Development of preovulatory follicles expected to form short-lived corpora lutea in beef cows.

Oestrus, expected to be followed by a short luteal phase, was induced in post-partum cows by weaning their calves at 35 days after parturition. Ovaries containing the first preovulatory follicles (Type F) formed after parturition were collected 3 h after the onset of oestrus. For comparison, preovulatory follicles (Type C) were collected 3 h after the onset of oestrus in normally cycling cows. The number of granulosa cells was determined and the concentrations of receptors for follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in granulosa cells and for LH in theca cells were measured. Concentrations of oestradiol-17 beta, testosterone, androstenedione and progesterone in follicular fluid were also measured. Type F follicles contained about twice the number of granulosa cells (based on DNA) as did Type C follicles (45.8 +/- 11.3 and 24.5 +/- 3.9 micrograms DNA/follicle, respectively; P less than 0.05) but these cells had fewer receptors for LH (0.13 +/- 0.02 vs 0.29 +/- 0.03 fmol/micrograms DNA; P less than 0.01) and FSH (0.61 +/- 0.08 vs 1.3 +/- 0.29 fmol/micrograms DNA; P less than 0.08) than did those from Type C follicles. Additionally, there were fewer receptors for LH in theca tissue from Type F than from Type C follicles (28.3 +/- 5.2 vs 51.3 +/- 6.1 fmol/follicle; P less than 0.01). Concentrations of oestradiol-17 beta (475.8 +/- 85.6 vs 112.9 +/- 40.0 ng/ml; P less than 0.01) and androstenedione (214.1 +/- 48.7 vs 24.7 +/- 7.7 ng/ml; P less than 0.01) in follicular fluid were higher in Type C than in Type F follicles.(ABSTRACT TRUNCATED AT 250 WORDS)