The efficacy of a single chain recombinant equine luteinizing hormone (reLH) in mares: induction of ovulation, hormone profiles, and inter-ovulatory intervals.

The objectives of this study were to determine the efficacy of recombinant equine luteinizing hormone (reLH) in shortening the time to ovulation in cycling mares and to determine the effects of treatment on endogenous hormones and inter-ovulatory intervals. In study 1, mares of light horse breeds (3-20 years) were treated with either a vehicle, various doses of reLH, or human chorionic gonadotropin (hCG). Cycling mares were examined by palpation and ultrasound per rectum daily or every 12h from the time of treatment to ovulation. In studies 2 and 3, jugular blood samples were collected daily or every 12h from the time of treatment to ovulation for analysis of LH, follicle stimulating hormone (FSH), estradiol-17beta (E(2)), and progesterone (P(4)) by radioimmunoassays (RIA). Increasing doses of reLH (0.3, 0.6, 0.75, and 0.9 mg) showed increasing effectiveness at inducing ovulation within 48 h of treatment. Treatments with the 0.75 and 0.9 mg doses of reLH resulted in 90% and 80% ovulation rates, which were similar to hCG treatment (85.7%). Except for the early rise in LH after treatment with 0.5, 0.65, and 1.0mg of reLH, hormone profiles appeared to be similar between control and treated cycles. Inter-ovulatory intervals were similar between control and treatment cycles. In conclusion, reLH is a reliable and effective ovulatory agent that does not significantly alter endogenous hormone profiles or affect inter-ovulatory intervals.

Evidence for a mate-attracting chemosignal in the dwarf African clawed frog Hymenochirus.

Many male frogs and toads possess sexually dimorphic skin glands (breeding glands). However, in most anuran species, the functional significance of the glands is unknown. Here we show that the breeding glands of male dwarf African clawed frogs (Hymenochirus sp. ) release a mate-attractant chemosignal. The mate-attractant activity was assessed using a two-choice aquatic Y-maze. Female Hymenochirus were allowed to choose between different treatment waters (e.g., plain water and water housing males) in the upstream arms of the maze, and the females' movements were monitored by computer-linked motion sensors. Females showed a positive chemotaxis to water housing males and to water containing homogenized breeding glands. Females showed no reaction to water housing conspecific females or to water housing breeding gland-ablated males. Additional choice tests demonstrated that females were more attracted to water housing males than to water housing females and to water containing homogenized breeding glands than to water housing breeding gland-ablated males. Males in the maze showed no response to water housing either females or other males, indicating that the attractant is specific for females and is therefore neither a species aggregation signal nor a food-related attractant. These results represent the first experimental demonstration of a mate-attractant function for anuran breeding glands. Because many anuran species possess breeding glands, these results suggest that pheromonal communication could be more widespread among frogs and toads than previously believed.