Species and fetal gender effects on the endocrinology of pregnancy in elephants Jordana M. Meyer a , Susan L. Walker a , Elizabeth W. Freeman a , Bernard G. Steinetz b , Janine L. Brown a, * a Department of Reproductive Sciences, Conservation and Research Center, National Zoological Park, Smithsonian Institution, Front Royal, VA 22630, USA b Department of Environmental Medicine, New York University School of Medicine, Tuxedo, NY 10987, USA Received 28 April 2004; revised 17 June 2004; accepted 29 June 2004 Abstract Quantitative and temporal progestin profiles vary during gestation in the elephant, sometimes making it difficult to determine if a pregnancy is progressing normally. The aim of the present study was to determine if circulating progestin variability was related to species or fetal gender effects. A similar comparison also was conducted for secretory profiles of prolactin, relaxin, and cortisol. Overall mean progestin concentrations during gestation in Asian (n = 19) and African (n = 8) elephants were similar; however, the temporal profiles differed (P < 0.001). Concentrations were higher in African elephants during the first half of pregnancy, but then declined to levels below those observed in Asian elephants (P < 0.05). There also was a fetal gender effect in Asian, but not African elephants. Progestin concentrations were higher in Asian cows carrying male calves (n = 9) as compared to those carrying females (n = 10) (P < 0.001). Overall prolactin concentrations were higher in Asian than in African elephants between 8 and 15 months of gestation (P < 0.001). There were no species differences in the secretory patterns of relaxin. Cortisol was relatively stable until the end of gestation when significant surges were observed, mainly between 8 and 11 days before parturition, and again on the day of birth. In sum, a comparison of progestin patterns between Asian and African elephants identified notable differences related to species and fetal gender. A role for cortisol in the initiation of parturition also was inferred from these data. From a practical standpoint, understanding the factors affecting gestational hormone characteristics and recognizing what the species differences are will help ensure that data used in diagnosing and monitoring elephant pregnancies are properly interpreted. Ó 2004 Elsevier Inc. All rights reserved. Keywords: Elephant; Pregnancy; Hormones; Progestins; Cortisol; Prolactin; Relaxin 1. Introduction Based on two decades of endocrine studies in Asian (Elephas maximus) and African (Loxodonta africana) elephants, it is generally accepted that females have a 13–16 week ovarian cycle (Brannian et al., 1988; Hess et al., 1983; Plotka et al., 1998) with two LH surges that occur 3 weeks apart during the interluteal phase (Brown et al., 1999; Kapustin et al., 1996). Gestation lasts 20–22 months (Brown and Lehnhardt, 1995; Hess et al., 1983; McNeilly et al., 1983; Olsen et al., 1994) and is charac- terized by increases in prolactin (Brown and Lehnhardt, 1995; Hodges et al., 1987) after the first third of gesta- tion. However, although endocrine mechanisms appear to be relatively conserved between species, there may be subtle differences that would not be evident without direct comparative studies (Hodges, 1998). The endocrine laboratory at the Conservation and Research Center works with zoos throughout North America to characterize ovarian cycles and diagnose and monitor pregnancy in elephants. Over the years 0016-6480/$ - see front matter Ó 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.ygcen.2004.06.010 * Corresponding author. Fax: 1-540-635-6506. E-mail address: jbrown@crc.si.edu (J.L. Brown). www.elsevier.com/locate/ygcen General and Comparative Endocrinology 138 (2004) 263–270 GENERAL AND COMPARATIVE ENDOCRINOLOGY