Structure/function relationships in active and inactive hamster Leydig cells: a correlative morphometric and endocrine study.

Abstract

Spermatogenesis can be turned on or off in the seasonally breeding golden (Syrian) hamster in a laboratory setting by exposure of animals to different photoperiod regimens. The present study provides the first detailed quantitative analysis of the subcellular features of hamster Leydig cells during active and inactive phases of spermatogenesis and correlates these features with the endocrine activity of the same animals. Conventional stereological principles and accepted morphometric techniques were used to determine changes in a variety of subcellular constituents of Leydig cells at the extreme phases of gonadal activity produced by maintaining adult hamsters in a long photoperiod (16 h of light, 8 h of darkness) or by exposing them to a short photoperiod (6 h of light, 18 h of darkness) for 12-13 weeks. Compared with Leydig cells from gonadally active animals, Leydig cells obtained from the regressed testis showed a significant reduction in the absolute volume of nearly all of its organelles, including nucleolus (77.0%), mitochondria (50.0%), total endoplasmic reticulum (ER) (86.4%; cisternal ER, 87.0%; tubular ER, 85.5%), lipid (84.2%), peroxisomes (82.5%), multi-vesicular bodies (71.9%), filament-rich area (95.5%), and Golgi complex (69.4%). There was also a significant reduction in organelle surface area, namely outer (76.5%) and inner (72.7%) mitochondrial membrane, total ER (85.0%), cisternal (85.3%) and tubular (84.4%) forms of ER, and Golgi complex (70.0%). The surface areas of the plasma membrane and nuclear membrane were also decreased by 58.3% and 33.7%, respectively. These results demonstrate that the short photoperiod-induced cellular inactivity of Leydig cells is associated with an overall diminution in the volume and surface area of all major organelles, not only those specifically associated with steroid biosynthesis. Virtually every structural parameter of the Leydig cell was significantly and positively correlated with plasma LH levels and with both plasma and testicular concentrations of testosterone. The total content of LH receptors per testis and per Leydig cell was reduced, but the concentration of receptors per unit area of the Leydig cell surface remained unchanged. Correlation of changes in hormonal status with alterations of all Leydig cell organelles suggests a general shut-down of cellular activity in the gonadally regressed animals, rather than a specific effect of pituitary hormones on selected cellular constituents.