Body weight-associated differences in ovarian morphology in captive common marmoset (Callithrix jacchus)

In captivity, Callithrix jacchus (common marmoset) is on average heavier than their wild-living counterparts, and has a tendency to produce triplet litters rather than the normal twins. To provide initial basic information about possible weight-related differences among the ovaries, a morphometric study of follicular phase ovaries from 48 young adult marmosets has been carried out. Nearly 90% of these ovaries were found to contain some degree of luteal tissue composed of large and/or small cells. The luteal structures, follicles of all stages, and stroma were subjected to morphometric analysis, and these results were compared with body weight, circulating triglyceride, androstenedione, and total estrogens. Where only large luteal cells were present, the median body weight was the highest (only this group included animals over 500 g) compared with mixed, or only small luteal cells, or absence of luteal cells. Furthermore, in this group plasma triglycerides were significantly higher compared to other groups, suggesting possible role of triglycerides in promoting luteinisation. Plasma androstenedione was also a critical discriminating factor, and was elevated where large luteal cells were present even as a mixture with small cells suggesting the large luteal cells to be the likely major ovarian source of this hormone and its metabolites. Additionally, the ovaries with large luteal cells compared to those containing only small or no luteal cells, had lower primordial follicle reserve associated with high levels of atresia and luteinisation among growing non-ovulatory follicles, indicating an accelerated activation, but at the same time a suboptimal environment for follicular growth.