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Effect of prolactin on tolerance and dependence to acute administration of morphine
Vol. 26, No. 213, pp. 11l-l 13, 1987 Printed in Great Britain. All rights reserved
W28-39-08/87 $3.00 + 0.00 Copyright 0 1987 Pergamon Journals Ltd
Neuropharmacology
EFFECT OF PROLACTIN ON TOLERANCE AND DEPENDENCE TO ACUTE ADMINISTRATION OF MORPHINE S. RAMASWAMY and J. S. BAPNA Department
of Pharmacology,
Jawaharlal Institute of Postgraduate Pondicherry-605 006, India (Accepted’20
Medical
Education
and Research,
March 1986)
Summary-The effect of exogenous prolactin on the development of acute tolerance to and dependence on morphine was studied. As described elsewhere, analgesia induced by prolactin was subject to tolerance. Pretreatment with prolactin enhanced the development of tolerance to analgesia induced by morphine while it effectively suppressed the withdrawal symptoms. These results indicate that prolactin behaves like an opioid agonist and suggest that it may have therapeutic implications in the management of opioid dependence. Key words: prolactin, morphine, analgesia, tolerance, dependence.
Hyperprolactinaemia in rats was found to induce an opioid mediated reduction in responsiveness to electrically induced foot-shock (Drago, Gispen and Bohus, 1981). Recently, Ramaswamy, Pillai and Bapna (1983) reported that the exogenous administration of prolactin in mice produced a dosedependent, analgesic effect in chemical assay. This effect was attenuated by naloxone; acute tolerance developed to this action of prolactin and there was a cross tolerance between prolactin and morphine (Ramaswamy, Viswanathan and Bapna, 1985). These findings suggest that prolactin essentially involves opioid mechanisms for inducing analgesia, resembling that of morphine. However, Drago, Kovacs and Scapagnini (1984), in their study on hyperprolactinaemic rats, reported that tolerance to morphine-induced analgesia did not develop in these rats. They explained this phenomenon on the potentiating effect of prolactin on the action of the morphine. The present study investigated the influence of exogenous prolactin on analgesia induced by acute administration on morphine and on the development of acute tolerance to and dependence on morphine. METHODS Swiss male
treated
albino
animals
Analgesic
mice (20-25
g) were used. Saline-
served as controls.
assay
The analgesia was studied by injecting acetic acid (0.6%, lOml/kg, i.p.) and observing the number of writhings for a period of 10 min. The reduction in the number of writhings was considered to be an analgesic effect.
The acute pattern of tolerance to the analgesic effect of morphine (1 mg/kg, s.c.) or prolactin (0.04 mg/kg, i.p.) was studied by exposing different groups of animals to the agonists at 9, 13 and 17 hr on the same day. The analgesia was tested as described above 15 min after each injection. Each animal was subjected to an analgesic test once only. A significant reduction in the degree of analgesia, as compared to that observed after the first injection, was considered as development of tolerance. The influence of prolactin on acute tolerance to morphine was studied by pretreating another group of animals with prolactin (O.O4mg/kg, i.p.) just before every injection of morphine as described in the above schedule for acute tolerance. The analgesia was determined 15 min after each injection of morphine. Acute dependence on morphine was induced as described by Pillai, Ramaswamy, Gopalakrishnan and Ghosh (1982). The animals were treated with a single injection of morphine sulphate (32 mg/kg s.c.; Govt. Opium and Alkaloid Works, Ghazipur). The withdrawal syndrome was precipitated by the administration of naloxone hydrochloride (16 mg/kg, i.p. Endo Labs) at 30 min after an injection of morphine to record wet shakes and, at 120min, to record jumping. These optimum time intervals were chosen following the report of Pillai er al. (1982). After the injection of naloxone the mouse was placed on a raised circular platform (30 cm high, 12 cm dia) and observed for a period of 20 min. As soon as the animal jumped, it was placed back on the platform for further observation. The number of jumps or wet shakes for each animal was recorded. In another group of animals, pretreatment with prolactin (O.O4mg/kg) was given 30 min before an
S. RAMASWAMY
112
and
J. S. BAPNA
Table 1. Influenceof prolactin (PRL)on acute tolerance to analgesia induced by morphine Pretreatment (mg/kg) Saline Satine Saline
PRL 0.04
Treatment (mg/kg)
1st injection
Saline Morphine 1
22.8 * I .4 7.3 * 0.5**
23.5 f 1.9 9.6 & 1P*
21.9+ 1.8 17.0 f. 1.3*t
PRL 0.04 Morphine1
11.2f 0.9** 2.1_+ 0.7**ff
16.2+ 1.4*‘t 15.4+ 1.4*t
21.4+0.8? Zl.Ok 1.7t
The values represent mean rt SEM of *P < 0.05 and **P < 0.01 as compared +P ~0.05 as compared with the value $P ~0.05 as compared with value for
6 experiments. with their corresponding saline value. for 1st injection. 1st injection of morphine.
