Quantitative ultrastructural characteristics relating to transport between luteal cell cytoplasm and blood in the corpus luteum of the pregnant rat

Abstract

The synthesis and secretion of progesterone by the corpus luteum (CL) may be limited or controlled by transport mechanisms operating between circulating blood and luteal cell cytoplasm. To examine this possibility, the structural features involved in transport, including membrane surface areas and diffusion distances, were quantitated in the CL of 16-day pregnant rats. One ovary from each of eight rats was fixed by perfusion via a cannula inserted into the parametrial artery, and two CL from each ovary were processed for electron microscopy and examined with standard morphometric techniques. For comparison, one CL from each of a further eight ovaries was diced into small cubes, fixed by immersion, and analyzed similarly. In perfusion-fixed CL, there was a substantial volume of vascular space (20% of the total) and interstitial space (5%) and an extensive surface area of capillaries (441 mm2 per CL). The luteal-cell membrane had numerous projections which increased its surface area by a factor of 3.08. Almost 60% of the luteal-cell surface directly faced a capillary, and a further 37% faced interstitial space which probably extended to a capillary surface. Only 3% was in direct contact with a neighboring luteal cell. Despite the extensive interstitial space the harmonic mean thickness, an estimate of likely effective diffusion distance between luteal cell cytoplasm and blood, was only 0.42 micron. This was less than half of the calculated arithmetic mean thickness owing to the presence of surface projections and an uneven capillary endothelium. Results from immersion-fixed CL were qualitatively similar; but the proportion of interstitial space was only 59% of that in perfusion-fixed CL, and the contribution of surface projections to the total area of luteal-cell membranes was significantly reduced. Collectively, these results suggest that membranes and spaces between blood and luteal-cell cytoplasm are structured so as to minimize transport distances.

Morphological features and vascularization study of caprine cyclic corpus luteum

“…The vascular density (VD) is another important parameter, which reflects vascularization of the tissue and, consequently, its blood perfusion level (Dharmarajan et al 1985, Asahara et al 1995. The study of VD in the CL of goats confirmed that, apart from the macroscopic and microscopic changes in the luteal structure, changes in the vascular network during the estrous cycle were observed, which reflected the functional activity of the organ.…”

Corpora lutea induced by gonadotrophin-releasing hormone treatment of anoestrous Welsh Mountain ewes: reduced sensitivity to luteinizing hormone in vivo and to chorionic gonadotrophin in vitro

“…4 animals is reported to have a probability of P , 0.05 (Cruz-Orive & Weibel 1990). Secondly, the effects of fixation cause significant cell shrinkage and affect measurement of vascular space (Dharmarajan et al 1983(Dharmarajan et al , 1985. Since luteal weights and the consistency of luteal tissue varied with both treatment group and stage of luteal phase, fixation effects may vary between treatment groups and luteal stage.…”

Physiologie der Lutealphase

“…Das Corpus luteum wird stark durchblutet und gehört zu den Organen mit dem höchsten Blutfluss. Jede Lutealzelle steht in direktem Kontakt mit einem dichten Kapillarnetz [27]. Das Corpus luteum hat in Relation zu seinem Gewicht einen 2-bis 6-fach höheren Sauerstoffverbrauch als beispielsweise die Leber, die Niere oder das Herz [31].…”