Relaxin concentrations in serum and urine of endangered species: correlations with physiologic events and use as a marker of pregnancy

Luteal phase length, endometrial edema, and behavior differentiate post-ovulatory events in a giant panda (Ailuropoda melanoleuca)

Despite decades of reproductive research on the giant panda (Ailuropoda melanoleuca), the post-ovulatory phase continues to confound zoologists in conservation and breeding centers around the world, often resulting in significant investments of time and resources without reproductive success. The purpose of this project was to document and compare post-ovulatory characteristics during a non-productive and productive breeding in the same individual in consecutive years. A multidisciplinary approach was used to monitor the visiting female giant panda at the Toronto Zoo through the luteal phase of her first two full reproductive cycles in 2014 and 2015. Monitoring occurred via urine-endocrine analysis, weekly ultrasound examinations, and continuous behavioral observations. The 2014 reproductive cycle consisted of a pseudopregnancy, characterized by an extended luteal phase (241 days), the identification of endometrial edema and folding during ultrasound examinations, and a lack of strong association between behavior patterns and urinary progestagen secretion. The 2015 reproductive cycle included increased feeding time through the primary progestagen rise compared to the previous year, followed by simultaneous decrease in appetite and increases in inactivity, resting, sitting upright, and pre-partum-associated behaviors. These changes began 25 days before the birth of twins on Day 153 post-ovulation. Both fetuses were detected via ultrasound 15 days pre-partum. These results suggest that an absence of pre-partum behaviors, ultrasound evidence of endometrial edema without a fetus, and an extended luteal phase may be indicative of pseudopregnancy in giant pandas. Simultaneous monitoring of morphology, behavior, and urinary-endocrine profiles showed clear differences between successful and unsuccessful reproductive years.

Urinary specific gravity as an alternative for the normalisation of endocrine metabolite concentrations in giant panda (Ailuropoda melanoleuca) reproductive monitoring

Reproductive monitoring for captive breeding in giant pandas is based on behavioural observation and non-invasive hormone analysis. In urine, interpretation of results requires normalisation due to an animal’s changing hydration. Correction of urinary concentrations based on creatinine is the gold standard. In this study, a largely unexplored, easy-to-perform normalisation technique, based on urinary specific gravity (USpG), was examined and compared to creatinine. To this extent, six cycles from two female pandas (SB741(1) and SB569(5)) were monitored through urine analysis for oestrogen, progesterone, ceruloplasmin and 13,14-dihydro-15-keto-PGF2a (PGFM). The Pearson’s correlation between creatinine and USpG was high (r = 0.805–0.894; p < 0.01), indicative for a similar performance of both normalisation methods. However, generally lower values were observed during pro-oestrus and primary (progesterone) rise. This could be associated with huge shifts in appetite, monitored by faecal output (kg) with an averaged > 50% decrease during oestrus and >50% increase during primary progesterone rise. In parallel, respectively highest and lowest creatinine and USpG levels, were measured, with creatinine obviously more affected as a result of linkage with muscle tissue metabolism affected by reproductive hormones. As a consequence, metabolite levels were significantly different between both corrected datasets with significantly higher oestrogen peak levels during oestrus ranging from 2.13–86.93 and 31.61–306.45 ng/mL (USpG correction) versus 2.33–31.20 and 36.36–249.05 ng/mL Cr (creatinine correction) for SB569 and SB741 respectively, and significant lower progesterone levels during primary progesterone rise ranging from 0.35–3.21 and 0.85–6.80 ng/mL (USpG correction) versus 0.52–10.31 and 2.10–272.74 ng/mL Cr (creatinine correction) for SB569 and SB741 respectively. Consequently, USpG correction rendered unbiased profiles, less subject to variation and metabolic artefacts and therefore allowed a more straightforward identification of peak oestrogen and onset of secondary progesterone rise, being potentially advantageous for future studies unravelling key giant panda reproductive events, including (delayed) implantation. The alternative application of USpG as a normalisation factor was further supported by its easy application and environmental and technical robustness.

