Life Sciences Vol . 20, pp . 1581-1584, 1977 . Printed in the U .S .A .
Pergamon Press
EFFECT OF METOCLOPRAMIDE ON RAT PROLACTIN SECRETION IN VIVO Jiro Ysmauchi, Jiro Takahara and Tadashi Ofuji Third Department of Internal Medicine, Okayama University School of Medicine, Okayama, Japan 700 (Received in final form April 4, 1977) Summary Metoclopramide, a potent antagonist to apomorphine, was used to the rats in vivo to determine its effect on the release of prolactin . A single i .p . Tn-jection of metoclopramide at 10 or 100 jig/100 g b .w . under urethane anesthesia increased serum prolactin levels by 1 .6 or 7 .2 fold, respectively, compared with basa levels . This prolactin increase was completely abolished by 2-bromo-a-ergocryptine (CB-154) . These data suggest that metoclopramide stimulates prolactin secretion in rat and this secretion is abolished by dopaminergic stimulant . Recently, it has been demonstrated that metoclopramide, a orthopramide derivative, can stimulate prolactin release in humans (1-3) . This prolactin release was partially blocked by 1-dopa and completely abolished by CB-154 in man (2) . To confirm these data, we have measured prolactin levels after administration of metoclopramide or CB-154 or both agents simultaneously in rat in vivo . Materials _ and Methods Mature male Wister rats weighing 150 to 200 g were used . Laboratory chow and water were given ad lib . All rats were anesthetized with 150 mg/100 g b .w . of urethane i .p . 30 to 4 min before starting the experiments . The animals were divided into 6 groups of five each . They were administered 1, 10 and 100 Ng/100 g b .w . of metoclopramide and/or 10 pg/100 g b .w . of CB-154 i .p . dissolved in 0 .9 % saline . The blood samples for prolactin were collected from the jugular vein at 0, 5, 15, 30 and 60 min after the injection . Prolactin concentrations were measured by using the NIAMDD rat prolactin radioimmunoassay kit . The significance between the groups was tested by Duncan's new multiple range test (4) . Results As shown in the Table, metoclopramide caused a marked increase in serum prolactin values in a dose of 100 jig/100 g b .w . from fifteen minutes thereafter (p(0 .01) . The peak value was 7 .2 fold compared with basal level . A dose of 10 pg/100 g b .w . also had a tendency to release prolactin . However, in a dose of 1 ug/100 g b .w ., there was no change in serum prolactin concentrations compared with the control group . One group was given 10 pg/100 g b .w . of CB-154 fifteen minutes prior to the administration of 100 pg/100 g b .w . of metoclopramide . Serum prolactin elevation induced by metoclopramide in this group was completely abolished . 1581
1582
Metoclopramide and Rat Prolactin
Vol . 20, No . 4, 1977
TABLE Effect of Metoclopramide and CB-154 under Urethane Anesthesia on Rat Prolactin Secretion In Vivo . Group
Rat Serum Prolactin (ng/ml) Before
Control
44 .6+13 .6
MC
1 Ng
MC
*
5
15
30
60 min .
29 .4+12 .6
71 .5+25 .3
62 .6+ 17 .2
51 .3+ 12 .4
41 .4+ 6 .5
18 .7+ 3 .0
15 .2+ 2 .7
30 .8+ 13 .8
34 .3+
10 pg
80 .0+13 .1
36 .3+11 .4
89 .5+22 .7
130 .5+ 50 .0
77 .4_+ 37 .0
MC 100 jug
49 .0+13 .0
104 .7+35 .7
267 .4+69 .4
340 .2+123 .6
355 .2+127 .5
CB-154 10 jig
43 .0+ 8 .7
25 .0+ 6 .2
32 .7+ 7 .2
44 .8+
9 .9
44 .2+ 18 .2
51 .8+13 .6
34 .9+17 .1
63 .7+26 .6
71 .2+ 20 .4
50 .5+ 16 .6
MC 100 jig CB-154 10 jug
4 .4
MC = metoclopramide * Mean+SEM . ** pc0.01 vs control or only CB-154 treated groups . Discussion The result presented here have demonstrated that metoclopramide, like sulpiride (5), is a potent stimulator of prolactin release in rat . A 100 Pg/100 g b .w . of metoclopramide caused a significant increase in serum prolactin levels, and this elevation was completely abolished by pretreatment with CB-154, a potent dopamine receptor stimulant that has been shown to be effective in suppressing prolactin secretion in animals (6,7), and in man (8,9) . The results of these studies lead us to the following hypothesis . Firstly, CB-154 act at the same level as metoclopramide to cancel the metoclopramide-induced prolactin release . Secondly, the action level of metoclopramide is probably anatomically upper site than that of CB-154 . Thirdly, the potency of metoclopramide is weaker than CB-154 for inhibiting prolactin release . The effect of metoclopramide on the central neurotransmitters have yet to be adequately conducted . However, metoclopramide occasionally