Immunohistochemical Studies of Insulin-Like Growth Factor-I in Corpora Lutea of Cycling and Pregnant Mice, Rats, Hamsters, Guinea Pigs and Cattle.

Immunohistochemical staining of insulin-like growth factor-I (IGF-I) in the corpora lutea (CL) during estrous cycle and pregnancy was compared among mice, rats, hamsters, guinea pigs and cattle. During the estrous cycle, while clear staining was not detected in the hamster CL, the CL of the mouse, rat and guinea pig showed modest staining except for the mouse CL 1 day after ovulation which showed very weak staining. In contrast, immunoreactive IGF-I in the bovine CL showed distinct changes. While very weak staining was noted during the follicular and early luteal phases, the intensity increased markedly thereafter, peaking at the late luteal phase. During preg-nancy, the mouse and rat CL showed positive staining, and the intensity increased at late preg-nancy, especially in the rat CL intense focal staining was noted. In the hamster CL, clear positive staining was detected only at late pregnancy. In contrast, in the guinea-pig and bovine CL, al-though intense staining was detected during mid-pregnancy, the staining decreased at late preg-nancy. The results revealed species differences in the accumulation of immunoreactive IGF-I in CL.