Use of urinary 13,14, dihydro-15-keto-prostaglandin F2α (PGFM) concentrations to diagnose pregnancy and predict parturition in the giant panda (Ailuropoda melanolecua)

Pregnancy determination is difficult in the giant panda (Ailuropoda melanolecua), representing a challenge for ex situ conservation efforts. Research in other species experiencing pseudopregnancy indicates that urinary/fecal concentrations of 13,14, dihydro-15-keto-prostaglandin F_2α (PGFM) can accurately determine pregnancy status. Our objective was to determine if urinary PGFM concentrations are associated with pregnancy status in the giant panda. Urinary PGFM concentrations were measured in female giant pandas (n = 4) throughout gestation (n = 6) and pseudopregnancy (n = 4) using a commercial enzyme immunoassay. Regardless of pregnancy status, PGFM excretion followed a predictable pattern: 1) baseline concentrations for 11–19 weeks following ovulation; 2) a modest, initial peak 14–36 days after the start of the secondary urinary progestagen rise; 3) a subsequent period of relatively low concentrations; and 4) a large, terminal peak at the end of the luteal phase. Pregnant profiles were distinguished by an earlier initial peak (P = 0.024), higher inter-peak concentrations (P < 0.001), and a larger terminal peak (P = 0.003) compared to pseudopregnancy profiles. Parturition occurred 23 to 25 days from the initial PGFM surge and within 24 hours of the start of the terminal increase. These pattern differences indicate that urinary PGFM monitoring can be used to predict pregnancy status and time parturition in the giant panda. Furthermore, this is the only species known to exhibit a significant PGFM increase during pseudopregnancy, suggesting a unique physiological mechanism for regulating the end of the luteal phase in the giant panda.

Relaxin as a hormonal aid to evaluate pregnancy and pregnancy loss in bottlenose dolphins (Tursiops truncatus)

This study was conducted to critically evaluate weekly and monthly circulating concentrations of immunoreactive relaxin throughout pregnancies that resulted in live births, stillbirths, and abortions in aquarium-based bottlenose dolphins. A relaxin RIA was used to analyze serum collected during 74 pregnancies involving 41 dolphins and 8 estrous cycles as well as 8 non-pregnant dolphins. Pregnancies resulted in live births (n=60), stillbirths (n=7), or abortions (n=7). Relative to parturition (Month 0), monthly changes (P<0.0001) in relaxin was indicated by relatively low concentrations during early pregnancy (Months -12 to -9) which subsequently increased (P<0.05) during mid- (Months -8 to -5) to late (Months -4 to -1) pregnancy; relaxin was highest (P<0.05) at the time of parturition. Post-parturition (Month 1), concentrations decreased (P<0.05). During the first 4weeks post-ovulation, relaxin concentrations were not different between pregnant and non-pregnant dolphins (status-by-week interaction, P=0.59). Status-by-month interaction (P<0.0002) involving different pregnancy outcomes was due, impart, to an increase in relaxin during early pregnancy (P<0.05) that was comparable among dolphins with live births, stillbirths, and abortions except concentrations were lower (P<0.05; 52%) at mid-pregnancy in association with pregnancy loss. Thereafter, concentrations increased (P<0.05) during late pregnancy in dolphins with stillbirths but not in dolphins with abortions. In conclusion, this study provided new information on the pregnancy-specific nature of relaxin, critical evaluation of the fundamental characteristics of relaxin during pregnancy and pregnancy loss, and clarification on the strengths and limitations of relaxin as a diagnostic aid to determine pregnancy status and assess maternal-fetal health in bottlenose dolphins.

Relaxin: a hormonal aid to diagnose pregnancy status in wild mammalian species

In the beginning of 1960s, seminal studies characterizing circulating concentrations of immunoreactive relaxin in companion dogs and evaluating the differences in concentrations among pregnant, nonpregnant, and pseudopregnant bitches indicated the potential for relaxin to be applied clinically as a diagnostic aid to detect pregnancy status in wild animal species. A brief historical overview of the nature of relaxin and early work to develop and validate immunologic methods to analyze relaxin in the blood of rodents and pigs is initially discussed, which is followed by a summary of the development and validation of relaxin immunoassays to diagnose pregnancy in companion dogs and cats. Thereafter, observation of the pregnancy-specific increase in circulating concentrations of relaxin in laboratory, companion, and farm animal species leads to discussion on the application of radioimmunoassays, enzyme immunoassays, and a rapid immunomigration assay to diagnose pregnancy in wild terrestrial (e.g., wolves, lions, elephants, rhinoceros, panda) and marine (e.g., seals, dolphins) mammal species. A reference table is included with a comprehensive list of numerous species and essential reagents that have been used in various in-house and commercial immunoassays to successfully analyze relaxin quantitatively and qualitatively in blood (serum or plasma) and to some extent in urine. Although the detection of relaxin concentrations has the potential to aid in the diagnosis of pregnancy in many wild animal species, there are challenges in other species. Future efforts should focus on validation of nonradiolabeled relaxin immunoassays for broader application among species and improving techniques (e.g., extraction, purification) to analyze relaxin in samples other than blood (e.g., urine, feces, saliva, blow, skin, blubber) that can be collected in a less-invasive or -stressful manner and processed accordingly for basic and applied purposes, especially with application toward conservation of threatened or endangered species.

