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Stimulation of contractions in the polyps of the soft coral Xenia elongata by compounds extracted from other alcyonacean soft corals
0306~4492/89$3.00 + 0.00 0 1990 Pergamon Press plc
Camp. Biochem. Physiol. Vol. 94C, No. 2, pp. 677-681, 1989 Printed in Great Britain
STIMULATION OF CONTRACTIONS IN THE POLYPS OF THE SOFT CORAL XENIA ELONGATA BY COMPOUNDS EXTRACTED FROM OTHER ALCYONACEAN SOFT CORALS MICHAEL A. PASS,*~MICHAELF. CAPRA,~CAROLH. CARLISLE,~ IAN LAWN§and JOHNC. COLLII *Department of Physiology and Pharmacology, IDepartment of Companion Animal Medicine and Surgery and $Heron Island Research Station, University of Queensland, St Lucia, Qld, 4067, Australia; TDepartment of Public Health and Nutrition, Queensland University of Technology, Brisbane, Qld, 4001, Australia, Tel. (07) 223-2111, Fax (07)229-1510 and [[Department of Chemistry and Biochemistry, James Cook University of North Queensland, Townsville, Qld, 48 11, Australia (Received
25 April 1989; revised 20 September
1989)
Abstract-l. Contractions of the polyps of the soft coral Xeniu elonguta were studied by suspending the polyps in an organ bath and recording changes in tension. 2. Spontaneous contractions included regular oscillations in tension occurring at a frequency of approximately l/min due to contractions of the column of the polyp. Contractions of the tentacles were superimposed on the column contractions and occurred with frequencies of lO-20/min. 3. The methyl ester of 15-epi-acetoxy PGA, and the diterpenes-( -)sarcophytoxide and thunbergol, isolated from soft coral eggs, stimulated contractions of the polyps. 4. Acetylcholine, methacholine, histamine, dimethylsulfoxide and the diterpene pukalide did not have any effects on the isolated polyps. 5. It is concluded that the egg-specific PGA, and some diterpenes caused contractions of soft coral polyps and could be involved in the expulsion of eggs during spawning.
INTRODUCr’ION Soft corals (Coelenterata, Octocorallia) are colonial marine invertebrates, the polyps of which consist of a cylindrical tube with eight pinnate tentacles at the distal end attached to the coenenchymal mass of the colony. Contractions of both the column and the tentacles occur. Contractions of the tentacles may be associated with feeding (Lewis, 1982). In some species, contraction of the column causes withdrawal of the polyp into the base of the colony. During spawning, eggs are expelled from the column of the coral polyps, a process requiring co-ordinated contractions of the coral polyps (Fig. 1). Little is known about the control of contractions in soft corals. It has been suggested that an electrical conducting system exists in the colony which coordinates contractile activities of the polyps (Horridge, 1956). The nature of this conducting system and its neuroeffector junctions have not been fully investigated in these organisms but neuronal synapses have been identified in a number of coelenterates (Chapman, 1974). The transmitter substances involved in the synapses have not been identified and therefore, some of the present experiments were carried out to determine if common neurotransmitters could stimulate contractions in soft coral polyps.
Research into chemical aspects of octocoral spawning has revealed that the chemical composition of the eggs of a number of soft corals differs significantly from that of the releasing colony (Bowden et al., 1985). Specifically, eggs released from Lobophytum crassum and Sarcophytum glaucum contain elevated levels of the diterpene (-)-sarcophytoxide (Heaton, 1988) while eggs from a number of Sinuluriu species the diterpenes epoxypukalide and/or contain pukalide, compounds completely absent from the releasing colony (Co11 et al., 1988). The eggs from Lobophytum planum contained the cembranoid diterpenes thunbergol and alcyonol-A, also undetectable in the coral tissue (Bowden et al., 1985) while eggs from L. plunum also contained the methyl ester of the prostaglandin 15-epi-acetoxy PGA,. In all cases the levels of these egg specific chemicals had decreased to levels below the limits of detection by the time of polyp settlement, 5-10 days after spawning (Heaton, 1988). They appeared to be associated with the spawning process at least temporally. The detection of a prostaglandin within this group of chemicals suggested a possible role in egg release-the stimulation of synchronised polyp contractions necessary for this broadcast spawning process. Experiments were carried out to determine if these egg specific metabolites induce contractions in soft coral polyps. MATERIALSAND METHODS
IAddress correspondence to: Dr Michael
F. Capra, Department of Public Health and Nutrition, Queensland University of Technology, Brisbane, Qld, 4001, Australia.
