The use of flufenamate and forskolin to evaluate the role of cAMP in gonadotropin-releasing hormone-stimulated luteinizing hormone secretion from pituitaries of ovariectomized rats

Abstract

Flufenamate which inhibited gonadotropin-releasing hormone (GnRH)-stimulated cAMP production in pituitaries from ovariectomized (72 hr) rats, was used to determine whether ovariectomy induces a change in the role of cAMP as a mediator of luteinizing hormone (LH) secretion. Additionally, the study evaluated the practicability of utilizing forskolin to restore intracellular cAMP concentrations in the presence of flufenamate. Infusions of flufenamate to perifused pituitary tissue blocks did not affect the protein synthesis-independent component of GnRH-stimulated LH secretion, but completely inhibited the protein synthesis-dependent component. Dibutyryl cAMP (dbcAMP) and forskolin potentiated the GnRH-stimulated responses, and restored the LH secretion inhibited by flufenamate, even though these agents were ineffective secretagogues when administered singly. The LH responses affected by forskolin were dependent on protein synthesis, while dbcAMP affected both the protein synthesis-dependent and -independent components of GnRH-stimulated LH secretion. Since the effects of dbcAMP on the protein synthesis-independent component of LH secretion might be due to interactions with GnRH receptors, the results suggest that forskolin might be a better choice for restoring intracellular cAMP levels in the presence of flufenamate when assessing the role of cAMP in gonadotropes. The study also indicates that ovariectomy does not result in a change in the role of cAMP, which appears to be a pivotal, but indirect mediator of the protein synthesis-dependent component of GnRH-stimulated LH secretion.