A cellular and endocrine characterization of the original and induced corpus luteum after administration of a gonadotropin-releasing hormone agonist or human chorionic gonadotropin on day five of the estrous cycle.
To determine whether injection of hCG or GnRH-agonist on d 5 after estrus (d 0) has a differential functional effect on an induced and the original corpus luteum (CL), two experiments were conducted. In Exp. 1, nonlactating Holstein cows were injected on d 5 with saline (n = 4; T1), a GnRH-agonist (Buserelin, 8 micrograms i.m.; n = 4; T2), or hCG (1,000 i.u., i.v., and 2,000 i.u., i.m.; n = 4; T3). Induced CL were removed on d 13 and weights were different (GnRH-agonist < hCG). In vitro production of progesterone by CL tissue (microgram/g; microgram/CL) was affected by treatment (GnRH-agonist < hCG) and dose of LH (ng.mL) in culture media. Experiment 2 was a replicate of Exp. 1, except that the original CL was removed on d 17 for in vitro culture. Day-17 CL weights and in vitro production of progesterone by original CL were not affected by treatment. The daily rate of increase of plasma progesterone from d 6 to d 13 differed: saline < GnRH-agonist < hCG (P < .01). From d 14 to 17, the rate of plasma progesterone decrease was not different between treatments. Electron micrographic study of the original and induced CL indicates that LH-like exposure delays involution of steroidogenic luteal cells. In summary, the higher levels of progesterone from d 6 to d 13 of the estrous cycle following an injection of hCG vs GnRH-agonist on d 5 is due to a greater response of hCG-induced CL.
Schmitt
E J
EJ
Department of Dairy and Poultry Sciences, University of Florida, Gainesville 32611, USA.
Barros
C M
CM
Fields
P A
PA
Fields
M J
MJ
Diaz
T
T
Kluge
J M
JM
Thatcher
W W
WW
D000818:Animals; D002064:Buserelin / Q000494:pharmacology*; D002417:Cattle / Q000378:metabolism / Q000502:physiology*; D006063:Chorionic Gonadotropin / Q000494:pharmacology*; D003338:Corpus Luteum / Q000166:cytology* / Q000378:metabolism* / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004971:Estrus / Q000502:physiology*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000819:agonists*; D006801:Humans; D007986:Luteinizing Hormone / Q000494:pharmacology; D008854:Microscopy, Electron / Q000662:veterinary; D009929:Organ Size; D011374:Progesterone / Q000097:blood / Q000378:metabolism; D011897:Random Allocation; D013997:Time Factors
D006063:Chorionic Gonadotropin; D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D007986:Luteinizing Hormone; D002064:Buserelin