An ultrastructural comparison of implantation in young and senescent golden hamsters.

Implantation was compared in young (3-5 month) and senescent (14-17 month) golden hamsters at 3, 3 1/2, 4, 4 1/2, 5, and 5 1/2 days of pregnancy (post-ovulation). One hundred twenty-two embryos (89 from 22 young females and 33 from 18 senescent females) located in utero by cutting thick sections (1-3 mum), were re-embedded and thin-sectioned for electron microscopy. Ultrastructurally implantation and embryonic differentiation was delayed approximately 12 hours in the senescent hamster when compared with young hamsters at the same stage of pregnancy. Failure of the blastocyst to implant would not appear to be a major cause of the declining litter size in aged golden hamsters.