Polyps of Xeniu ekmgatu Dana were selected for these studies because of their size. Polyps of Lobophyton, Sarcophyton and Sinulariu were generally too small to be used in the organ baths. 677
678
MICHAEL A.
PASS
et al.
Fig. 1. Spawning of Lobophytum sp. showing contraction of some polyps.
Colonies of the soft coral Xenia e~o~gafa Dana were collected from the reef around Heron Island, Queensland, Australia. Experiments were performed on the day of collection as the colonies were usually not viable for more than 24 hr after collection. Polyps were cut off the colony and ligatures tied around the base of the column and around the tentacles. The polyps were suspended in sea water in a 25 ml organ bath by tying the column ligature to the iower
support in the bath. The ligature around the tentacles was attached to a Grass FT03 strain gauge to record tension in the polyp. The sea water in the bath was bubbled with oxygen and maintained at sea temperature by flowing sea water through the water jacket of the organ bath. Acetylcholine, methacholine, histamine, ATP and dimethylsulfoxide were obtained from Sigma. The PGA, derivative, pukahde, (-)-sarcophytoxide and thunbergol
Contraction in coral polyps
t I
min
619
4
Fig. 2. Changes in resting tension recorded from an isolated Xenia elonguta polyp. The fluctuations in tension occurring at a rate of about l/min are due to contractions of the column. The changes in tension occurring at about 20/min are due to contractions of the tentacles.
c
I
I min Fig. 3. Elffect of ATP (2 x lo-’ M) given at the arrow on the tension of an isolated Xenia elo?tgata polyp. There is an increase in the basal tension and in the rate of contraction of the tentacles after addition of ATP to the organ bath. were extracted from the appropriate soft corals (Heaton, 1988). Acetylcholine, methacholine, histamine and ATP were dissolved in distilled water before addition to the organ bath. The other compounds were dissolved in dimethylsulfoxide. Dimethylsulfoxide was added alone to some organ bath preparations as a control. Two extracts of Xenia were prepared in an effort to detect peptides that might stimulate contractions. The extraction method of Grimmelikhuijzen and Graff (1986) was used. Polyps were cut off the Xenia colony, boiled for 15 min, cooled to 0°C and acidified to pH 3.2 with acetic acid. The preparation was centrifuged at 3000g for 15 min and the pellet re-extracted with 0.2 M acetic acid and re-centrifuged. The supematants were brought to pH 7.0 with ammonia. Reverse phase C,* Sep-paks (Waters Associates) were flushed with methanol (3 ml) and then water (10 ml). Ten ml of the extract was loaded onto each Sep-pak which was eluted with distilled water (10 ml) and then 60% methanol (10 ml). The methanol eluant was added to the organ bath
directly or after the methanol was evaporated under a
I
4 min
I~6xlO~M 9~6~lO-~Y I
Fig. 4. Effect of adding (-)-sarcophytoxide
CBPIC) 94,2--v
stream of nitrogen. Aliquots of methanol were added to the organ bath as a control. RESULTS
Two types of spontaneous contractions were recorded from the coral polyps. Fluctuations of the basal tension occurred at a frequency of approximately l/min and they appeared to he due to contractions of the column of the polyp (Fig. 2). The second type of contraction occurred at a rate of lO-20/min and was due to contractions of the tentacles (Fig. 2). Addition of acetylcholine ( 10-6-10-3 M; N = 6), methacholine (1O-3 M; N = 3), histamine (10e610m5M; N = 6), pukalide (8.2 x 10m5-2 x 10e4 M; N = 3) or dimethylsulfoxide (2.8 x 10-2-0.13 M; N = 6) did not change the contractile activity of the coral polyps.
3XlQ3Y
at the arrows on the tension of an isolated Xeniu elongafa polyp.
