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A sex-specific endogenous stimulatory rhythm regulating prolactin secretion
B J Arey1, R L Averill, M E Freeman
1Department of Biological Sciences, Florida State University, Tallahassee 32306.
Endocrinology
|January 1, 1989
Summary
Female rats exhibit an endogenous prolactin (PRL) secretion rhythm, distinct from male rats. This rhythm, influenced by neonatal steroid environment, suggests a complex regulatory mechanism for PRL release.
Area of Science:
- Neuroendocrinology
- Reproductive Biology
- Hormone Regulation
Background:
- Prolactin (PRL) secretion in rats is primarily under inhibitory control by tuberoinfundibular dopaminergic (DA) neurons.
- Dopamine (DA) levels in hypophysial portal blood decrease during PRL surges, but this alone doesn't fully explain the PRL release.
- The study hypothesizes an endogenous stimulatory rhythm for PRL secretion, masked by tonic DA inhibition and revealed by DA reduction.
Purpose of the Study:
- To investigate the existence of an endogenous stimulatory rhythm for prolactin (PRL) secretion in rats.
- To determine if this rhythm is masked by dopamine (DA) and unmasked by DA-lowering stimuli.
- To examine the influence of the neonatal steroid environment on sex-specific PRL secretory characteristics.
Main Methods:
- Pharmacological depression of DA-ergic tone using domperidone (DOM) in ovariectomized (OVX) female, adult castrated (AC) male, neonatally androgen-sterilized (TP) female, and neonatally castrated (NC) male rats.
- DOM was administered at specific times: 0300 h, 1700 h (known PRL surge times in mated rats), and 1200 h (intersurge interval).
- Serial blood samples were collected to measure serum PRL levels following DOM injection.
Main Results:
- Ovariectomized (OVX) female rats showed significantly higher serum PRL responses to DOM at 0300 h and 1700 h compared to 1200 h.
- Adult castrated (AC) male rats exhibited lower PRL responses to DOM than OVX rats, with no significant time-dependent differences.
- Neonatally androgen-sterilized (TP) and neonatally castrated (NC) male rats displayed PRL secretory patterns similar to AC males, indicating the critical role of the neonatal steroid environment.
Conclusions:
- The study provides evidence for an endogenous, time-specific stimulatory rhythm for PRL secretion in female rats.
- This rhythm appears to be masked by tonic dopamine inhibition and is unmasked by domperidone administration.
- Neonatal steroid exposure is crucial for the development of sex-specific PRL secretion patterns.