Increased formation of corpora lutea in neurokinin 1-receptor deficient mice

There is evidence to suggest that the tachykinin-receptor system may be involved in female reproduction. Recently, we have shown that the mRNA transcripts of the preprotachykinin-A which encodes substance P (SP), a member of the tachykinin family, and of NK1-R (preferred receptor of SP) are expressed in the bovine corpus luteum (CL) of early developmental stage. The question arises whether the system is expressed at the protein level and influences the ovulatory process and CL formation. For this reason, ovaries from a mouse mutant in which the NK1-R gene had been disrupted were studied. By using RT-PCR, mRNA expression of NK1-R was confirmed in both the ovary and the uterus of wild-type mice. Weaning frequency and litter size, as recorded over 6 months, were similar in both groups. However, counting of CL in serial paraffin sections revealed a significant higher number of CL in the NK1-R deficient mice in comparison to the wild-type group (P < 0.01). The increased formation of CL in NK1-R deficient mice corresponded to a considerable number of CL with retained oocyte not found in ovaries of the wild-type group. We conclude: The CL with a retained oocyte may indicate that the muscular apparatus of the preovulatory follicle plays a role in oocyte expulsion and that contractility of the follicle wall is deficient in the mutant group. Our observation may have implications for the luteinized unruptured follicle syndrome in humans.