title: Endocrine and ovarian responses to prolonged adrenal stimulation at the time of induced corpus luteum regression.
abstract: The endocrine and ovarian responses to prolonged adrenal stimulation at the time of corpus luteum (CL) regression were studied in non-lactating non-pregnant Friesian cows. Cows were synchronized with two cloprostenol (PG) injections 11 days apart (second PG referred as time 0). Experiment 1 was carried out on five animals in two phases with a resting period in between. Between -48 and 84 h, animals received 12 injections of either saline (CTR) or adrenocorticotrophic hormone (ACTH) agonist (Synacthen; SYN) every 12 h. Cortisol (C), progesterone (P4), oestradiol (E2) and LH were analysed in the blood samples collected every 8-12 h between days -3 and 4. Pulsatile LH release was studied 4 h before and 4 h after naloxone administration beginning at 96 h. Experiment 2 was carried out on four cows in a cross-over experimental design (two phases, with a resting period in between). Treatments were performed by administering either saline (CTR) or Synacthen (SYN) every 12 h between -36 and 24 h. The concentrations of C, P4 and E2 were measured in blood plasma every 4-12 h from days -3 to 3, then every day from days 5 to 9. In both experiments, ovaries were examined by ultrasonography every 1-3 days. ACTH administration induced a significant increase (p < 0.001) of plasma C lasting for 7 days (experiment 1), and for 3-4 days (experiment 2). Plasma C returned to baseline levels within 6 days (expt 1) or 36 h (expt 2) after treatment interruption. During the SYN phase, LH pre-ovulatory surge was not detectable. During the CTR phase, naloxone administration induced a significant increase (p < 0.05) of average LH concentrations that was not evident during the SYN phase. The dominant follicle development was retarded and mean plasma E2 concentrations were significantly lower during the SYN phase (p < 0.01). Luteolysis was completed within 2 days. However, P4 decline between 0 and 4 h was slower (p < 0.01) during the SYN phase. Our results indicate that, under prolonged adrenal stimulation, follicular development is delayed and LH release is impaired, which are independent of CL function.
authors.affiliation: Dipartimento di Scienze Sperimentali Veterinarie, Università di Padova, Legnaro (PD), Italy. gianfranco.gabai@unipd.it
authors.forename: G
authors.initials: G
authors.lastname: Gabai
authors.forename: A
authors.initials: A
authors.lastname: Mollo
authors.forename: L
authors.initials: L
authors.lastname: Marinelli
authors.forename: M
authors.initials: M
authors.lastname: Badan
authors.forename: G
authors.initials: G
authors.lastname: Bono
mesh_terms: D000324:Adrenocorticotropic Hormone / Q000097:blood / Q000494:pharmacology*; D000818:Animals; D002417:Cattle / Q000097:blood / Q000502:physiology*; D018592:Cross-Over Studies; D004967:Estrogens / Q000097:blood; D005260:Female; D006728:Hormones / Q000097:blood / Q000494:pharmacology; D006854:Hydrocortisone / Q000097:blood; D007986:Luteinizing Hormone / Q000097:blood*; D003341:Luteolysis / Q000097:blood / Q000502:physiology*; D009270:Naloxone / Q000494:pharmacology*; D006080:Ovarian Follicle / Q000000981:diagnostic imaging / Q000187:drug effects / Q000502:physiology; D010053:Ovary / Q000000981:diagnostic imaging / Q000187:drug effects / Q000502:physiology; D010060:Ovulation / Q000097:blood / Q000187:drug effects / Q000502:physiology*; D011374:Progesterone / Q000097:blood; D014463:Ultrasonography
chemical_list: D004967:Estrogens; D006728:Hormones; D009270:Naloxone; D011374:Progesterone; D000324:Adrenocorticotropic Hormone; D007986:Luteinizing Hormone; D006854:Hydrocortisone