Characterization of serum follicle stimulating hormone, growth hormone, leptin, luteinizing hormone, and prolactin in female polar bears (Ursus maritimus) via multiplex immunoassay.

Reproductive failure is an increasing concern for polar bear (Ursus maritimus) populations. Although hormone monitoring has improved understanding of reproductive function, serum-based assessments have been underutilized. This study evaluated the use of multiplex immunoassays to characterize key hormones in females. Serum samples (n = 103; 2-8 per bear) were collected from 25 females and used to characterize follicle-stimulating hormone (FSH), growth hormone (GH), leptin, luteinizing hormone (LH), and prolactin (PRL) using commercial panels. Assay validation confirmed biologically meaningful profiles parallelism, acceptable spike-and-recovery (range: 91.6-99.8%), and analyte stability across four freeze-thaw cycles (< 15% difference). Age groups were defined as juvenile (0-5.0 y), young adult (5.1-12.0 y), adult (12.1-20.0 y), and senior (> 20.0 y). Juveniles were excluded from analyses except where age group was evaluated. Seasons were classified based on northern hemisphere astronomical seasons. FSH was frequently below the assay's minimum detectable limit (MDL), indicating that although assay specificity was confirmed, the sensitivity was insufficient to reliably quantify physiological concentrations in this species. Detectable values (range: 7.8 to 22.4 ng/mL) were mostly restricted to the breeding season, with no samples above the MDL from May through November. GH concentrations differed significantly by season (P = 0.001), with the greatest model-adjusted mean during winter (4.29 ± 2.0 ng/mL) and lowest during summer (0.59 ± 0.28 ng/mL). Leptin concentrations differed by age group (P = 0.001), with the greatest model-adjusted mean in seniors (1.69 ± 0.50 ng/mL) and lowest in young adults (0.58 ± 0.42 ng/mL). LH also varied by age (P = 0.0002), with seniors showing the greatest model-adjusted mean (0.65 ± 0.18 ng/mL) and immature bears, the lowest (0.16 ± 0.04 ng/mL). PRL model-adjusted mean peaked in winter (38.05 ± 9.71 ng/mL) and spring (36.38 ± 8.49 ng/mL; P = 0.0001) and age group (P = 0.04); however, post-hoc tests revealed no significant difference in pairwise comparisons among the age groups. These results demonstrate the applicability of multiplex technology for reproductive hormone monitoring in polar bears. Notably, this study provides the first comprehensive characterization of several key hormones in female polar bears.