ABSTRACT
Mature female hamsters bearing subcutaneous polyacrylamide (PAA) implants, with ethinyloestradiol (EO), for at least 10 days prior to mating revealed:
0.5 and 2.5 mg EO in 7% PAA significantly disturb the timing of oestrus and mating, but have no apparent effect on rate of pregnancy, ovulation and implantation. 2.5 mg EO in 20 and 40% PAA conspicuously reduces the likelihood of pregnancy, although the occurrence of oestrus and mating are affected only slightly. Fertility in these hamsters was virtually restored, judging from pregnancy rates, when they were remated 11 days, or more, following removal of their implants (37 days after implantation), but significantly more foetuses were resorbed in these litters. From tissue sections of skin and muscle at the implant site, ovary, uterus, pituitary, adrenals and liver, PAA implants, without EO, cause no overt pathological changes in the bearer. Effects characteristic of oestrogen are present when these implants contain EO, and these include a conspicuous thickening of the epidermis and dermis; haemorrhagic lesions were also noted in the maternal placenta of animals with EO implants. There is an association between reproductive performance and the rate of EO release by an implant. A 7% PAA implant with 2.5 mg EO can release most of it within 2 days, and principally influences events (oestrus and mating) that precede the main target (pregnancy) of a 20% PAA implant, which releases the steroid over the longer interval of 7 days.