MICHAEL
A. PASSet al.
4 min Fig. 5. Effect of methanol (0.5 M) added at the arrow on the tension of an isolated Xenia elongata
ATP (2 x 10-S M) stimulated an increase in contractions in 17 of the 25 polyps tested. In most cases there was an increase in the rate of contractions of the tentacles and a small increase in the basal tone of the preparation (Fig. 3). The PGAz derivative (4 x 10e5-1.6 x 10m4M; N = 4) induced contractions, and thunbergol (8 x 1O-5-2.4 x 10m4M) induced contractions in one of the two polyps tested. The strongest contractions were induced by (-)sarcophytoxide (9.6 x 10M5-3 x 10m3M; N = 10) and, like those induced by the PGAl derivative and thunbergol, were different from those induced by ATP. The contractions were discrete and of large amplitude (Fig. 4). Often, during these large contractions, the tentacle contractions were not evident on the recordings but contractions of tentacles not ensnared by the upper ligature could frequently be observed. In some instances, multiple contractions were elicited (Fig. 4). At least, in the case of (-)sarcophytoxide, the responses appeared to be dose related (Fig. 4). Insufficient amounts of the other compounds derived from the corals were available to examine dose responses. Application of the methanolic extract of Xeniu to the isolated preparations elicited contractions but so too did the methanol (Fig. 5). Contractions were stimulated inconsistently when the methanol evaporated extracts were added to the organ bath. The first of these (200 ~1) elicited contractions in both of the strips tested but the second extract was inactive. DISCUSSION
The isolated coral polyps showed spontaneous contractions of the column and tentacles, which occurred independently of each other. The common mammalian transmitter chemicals acetylcholine, methacholine and histamine had no effect on contractions. In contrast, ATP stimulated contractions of the coral polyps. This could have been due to stimulation of ATP sensitive receptors or to an increase in the energy available for contraction. The effect occurred at concentrations which were similar to those that
POlYP.
stimulate purinergic transmitter systems in mammalian tissues (Axelsson and Holmberg, 1969; Burnstock et al., 1972). Grimmelikhuijzen and Graff (1986) isolated a peptide from coelenterates and it was found to act as a neurotransmitter in anemone muscle. The extracts of Xenia, prepared in a similar manner to those of Grimmelikhuijzen and Graff (1986), showed little activity towards the coral polyps. Inconsistent contractile responses occurred with some polyps and some responses occurred with one of the methanol evaporated extracts. Contractile responses to methanol were frequently elicited. It is probable that these responses were due to stimulation of chemoreceptors in the polyps but they could also be due to a direct action of the methanol on membranes of the contractile elements of the coral. The PGA, derivative and thunbergol stimulated contractions occasionally but the strongest stimulant to contraction was the diterpene (-)-sarcophytoxide isolated from soft corals. These compounds caused contractions of the column of the polyps, although changes in contractions of the tentacles were not detected. It is not known if these compounds act on sensory chemoreceptors, at nerve or muscular synaptic receptors, or directly on the membranes of the contractile elements of the coral polyp. Whatever their mode of action, it is clear that they are strong stimulants to contractions of the coral polyps. What role they play in controlling normal activities in corals is also unknown but the fact that their concentrations increase in coral eggs prior to spawning suggests that they could be involved in this process. These results are consistent with the premise that these compounds reach a threshold level in the eggs just prior to spawning (Co11et al., 1989), and that the presence of high concentrations of these compounds triggers contractions of the column of the coral polyps which expel the eggs into the surrounding water. Future studies will focus on methods for testing the egg specific terpenes against the actual polyps of the
Contraction in coral polyps colonies from which they are derived. Certain technological problems will have to be overcome before this can be done. The present findings certainly provide an impetus for such undertakings. Acknowledgement-A
Queensland University of Technology grant to M. F. Capra supported this project. REFERENCES
Axelsson J. and Holmberg B. (1969) The effects of extracellularly applied ATP and related compounds on electrical and mechanical activity of the smooth muscle taenia coli from the guinea-pig. Acra Physiol. stand. 75, 149-156. Bowden B. F., Co11 J. C., Heaton A., Konig G., Bruck M. A., Cramer R. E., Klein D. M. and Scheuer P. J. (1985) The structures of four isomeric dihydrofurancontaining cembranoid diterpenes from several species of soft coral. J. Nat. Prod. 50, 650-659. Burnstock G., Dumsday B. and Smythe A. (1972) Atropine resistant excitation of the urinary bladder: the possibility of transmission via nerves releasing a purine nucleotide. Br. J. Pharmac. 44, 451-461.