injection of naloxone and the withdrawal symptoms were recorded as described above. The results were analysed using Dunnet’s t-test. For dependence studies Mann-Whitney’s I.J test was employed. The following drugs were used: prolactin (Ovine, NIH, Bethseda), morphine hydroxhloride (Govt. Opium and Alkaloid Works, Ghazipur) and naioxone hydrochloride (Endo Labs, New York). RESULTS The first injection of prolactin produced a significant reduction in the number of writhings, thus indicating an analgesic effect. This effect decreased after the second injection, while the third injection did not produce any analgesia (Table 1). Similar results were observed for morphine; however, a mild but significant degree of analgesia was seen even after the third injection (Table f). In animals pretreated with prolactin, a potentiated analgesic effect after the first injection of morphine was observed. However, in these animals, the second injection of morphine produced a reduced analgesic effect, as compared to that of morphine alone (Table 1). The third injection of morphine in these prolactin-treated animals failed to produce any analgesia (Table 1). Pretreatment with prolactin suppressed the withdrawal syndrome precipitated by naloxone as shown by the reduced number of jumps and wet shakes (Table 2). The total number of animals showing these symptoms was also reduced.
Table 2. Effect of prolactin (PRL) on acute dependence on morphine 1 Mean withdrawal symptoms Pretreatment’
Control PRL 0.04 mg/kg
Number of writhings .--.2nd injection 3rd injection
Jumoine
Wet shakes
6.8 (S/IO) 2.9 (4/13)’
5.7 (7/l I) 0.2 (Z/12)”
‘Acute dependence was induced by the injection of morphine (32 mg/kg, s.c.). Wet shakes and jumping were precipitated by naloxone (16 mg/kg,i.p.)at 30 or 120min, respectively after injection of morphine. Ifhe pretreatment was given 30min before naloxone. The numbers in parenthesis indicate the number of animals cxhibit~ng the s~ptoms/num~r tested. compared 10 control *p eO.05 and **P
DISCUSSION
The present data confirms earlier observations that acute tolerance developed to the analgesic effect of morphine as well as prolactin (Ramaswamy, Pillai, Gopalakrishnan and Ghosh, 1983b; Ramaswamy et ai., 1985). In the acetic acid_ test, pretreatment with prolactin potentiated the acute analgesic effect of morphine on the first exposure. This finding conforms with that of Drago et al. (1984) who used the thermal assay in hyperprolactinaemic rats. However, there was no potentiation on subsequent treatment with these drugs. The development of acute tolerance to morphineinduced analgesia was gradual and partial, since a mild degree of analgesia was observed even after the third injection. However, in animals pretreated with prolactin the analgesic effect of morphine was reduced to a greater extent from a potentiated level after the second injection, and the effect was absent after the third injection. This indicates that prolactin enhanced the development of tolerance to morphine which was complete in animals pretreated with prolactin. This observation is in contrast to the findings of Drago et al. (1984) that higher levels of endogenous prolactin prevented the development of tolerance to morphine-induced analgesia in rats. They explained this antagonism by way of the potentiating effect of prolactin on morphine-induced analgesia. In the present study though, a significant potentiation of acute morphine-induced analgesia by pretreatment with proiactin was observed, there was an enhanced development of tolerance to mo~hine-indu~d analgesia. The possibility that differences in species of animal and assay procedures employed may contribute to the varied results cannot be ruled out. However, Drago and Scapagnini (1985), in their subsequent study on hyperprolactinaemic rats, observed a definite facilitation of the development of tolerance to morphine which is in accordance with the results of this study. The determination of wet shakes and jumping behaviour was considered to be a reliable parameter to quantify dependence. These symptoms can be precipitated by naloxone or by withdrawal of the drug (abrupt withdrawal). The present study reveals that pretreatment with prolactin suppressed the withdrawal symptoms.