produces acute extrapyramidal effects ; acute dyskinesia such as torticollis, trismus, facial spasm, opistotonos and oculogyric crises (10) . Such reactions are identical to the acute dystonias produced by phenothiazines and butyrophenons, which are known to be potent cerebral dopamine receptor blocking agents (11,12) . In addition, metoclopramide antagonizes the central emetic action of apomorphine which is believed to be due to the stimulation of dopamine receptors in the medullary chemoreceptor trigger zone (13) . In animal studies, metoclopramide causes a dose-dependent increase in the striatal homovanillic acid content in mice (14,15), and apparently antagonizes or blocks the striatal dopamine receptors . Therefore, the striatal dopaminergic activity is decreased (15,16) . In rat behavioural and biochemical studies, metoclopramide resembles pimozide (16), which is a blocker of dopamine receptors (12,17) and has prolactin releasing activity (18,19) . The site and mode of action of metoclopramide in elevating serum prolactin are not fully clarified from our present data .
Vol . 20, No . 9, 1977
Metoclopramide and Rat Prolactin
1583
However, it seems likely that the prolactin releasing activity caused by metoclopramide might be due to the blockage of dopamine receptors at the central . nervous system level . Aknowle dgem ents The authors are grateful to the National Institute of Arthritis, Metabolism and Digestive Disease, National Institute of Health, for the supply of rat prolactin radioimmunoassay kit . CB-154 was kindly provided by Sandoz Ltd ., and metoclopramide was obtained from Fujisawa Pharmaceutical Co ., Ltd . . References 1 . A .S .McNeilly, M .O .Thorner, G .Volans, and G .M .Besser, Br . Med . J . 2 729 (1974) 2 . G .Delitala, A .Masala, S .Alagna, and L .Devilla, I R C S Medical Science 3 274 (1975) 3 . R .W .McCallum, J .R .Sowers, J .M .Hershman, and R .A .L .Sturdevant, J . Clin . Endocrinol . Metab . 422 1148-1153 (1976) 4 . R .D .G .Steel, and J .H .Torrie, Principles and Procedures of Statistics, p . 107 McGraw-Hill Book Co . 5 . J .Calaf, In J .L .Pasteels, and C .Robyn (eds .), Human Prolactin , p . 220-221, Excepta Medica, Amsterdam (1973) 6 . E .FlUckiger, and H .R .Wagner, Experientia (Basel) 24 1130-1131 (1968) 7 . C .W .Welsche, M .D .Squiers, E .Cassell, C .L .Chen, and J .Meites, Am . J . Physiol . 221 1714-1717 (1971) 8 . J .L .Pasteels, A .Danguy, M .Frérotte, and F .Ectors, Ann . Endocr . (Paris), 32 188-192 (1971) 9 . R .M .Lutterbeck, J .S .Pryor, L .Varga, and R .Wenner, Br . Med . J .3 228 (1971) 10 . P .Brownstein, and Bles, Thérapie 20 975-995 (1971) 11 . A .M .Ernst, Ps cho harmacolo ia Bérl .) 10 316-323 (1967) 12 . N .E .Anden, .G .Bucher, H .Corrodi, K .Fuxe, and U .Ungerstedt, Europ . J . Pharmacol . ].1 303-314 (1970) 13 . H .L .Borison, and S .C .Wang, Pharmacol . Rev . 1193-230 (1953) 14 . L .Atee, and G .Buncombe, Acta Pharmacol . Toxicol . 35 429-432 (1974) 15 . P .Jenner, C .D .Marsden, and E .Peringer, Brit . J . Pharmacol . ~4 275-276 (1975) 16 . A .Dolphin, P .Jenner, C .D .Marsden, C .Pycock, and D .Tarsy, Psychopharmacologia (Berl .) Al 133-139 (1975) 17 . P .A .Jannsen, and F .T .N .Allewijin, Arzneimittel-Forschun 18 279-282 (1968) 18 . S .R .Ojeda, P .G .Harms, and S .M .McCann, ~Endocrinol~o 9 650-1657 (1974) 19 . E .B .Smalstig, B .D .Sawyer, and J .A .Clemens ology 95 123-129 (1974)
Pergamon Press
EFFECT OF METOCLOPRAMIDE ON RAT PROLACTIN SECRETION IN VIVO Jiro Ysmauchi, Jiro Takahara and Tadashi Ofuji Third Department of Internal Medicine, Okayama University School of Medicine, Okayama, Japan 700 (Received in final form April 4, 1977) Summary Metoclopramide, a potent antagonist to apomorphine, was used to the rats in vivo to determine its effect on the release of prolactin . A single i .p . Tn-jection of metoclopramide at 10 or 100 jig/100 g b .w . under urethane anesthesia increased serum prolactin levels by 1 .6 or 7 .2 fold, respectively, compared with basa levels . This prolactin increase was completely abolished by 2-bromo-a-ergocryptine (CB-154) . These data suggest that metoclopramide stimulates prolactin secretion in rat and this secretion is abolished by dopaminergic stimulant . Recently, it has been demonstrated that metoclopramide, a orthopramide derivative, can stimulate prolactin release in humans (1-3) . This prolactin release was partially blocked by 1-dopa and completely abolished by CB-154 in man (2) . To confirm these data, we have measured prolactin levels after administration of metoclopramide or CB-154 or both agents simultaneously in rat in vivo . Materials _ and Methods Mature male Wister rats weighing 150 to 200 g were used . Laboratory chow and water were given ad lib . All rats were anesthetized with 150 mg/100 g b .w . of urethane i .p . 