681
Chapman D. M. (1974) Cnidarian histology. In Coelenterate Biology Reviews and New Perspectives (Edited by Muscatine, L. and Lenhoff, H. M.), pp. l-92. Academic Press, New York. Co11 J. C.. Bowden B. F.. Heaton A.. Scheuer P. J.. Li M. K. w., Clardy J., Schulte G. K. and Finer-Moore J. (1989) Structures and possible functions of epoxypukalide and pukalide: diterpenes associated with the eggs of Sinularian soft corals (Cnidaria, Anthozoa, Cktocorallia, Alcyonacea, Alcyoniidae). J. them. Ecol. 15, 1177-l 191. Grimmelikhuijzen C. J. P. and Graff D. (1986) Isolation of Glu-Gly-Arg-Phe-NH, (Antho-RFamide), a neuropeptide from sea anenomes. Proc. natn. Acad. Sci. U.S.A. 83, 98 17-9821.
Heaton A. (1988) Chemical Studies of Soft Corals. PhD Thesis, James Cook University of North Queensland, Townsville, Qld., Australia. Horridge G. A. (1956) The response of Heteroxenia (Alcyonaria) to stimulation and to some inorganic ions. J. exp. Biol. 33, 604-614.
Lewis J. B. (1982) Feeding behaviour and feeding ecology of the Gctocorallia (Coelenterata: Anthozoa). J. Zool. Lond. 196,371-384.
Camp. Biochem. Physiol. Vol. 94C, No. 2, pp. 677-681, 1989 Printed in Great Britain
STIMULATION OF CONTRACTIONS IN THE POLYPS OF THE SOFT CORAL XENIA ELONGATA BY COMPOUNDS EXTRACTED FROM OTHER ALCYONACEAN SOFT CORALS MICHAEL A. PASS,*~MICHAELF. CAPRA,~CAROLH. CARLISLE,~ IAN LAWN§and JOHNC. COLLII *Department of Physiology and Pharmacology, IDepartment of Companion Animal Medicine and Surgery and $Heron Island Research Station, University of Queensland, St Lucia, Qld, 4067, Australia; TDepartment of Public Health and Nutrition, Queensland University of Technology, Brisbane, Qld, 4001, Australia, Tel. (07) 223-2111, Fax (07)229-1510 and [[Department of Chemistry and Biochemistry, James Cook University of North Queensland, Townsville, Qld, 48 11, Australia (Received
25 April 1989; revised 20 September
1989)
Abstract-l. Contractions of the polyps of the soft coral Xeniu elonguta were studied by suspending the polyps in an organ bath and recording changes in tension. 2. Spontaneous contractions included regular oscillations in tension occurring at a frequency of approximately l/min due to contractions of the column of the polyp. Contractions of the tentacles were superimposed on the column contractions and occurred with frequencies of lO-20/min. 3. The methyl ester of 15-epi-acetoxy PGA, and the diterpenes-( -)sarcophytoxide and thunbergol, isolated from soft coral eggs, stimulated contractions of the polyps. 4. Acetylcholine, methacholine, histamine, dimethylsulfoxide and the diterpene pukalide did not have any effects on the isolated polyps. 5. It is concluded that the egg-specific PGA, and some diterpenes caused contractions of soft coral polyps and could be involved in the expulsion of eggs during spawning.
INTRODUCr’ION Soft corals (Coelenterata, Octocorallia) are colonial marine invertebrates, the polyps of which consist of a cylindrical tube with eight pinnate tentacles at the distal end attached to the coenenchymal mass of the colony. Contractions of both the column and the tentacles occur. Contractions of the tentacles may be associated with feeding (Lewis, 1982). In some species, contraction of the column causes withdrawal of the polyp into the base of the colony. During spawning, eggs are expelled from the column of the coral polyps, a process requiring co-ordinated contractions of the coral polyps (Fig. 1). Little is known about the control of contractions in soft corals. It has been suggested that an electrical conducting system exists in the colony which coordinates contractile activities of the polyps (Horridge, 1956). The nature of this conducting system and its neuroeffector junctions have not been fully investigated in these organisms but neuronal synapses have been identified in a number of coelenterates (Chapman, 1974). The transmitter substances involved in the synapses have not been identified and therefore, some of the present experiments were carried out to determine if common neurotransmitters could stimulate contractions in soft coral polyps.
