Effects of human chorionic gonadotropin on luteal blood flow and progesterone secretion in cows and in vitro-microdialyzed corpora lutea

To check human chorionic gonadotropin (hCG) effects on luteal blood flow (LBF) and progesterone (P-4) synthesis, six cows received either 3000 IU hCG or saline (NaCl) on Day 7 (Day 1 = ovulation) during two estrous cycles. Plasma P-4 and LBF were measured before (0 h) and up to 48 h after treatment. Luteal blood flow increased by 51% (P < 0.05) at I h after hCG administration and returned to baseline levels thereafter. Plasma P-4 levels were increased from pretreatment levels by 30% at I h (P = 0.05) and 81 % at 48 h (P = 0.02) after hCG treatment. In contrast, NaCl did not cause changes in LBF and P-4 (P > 0.05). Additionally, central and peripheral parts of 14 abattoir-derived corpora lutea of the mid-luteal phase (Day 8 to 12) were perfused with Ringer solution in an in vitro microdialysis system, supplemented with 50 or 150 IU/mL hCG for I h. Application of 50 IU/mL hCG showed no influence on P-4 response (P > 0.05) in both central and peripheral parts, whereas 150 IU/mL hCG resulted in an increase of P-4 synthesis (P = 0.002) in the central parts only. In vivo, hCG provoked an immediate and long-term rise in P-4 but only a temporary elevation of LBF Luteal blood flow itself does not seem to be the exclusive cause for an increase in P-4, because the in vitro data clearly showed direct effects of hCG on P-4 secretion. Interestingly, different P-4 secretion patterns could be found between central and peripheral parts of the corpus luteum in both control and hCG perfused corpora lutea. (C) 2009 Elsevier Inc. All rights reserved.