Pregnancy diagnosis in wild canids using a commercially available relaxin assay

Accurate detection of pregnancy is a useful tool in zoo management and husbandry, conservation breeding programs and research settings. Our study evaluated the ability of a commercial relaxin hormone assay used in domestic dogs (ReproCHEK(TM)) to accurately detect pregnancy through plasma analysis in two wolf and two fox species. The relaxin assay detected all of the pregnancies greater than 25 days gestation for island foxes, fennec foxes, gray wolves, and Mexican gray wolves. For island foxes, three negative relaxin results were attributed to using the test earlier postconception than manufacturer recommendation (before day 20). Five other negative results were found for females estimated at 15-25 days gestation, spanning the early and intermediate period (21-30 days gestation) when relaxin may be detected but less reliably. There were no false-positive results in nonmated negative control animals. Relaxin assay results were highly correlated with ultrasound results and the intra-assay replicate agreement was 100%. Our results show that the ReproCHEK(TM) commercial relaxin assay is a minimally invasive and reliable method for pregnancy detection in these wild species when used after 25 days gestation and might be applied to other canids as well. Furthermore, this assay is easy to run and requires no specialized equipment, making it extremely useful for zoo and field research applications. Zoo Biol 27:406-413, 2008. (c) 2008 Wiley-Liss, Inc.

The acute phase protein ceruloplasmin as a non-invasive marker of pseudopregnancy, pregnancy, and pregnancy loss in the giant panda

After ovulation, non-pregnant female giant pandas experience pseudopregnancy. During pseudopregnancy, non-pregnant females exhibit physiological and behavioral changes similar to pregnancy. Monitoring hormonal patterns that are usually different in pregnant mammals are not effective at determining pregnancy status in many animals that undergo pseudopregnancy, including the giant panda. Therefore, a physiological test to distinguish between pregnancy and pseudopregnancy in pandas has eluded scientists for decades. We examined other potential markers of pregnancy and found that activity of the acute phase protein ceruloplasmin increases in urine of giant pandas in response to pregnancy. Results indicate that in term pregnancies, levels of active urinary ceruloplasmin were elevated the first week of pregnancy and remain elevated until 20–24 days prior to parturition, while no increase was observed during the luteal phase in known pseudopregnancies. Active ceruloplasmin also increased during ultrasound-confirmed lost pregnancies; however, the pattern was different compared to term pregnancies, particularly during the late luteal phase. In four out of the five additional reproductive cycles included in the current study where females were bred but no birth occurred, active ceruloplasmin in urine increased during the luteal phase. Similar to the known lost pregnancies, the temporal pattern of change in urinary ceruloplasmin during the luteal phase deviated from the term pregnancies suggesting that these cycles may have also been lost pregnancies. Among giant pandas in captivity, it has been presumed that there is a high rate of pregnancy loss and our results are the first to provide evidence supporting this notion.

Relaxin and progesterone during pregnancy and the post-partum period in association with live and stillborn calves in bottlenose dolphins (Tursiops truncatus)

