Effects of Delta-9 Tetrahydrocannabinol (D9-THC) on Growth and Cardiovascular Function of the Chick Embryo

Effects of Delta-9 Tetrahydrocannabinol (D9-THC) on Growth and Cardiovascular Function of the Chick Embryo. Introduction: Over the past decade, use of marijuana (Cannabis sativa) has increased, including use by pregnant women (1).Infants exposed to marijuana in utero have lower birth weights and reduced head circumference (2). Similarly, mouse offspring exposed to the psychoactive component of marijuana, Δ9-THC, in utero were born small (3). The current study used a chick embryo model to study the direct effects of Δ9-THC on cardiovascular function and growth in ovo without the complications of confounding changes in maternal or placental physiology. We hypothesized that exposure to Δ9-THC alters the homeothermic response of heart rate to decreased ambient temperature (4) and causes growth restriction of the chick embryo. Methods: All experiments were approved by the Institutional Animal Care and Use Committee at Cal Poly Pomona. Chicken eggs (Gallus gallus domesticus) were injected with 0.025 mg Δ9-THC in vehicle (THC group; n=20), or with ethanol cremaphor saline vehicle (1:1:18; vehicle group; n=19) on alternate days starting on embryonic day (ED) 6. A third group of eggs was not injected (sham control group; n=16). One hour after treatment on ED16, embryonic heart rate was measured every 30 seconds for 10 minutes at 37 °C and then at 22 °C (Buddy Heart Rate Monitor, Avitronics, UK). After euthanasia on embryonic day 20 (term = 21-days), the egg, chick embryo, heart and liver tissues were weighed, and crown-rump length was measured. Data (mean ± sem) were analyzed by one way ANOVA or two-way ANOVA with repeated measures, as appropriate. Results: On ED 16, embryonic heart rates in the vehicle- (268 ± 4 bpm) and ∆9-THC-treated (271 ± 4 bpm) groups were higher than untreated control embryos (254±4 bpm). When chicken eggs were maintained at 37˚C, embryonic heart rate did not change over the 10-minute recording period (P>0.05). At room temperature (22˚C), embryonic heart rate decreased over the 10-minute recording period in all groups (p<0.05). The magnitude of the decrease in heart rate was not different between the control (-15±1%), vehicle (-13 ±1%) and ∆9-THC-treated (-14±1%) groups (P > 0.05). Embryo body weight and crown-rump length were lower in vehicle- (23.3±0.6 g; 65.5±0.8 mm) and THC- treated (24.4±0.4g;67.3±0.6 mm) than control (27.4±0.5 g; 71.1±0.8 mm; p<0.05) chick embryos, respectively. Liver weight was lower in vehicle-(0.41±0.02 g) and THC-injected (0.43±0.01 g) embryos than in controls (0.51±0.01 g), but there were no differences in heart weights between the groups. Conclusion: Exposure to Δ9-THC did not alter the homeothermic response of heart rate to decreased ambient temperature in the chicken embryo on ED 16. However, the data suggest that direct exposure of the embryo to Δ9-THC or ethanol cremaphor saline vehicle in ovo may result in asymmetric growth restriction. (1) Warner TD et al. 2014; (2) Gunn JK, et al. 2016; (3) Benevenuto SG et al. 2017; (4) Tazawa & Nakagawa, 1985. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.