Effect of carrier and administration on luteinizing hormone release by gonadotropin releasing hormone

Ovariectomized ewes in groups of four were administered either saline (I) or 50 micrograms of gonadotropin releasing hormone (II to VII). Methods of administration and carriers were : II, intramuscular saline; III, intravenous saline; IV, subcutaneous saline; V, subcutaneous gelatin; VI, subcutaneous carboxymethylcellulose; and VII, subcutaneous gelatin capsule. Only subcutaneous administration of gonadotropin releasing hormone in the gelatin capsule (VII) prolonged the interval from treatment to luteinizing hormone peak; however, there were fewer ewes with peak luteinizing hormone concentrations equal to or greater than 100 ng/ml in VII than II, IV, V, and VI. Ewes in V, VI, and VII had luteinizing hormone surges of longer duration than II and III. Ewes in VII had the longest luteinizing hormone surge, which was 7.5 h, even though luteinizing hormone concentrations did not return to pretreatment concentrations by 8 h posttreatment in three of the four ewes.