The role of second messenger interactions in the control of androgen production in the mouse Leydig cell.
Date
1991
Authors
Hipkin, Richard William George.
Journal Title
Journal ISSN
Volume Title
Publisher
Dalhousie University
Abstract
Description
The goal of the studies in this thesis was to characterize the role of second messenger interactions in regulation of androgen (T) output by the Leydig cell (LC).
Analogues of cyclic adenosine 3$\sp\prime,5\sp\prime$-monophosphate (cAMP) selective for either binding site (S1 and S2) on the regulatory subunits of cAMP-dependent protein kinases (PK-A) were used to assess the role of type 1 (T1) and type 2 (T2) PK-A in LC function. As S1 and S2 exhibit positive cooperativity, coexposure to analogue pairs will synergistically increase T output should T1 or T2 PK-A be present. Both T1 and T2 PK-A were active in the LC, though T1 PK-A activity was predominant. Coincubation with cAMP, luteinizing hormone (LH) or forskolin also synergistically increased T though the response with forskolin was reduced suggesting cAMP-independent activities.
Although atrial natriuretic factor (ANF) stimulates T output via cyclic guanosine 3$\sp\prime,5\sp\prime$-monophosphate (cGMP), coexposure of LC to ANF and LH or ANF/cGMP and the same cAMP analogues resulted in a synergistic increase in T production suggesting cyclic nucleotide interaction mediates a cooperative hormonal control of the mouse LC in vivo.
The role of calmodulin (CaM) in LC function was assessed using a CaM antagonist, N-(6-aminohexyl)-5-chloro-1-napthalenesulfonamide (W7) and a multichambered cell perifusion system. Exposure to W7 caused an initial nonspecific inhibition followed by a CaM-dependent increase in T synthesis suggesting the presence of a novel inhibitory CaM-sensitive process in the LC. The response did not involve inhibition of a CaM-dependent phosphodiesterase (PDE) but could be abolished with a phospholipase A$\sb2$ inhibitor and mimicked by a lipoxygenase inhibitor, nordihydroguaiaretic acid (NDGA). The response to W7 and NDGA co-infusion was not additive, suggesting a common mechanism of action, possibly mediated by arachidonic acid.
Thesis (Ph.D.)--Dalhousie University (Canada), 1991.
Analogues of cyclic adenosine 3$\sp\prime,5\sp\prime$-monophosphate (cAMP) selective for either binding site (S1 and S2) on the regulatory subunits of cAMP-dependent protein kinases (PK-A) were used to assess the role of type 1 (T1) and type 2 (T2) PK-A in LC function. As S1 and S2 exhibit positive cooperativity, coexposure to analogue pairs will synergistically increase T output should T1 or T2 PK-A be present. Both T1 and T2 PK-A were active in the LC, though T1 PK-A activity was predominant. Coincubation with cAMP, luteinizing hormone (LH) or forskolin also synergistically increased T though the response with forskolin was reduced suggesting cAMP-independent activities.
Although atrial natriuretic factor (ANF) stimulates T output via cyclic guanosine 3$\sp\prime,5\sp\prime$-monophosphate (cGMP), coexposure of LC to ANF and LH or ANF/cGMP and the same cAMP analogues resulted in a synergistic increase in T production suggesting cyclic nucleotide interaction mediates a cooperative hormonal control of the mouse LC in vivo.
The role of calmodulin (CaM) in LC function was assessed using a CaM antagonist, N-(6-aminohexyl)-5-chloro-1-napthalenesulfonamide (W7) and a multichambered cell perifusion system. Exposure to W7 caused an initial nonspecific inhibition followed by a CaM-dependent increase in T synthesis suggesting the presence of a novel inhibitory CaM-sensitive process in the LC. The response did not involve inhibition of a CaM-dependent phosphodiesterase (PDE) but could be abolished with a phospholipase A$\sb2$ inhibitor and mimicked by a lipoxygenase inhibitor, nordihydroguaiaretic acid (NDGA). The response to W7 and NDGA co-infusion was not additive, suggesting a common mechanism of action, possibly mediated by arachidonic acid.
Thesis (Ph.D.)--Dalhousie University (Canada), 1991.
Keywords
Biology, Cell., Biology, Animal Physiology., Chemistry, Biochemistry.