Life Sciences, Vol. 48, pp. 1837-1844 Printed in the U.S.A.
Pergamon Press
EFFECTS OF CAFFEINE AND BOMBESIN ON ETHANOL AND FOOD INTAKE Max A. Dietze and Paul J. Kulkosky Department of Psychology University of Southern Colorado Pueblo, CO 81001 U.S.A. (Received in final form March i, 1991)
Summary The methylxanthine caffeine and ethyl alcohol are widely used and powerful psychotropic drugs, but their interactions are not well understood. Bombesin is a brain-gut neuropeptide which is thought to function as a neurochemical factor in the inhibitory control of voluntary alcohol ingestion. We assessed the effects of combinations of intraperitoneal (i.p.) doses of caffeine (CAF, 0.1-50 mg/kg) and bombesin (BBS, 1-10/zg/kg) on 5% w/v ethanol solution and food intake in deprived rats. Deprived male and female Wistar rats received access to 5% ethanol or Purina chow for 30 minutes after i.p. injections. In single doses, CAF and BBS significantly decreased both ethanol and food consumption, at 50 mg/kg and 10/~g/kg, respectively. CAF and BBS combinations produced infra-additive, or lessthan-expected inhibitory effects on ethanol intake, but simple additive inhibitory effects on food intake. This experimental evidence suggests a reciprocal blocking of effects of CAF and BBS on ethanol intake but not food intake. Caffeine, when interacting with bombesin, increases alcohol consumption beyond expected values. Caffeine could affect the operation of endogenous satiety signals for alcohol consumption. The methylxanthine caffeine and ethyl alcohol are powerful psychotropic drugs which are widely used, although their combined effects are not well understood. A "research front" has recently been identified, by the Institute for Scientific Information, in the study of ethanol/caffeine interactions with nutrition. There are apparently conflicting reports of the main effect of caffeine on ethanol (ETOH) intake. Caffeine (CAF) administration has been shown to augment ethanol intake in marginally nourished and malnourished rats (1,2,3,4). In contrast, others reported that intraperitoneal injection of a high dose of CAF decreased ethanol intake (5). CAF also increases operant responding for food reinforcement at moderate doses, and decreases responding at high doses in animals (6,7,8,9). Previous studies of the effects of combinations of CAF and ETOH in various experimental paradigms have shown a variety of results. A high dose (25 mg/kg) of caffeine increases the stimulation of locomotion by ethanol (1-2 g/kg) in female mice, while a higher dose
Corresponding Author: Paul J. Kulkosky, Department of Psychology, University of Southern Colorado, Pueblo, CO 81001-490l. 0024-3205/91 $3.00 + .00 Copyright (c) 1991 Pergamon Press plc
1838
Caffeine, Bombesin and Ethanol
Vol. 48, No. 19, 1991
(100 mg/kg) abolished the ethanol-induced stimulation (10). Both CAF (25,50 mg/kg) and ETOH (0.5, 1 g/kg) separately and dose-dependently decrease measures of responding for water reinforcement in thirsty male rats, and in combination, CAF decreased and increased the effects of ETOH, depending on the specific measure of operant performance (11). A h;gh dose of CAF (60 mg/kg) reduced social behavior and locomotor activity, and antagonized ETOH-induced (2 g/kg) increases in locomotor activity in male mice (12). CAF (1 mM) and ETOH (0.95%) combinations were synergistically toxic in a motor performance task in guppies (!3). CAF (45,95 mg/kg) administered in drinking water increased ethanol-induced (1.5 g/kg) motor discoordination in male mice (14), and an injected high dose of CAF (62.5 mg/kg) increased ethanol-induced (1.75 g/kg) ataxia in male mice (15). CAF at moderate doses (I-10 mg/kg) attenuated ethanol's (0.5-3.0 g/kg) response-decreasing properties in a multiple-schedule operant in male pigeons (16). A large dose of CAF (100 mg/kg) had no significant effect on ethanolinduced (>1.25 g/kg) decreases in active avoidance behaviors in male rats (17), but high doses of CAF (100,15C mg/kg) potentiated the decrease of conditioned and unconditioned avoidance responses by alcohol (1 g/kg) in male rats (18). In conclusion, there are