Prolactin and morphine tolerance Prolactin exhibits several opioid-like actions, such as analgesia, development of tolerance, presence of cross tolerance and antagonism to naloxone (Ramaswamy et al., 1985). Considering these actions, it can be stated that prolactin behaves like an opioid agonist. Generally, a combination of an opioid-like drug with morphine will enhance the analgesic activity and development of tolerance to the latter. Since prolactin produced opioid-like effects, the enhanced analgesia and development of tolerance to morphine by prolactin can be explained as discussed above. Similarly, an opioid-like compound, administered during or prior to withdrawal from morphine, will suppress the withdrawal symptoms. Pretreatment with prolactin suppressed the withdrawal symptoms, confirming a morphine like activity for prolactin. Furthermore, it has previously been suggested that prolactin may be physiologically involved in the development of tolerance to morphine (Wimersna Greidanus, Tjon Kon Fat-Bronstein and Ree, 1978). The present results support this view and, in addition, suggest a role for prolactin in the development of physical dependence. The suppression of withdrawal symptoms by prolatin, recorded in this study, and the earlier observed inhibition of heroin self-administration by prolactin (Drag0 et al., 1984), favour the suggestion that prolactin may have clinical significance in the management of opioid dependence and its use is worth considering.
113 REFERENCES
Drago F., Gispen W. H. and Bohus B. (1981) Behavioral effects of prolactin: Involvement of opioid receptors. In: Advances in Endogenous and Exogenous Opioids. Proc. Int. Narcotic Research Conf., Japan, pp. 335-337. Kodansha,
Tokyo. Drago F., Kovacs G. L. and Scapagnini U. (1984) Prolactin induced behavioral effects and opioids. In: Opioid., Modulation of Endocrine Functions (Delitala G., Cotta M. and Sbrio M.. Eds) DD. 137-145. Raven Press. New York. Drago F. and Scapagnini U. (1985) Effects of endogenous hyperprolactinaemia on opioid induced behavioral changes in rats. Brain Res. 336: 215-221. Pillai N. P., Ramaswamy S., Gopalakrishnan V. and Ghosh M. N. (1982) Effect of cholinerigic drugs on acute and chronic morphine dependence. Archs int. Pharmacodyn. Ther. 257: 146154.
Ramaswamy S., Pillai N. P. and Bapna J. S. (1983a) Analgesic effect of prolactin: Possible mechanism of action Eur. J. Pharmac. 96: 171L173. Ramaswamy S., Pillai N. P., Gopalakrishnan V. and Ghosh M. N. (1983b) The development of acute tolerance to analgesia and the sensitivity changes in mouse vas deferens and ileum produced by morphine. Archs inr. Pharmacodyn. Thtr. 261: 214222.
Ramaswamy S., Viswanathan S. and Bapna J. S. (1985). Prolactin analgesia tolerance and cross-tolerance with morphine. Eur. J. Pharmac. 112: 123-125. Van Wimersma Greidanus Tj. B., Tjon Kon Fat-Bronstein H. and van Ree J. M. (1978) Antisera to pituitary hormones modulate development of tolerance to morphine. In: Characteristics and Functions of Opioids (Van Rec. J. M. and Terenius L., Eds), pp. 73-74. Elsevier/ North Holland, Amsterdam.
