Comparison of the steroidogenic capacity of bovine follicular and luteal cells, and corpora lutea originating from dominant follicles of the first orsecond follicular wave

This study compared the endocrine function of dominant follicles of the fir st and second follicular waves (DF1 and DF2, respectively) and the corpora lutea that were subsequently formed. In the experiments conducted in vitro, ovaries were collected from dairy cows on day 6.1 +/- 0.2 or day 14.8 +/- 0.2 of the oestrous cycle to obtain steroidogenically active DF1 (n = 8) an d DF2 (n = 7). Granulosa and thecal cells were isolated, dispersed and incu bated for 16 h with testosterone (granulosa cells) or forskolin or bLH (the cal cells). Both types of cell were subsequently cultured for 9 days with f orskolin and insulin. The viability of the granulosa cells was similar in D F1 and DF2, but the concentration of oestradiol in the follicular fluid was higher in DF1 than in DF2. Production of oestradiol and progesterone by gr anulosa cells was similar in DF1 and DF2, but androstenedione and progester one production by thecal cells were 3.5-6.5-fold higher in DF1 than in DF2. During the 9 days of luteinization, progesterone production was similar in DF1- and DF2-derived granulosa cells, but was two- to threefold higher in DF1- than in DF2-derived thecal cells. Experiments were also conducted in v ivo. Ln Expt 1 in vivo, lactating cows that were assigned to ovulate DF1 or DF2 (n = 9 and 13 in replicate 1 and 2, respectively) were injected with P GF(2 alpha) on days 6 and 7 or on days 14 and 15 of the oestrous cycle, res pectively. A wave by replicate interaction was detected for plasma progeste rone concentration in the subsequent cycle: in the first replicate, progest erone production was approximately 40% higher in cows that ovulated DF1; in the second replicate, progesterone production was similar in cows that ovu lated DF1 or DF2. In Expt 2, pooled plasma progesterone in the mid-luteal p hase (days 12-15) after insemination of pregnant and non-pregnant cows was approximately 30% higher in cows that had ovulated DF1 (n = 32) than in cow s that had ovulated DF2 (n = 22). This study showed DF1 had a higher steroi dogenic capacity compared with DF2, which may be related to the hormonal en vironment in which the follicles developed.