Effect of synthetic gonadotrophin-releasing hormone (Gn-RH) on circulating luteinizing hormone (LH) and testosterone in young post-pubertal bulls.
The reproducibility of LH and testosterone responses after Gn-RH treatment in young post-pubertal bulls was tested. Ten bulls were injected im (250 mug) twice with an interval of 4 weeks. Blood samples were collected every 15 min for 21/2 h and then on the second occasion, every hour. LH increases very rapidly and reaches an initial peak by 30 min after Gn-RH injection. This increase over basal level was 25 to 30-fold. After a plateau of high levels lasting 40 to 50 min, a second peak of LH concentration occurs. LH then decreases and returns to basal levels by 6 to 7 h after treatment. The increase of plasma testosterone was more prolonged and of smaller magnitude than that of LH: 3 to 4-fold. There was a large and significant variation between bulls; but with LH, a given individual responded in a consistent manner on the two separate occasions. It is concluded that LH response to Gn-RH treatment might be useful and should be tested as a diagnostic value for clinical or breeding purposes. The testosterone response does not seem to be as valuable and reliable as that of LH.
D000818:Animals; D002417:Cattle / Q000097:blood*; D006062:Gonadotropins / Q000494:pharmacology*; D007986:Luteinizing Hormone / Q000097:blood*; D008297:Male; D013268:Stimulation, Chemical; D013739:Testosterone / Q000097:blood*
D006062:Gonadotropins; D013739:Testosterone; D007986:Luteinizing Hormone