Synthetic contraceptive hormones occlude the ability of nicotine to reduce ethanol consumption in ovary-intact female rats

Abstract

Rates of tobacco and alcohol use in women are rising, and women are more vulnerable than men to escalating tobacco and alcohol use. Many women use hormonal birth control, with the oral contraceptive pill being the most prevalent. Oral contraceptives contain both a progestin (synthetic progesterone) and a synthetic estrogen (ethinyl estradiol; EE) and are contraindicated for women over 35 years who smoke. Despite this, no studies have examined how synthetic contraceptive hormones impact this pattern of polysubstance use in females. To address this critical gap in the field, we treated ovary-intact female rats with either sesame oil (vehicle), the progestin levonorgestrel (LEVO; contained in formulations such as Alesse®), or the combination of EE+LEVO in addition to either undergoing single (nicotine or saline) or polydrug (nicotine and ethanol; EtOH) self-administration (SA) in a sequential use model. Rats preferred EtOH over water following extended EtOH drinking experience as well as after nicotine or saline SA experience, and rats undergoing only nicotine SA (water controls) consumed more nicotine as compared to rats co-using EtOH and nicotine. Importantly, this effect was occluded in groups treated with contraceptive hormones. In the sequential use group, both LEVO alone and the EE+LEVO combination occluded the ability of nicotine to decrease EtOH consumption. Interestingly, demand experiments suggest an economic substitute effect between nicotine and EtOH. Together, we show that chronic synthetic hormone exposure impacts nicotine and EtOH sequential use, demonstrating the crucial need to understand how chronic use of different contraceptive formulations alter patterns of polydrug use in women.

Keywords: Contraceptive hormones; Economic substitute; Ethanol; Ethinyl estradiol; Levonorgestrel; Nicotine.

Figure 1.. EtOH Drinking Acquisition and Two-Bottle Preference Test.

(A) The timeline of experimental procedures. Red box indicates data collection for current figure during Phase 1 of EtOH acquisition. (B) A main effect of session (day) was found on EtOH consumption (p<0.05). (C) A main effect of session (day) was found on EtOH consumption (p<0.05). (D) No differences in EtOH consumption were found between eventual hormone treatment groups (these data represent EtOH consumption as a function of pre-hormone treatment groups averaged across the 15 sessions of Phase 1; p>0.05). (E) Preference for EtOH was significantly greater than preference for water (dotted line = indifference set at 50%; p<0.05).

Figure 2.. Nicotine but not Saline Sequential Use Decreases EtOH Consumption, which is Occluded by LEVO and EE+LEVO Treatment During Nicotine EtOH Sequential Use.

(A) The timeline of experimental procedures. Red boxes indicate data collection for current figure, which includes EtOH consumption prior to (Phase 1) and during nicotine SA (Phase 2). (B₁) A main effect of nicotine sequential use on EtOH consumption in the vehicle treatment nicotine SA group whereby rats co-using nicotine consumed less EtOH (individual values represent average consumption across animals on each session; *p<0.05). (B₂) EtOH consumption during EtOH acquisition (Phase 1) and during nicotine sequential use (morning DID sessions during Phase 2) in vehicle-treated rats (*p<0.05 comparing EtOH consumption before versus during nicotine SA), graphed across sessions. (B₃) EtOH consumption did not differ when compared between pre-versus during saline SA in vehicle-treated rats (individual values represent average consumption across animals on each session; p>0.05). (B₄) EtOH consumption on during EtOH acquisition (Phase 1) and during saline sequential use (morning DID sessions during Phase 2) in vehicle-treated rats, graphed across sessions. (C₁) There was no main effect of nicotine sequential use on EtOH consumption in the EE+LEVO treatment group (individual values represent average consumption across animals on each session; p>0.05). (C₂) EtOH consumption during EtOH acquisition (Phase 1) and during nicotine sequential use (morning DID sessions during Phase 2) in EE+LEVO-treated rats, graphed across sessions. (C₃) EtOH consumption did not differ when compared prior to versus during saline SA in EE+LEVO-treated saline SA rats (individual values represent average consumption across animals on each session; p>0.05). (C₄) EtOH consumption during EtOH acquisition (Phase 1) and during saline sequential use (morning DID sessions during Phase 2) in EE+LEVO-treated rats, graphed across sessions. (D₁) There was no main effect of nicotine sequential use on EtOH consumption in the LEVO treatment group (individual values represent average consumption across animals on each session; p>0.05). (D₂) EtOH consumption during EtOH acquisition (Phase 1) and during nicotine sequential use (morning DID sessions during Phase 2) in LEVO-treated rats, graphed across sessions. (D₃) EtOH consumption did not differ when compared prior to versus during saline SA in EE+LEVO-treated saline SA rats (individual values represent average consumption across animals on each session; p>0.05). (D₄) EtOH consumption during EtOH acquisition (Phase 1) and during nicotine sequential use (morning DID sessions during Phase 2) in LEVO-treated rats, graphed across sessions.

