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Short-loop feedback control of luteinizing hormone in the rabbit
The American Journal of Physiology
|April 1, 1976
Summary
This study investigated short-loop feedback for luteinizing hormone (LH) in rabbits. Human LH and hCG suppressed circulating rabbit LH, demonstrating a negative feedback mechanism that changes with time post-castration.
Area of Science:
- Reproductive Endocrinology
- Endocrinology
- Animal Physiology
Background:
- The regulation of luteinizing hormone (LH) secretion is complex.
- Short-loop feedback mechanisms, where pituitary hormones inhibit their own release, are known for some hormones but require further investigation in rabbits.
Purpose of the Study:
- To investigate the existence of a short-loop negative feedback for LH in rabbits.
- To determine if exogenous human LH (hLH) or human chorionic gonadotropin (hCG) can suppress endogenous rabbit LH (rLH) levels.
Main Methods:
- Development of a specific radioimmunoassay for rLH, ensuring no cross-reactivity with hLH or hCG.
- Intravenous administration of hLH or hCG to rabbits at two weeks post-castration.
- Measurement of circulating rLH levels before and after hormone administration.
Main Results:
- Intravenous injection of hLH (10 ng or 100 IU) significantly reduced circulating rLH within 30-60 minutes.
- Intravenous injection of hCG (2,000 IU) also significantly decreased rLH levels.
- hCG failed to suppress rLH in rabbits castrated 6 weeks prior, indicating a time-dependent sensitivity.
Conclusions:
- Direct radioimmunoassay quantification confirms the existence of a short-loop negative feedback for LH in rabbits.
- The sensitivity of this short-loop feedback mechanism appears to change over time following castration.