Failure of hCG to support luteal function in bitches after estrus induction using deslorelin implants

• Published in: Theriogenology 2006-10, Vol.66 (6), p.1502-1506
• Main Authors: Volkmann, D.H., Kutzler, M.A., Wheeler, R., Krekeler, N., Klewitz, J., Lamb, S.V.
• Format: Article
• Language: English
• Subjects: abortion (animals); Animals; Bitch; Chorionic Gonadotropin - pharmacology; corpus luteum; Corpus Luteum - drug effects; Corpus Luteum - physiology; dogs; Dogs - physiology; dosage; Drug Implants; Estrus - drug effects; Estrus - physiology; Estrus induction; estrus synchronization; Female; females; GnRH; gonadotropin-releasing hormone; hCG; hormone receptors; hormone secretion; human chorionic gonadotropin; Luteal function; luteinizing hormone; Luteinizing Hormone - secretion; Male; Ovulation Induction - methods; Ovulation Induction - veterinary; Pregnancy; pregnancy outcome; progesterone; Progesterone - blood; Triptorelin Pamoate - administration & dosage; Triptorelin Pamoate - analogs & derivatives
• ISSN: 0093-691X; 1879-3231
• DOI: 10.1016/j.theriogenology.2006.01.045

Induction of estrus with deslorelin implants was followed by abortions in bitches that conceived during the induced estrus. Lowering the deslorelin dose and choosing a better implantation site prevented the abortions. This study investigated the hypothesis that induction of estrus with deslorelin is followed by reduced serum progesterone concentrations (SPC) during the ensuing diestrus. Assuming that reduced luteal function resulted from reduced LH secretion due to hypophyseal down-regulation of GnRH receptors, the effect of human chorionic gonadotropin (hCG) treatment on the SPC of diestrous bitches was also investigated. In Experiment 1, 10 spontaneously cycling bitches served as controls, whereas estrus was induced with deslorelin implants in 24 others. In Experiment 2, six diestrous bitches were treated with a single dose of hCG between Days 39 and 45 of diestrus. The SPC was lower in deslorelin-induced bitches from Days 35 to 56 of diestrus and hCG increased SPC during the first 24 h after treatment, followed by a dramatic decline thereafter. Although SPC recovered in pregnant bitches, it remained much lower (≤1 ng/mL) than in untreated, non-pregnant bitches. The suppression of progesterone secretion after hCG treatment suggested that decreased luteal activity in deslorelin-induced bitches may not be a simple consequence of down-regulation of hypophyseal GnRH receptors.