Immunolocalization of neurophysin in cytokeratin-positive luteal cells of cows.

We have recently detected a subgroup of cytokeratin (CK)-positive luteal cells in the bovine corpus luteum of the early and mid-luteal phase, but not in that of pregnancy. Since, according to the literature, neurophysin (NP)-positive luteal cells behave comparably, simple immunohistochemistry and double labeling were used to identify in serial sections whether the presence of NP co-incided with that of CK. The numbers of CK-positive cells and NP-positive luteal cells were comparable throughout the estrous cycle, decreasing from early to late luteal phase. While few CK-positive cells were found in the former thecal layer during the early luteal phase, many CK-positive cells appeared in the former granulosal layer. NP-positive cells were only detected in the former granulosal layer. During the mid-luteal phase, the CK-positive cells consisted of small and large luteal cells, but only large NP-positive cells were found. Roughly 80% of the large CK-positive cells contained NP, whereas CK was lacking in more than 50% of the NP-positive cells. The corpora lutea of pregnancy contained neither CK-positive nor NP-positive cells. The significance of the simultaneous occurrence of CK and NP remains to be elucidated.