LUTEOTROPHIC FACTORS IN THE COW: EVIDENCE FOR LH RATHER THAN PROLACTIN

Summary. The luteotrophic properties of endogenously secreted LH and prolactin were studied by measuring CL function after neutralization of circulating LH and prolactin by the administration of highly specific antisera against these hormones on the 11th and 12th day of the oestrous cycle. In addition, the effect of a prolactin inhibitor (CB-154), which reduced prolactin concentration in peripheral blood by 80 to 90% was studied. A hysterectomized heifer carrying a persistent CL was treated with CB-154, a combination of CB-154 and prolactin antiserum and then with LH antiserum. In all animals treated with the LH antiserum, CL function ceased or was quantitatively inhibited. No change in circulating progesterone was seen after treatment with the prolactin antiserum or the prolactin inhibitor. It is concluded that LH is the dominant luteotrophic factor in the bovine species while prolactin has little or no activity.