Homologous radioimmunoassay for canine prolactin

A homologous double antibody radioimmunoassay has been developed for canine prolactin. Purified canine prolactin was iodinated by lactoperoxidase/H2O2 to an average of 101 "+/- 10.1 muCi/microgram. Antiserum was used at a final dilution of 1:80 000 and at this concentration bound approximately 20% of the added tracer in the absence of competing unlabelled prolactin. Partial cross-reaction was observed with ovine and bovine prolactin but there was no cross-reaction with a highly purified canine growth hormone preparation. Dilutions of pregnant and lactating bitch sera were parallel to the purified canine prolactin standard curve. Mean prolactin levels in normal male and anoestrous females were 8.8 +/- 0.8 and 12.6 +/- 2.6 ng/ml, respectively. Thyrotrophin-releasing hormone (TRH) induced a consistent elevation in prolactin levels 15--30 min after intravenous injection.