Immunohistochemical aspects of insulin-like growth factors I and II in the bovine corpus luteum.

The cellular distribution of insulin-like growth factors I and II (IGF-I and -II) was examined in bovine corpora lutea at different stages of the luteal phase using specific antibodies and the avidin-biotin immunoperoxidase technique. At the cellular level, intense immunostaining for IGF-I was exclusively observed in large and small luteal cells and in a limited number of endothelial cells. Positive IGF-I immunoreactivity in luteal cells was thereby distributed in a distinct topographical, lobule-specific manner. Immunoreactivity in central areas of luteal lobules was most abundant in large luteal cells, whereas in peripheral zones significantly (P < 0.05) more small luteal cells exhibited IGF-I immunoreactivity. This distribution pattern was evident from day 4 of the cycle onwards and occurred at all the stages investigated. The percentage of positive small (SLC) and large (LLC) luteal cells revealed by semiquantitative analysis depended on the stage of the cycle as follows: days 4-7: 34% LLC versus 21.3% SLC in central areas and 25.1% LLC versus 32.7% SLC in peripheral zones; days 8-12: 42.9% LLC versus 19.9% SLC in central areas and 23.5% LLC versus 35.2% SLC in peripheral zones; days 13-16: 47.7% LLC versus 19.4% SLC in central areas and 19.2% LLC versus 41.4% SLC in peripheral zones. In contrast to IGF-I, no expression of IGF-II immunoreactivity was seen in large or small luteal cells. Positive immunoreactivity was restricted to the perivascular fibroblasts of large blood vessels and to the pericytes of capillaries.(ABSTRACT TRUNCATED AT 250 WORDS)