LUTEINIZING-HORMONE AND PROLACTIN IN MATED FEMALE MEADOW VOLES HOUSEDIN LONG AND SHORT-DAY LENGTHS

Fertility differs dramatically between female meadow voles (Microtus p ennsylvanicus) 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% pro duce 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 m uch lower(30-40% produce litters overall). Because copulation causes t he surge in LH required for ovulation and the increase in prolactin (P RC) needed to maintain corpora lutea, we hypothesized that SD females might have lower ovulation rates and litter production because of inad equate hormonal responses. Serum LH was measured 24 h before, and 30, 60, 30, 120, and 180 min after, mating. Prolactin was measured before, and 24 and 48 h after, copulation. LD and SD females that ovulated de monstrated 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 fema les 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 ov ulation. 2) PRL may not remain elevated long enough to support functio nal corpora lutea in some females that ovulate.