Luteinization and proteolysis in ovarian follicles of Meishan and Large White gilts during the preovulatory period

This experiment was conducted to determine why follicles luteinize faster i n the Meishan breed than in the Large White breed of pig. Follicles were re covered during the late follicular phase from ovaries of both breeds before and after administration of hCG given to mimic the LH surge. First, the pa tterns of cholesterol transporters thigh and low density lipoproteins: HDL and LDL) were compared. Cholesterol transporters detected in follicular flu id consisted of HDL only. Similar amounts of Apolipoprotein A-I were found in all samples. There was no obvious breed effect on minor lipoproteins fou nd in the HDL-rich fraction, and this pattern was altered similarly by hCG in the two breeds. The LDL-rich samples of serum from both breeds contained similar amounts of protein. Second, three steroidogenic enzymes, adrenodox in, 17 alpha-hydroxylase-lyase (P450(17 alpha)) and 3 beta-hydroxysteroid-d ehydrogenase (3 beta-HSD) were detected by immunohistochemistry and quantif ied by image analysis on sections of the two largest follicles. Before hCG treatment, theca interna cells demonstrated immunoreactivities for adrenodo xin (strong), P450(17 alpha) and 3 beta-HSD (very strong), whereas granulos a cells displayed immunoreactivities for adrenodoxin only. After hCG treatm ent, the localization of the enzymes was unchanged but the staining intensi ty of adrenodoxin on granulosa cells and 3 beta-HSD on theca cells increase d (P < 0.01 and P < 0.05, respectively). Breed effects were detected for th e amounts of adrenoxin in theca cells (Meishan > Large White; P < 0.05) and of 17 alpha-hydroxylase (Large White > Meishan, P < 0.01). Breed x treatme nt interactions were never detected. Finally, gelatinases, plasminogen acti vator, plasminogen activator inhibitor tissue inhibitors of metalloprotease s (TIMP-1 and TIMP-2) were visualized by direct or reverse zymography or we stern blotting. Whatever the stage relative to LH administration, follicula r fluid from Large White gilts contained more TIMP-1, and TIMP-2 (P < 0.02 and P < 0.01, respectively). No breed effect was detected for the amounts o f gelatinases and plasminogen activator inhibitor 1. However, for these par ameters, a significant breed x time interaction was obvious, as the Meishan follicles had a greater response to hCG (P < 0.01). Since proteolysis play s a key role in the bioavailability of growth factors such as insulin-like growth factor 1, fibroblast growth factor and transforming growth factor be ta, which have the ability to alter gonadotrophin-induced progesterone prod uction in pigs, the differences observed in its control in the present stud y may explain, at least in part, the different patterns of luteinization ob served in Meishan and Large White follicles.