30 to 4 min before starting the experiments . The animals were divided into 6 groups of five each . They were administered 1, 10 and 100 Ng/100 g b .w . of metoclopramide and/or 10 pg/100 g b .w . of CB-154 i .p . dissolved in 0 .9 % saline . The blood samples for prolactin were collected from the jugular vein at 0, 5, 15, 30 and 60 min after the injection . Prolactin concentrations were measured by using the NIAMDD rat prolactin radioimmunoassay kit . The significance between the groups was tested by Duncan's new multiple range test (4) . Results As shown in the Table, metoclopramide caused a marked increase in serum prolactin values in a dose of 100 jig/100 g b .w . from fifteen minutes thereafter (p(0 .01) . The peak value was 7 .2 fold compared with basal level . A dose of 10 pg/100 g b .w . also had a tendency to release prolactin . However, in a dose of 1 ug/100 g b .w ., there was no change in serum prolactin concentrations compared with the control group . One group was given 10 pg/100 g b .w . of CB-154 fifteen minutes prior to the administration of 100 pg/100 g b .w . of metoclopramide . Serum prolactin elevation induced by metoclopramide in this group was completely abolished . 1581
1582
Metoclopramide and Rat Prolactin
Vol . 20, No . 4, 1977
TABLE Effect of Metoclopramide and CB-154 under Urethane Anesthesia on Rat Prolactin Secretion In Vivo . Group
Rat Serum Prolactin (ng/ml) Before
Control
44 .6+13 .6
MC
1 Ng
MC
*
5
15
30
60 min .
29 .4+12 .6
71 .5+25 .3
62 .6+ 17 .2
51 .3+ 12 .4
41 .4+ 6 .5
18 .7+ 3 .0
15 .2+ 2 .7
30 .8+ 13 .8
34 .3+
10 pg
80 .0+13 .1
36 .3+11 .4
89 .5+22 .7
130 .5+ 50 .0
77 .4_+ 37 .0
MC 100 jug
49 .0+13 .0
104 .7+35 .7
267 .4+69 .4
340 .2+123 .6
355 .2+127 .5
CB-154 10 jig
43 .0+ 8 .7
25 .0+ 6 .2
32 .7+ 7 .2
44 .8+
9 .9
44 .2+ 18 .2
51 .8+13 .6
34 .9+17 .1
63 .7+26 .6
71 .2+ 20 .4
50 .5+ 16 .6
MC 100 jig CB-154 10 jug
4 .4
MC = metoclopramide * Mean+SEM . ** pc0.01 vs control or only CB-154 treated groups . Discussion The result presented here have demonstrated that metoclopramide, like sulpiride (5), is a potent stimulator of prolactin release in rat . A 100 Pg/100 g b .w . of metoclopramide caused a significant increase in serum prolactin levels, and this elevation was completely abolished by pretreatment with CB-154, a potent dopamine receptor stimulant that has been shown to be effective in suppressing prolactin secretion in animals (6,7), and in man (8,9) . The results of these studies lead us to the following hypothesis . Firstly, CB-154 act at the same level as metoclopramide to cancel the metoclopramide-induced prolactin release . Secondly, the action level of metoclopramide is probably anatomically upper site than that of CB-154 . Thirdly, the potency of metoclopramide is weaker than CB-154 for inhibiting prolactin release . The effect of metoclopramide on the central neurotransmitters have yet to be adequately conducted . However, metoclopramide occasionally produces acute extrapyramidal effects ; acute dyskinesia such as torticollis, trismus, facial spasm, opistotonos and oculogyric crises (10) . Such reactions are identical to the acute dystonias produced by phenothiazines and butyrophenons, which are known to be potent cerebral dopamine receptor blocking agents (11,12) . In addition, metoclopramide antagonizes the central emetic action of apomorphine which is believed to be due to the stimulation of dopamine receptors in the medullary chemoreceptor trigger zone (13) . In animal studies, metoclopramide causes a dose-dependent increase in the striatal homovanillic acid content in mice (14,15), and apparently antagonizes or blocks the striatal dopamine receptors . Therefore, the striatal dopaminergic activity is decreased (15,16) . In rat behavioural and biochemical studies, metoclopramide resembles pimozide (16), which is a blocker of dopamine receptors (12,17) and has prolactin releasing activity (18,19) . The site and mode of action of metoclopramide in elevating serum prolactin are not fully clarified from our present data .
