# Endometrial Collagen in Woolly Monkey (Lagothrix l. poeppiggi) and the Uakari ( Cacajao calvus )

## TL;DR

This study examines collagen changes in the endometrium of two Neotropical primates to understand their reproductive phases.

## Contribution

The study provides new insights into collagen distribution and its correlation with reproductive phases in woolly monkeys and uakaris.

## Key findings

- Collagen is highest in the early proliferative phase of the functional layer in both species.
- Type I collagen predominates, while Type III collagen peaks in the functional and basal layers.
- Picrosirius Red staining with polarized light effectively identifies collagen organization and reproductive phases.

## Abstract

This study microscopically characterizes collagen changes and their relationship with endometrial architecture in two Neotropical primates.

Uterine fragments from six Lagothrix l. poeppigii and six
Cacajao calvus
in different reproductive phases were histologically processed using Picrosirius Red staining.

In the functional layer, collagen was highest in the early proliferative phase (5.19% ± 2.53%; p < 0.001), whereas the basal layer had the lowest percentage (5.85% ± 4.69%; p < 0.01). Type I collagen predominated, while type III was less expressed. Type I collagen varied significantly between proliferative phases (p < 0.001). The basal layer exhibited more fibers in the secretory phase (14.03% ± 8.50%; p < 0.001). Type III collagen peaked in the functional layer (0.41% ± 0.17%; p < 0.001) and basal layer (0.69% ± 0.46%; p < 0.05).

Picrosirius Red staining with polarized light effectively highlights collagen organization, aiding reproductive phase characterization in Neotropical primates.