Submission Number: LES-4-20-12

Abstract Number: 551

LUTEINIZING HORMONE INCREASES FOLLOWING PHEROMONAL STIMULATION DURING INDUCTION OF ESTRUS IN GRAY SHORT-TAILED OPOSSUMS.

Leslie M Jackson* and John D Harder*

Department of Evolution, Ecology, and Organismal Biology, The Ohio State University, Columbus, OH ¹

Abstract:
Estrus is induced in gray short-tailed opossums by male pheromones. Exposure to male scentmarks produces a transient increase in circulating luteinizing hormone (LH) and typically induces estrus within 10 days. The purpose of this study was to measure plasma estradiol (E) during induction of estrus and examine the relationship between E levels and LH released in response to pheromonal exposure or physical contact with a male. Anestrous females (n=39) received a standardized, daily exposure to scentmarks either from intact or castrated males. Females (n=5 or 6/group) were euthanatized 2 h after pheromone exposure on the first day of exposure (day 0), on day 4, or on the first of day of urogenital sinus (UGS) estrus. Two groups of estrous females (n=6 each) were paired with males and euthanatized 5 or 10 h later. Control females were killed 2 h after initial exposure (n=5) or after 5 h of pairing with an intact male on the 8th day of castrate scentmark exposure (n=5). Blood samples were collected from all animals prior to pheromonal stimulation on day 0 and immediately prior to euthanasia. Additional samples were collected on days 2, 4, and 6 from females who were paired with males at estrus (or on day 8 for controls). Ovaries, uteri, and lateral vaginal canals (LVC) were removed and weighed. Plasma LH levels were measured with an opossum Leydig cell bioassay; E was measured by radioimmunoassay. Mean ( SEM) E concentrations were higher (p<0.05) at UGS estrus (29.8 4.5 pg/ml) than on day 0 (15.7 4.0 pg/ml), and remained elevated (32.1 10.6 pg/ml) through 10 h of pairing. E levels in castrate-exposed females were not different between day 0 (18.5 5.7 pg/ml) and day 8 (19.0 3.8 pg/ml). Uteri and LVC (0.38 0.06 g and 1.31 0.09 g, respectively) were heavier (p < 0.01) at estrus than on day 0 (0.12 0.02 g and 0.47 .12 g) and day 4 (0.17 0.04 g and 0.65 0.18 g). LH concentrations following pheromone exposure increased (p<0.01) from 0.24 0.03 ng/ml on day 0 to 0.36 0.06 ng/ml and 1.15 .23 ng/ml on day 4 and the first day of UGS estrus, respectively. After 10 hours of pairing, but prior to copulation, mean LH was 1.85 0.76 pg/ml. These data indicate that a rise in plasma E during induction of estrus is associated with increased LH levels following pheromone stimulation. This study was sponsored by NSF (IBN 9616588).

Keywords: opossum, LH, pheromone

This abstract is being presented at: 8:00 AM in session:
Neuroendocrinology II