Research into chemical aspects of octocoral spawning has revealed that the chemical composition of the eggs of a number of soft corals differs significantly from that of the releasing colony (Bowden et al., 1985). Specifically, eggs released from Lobophytum crassum and Sarcophytum glaucum contain elevated levels of the diterpene (-)-sarcophytoxide (Heaton, 1988) while eggs from a number of Sinuluriu species the diterpenes epoxypukalide and/or contain pukalide, compounds completely absent from the releasing colony (Co11 et al., 1988). The eggs from Lobophytum planum contained the cembranoid diterpenes thunbergol and alcyonol-A, also undetectable in the coral tissue (Bowden et al., 1985) while eggs from L. plunum also contained the methyl ester of the prostaglandin 15-epi-acetoxy PGA,. In all cases the levels of these egg specific chemicals had decreased to levels below the limits of detection by the time of polyp settlement, 5-10 days after spawning (Heaton, 1988). They appeared to be associated with the spawning process at least temporally. The detection of a prostaglandin within this group of chemicals suggested a possible role in egg release-the stimulation of synchronised polyp contractions necessary for this broadcast spawning process. Experiments were carried out to determine if these egg specific metabolites induce contractions in soft coral polyps. MATERIALSAND METHODS
IAddress correspondence to: Dr Michael
F. Capra, Department of Public Health and Nutrition, Queensland University of Technology, Brisbane, Qld, 4001, Australia.
Polyps of Xeniu ekmgatu Dana were selected for these studies because of their size. Polyps of Lobophyton, Sarcophyton and Sinulariu were generally too small to be used in the organ baths. 677
678
MICHAEL A.
PASS
et al.
Fig. 1. Spawning of Lobophytum sp. showing contraction of some polyps.
Colonies of the soft coral Xenia e~o~gafa Dana were collected from the reef around Heron Island, Queensland, Australia. Experiments were performed on the day of collection as the colonies were usually not viable for more than 24 hr after collection. Polyps were cut off the colony and ligatures tied around the base of the column and around the tentacles. The polyps were suspended in sea water in a 25 ml organ bath by tying the column ligature to the iower
support in the bath. The ligature around the tentacles was attached to a Grass FT03 strain gauge to record tension in the polyp. The sea water in the bath was bubbled with oxygen and maintained at sea temperature by flowing sea water through the water jacket of the organ bath. Acetylcholine, methacholine, histamine, ATP and dimethylsulfoxide were obtained from Sigma. The PGA, derivative, pukahde, (-)-sarcophytoxide and thunbergol
Contraction in coral polyps
t I
min
619
4
Fig. 2. Changes in resting tension recorded from an isolated Xenia elonguta polyp. The fluctuations in tension occurring at a rate of about l/min are due to contractions of the column. The changes in tension occurring at about 20/min are due to contractions of the tentacles.
c
I
I min Fig. 3. Elffect of ATP (2 x lo-’ M) given at the arrow on the tension of an isolated Xenia elo?tgata polyp. There is an increase in the basal tension and in the rate of contraction of the tentacles after addition of ATP to the organ bath. were extracted from the appropriate soft corals (Heaton, 1988). Acetylcholine, methacholine, histamine and ATP were dissolved in distilled water before addition to the organ bath. The other compounds were dissolved in dimethylsulfoxide. Dimethylsulfoxide was added alone to some organ bath preparations as a control. Two extracts of Xenia were prepared in an effort to detect peptides that might stimulate contractions. The extraction method of Grimmelikhuijzen and Graff (1986) was used. Polyps were cut off the Xenia colony, boiled for 15 min, cooled to 0°C and acidified to pH 3.2 with acetic acid. The preparation was centrifuged at 3000g for 15 min and the pellet re-extracted with 0.2 M acetic acid and re-centrifuged. The supematants were brought to pH 7.0 with ammonia. Reverse phase C,* Sep-paks (Waters Associates) were flushed with methanol (3 ml) and then water (10 ml). Ten ml of the extract was loaded onto each Sep-pak which was eluted with distilled water (10 ml) and then 60% methanol (10 ml). The methanol eluant was added to the organ bath
directly or after the methanol was evaporated under a
I
4 min
I~6xlO~M 9~6~lO-~Y I
Fig. 4. Effect of adding (-)-sarcophytoxide
CBPIC) 94,2--v
stream of nitrogen. Aliquots of methanol were added to the organ bath as a control. RESULTS
Two types of spontaneous contractions were recorded from the coral polyps. Fluctuations of the basal tension occurred at a frequency of approximately l/min and they appeared to he due to contractions of the column of the polyp (Fig. 2). The second type of contraction occurred at a rate of lO-20/min and was due to contractions of the tentacles (Fig. 2). Addition of acetylcholine ( 10-6-10-3 M; N = 6), methacholine (1O-3 M; N = 3), histamine (10e610m5M; N = 6), pukalide (8.2 x 10m5-2 x 10e4 M; N = 3) or dimethylsulfoxide (2.8 x 10-2-0.13 M; N = 6) did not change the contractile activity of the coral polyps.