W28-39-08/87 $3.00 + 0.00 Copyright 0 1987 Pergamon Journals Ltd
Neuropharmacology
EFFECT OF PROLACTIN ON TOLERANCE AND DEPENDENCE TO ACUTE ADMINISTRATION OF MORPHINE S. RAMASWAMY and J. S. BAPNA Department
of Pharmacology,
Jawaharlal Institute of Postgraduate Pondicherry-605 006, India (Accepted’20
Medical
Education
and Research,
March 1986)
Summary-The effect of exogenous prolactin on the development of acute tolerance to and dependence on morphine was studied. As described elsewhere, analgesia induced by prolactin was subject to tolerance. Pretreatment with prolactin enhanced the development of tolerance to analgesia induced by morphine while it effectively suppressed the withdrawal symptoms. These results indicate that prolactin behaves like an opioid agonist and suggest that it may have therapeutic implications in the management of opioid dependence. Key words: prolactin, morphine, analgesia, tolerance, dependence.
Hyperprolactinaemia in rats was found to induce an opioid mediated reduction in responsiveness to electrically induced foot-shock (Drago, Gispen and Bohus, 1981). Recently, Ramaswamy, Pillai and Bapna (1983) reported that the exogenous administration of prolactin in mice produced a dosedependent, analgesic effect in chemical assay. This effect was attenuated by naloxone; acute tolerance developed to this action of prolactin and there was a cross tolerance between prolactin and morphine (Ramaswamy, Viswanathan and Bapna, 1985). These findings suggest that prolactin essentially involves opioid mechanisms for inducing analgesia, resembling that of morphine. However, Drago, Kovacs and Scapagnini (1984), in their study on hyperprolactinaemic rats, reported that tolerance to morphine-induced analgesia did not develop in these rats. They explained this phenomenon on the potentiating effect of prolactin on the action of the morphine. The present study investigated the influence of exogenous prolactin on analgesia induced by acute administration on morphine and on the development of acute tolerance to and dependence on morphine. METHODS Swiss male
treated
albino
animals
Analgesic
mice (20-25
g) were used. Saline-
served as controls.
assay
The analgesia was studied by injecting acetic acid (0.6%, lOml/kg, i.p.) and observing the number of writhings for a period of 10 min. The reduction in the number of writhings was considered to be an analgesic effect.
The acute pattern of tolerance to the analgesic effect of morphine (1 mg/kg, s.c.) or prolactin (0.04 mg/kg, i.p.) was studied by exposing different groups of animals to the agonists at 9, 13 and 17 hr on the same day. The analgesia was tested as described above 15 min after each injection. Each animal was subjected to an analgesic test once only. A significant reduction in the degree of analgesia, as compared to that observed after the first injection, was considered as development of tolerance. The influence of prolactin on acute tolerance to morphine was studied by pretreating another group of animals with prolactin (O.O4mg/kg, i.p.) just before every injection of morphine as described in the above schedule for acute tolerance. The analgesia was determined 15 min after each injection of morphine. Acute dependence on morphine was induced as described by Pillai, Ramaswamy, Gopalakrishnan and Ghosh (1982). The animals were treated with a single injection of morphine sulphate (32 mg/kg s.c.; Govt. Opium and Alkaloid Works, Ghazipur). The withdrawal syndrome was precipitated by the administration of naloxone hydrochloride (16 mg/kg, i.p. Endo Labs) at 30 min after an injection of morphine to record wet shakes and, at 120min, to record jumping. These optimum time intervals were chosen following the report of Pillai er al. (1982). After the injection of naloxone the mouse was placed on a raised circular platform (30 cm high, 12 cm dia) and observed for a period of 20 min. As soon as the animal jumped, it was placed back on the platform for further observation. The number of jumps or wet shakes for each animal was recorded. In another group of animals, pretreatment with prolactin (O.O4mg/kg) was given 30 min before an
S. RAMASWAMY
112
and
J. S. BAPNA
Table 1. Influenceof prolactin (PRL)on acute tolerance to analgesia induced by morphine Pretreatment (mg/kg) Saline Satine Saline
PRL 0.04
Treatment (mg/kg)
1st injection
Saline Morphine 1
22.8 * I .4 7.3 * 0.5**
23.5 f 1.9 9.6 & 1P*
21.9+ 1.8 17.0 f. 1.3*t
PRL 0.04 Morphine1
11.2f 0.9** 2.1_+ 0.7**ff
16.2+ 1.4*‘t 15.4+ 1.4*t
21.4+0.8? Zl.Ok 1.7t
The values represent mean rt SEM of *P < 0.05 and **P < 0.01 as compared +P ~0.05 as compared with the value $P ~0.05 as compared with value for
6 experiments. with their corresponding saline value. for 1st injection. 1st injection of morphine.
