Ovulated oocytes collected from PMSG/hCG-treated and cycling Djungarian or Siberian hamsters (Phodopus sungorus) are structurally similar with no evidence of polar body formation, indicating arrest in meiosis I.

Abstract

This study was undertaken (1) to devise a method of inducing multiple follicular development and subsequent ovulation in the Djungarian or Siberian hamster (Phodopus sungorus) and (2) to assess the quality of ovulated oocytes collected from PMSG/hCG treated animals in comparison to naturally ovulating animals. Hamsters (4-5 weeks; n = 70) received 5 IU PMSG followed 50-52 hr later by 10 IU hCG. Ovulated oocytes were collected 14-20 hr after hCG injection. Ovulated oocytes were flushed from oviducts of cycling animals (7-12 weeks; n = 30) exhibiting two consecutive estrous cycles. Oocytes were fixed and subjected to triple fluorescence immunostaining using anti-tubulin antibodies, fluorescein phalloidin, and Hoechst 33258. The mean number of ovulated oocytes collected from cycling animals was 4.8 +/- 0.4 (range 1-7). Ovulation occurred in 73% of the PMSG/hCG-stimulated animals. The mean number of oocytes ovulated from stimulated animals was 9.2 +/- 0.8 (range 0-22). The ovaries of animals that did not ovulate or that ovulated few oocytes did respond to PMSG, as indicated by the presence of multiple follicular development and pre-ovulatory stigmata. There was no evidence of a polar body in ovulated oocytes collected from PMSG/hCG-treated or cycling animals, indicating that oocytes were arrested in meiosis I. In the majority (80%) of ovulated oocytes from PMSG/hCG-treated and cycling animals, cortically placed chromosomes were aligned on a metaphase plate equidistant from a bipolar spindle. Sparse f-actin staining was observed in the region of the ooplasm surrounding the chromosomes.(ABSTRACT TRUNCATED AT 250 WORDS)