disparate reports on caffeine's effects on voluntary, behaviors. Caffeine's ~ctions are complexly dose-dependent and paradigm specific, and the direction of the effects produced by caffeine often reverse with increases in doses. Apparently nonspecific inhibitou; effects on behaviors, e.g., debilitation, have often been ,eported at relatively large doses ( > 25 mg/kg). Bombe~in (BBS) is a brain-gut peptide and a candidate ne.lromodulator which has been shown to inhibit intake of both food and ethanol (19-24). Little is known of potential interactions of CAF and BBS, although ~heophylline, a methylxanthine metabolite of caffeine, doubles Me secretion rate of bombesin from small ce.ll lung cancer cells in vitro (25). That finding suggests a possible interaction of caffeine witl. an endogenous neuropeptide which ,'nay function to regulate voluntar~ intake of ethanol. Caffeine consumption could affect a potential neuroendocrine c,mtrol of alcohol consumption, and thereby influ,mce the intake of alcohol. The following experiments attempt to clarify, firstly, the direct actions of CAF on ethanol and food intake, and secondly, the interactions of CAF with bombesin in the control of ethanol and food consumption. Obtained data should provide evidence on whether combinations of doses of CAF and BBS produce infra-additive, additive or supra-additive effects on ingestive behaviors. This informalion will help to determine if an interaction of caffeine with an endogenous neuropeptide can provide an explanation of some of caffeine's actions on ethanolrelated behavior. Method Animal~. Six male and nineteen female, experimentally naive, Wistar rats (Charles River, Crl: (WI)BR) were used in this experiment. The rats' weights ranged from 270-630 g and they were individually housed and maintained in wire-mesh, steel cages, in a room with ambient temperature of approximately 23 ° C, relative humidity of approximately 55 %, and a 12:12 light:dark lighting cycle (0700 on). The rats were provided with PurL-m Rodent Laboratory Chow (5001) and deionized water lid libitum, except as specified. Procedure. Phase 1: Ethanol Consumption. Eleven female and six male rats were deprived of water and continued on ad libitum access to food. Twenty-three hours later (1400), the rats were weighed and given access to a calibrated cylinder of 5% w/v ethanol for 30 minutes. At the end of thirty minutes, the ethanol bottles were taken off and measured for amount drunk. A calibrated tube of water was given for another thirty minutes and measured.
Vol. 48, No. 19, 1991
Caffeine, Bombesin and Ethanol
1839
This adaptation procedure was repeated for a total of 18 days, with two 1 ml/kg i.p. injections of 0.9% w/v NaCI (.saline) given immediately (within 1 minute) prior to presentation of ethanol on the last 5 days. At that point, mean ethanol consumption of the rats did not differ significantly (12> 0.05) across three consecutive days in a repeated measures analysis of variance. Following this baseline phase, rats were then randomly assigned to be injected i.p. with one dose of CAF (anhydrous, Sigma; 0.0, 1.0, 10.0, and 50.0 mg/kg) and one dose of BBS (tetradecapeptide, Sigma; 0.0, 1.0, and 10.0 ~g/kg). This procedure was repeated for a total of twelve days, until each rat had received all dose combinations. Data on ethanol consumption were analyzed with a 3 x 4 repeated measures analysis of variance, followed by Duncan's multiple range test, at an alpha significance level of 12 0.05) across three consecutive days in a repeated measures analysis of variance. Following this baseline phase, rats were then randomly assigned to be injected i.p. with one dose of CAF (0.0, 0.1, 1.0, 10.0, or 50.0 mg/kg) and then a dose of BBS (0.0, 1.0, or 10.0 ~g/kg). This procedure was repeated for fifteen days, until each rat had received all dose combinations. Data on food consumption were analyzed with a 3 x 5 repeated measures analysis of variance, followed by Duncan's multiple range test, at an alpha significance level of la 0.05; therefore data from both genders were combined in all subsequent analyses. Analysis revealed significant main effects of caffeine, F(3,48)=27.22, 12
