Luteinizing hormone and prolactin in mated female meadow voles housed in long and short day lengths.

Fertility differs dramatically between female meadow voles (Microtus pennsylvanicus) housed in long (LD; 14 h light/day) and short (SD; 10 h light/day) day lengths. All mated LD females ovulate, and 75-100% produce litters. In contrast, 40% of SD females that mate only after long contact with a male do not ovulate, and fertility for SD females is much lower (30-40% produce litters overall). Because copulation causes the surge in LH required for ovulation and the increase in prolactin (PRL) needed to maintain corpora lutea, we hypothesized that SD females might have lower ovulation rates and litter production because of inadequate hormonal responses. Serum LH was measured 24 h before, and 30, 60, 90, 120, and 180 min after, mating. Prolactin was measured before, and 24 and 48 h after, copulation. LD and SD females that ovulated demonstrated a sharp increase in LH levels at 30 and 60 min post mating, but LH in non-ovulating females was approximately 50% lower than that of ovulating females at 30 and 60 min post mating. PRL in LD females was double baseline levels at 24 and 48 h after mating. PRL in SD females increased at 24 h, but declined to pre-mating levels by 48 h post mating. These data suggest that reduced fertility in short day lengths in female voles may be related to two separate problems: 1) The rise in LH following copulation is insufficient in some females to cause ovulation. 2) PRL may not remain elevated long enough to support functional corpora lutea in some females that ovulate.