Vol . 20, No . 9, 1977
Metoclopramide and Rat Prolactin
1583
However, it seems likely that the prolactin releasing activity caused by metoclopramide might be due to the blockage of dopamine receptors at the central . nervous system level . Aknowle dgem ents The authors are grateful to the National Institute of Arthritis, Metabolism and Digestive Disease, National Institute of Health, for the supply of rat prolactin radioimmunoassay kit . CB-154 was kindly provided by Sandoz Ltd ., and metoclopramide was obtained from Fujisawa Pharmaceutical Co ., Ltd . . References 1 . A .S .McNeilly, M .O .Thorner, G .Volans, and G .M .Besser, Br . Med . J . 2 729 (1974) 2 . G .Delitala, A .Masala, S .Alagna, and L .Devilla, I R C S Medical Science 3 274 (1975) 3 . R .W .McCallum, J .R .Sowers, J .M .Hershman, and R .A .L .Sturdevant, J . Clin . Endocrinol . Metab . 422 1148-1153 (1976) 4 . R .D .G .Steel, and J .H .Torrie, Principles and Procedures of Statistics, p . 107 McGraw-Hill Book Co . 5 . J .Calaf, In J .L .Pasteels, and C .Robyn (eds .), Human Prolactin , p . 220-221, Excepta Medica, Amsterdam (1973) 6 . E .FlUckiger, and H .R .Wagner, Experientia (Basel) 24 1130-1131 (1968) 7 . C .W .Welsche, M .D .Squiers, E .Cassell, C .L .Chen, and J .Meites, Am . J . Physiol . 221 1714-1717 (1971) 8 . J .L .Pasteels, A .Danguy, M .Frérotte, and F .Ectors, Ann . Endocr . (Paris), 32 188-192 (1971) 9 . R .M .Lutterbeck, J .S .Pryor, L .Varga, and R .Wenner, Br . Med . J .3 228 (1971) 10 . P .Brownstein, and Bles, Thérapie 20 975-995 (1971) 11 . A .M .Ernst, Ps cho harmacolo ia Bérl .) 10 316-323 (1967) 12 . N .E .Anden, .G .Bucher, H .Corrodi, K .Fuxe, and U .Ungerstedt, Europ . J . Pharmacol . ].1 303-314 (1970) 13 . H .L .Borison, and S .C .Wang, Pharmacol . Rev . 1193-230 (1953) 14 . L .Atee, and G .Buncombe, Acta Pharmacol . Toxicol . 35 429-432 (1974) 15 . P .Jenner, C .D .Marsden, and E .Peringer, Brit . J . Pharmacol . ~4 275-276 (1975) 16 . A .Dolphin, P .Jenner, C .D .Marsden, C .Pycock, and D .Tarsy, Psychopharmacologia (Berl .) Al 133-139 (1975) 17 . P .A .Jannsen, and F .T .N .Allewijin, Arzneimittel-Forschun 18 279-282 (1968) 18 . S .R .Ojeda, P .G .Harms, and S .M .McCann, ~Endocrinol~o 9 650-1657 (1974) 19 . E .B .Smalstig, B .D .Sawyer, and J .A .Clemens ology 95 123-129 (1974)