injection of naloxone and the withdrawal symptoms were recorded as described above. The results were analysed using Dunnet’s t-test. For dependence studies Mann-Whitney’s I.J test was employed. The following drugs were used: prolactin (Ovine, NIH, Bethseda), morphine hydroxhloride (Govt. Opium and Alkaloid Works, Ghazipur) and naioxone hydrochloride (Endo Labs, New York). RESULTS The first injection of prolactin produced a significant reduction in the number of writhings, thus indicating an analgesic effect. This effect decreased after the second injection, while the third injection did not produce any analgesia (Table 1). Similar results were observed for morphine; however, a mild but significant degree of analgesia was seen even after the third injection (Table f). In animals pretreated with prolactin, a potentiated analgesic effect after the first injection of morphine was observed. However, in these animals, the second injection of morphine produced a reduced analgesic effect, as compared to that of morphine alone (Table 1). The third injection of morphine in these prolactin-treated animals failed to produce any analgesia (Table 1). Pretreatment with prolactin suppressed the withdrawal syndrome precipitated by naloxone as shown by the reduced number of jumps and wet shakes (Table 2). The total number of animals showing these symptoms was also reduced.
Table 2. Effect of prolactin (PRL) on acute dependence on morphine 1 Mean withdrawal symptoms Pretreatment’
Control PRL 0.04 mg/kg
Number of writhings .--.2nd injection 3rd injection
Jumoine
Wet shakes
6.8 (S/IO) 2.9 (4/13)’
5.7 (7/l I) 0.2 (Z/12)”
‘Acute dependence was induced by the injection of morphine (32 mg/kg, s.c.). Wet shakes and jumping were precipitated by naloxone (16 mg/kg,i.p.)at 30 or 120min, respectively after injection of morphine. Ifhe pretreatment was given 30min before naloxone. The numbers in parenthesis indicate the number of animals cxhibit~ng the s~ptoms/num~r tested. compared 10 control *p eO.05 and **P
DISCUSSION
The present data confirms earlier observations that acute tolerance developed to the analgesic effect of morphine as well as prolactin (Ramaswamy, Pillai, Gopalakrishnan and Ghosh, 1983b; Ramaswamy et ai., 1985). In the acetic acid_ test, pretreatment with prolactin potentiated the acute analgesic effect of morphine on the first exposure. This finding conforms with that of Drago et al. (1984) who used the thermal assay in hyperprolactinaemic rats. However, there was no potentiation on subsequent treatment with these drugs. The development of acute tolerance to morphineinduced analgesia was gradual and partial, since a mild degree of analgesia was observed even after the third injection. However, in animals pretreated with prolactin the analgesic effect of morphine was reduced to a greater extent from a potentiated level after the second injection, and the effect was absent after the third injection. This indicates that prolactin enhanced the development of tolerance to morphine which was complete in animals pretreated with prolactin. This observation is in contrast to the findings of Drago et al. (1984) that higher levels of endogenous prolactin prevented the development of tolerance to morphine-induced analgesia in rats. They explained this antagonism by way of the potentiating effect of prolactin on morphine-induced analgesia. In the present study though, a significant potentiation of acute morphine-induced analgesia by pretreatment with proiactin was observed, there was an enhanced development of tolerance to mo~hine-indu~d analgesia. The possibility that differences in species of animal and assay procedures employed may contribute to the varied results cannot be ruled out. However, Drago and Scapagnini (1985), in their subsequent study on hyperprolactinaemic rats, observed a definite facilitation of the development of tolerance to morphine which is in accordance with the results of this study. The determination of wet shakes and jumping behaviour was considered to be a reliable parameter to quantify dependence. These symptoms can be precipitated by naloxone or by withdrawal of the drug (abrupt withdrawal). The present study reveals that pretreatment with prolactin suppressed the withdrawal symptoms.
