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FSH-response adenylyl cyclase in rat testes: desensitization by homologous hormone
Abstract:
Injection of high doses of FSH causes a partial desensitization of the FSH-responsive adenylyl cyclase (AC) in adult rat testes. The loss of responsiveness to FSH is dependent on time. Two hours after injection of one dose of human FSH (256 micrograms hFSH-PT2) in vivo, no effect was seen on FSH-stimulated AC activity (Km and maximal activation). After 24 hr there was an approximately 40% decrease in FSH activated AC. Injection of two doses of FSH (256 micrograms hFSH-PT2) 24 and 48 hr before being killed, gave a loss in FSH-responsive AC activity of approximately 60%. The decreased FSH-stimulated AC activity after FSH injections in vivo was associated with a comparable decrease in specific FSH binding. Whether this is a reflection of receptor occupancy or down regulation of the number of FSH receptors is not known. Desensitization of the FSH-responsive AC caused by FSH was not associated with a change in its Km.
Insights
High doses of follicle-stimulating hormone (FSH) desensitize the FSH-responsive adenylyl cyclase (AC) in rat testes over time. This desensitization correlates with reduced FSH binding, impacting reproductive signaling.
Area of Science:
- Reproductive Endocrinology
- Molecular Endocrinology
- Cell Signaling
Background:
- Follicle-stimulating hormone (FSH) plays a crucial role in testicular function.
- FSH signaling in the testes involves the adenylyl cyclase (AC) pathway.
- Understanding FSH receptor regulation is key to reproductive health.
Purpose of the Study:
- To investigate the effects of high-dose FSH administration on FSH-responsive adenylyl cyclase (AC) activity in adult rat testes.
- To determine the time-dependent nature of FSH-induced desensitization.
- To explore the relationship between FSH desensitization and FSH receptor binding.
Main Methods:
- Adult rats were injected with varying doses and frequencies of human FSH (hFSH-PT2).
- FSH-stimulated adenylyl cyclase (AC) activity was measured in testicular tissue.
- Specific FSH binding to testicular receptors was quantified.
Main Results:
- A single high dose of FSH caused no immediate change in FSH-stimulated AC activity.
- After 24 hours, a single FSH dose resulted in approximately 40% decrease in FSH-activated AC.
- Two FSH doses led to a ~60% loss in FSH-responsive AC activity, associated with decreased FSH binding.
Conclusions:
- High-dose FSH induces time-dependent desensitization of the testicular FSH-responsive adenylyl cyclase (AC).
- The observed desensitization is linked to a reduction in specific FSH binding.
- Further research is needed to determine if receptor occupancy or downregulation causes the decreased binding.