Expression of the bovine oestrogen receptor-β (bERβ) messenger ribonucleic acid (mRNA) during the first ovarian follicular wave and lack of change in the expression of bERβ mRNA of second wave follicles after LH infusion into cows

Abstract

In a previous study, the ERβ cDNA protein-coding region was utilised to clone bovine ERβ. The objectives in this study were to examine (1) ERβ mRNA expression in ovarian follicles throughout the bovine first follicular wave, and (2) effect of LH infusion into cows on bERβ mRNA expression during the second follicular wave. In experiment 1, heifers (4–5 per time point) were ovariectomized at 12, 24, 36, 48, 60, 72, 84, 96, 144, or 216 h after emergence of the first follicular wave after oestrus. In experiment 2, saline or LH was pulsed hourly (computer-controlled syringe pump) into cows ( n=31; 5–6 per treatment) at wave emergence for 2 or 4 days: wave 1-saline (W1S), wave 2-saline (W2S), or wave 2-LH (25 μg/h; W2LH). Ovaries were removed on day 2 or day 4 after wave emergence. Follicles, 2–19 mm in size, were dissected, frozen, and stored at −80°C for in situ hybridisation with two bERβ cRNA probes. Expression of bERβ mRNA was localised in granulosa cells of healthy follicles. In experiment 1, bERβ mRNA expression did not change with time points of the wave showing no association of bERβ mRNA expression with follicular selection and dominance. However, bERβ mRNA expression decreased with increase in size of all follicles. Expression of bERβ mRNA was greater in very small follicles (2–4 mm) than in large (≥9 mm) follicles. In experiment 2, expression of bERβ mRNA in follicles did not differ either between W1S and W2S or between W2S and W2LH. In summary, bERβ mRNA expression decreased with increasing follicular size. However, neither stage of the wave (selection or dominance), nor pulsatile infusion of LH influenced bERβ mRNA expression.