The regulation of the phospholipase C (PLC) and the expression of inositol 1,4,5-trisphosphate receptors (IP3Rs) in terms of mRNA, proteins, and binding capacity were examined in the rat myometrium and endometrium at midgestation (Day 12) and at term (Day 21) comparatively to the estrogen-treated tissues (Day 0). In both uterine tissues, the production of inositol phosphates mediated by carbachol as well as by AlF4− was enhanced with advancing gestation. 3[H]IP3 binding sites in membranes also increased during pregnancy (Day 21 > Day 12 > Day 0). The mRNAs encoding for three isoforms of IP3R as well as their corresponding proteins, IP3R-1, IP3R-2, and IP3R-3 were coexpressed, albeit to different extents, in the myometrium and endometrium. The expression of IP3Rs increased with advancing gestation, except for IP3R-2 that increased only in the endometrium at term. Thus, the pregnancy-related upregulation of the PLC cascade coincided with an increase in the expression of IP3Rs. The difference noted between the two uterine tissues suggests that IP3Rs may have cell-specific functions.