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Recent evidence supports involvement of the acute phase protein haptoglobin in numerous events of mammalian reproduction. The objective of this study was to determine whether haptoglobin mRNA was expressed in the bovine ovary and oviduct, and to evaluate whether expression of haptoglobin mRNA in reproductive tissues and liver was associated with a specific phase of the bovine oestrous cycle. Oestrus was synchronized in Holstein cows by prostaglandin injection and tissues were collected during the luteal and peri-oestrous stages of the oestrous cycle. Total RNA was isolated and reverse-transcription polymerase chain reaction (RT-PCR) was performed using primers designed against regions of similarity in human, rat and mouse haptoglobin sequences. Haptoglobin mRNA expression was detected in oviductal cells and liver, during both stages of the oestrous cycle, but not in ovarian follicular cells. The 302 bp PCR product was determined to share 82-83% identity with reported primate haptoglobin sequences. Analysis by Northern blotting revealed 1.2 and 1.4 kb haptoglobin mRNA transcripts in the oviduct and liver, and indicated that hepatic haptoglobin mRNA expression was elevated above basal levels in a greater proportion of peri-oestrous cows (4/4) than luteal cows (1/5). Haptoglobin cDNA was cloned and in vitro transcribed to generate probes for in situ hybridization. Haptoglobin mRNA was detected in the liver, but not in the ovary or oviduct. We conclude that haptoglobin mRNA expression in the bovine liver is up-regulated during the peri-oestrous phase of the oestrous cycle, and that the bovine oviduct expresses a low level of haptoglobin mRNA constitutively. This temporal pattern of haptoglobin mRNA expression would expose reproductive tissues to elevated concentrations of serum haptoglobin during the peri-oestrous stage, and suggests that haptoglobin may be important in reproductive events occurring during this time period.