Paternal Eucalyptus Smoke During Sperm Maturation in Long Evans Rats Results in Delayed Pubertal Timing and Estrous Cycle Irregularity in F1 Female Progeny
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Climate change has been associated with increased incidence and severity of wildland fires. With firefighters at greatest risk and in an occupation dominated by males of reproductive age, it is important to understand not only cardiopulmonary risks but reproductive health as well. We have shown that laboratory-generated wildfire (WF) smoke alters sperm motility and the epigenome, which may increase the risk of adverse health outcomes in offspring. Given these relationships, we investigated whether paternal smoke exposure could program an increased risk of endocrine disruption in female F1 offspring. Male Long-Evans rats (14-15-week-old) were episodically exposed to filtered air (FA) or eucalyptus smoke (WF; 4-5 mg/m3 PM, 10 ppm CO) for 1hr/d over 2 weeks during sperm maturation. The day following the final exposure, male rats were bred with age-matched, luteinizing hormone releasing hormone (LHRH)-stimulated, and receptive female rats. The extent of vaginal opening (VO), an index of pubertal timing, was recorded across postnatal day (PND) 28-36. To investigate the susceptibility of offspring to a known reproductive stressor, heat, a subset of females was housed for 2 weeks at an elevated temperature (H; 79oF) at ~PND 120. Controls were housed at a standard vivarium housing temperature (N; 72°F) (n=10/group). Vaginal lavage was performed every morning for the final 10 days of the postnatal heat exposure. Group differences were assessed using Dunnett’s test. Results showed the average day of VO was significantly delayed in the offspring of smoke-exposed fathers (PND 33) compared to the paternal air group (PND 31.6, p=0.001). Exposure to elevated housing temperature did not produce overt toxicity in offspring and did not increase rectal (internal) body temperature. Over the 10 days assessed, WFxH offspring had fewer estrous cycles (1.5x) than FAxN controls (2.3x, p=0.02) owing to their disproportionate time spent in metestrus/diestrus (61%) compared to controls (41%, p=0.003). There was a tendency for increased time spent in metestrus/diestrus (54%, p =0.15) in WFxN, but this did not affect overall number of cycles recorded (1.9x). Serum estradiol levels were significantly lower in WFxN (44%, p=0.02) and WFxH (39%, p=0.04) rats compared to FAxN controls. Serum testosterone was also 43% lower than controls in the WFxH group (p=0.02). No differences in progesterone levels were detected. In summary, paternal smoke exposure resulted in pubertal disruption and cycle irregularity in female offspring, which may be attributable to reduced estradiol and testosterone levels. Altogether, our data suggests that repeated WF smoke exposure during sperm maturation may program intergenerational reproductive risk in female offspring, especially if compounded by postnatal stressors such as heat. Effects of these exposures on sperm motility and fertility in male F1 offspring are currently under investigation. This abstract does not reflect U.S. EPA policy.