Prolactin and morphine tolerance Prolactin exhibits several opioid-like actions, such as analgesia, development of tolerance, presence of cross tolerance and antagonism to naloxone (Ramaswamy et al., 1985). Considering these actions, it can be stated that prolactin behaves like an opioid agonist. Generally, a combination of an opioid-like drug with morphine will enhance the analgesic activity and development of tolerance to the latter. Since prolactin produced opioid-like effects, the enhanced analgesia and development of tolerance to morphine by prolactin can be explained as discussed above. Similarly, an opioid-like compound, administered during or prior to withdrawal from morphine, will suppress the withdrawal symptoms. Pretreatment with prolactin suppressed the withdrawal symptoms, confirming a morphine like activity for prolactin. Furthermore, it has previously been suggested that prolactin may be physiologically involved in the development of tolerance to morphine (Wimersna Greidanus, Tjon Kon Fat-Bronstein and Ree, 1978). The present results support this view and, in addition, suggest a role for prolactin in the development of physical dependence. The suppression of withdrawal symptoms by prolatin, recorded in this study, and the earlier observed inhibition of heroin self-administration by prolactin (Drag0 et al., 1984), favour the suggestion that prolactin may have clinical significance in the management of opioid dependence and its use is worth considering.
113 REFERENCES
Drago F., Gispen W. H. and Bohus B. (1981) Behavioral effects of prolactin: Involvement of opioid receptors. In: Advances in Endogenous and Exogenous Opioids. Proc. Int. Narcotic Research Conf., Japan, pp. 335-337. Kodansha,
Tokyo. Drago F., Kovacs G. L. and Scapagnini U. (1984) Prolactin induced behavioral effects and opioids. In: Opioid., Modulation of Endocrine Functions (Delitala G., Cotta M. and Sbrio M.. Eds) DD. 137-145. Raven Press. New York. Drago F. and Scapagnini U. (1985) Effects of endogenous hyperprolactinaemia on opioid induced behavioral changes in rats. Brain Res. 336: 215-221. Pillai N. P., Ramaswamy S., Gopalakrishnan V. and Ghosh M. N. (1982) Effect of cholinerigic drugs on acute and chronic morphine dependence. Archs int. Pharmacodyn. Ther. 257: 146154.
Ramaswamy S., Pillai N. P. and Bapna J. S. (1983a) Analgesic effect of prolactin: Possible mechanism of action Eur. J. Pharmac. 96: 171L173. Ramaswamy S., Pillai N. P., Gopalakrishnan V. and Ghosh M. N. (1983b) The development of acute tolerance to analgesia and the sensitivity changes in mouse vas deferens and ileum produced by morphine. Archs inr. Pharmacodyn. Thtr. 261: 214222.
Ramaswamy S., Viswanathan S. and Bapna J. S. (1985). Prolactin analgesia tolerance and cross-tolerance with morphine. Eur. J. Pharmac. 112: 123-125. Van Wimersma Greidanus Tj. B., Tjon Kon Fat-Bronstein H. and van Ree J. M. (1978) Antisera to pituitary hormones modulate development of tolerance to morphine. In: Characteristics and Functions of Opioids (Van Rec. J. M. and Terenius L., Eds), pp. 73-74. Elsevier/ North Holland, Amsterdam.