Pergamon Press
EFFECTS OF CAFFEINE AND BOMBESIN ON ETHANOL AND FOOD INTAKE Max A. Dietze and Paul J. Kulkosky Department of Psychology University of Southern Colorado Pueblo, CO 81001 U.S.A. (Received in final form March i, 1991)
Summary The methylxanthine caffeine and ethyl alcohol are widely used and powerful psychotropic drugs, but their interactions are not well understood. Bombesin is a brain-gut neuropeptide which is thought to function as a neurochemical factor in the inhibitory control of voluntary alcohol ingestion. We assessed the effects of combinations of intraperitoneal (i.p.) doses of caffeine (CAF, 0.1-50 mg/kg) and bombesin (BBS, 1-10/zg/kg) on 5% w/v ethanol solution and food intake in deprived rats. Deprived male and female Wistar rats received access to 5% ethanol or Purina chow for 30 minutes after i.p. injections. In single doses, CAF and BBS significantly decreased both ethanol and food consumption, at 50 mg/kg and 10/~g/kg, respectively. CAF and BBS combinations produced infra-additive, or lessthan-expected inhibitory effects on ethanol intake, but simple additive inhibitory effects on food intake. This experimental evidence suggests a reciprocal blocking of effects of CAF and BBS on ethanol intake but not food intake. Caffeine, when interacting with bombesin, increases alcohol consumption beyond expected values. Caffeine could affect the operation of endogenous satiety signals for alcohol consumption. The methylxanthine caffeine and ethyl alcohol are powerful psychotropic drugs which are widely used, although their combined effects are not well understood. A "research front" has recently been identified, by the Institute for Scientific Information, in the study of ethanol/caffeine interactions with nutrition. There are apparently conflicting reports of the main effect of caffeine on ethanol (ETOH) intake. Caffeine (CAF) administration has been shown to augment ethanol intake in marginally nourished and malnourished rats (1,2,3,4). In contrast, others reported that intraperitoneal injection of a high dose of CAF decreased ethanol intake (5). CAF also increases operant responding for food reinforcement at moderate doses, and decreases responding at high doses in animals (6,7,8,9). Previous studies of the effects of combinations of CAF and ETOH in various experimental paradigms have shown a variety of results. A high dose (25 mg/kg) of caffeine increases the stimulation of locomotion by ethanol (1-2 g/kg) in female mice, while a higher dose
Corresponding Author: Paul J. Kulkosky, Department of Psychology, University of Southern Colorado, Pueblo, CO 81001-490l. 0024-3205/91 $3.00 + .00 Copyright (c) 1991 Pergamon Press plc
1838
Caffeine, Bombesin and Ethanol
Vol. 48, No. 19, 1991
(100 mg/kg) abolished the ethanol-induced stimulation (10). Both CAF (25,50 mg/kg) and ETOH (0.5, 1 g/kg) separately and dose-dependently decrease measures of responding for water reinforcement in thirsty male rats, and in combination, CAF decreased and increased the effects of ETOH, depending on the specific measure of operant performance (11). A h;gh dose of CAF (60 mg/kg) reduced social behavior and locomotor activity, and antagonized ETOH-induced (2 g/kg) increases in locomotor activity in male mice (12). CAF (1 mM) and ETOH (0.95%) combinations were synergistically toxic in a motor performance task in guppies (!3). CAF (45,95 mg/kg) administered in drinking water increased ethanol-induced (1.5 g/kg) motor discoordination in male mice (14), and an injected high dose of CAF (62.5 mg/kg) increased ethanol-induced (1.75 g/kg) ataxia in male mice (15). CAF at moderate doses (I-10 mg/kg) attenuated ethanol's (0.5-3.0 g/kg) response-decreasing properties in a multiple-schedule operant in male pigeons (16). A large dose of CAF (100 mg/kg) had no significant effect on ethanolinduced (>1.25 g/kg) decreases in active avoidance behaviors in male rats (17), but high doses of CAF (100,15C mg/kg) potentiated the decrease of conditioned and unconditioned avoidance responses by alcohol (1 g/kg) in male rats (18). In conclusion, there are disparate reports on caffeine's