The objectives of this study were to validate a relaxin and progesterone RIA for use in bottlenose dolphins, and quantify and characterize both hormones in extracts of placental tissue and serum collected during pregnancy and the post-partum period, and compare the results between dolphins with live and stillborn calves. In Experiment 1, validation of a heterologous relaxin and progesterone RIA involved specific displacement of antibody-bound radiolabeled human relaxin or progesterone in response to increasing volumes of pooled pregnant dolphin serum and amounts of respective hormone standards added to a fixed volume of serum. The displacement curves were considered parallel and additive relative to respective standard curves. In Experiment 2, immunoreactive relaxin and progesterone were detected in placental extracts and, in corresponding serum samples, concentrations of both hormones were higher during the pre-partum than post-partum periods. Circulatory concentrations of progesterone decreased (P < 0.05) from relatively high concentrations during early and mid-pregnancy to intermediate concentrations by late pregnancy (month effect, P < 0.0001) in dolphins with live births, whereas, in dolphins with stillbirths, the decrease in progesterone began earlier (month-by-birth status interaction, P < 0.007); mean concentrations were lower at mid- (37%, P < 0.06) and late (25%) pregnancy. Temporally, relaxin increased (P < 0.05) progressively from relatively low concentrations during early pregnancy to high concentrations during late pregnancy (month effect, P < 0.0001) and was not different between birth statuses (birth status effect, P = 0.76; month-by-birth status interaction, P = 0.17). Even though the interaction did not reach significance, mean relaxin concentrations were 42%, 29%, and 34% lower at early, mid-, and late pregnancy, respectively, in dolphins with stillbirths than in those with live births. In conclusion, the pregnancy-specific increase in serum concentrations of relaxin and lower concentrations of both relaxin and progesterone in association with stillbirths suggest the potential for relaxin to be used diagnostically to determine pregnancy status, and one or both hormones to be used to assess placental function, and, perhaps, fetal well-being in bottlenose dolphins and other cetaceans.

Validation of a homologous canine relaxin radioimmunoassay and application with pregnant and non-pregnant Northern fur seals (Callorhinus ursinus)

The primary objectives of this study were to validate a canine relaxin RIA for use in otariids and phocids and consider practical applications. For 6 captive Northern fur seal females, serum samples were grouped and examined according to pregnancy (n=13), post-partum (n=8) and non-pregnancy (n=6), and, for 2 captive Northern fur seal males, serum samples were grouped and examined together regardless of age (2 mo-15 yrs, n=6). Placental tissue was available for examination from one Northern fur seal, Steller sea lion and harbor seal. The validation process involved several steps using an acid-acetone extraction process to isolate a relaxin-containing fraction in pools of serum from each group of fur seals and placental tissue from each seal species. A relaxin-like substance was detected in extracts of pregnant, non-pregnant and male serum and placental tissue in a dose-responsive manner as increasing volumes of respective extracts or amounts of canine relaxin were introduced into the assay. In raw serum samples, mean immuno-reactive relaxin concentrations were higher (P<0.05) during pregnancy than post-partum and non-pregnancy, and lower (P<0.05) in male than female fur seals. During pregnancy, mean serum concentrations of relaxin progressively increased (P<0.05) over Months 4-10 and, in serial samples collected from the same fur seals before and after parturition, mean concentrations were higher (P<0.06) pre-partum than post-partum. In conclusion, validation of a homologous canine relaxin RIA for use in otariids and phocids resulted in the discovery of a relaxin-like substance in extracted and raw serum and placental tissue from Northern fur seals, a Steller sea lion and harbor seal. Distinctly higher immuno-reactive concentrations during pregnancy indicated the potential for relaxin to serve as a hormonal marker to differentiate between pregnant and non-pregnant or pseudopregnant pinnipeds.

Development, Validation, and Application of a Urinary Relaxin Radioimmunoassay for the Diagnosis and Monitoring of Pregnancy in Felids1

Many nondomestic felids are highly endangered, and captive breeding programs have become essential components of holistic conservation efforts for these species. The ability to diagnose pregnancy early in gestation is fundamental to developing effective breeding programs. The purpose of this study was to develop a radioimmunoassay (RIA) for the detection of urinary relaxin in felids and assess its applicability for early, noninvasive pregnancy diagnosis in domestic cats (Felis silvestris catus) and leopards (Panthera pardus). Urine was collected from pregnant and nonpregnant domestic cats and leopards at mating, and then weekly thereafter for the duration of gestation. Paired serum samples were also collected from the domestic cats. A RIA for relaxin that uses an antiserum against synthetic canine relaxin was validated for felid urine and shown to detect relaxin immunoreactivity in pregnant cat urine subjected to acid-acetone extraction. In the cat, urinary relaxin was first detected between Days 21 and 28 of gestation; levels peaked at 42-49 days, and the concentrations then declined over 2 wk prior to parturition. The urinary relaxin profiles of the cat mirrored those in serum. In the leopard, urinary relaxin was first detected at Day 25-28 of gestation; levels peaked at Day 60-64 and declined in the last 3-4 wk of pregnancy. These results indicate that measurement of urinary relaxin in the cat and leopard provides a reliable method for pregnancy determination from as early as 3-4 wk of gestation. This method of pregnancy diagnosis and monitoring may prove useful in the breeding management of domestic cats and other felid and canid species, and provides a foundation for future studies on pregnancy in captive exotic carnivores.