Stage-Dependent Differences in FSH Binding and Cyclic Nucleotide Secretion and Metabolism during the Cycle of the Rat Seminiferous Tubule
In living, freshly isolated rat seminiferous tubules, cyclic changes in FSH binding, cAMP secretion (basal and FSH stimulated) and the activities of cAMP and cGMP phosphodiesterases could be detected which were related to specific stages of spermatogenesis. FSH binding (per cm stage) increased gradually between stages VII and IX and then, after remaining relatively constant, was elevated further in stages XIV-I. Thereafter, binding fell to a nadir stage VIIa-b. FSH stimulated cAMP secretion was at its lowest in stage VIIa-b and maximal between stages XIV-V. The greatest specific activities of the cAMP and cGMP phosphodiesterases were detected in stages VII-VIII which are associated with spermiation in the rat. A degree of dissociation was found to exist in the cAMP and cGMP hydrolysing capacities at certain stages (IX-XII), suggesting the existence of different isoforms of the enzyme which may be differentially controlled. Exposure of the various stages to FSH or dibutyryl cAMP for 4 hr in vitro did not alter the profiles of phosphodiesterase activity.
The phosphodiesterase profiles were inversely related to the quantity of cAMP produced by the tubular segments after stimulation with FSH, both in the presence and absence of the phosphodiesterase inhibitor, methyl isobutyl xanthine (MIX). However, MIX elicited the greatest effect from the tubular segments, in terms of FSH stimulated cAMP production, in stages XIV-V, where direct measurements of phosphodiesterase indicate the enzyme activity is relatively low. The reasons for this apparent contradiction are discussed in relation to previous findings on stage-dependent alterations in various aspects of tubular function.
KeywordsSertoli Cell Adenylyl Cyclase Seminiferous Tubule Methyl Isobutyl Xanthine Phosphodiesterase Activity
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