REGULATION OF MESSENGER-RNA ENCODING LOW-DENSITY-LIPOPROTEIN RECEPTORAND HIGH-DENSITY LIPOPROTEIN-BINDING PROTEIN IN-OVINE CORPORA-LUTEA

Three experiments were conducted to examine the regulation of steady-s tate concentrations of mRNA encoding ovine low density lipoprotein rec eptor (LDL-R) and high density lipoprotein-binding protein (HBP) in co rpora lutea. In Experiment 1, corpora lutea were collected from ewes o n Days 3, 6, 9, 12 and 15 (Day 0, oestrus) of the oestrous cycle. Enri ched preparations of small and large steroidogenic luteal cells were a lso obtained on Days 6, 9, 12 and 15 of the oestrous cycle. In Experim ent 2, 16 ewes were hypophysectomized on Day 5 of the oestrous cycle a nd received saline, luteinizing hormone (LH), growth hormone (GH) or a combination of LH+GH until collection of luteal tissue on Day 12 of t he oestrous cycle. Corpora lutea were also collected from pituitary-in tact control ewes on Day 5 and Day 12 of the oestrous cycle. In Experi ment 3, 13 ewes on Day 11 or Day 12 of the oestrous cycle were adminis tered prostaglandin F-2 alpha (PGF(2 alpha)) and corpora lutea were co llected 4 h, 12 h and 24 h later. Corpora lutea were also collected fr om 4 non-injected and 4 saline-injected (at 24 h) ewes. Results demons trated that concentrations of mRNA encoding LDL-R did not differ throu ghout the oestrous cycle. Luteal tissue collected on Day 3 of the oest rous cycle had higher concentrations of mRNA encoding HBP than luteal tissue collected on any other day of the oestrous cycle. Hypophysectom y increased concentrations of mRNA encoding LDL-R but had no effect on concentrations of mRNA encoding HBP. Twelve hours following PGF(2 alp ha) injection concentrations of mRNA encoding LDL-R were decreased but concentrations of mRNA encoding HBP were increased. Concentrations of both LDL-R and HBP mRNA were decreased 24 h following injection of PG E(2 alpha). Thus, long-term positive and acute negative regulation of progesterone secretion from the corpus luteum by luteotrophic and lute olytic hormones was not mediated by changes in steady-state concentrat ions of mRNA encoding LDL-R or HBP.