The splice variants of the Insulin-like Growth Factor (IGF-1) gene, IGF-1Ea and MGF, are believed to have distinct roles in skeletal muscle hypertrophy and repair (Yang et al. 1996; Owino et al. 2001 and Hameed et al. 2003). Myometrial smooth muscle hypertrophy and repair are fundamental features of pregnancy and uterine involution following parturition, yet the molecular mechanisms involved in these processes are poorly understood.

15 female Sprague Dawley rats were used in the present study to determine the mRNA expression of the IGF-1Ea and MGF in the myometrium using real time quantitative PCR (Roche LightCycler, UK).

Measurements were made at day 18 of pregnancy (n = 5) and day 14 post parturition (n = 5) and compared to levels in the non-pregnant uterus (n = 5). Data was analysed using the ANOVA and Tukey HSD tests. During pregnancy mRNA expression levels of MGF and IGF-1Ea increased by 21 % and 310 % respectively compared to the controls. This increase was significant for IGF-1Ea (P < 0.05), but not for MGF. Interestingly, at day 14 post parturition, levels of MGF mRNA were markedly increased showing a 1536 % increase, whilst IGF-1Ea showed a 349 % increase compared to the non-pregnant controls. In both cases the increase was significant (P < 0.01 and P < 0.05 respectively) compared to the control. However, compared to day 18 gestation only the increase in MGF was significant (P < 0.05).

These results suggest that the two isoforms have distinct roles, with IGF-1Ea thought to be involved in myometrial hypertrophy during pregnancy. In contrast, it seems that MGF is involved later, in the repair and remodelling phase following parturition.