PRL secretion in hypothyroid female rats.
- To determine the role of estrogen and thyroid hormone status on PRL regulation.
Main Methods:
- Adult female Sprague-Dawley rats underwent ovariectomy (OVX) and/or thyroidectomy (Tx).
- Polyestradiol phosphate (PEP) and/or TRH were administered.
- Plasma PRL, TSH, and TRH levels were measured via RIA.
- Dopamine antagonist (domperidone) and agonist (CB154) effects were assessed.
Main Results:
- Ovariectomized and thyroidectomized (OVX + Tx) rats treated with estrogen (PEP) showed higher basal and surge PRL levels than controls.
- Estrogen treatment significantly increased PRL and TSH response to TRH in OVX + Tx rats.
- Thyroid hormone replacement (T4) dose-dependently decreased both basal and TRH-stimulated PRL secretion.
- Dopamine manipulation did not alter the observed differences in PRL secretion.
Conclusions:
- Increased PRL in estrogenized, hypothyroid female rats is linked to enhanced pituitary sensitivity to TRH.
- Dopamine pathways do not appear to mediate this increased PRL secretion.
- Thyroid hormone levels are inversely correlated with plasma PRL levels.