effects on voluntary, behaviors. Caffeine's ~ctions are complexly dose-dependent and paradigm specific, and the direction of the effects produced by caffeine often reverse with increases in doses. Apparently nonspecific inhibitou; effects on behaviors, e.g., debilitation, have often been ,eported at relatively large doses ( > 25 mg/kg). Bombe~in (BBS) is a brain-gut peptide and a candidate ne.lromodulator which has been shown to inhibit intake of both food and ethanol (19-24). Little is known of potential interactions of CAF and BBS, although ~heophylline, a methylxanthine metabolite of caffeine, doubles Me secretion rate of bombesin from small ce.ll lung cancer cells in vitro (25). That finding suggests a possible interaction of caffeine witl. an endogenous neuropeptide which ,'nay function to regulate voluntar~ intake of ethanol. Caffeine consumption could affect a potential neuroendocrine c,mtrol of alcohol consumption, and thereby influ,mce the intake of alcohol. The following experiments attempt to clarify, firstly, the direct actions of CAF on ethanol and food intake, and secondly, the interactions of CAF with bombesin in the control of ethanol and food consumption. Obtained data should provide evidence on whether combinations of doses of CAF and BBS produce infra-additive, additive or supra-additive effects on ingestive behaviors. This informalion will help to determine if an interaction of caffeine with an endogenous neuropeptide can provide an explanation of some of caffeine's actions on ethanolrelated behavior. Method Animal~. Six male and nineteen female, experimentally naive, Wistar rats (Charles River, Crl: (WI)BR) were used in this experiment. The rats' weights ranged from 270-630 g and they were individually housed and maintained in wire-mesh, steel cages, in a room with ambient temperature of approximately 23 ° C, relative humidity of approximately 55 %, and a 12:12 light:dark lighting cycle (0700 on). The rats were provided with PurL-m Rodent Laboratory Chow (5001) and deionized water lid libitum, except as specified. Procedure. Phase 1: Ethanol Consumption. Eleven female and six male rats were deprived of water and continued on ad libitum access to food. Twenty-three hours later (1400), the rats were weighed and given access to a calibrated cylinder of 5% w/v ethanol for 30 minutes. At the end of thirty minutes, the ethanol bottles were taken off and measured for amount drunk. A calibrated tube of water was given for another thirty minutes and measured.
Vol. 48, No. 19, 1991
Caffeine, Bombesin and Ethanol
1839
This adaptation procedure was repeated for a total of 18 days, with two 1 ml/kg i.p. injections of 0.9% w/v NaCI (.saline) given immediately (within 1 minute) prior to presentation of ethanol on the last 5 days. At that point, mean ethanol consumption of the rats did not differ significantly (12> 0.05) across three consecutive days in a repeated measures analysis of variance. Following this baseline phase, rats were then randomly assigned to be injected i.p. with one dose of CAF (anhydrous, Sigma; 0.0, 1.0, 10.0, and 50.0 mg/kg) and one dose of BBS (tetradecapeptide, Sigma; 0.0, 1.0, and 10.0 ~g/kg). This procedure was repeated for a total of twelve days, until each rat had received all dose combinations. Data on ethanol consumption were analyzed with a 3 x 4 repeated measures analysis of variance, followed by Duncan's multiple range test, at an alpha significance level of 12 0.05) across three consecutive days in a repeated measures analysis of variance. Following this baseline phase, rats were then randomly assigned to be injected i.p. with one dose of CAF (0.0, 0.1, 1.0, 10.0, or 50.0 mg/kg) and then a dose of BBS (0.0, 1.0, or 10.0 ~g/kg). This procedure was repeated for fifteen days, until each rat had received all dose combinations. Data on food consumption were analyzed with a 3 x 5 repeated measures analysis of variance, followed by Duncan's multiple range test, at an alpha significance level of la 0.05; therefore data from both genders were combined in all subsequent analyses. Analysis revealed significant main effects of caffeine, F(3,48)=27.22, 12
