Background: The spiny mouse is a precocial rodent, particularly comparable in relative gestation length, fetal development and embryo cleavage rate to that of humans. Utilisation of such a model will enable us to undertake comprehensive embryological studies; the ultimate goal to achieve improved success rates of IVF. To do so, we require a robust technique to induce pseudopregnancy. Aims: We sought to trial 3 protocols previously used in rodents in spiny mice. We hypothesised progesterone would induce decidualisation, establishing pseudopregnancy. Methods: Females aged between 90-150 days were divided randomly into one of several groups (Table 1). Spiny mice were deemed pseudopregnant if presenting with an extended luteal phase, characterised by >4 consecutive days of leukocytic smears.
Table 1: Treatment groups and vaginal smear protocols for inducing pseudopregnancy
Group # | Subjects (n) | Treatment | Smears Conducted |
1 | 10 | Control | Every two days |
2 | 5 | Progesterone 4mg | Daily after treatment |
3 | 5 | Progesterone 4mg | Day 3 onwards after treatment |
4 | 5 | Mechanical Stimulation | Daily |
5 | 5 | Mechanical Stimulation | Day 3 |
6 | 5 | Sterile Mating | Daily |
7 | 10 | Sterile Mating | Day 3 |
8 | 5 | Progesterone 2 mg | Day 3 |
9 | 5 | Progesterone 5 mg | Day 3 |
Results: The average length of luteal phase in untreated animals was 2.8 ± 0.2 days. This was significantly prolonged by 3-5 days in most groups, excluding 2 and 5. Though the luteal phase was prolonged in 7, 50% of subjects exhibited delayed pseudopregnancy. 40% of subjects from 6 experienced prolonged oestrus by 1-2 days. Conclusion: We found a single dose of progesterone (2-5 mg) was the most efficacious method of immediate pseudopregnancy induction. Altered concentrations did not have an effect on luteal phase length, hence any dosage within this range may be used. Ongoing analysis will examine hormonal profiles. Embryo transfers will be conducted to confirm protocol success.