| Abstrakt: |
Four experiments were carried out in Merino ewes during a period of 4 years to determine the long-term effects of immunization against different synthetic peptides mimicking the amine terminal of the a subunit of porcine inhibin. Peptides were conjugated to human serum albumin and 100200 g emulsified in Freunds complete adjuvant for the primary immunization. Usually two booster injections were given at monthly intervals with 50100 g conjugated peptide using either incomplete Freunds adjuvant or Montanide : Marcol. In some experiments a further immunization was carried in the next year. Blood samples were taken 10 days after each immunization, during the luteal phase, for estimation of gonadotrophin concentrations and determination of inhibin antibody titres. One day after blood sampling cloprostenol was used to induce luteolysis and laparoscopy was performed in the subsequent oestrous cycle. Immunization of ewes with synthetic peptides 132, 126, 726 and 830 resulted in large increases in the ovulation rate (OR). An approximately two-fold increase in OR was observed following the first booster immunization with these peptides and a three- to five-fold increase after the second booster immunization. Immunization with these large peptides resulted in a sustained increase in OR for a period of at least 1 year after the second booster immunization. Of the shorter peptides, peptides 1026 and 1326 gave a reasonable ovulatory response, although it was more difficult to obtain a response with peptides 116, 822, 1325, 819 and 1019; peptides 713 and 16 gave no response (but were examined for one breeding season only). The smaller peptides led to lower inhibin antibody titres that were not necessarily associated with increased follicle-stimulating hormone (FSH) or OR. More intensive blood sampling in one experiment showed that following primary immunization against peptide 132 there was a transient increase in plasma FSH, which did not lead to an increased OR. Moreover, a prolonged period of raised FSH after the first booster was significantly correlated with increased OR. In these animals antibody titres were only slightly increased after primary immunization, but after the first booster immunization higher titres were observed that were significantly correlated with trough FSH values and the subsequent OR. These results are interpreted as showing that (1) to obtain an increase in OR peptides 132, 126 and 726 are suitable as immunogens; (2) smaller peptides are less reliable, often require multiple injections, and the response may be delayed; and (3) an extended period of raised plasma FSH is needed to give a large ovulatory response. Extra keywords: follicle-stimulating hormone (FSH), immunization, inhibin, ovulation, peptide, sheep. |