Figure 3.. EtOH Sequential Use Decreases Nicotine Consumption, which is Occluded by Contraceptive Hormone Treatment.

(A) The timeline of experimental procedures. Red box indicates nicotine self-administration (SA) data collection for current figure during Phase 2. (B) A main effect of EtOH drinking on nicotine sequential use was found in the vehicle treatment group whereas rats co-using nicotine consumed less EtOH (individual values represent average consumption across animals on each session; *p<0.05). (C) Nicotine consumption on days 1–15 of nicotine SA in vehicle-treated rats. (D) No main effect of EtOH drinking on nicotine consumption was found in the EE+LEVO treatment group (individual values represent average consumption across animals on each session; p>0.05). (E) Nicotine consumption on days 1–15 of nicotine SA in EE+LEVO-treated rats. (F) No main effect of EtOH drinking on nicotine consumption in the LEVO treatment group (individual values represent average consumption across animals on each session; p>0.05). (G) Nicotine consumption on days 1–15 of nicotine SA in LEVO-treated rats. (H) Percent active lever pressing did not differ as a function of hormone treatment during nicotine SA in either the water or (I) EtOH groups. The dotted line represents a 66.67% active lever pressing criterion (or a 2:1 ratio using the following equation: active/active+inactive).

Figure 4.. Hormone Treatment and EtOH Experience Influence Nicotine Demand.

(A) The timeline of experimental procedures. Red box indicates data collection for current figure. (B) Population demand curves for each hormone group and drug treatment (EtOH vs water). Faded lines represent individual animal curves, and darker lines represent group averages. Dotted lines = water control, solid lines = EtOH groups. (C) Estimates for Q₀. NLME revealed a main effect of day on Q₀ (p<0.05). (D) Estimates for α. NLME revealed a main effect of day (p<0.05), EtOH experience (p<0.05), and hormone (p<0.05) on α. (E) Correlation of daily Q₀ estimate over five days with EtOH and water consumption. Q₀ was significantly correlated with water consumption in animals treated with EE+LEVO (p<0.05). (F) Correlation of daily α estimate over five days with EtOH and water consumption. α was significantly correlated with water consumption in animals treated with EE+LEVO (p<0.05).

Figure 5.. EtOH Drinking and Preference Persists after Completion of Nicotine SA.

(A) The timeline of experimental procedures. Red box indicates data collection for current figure (Phase 3). (B) Past EtOH experience did not affect amount of EtOH consumed as compared to water-experienced rats during two-bottle preference tests (p>0.05), however, there was a significant main effect of session, indicating that EtOH consumption increased across time (p<0.05). (C₁) Past EtOH experience did not affect percent of EtOH consumption during two-bottle preference tests (individual values represent average percent EtOH consumption across animals on each preference session; p>0.05). (C₂) Percent EtOH consumption in EtOH-experienced and water control rats for days 1–3. *p<0.05; main effect of group. (D) EtOH to water consumption ratio from post-nicotine or saline SA two-bottle EtOH preference tests was positively correlated to pre-nicotine SA EtOH consumption (*p<0.05). (E) BEC was significantly correlated with EtOH consumption both after 30 minutes (black) and after 240 minutes (red) of DID (p<0.05).