3XlQ3Y
at the arrows on the tension of an isolated Xeniu elongafa polyp.
MICHAEL
A. PASSet al.
4 min Fig. 5. Effect of methanol (0.5 M) added at the arrow on the tension of an isolated Xenia elongata
ATP (2 x 10-S M) stimulated an increase in contractions in 17 of the 25 polyps tested. In most cases there was an increase in the rate of contractions of the tentacles and a small increase in the basal tone of the preparation (Fig. 3). The PGAz derivative (4 x 10e5-1.6 x 10m4M; N = 4) induced contractions, and thunbergol (8 x 1O-5-2.4 x 10m4M) induced contractions in one of the two polyps tested. The strongest contractions were induced by (-)sarcophytoxide (9.6 x 10M5-3 x 10m3M; N = 10) and, like those induced by the PGAl derivative and thunbergol, were different from those induced by ATP. The contractions were discrete and of large amplitude (Fig. 4). Often, during these large contractions, the tentacle contractions were not evident on the recordings but contractions of tentacles not ensnared by the upper ligature could frequently be observed. In some instances, multiple contractions were elicited (Fig. 4). At least, in the case of (-)sarcophytoxide, the responses appeared to be dose related (Fig. 4). Insufficient amounts of the other compounds derived from the corals were available to examine dose responses. Application of the methanolic extract of Xeniu to the isolated preparations elicited contractions but so too did the methanol (Fig. 5). Contractions were stimulated inconsistently when the methanol evaporated extracts were added to the organ bath. The first of these (200 ~1) elicited contractions in both of the strips tested but the second extract was inactive. DISCUSSION
The isolated coral polyps showed spontaneous contractions of the column and tentacles, which occurred independently of each other. The common mammalian transmitter chemicals acetylcholine, methacholine and histamine had no effect on contractions. In contrast, ATP stimulated contractions of the coral polyps. This could have been due to stimulation of ATP sensitive receptors or to an increase in the energy available for contraction. The effect occurred at concentrations which were similar to those that
POlYP.
stimulate purinergic transmitter systems in mammalian tissues (Axelsson and Holmberg, 1969; Burnstock et al., 1972). Grimmelikhuijzen and Graff (1986) isolated a peptide from coelenterates and it was found to act as a neurotransmitter in anemone muscle. The extracts of Xenia, prepared in a similar manner to those of Grimmelikhuijzen and Graff (1986), showed little activity towards the coral polyps. Inconsistent contractile responses occurred with some polyps and some responses occurred with one of the methanol evaporated extracts. Contractile responses to methanol were frequently elicited. It is probable that these responses were due to stimulation of chemoreceptors in the polyps but they could also be due to a direct action of the methanol on membranes of the contractile elements of the coral. The PGA, derivative and thunbergol stimulated contractions occasionally but the strongest stimulant to contraction was the diterpene (-)-sarcophytoxide isolated from soft corals. These compounds caused contractions of the column of the polyps, although changes in contractions of the tentacles were not detected. It is not known if these compounds act on sensory chemoreceptors, at nerve or muscular synaptic receptors, or directly on the membranes of the contractile elements of the coral polyp. Whatever their mode of action, it is clear that they are strong stimulants to contractions of the coral polyps. What role they play in controlling normal activities in corals is also unknown but the fact that their concentrations increase in coral eggs prior to spawning suggests that they could be involved in this process. These results are consistent with the premise that these compounds reach a threshold level in the eggs just prior to spawning (Co11et al., 1989), and that the presence of high concentrations of these compounds triggers contractions of the column of the coral polyps which expel the eggs into the surrounding water. Future studies will focus on methods for testing the egg specific terpenes against the actual polyps of the
Contraction in coral polyps colonies from which they are derived. Certain technological problems will have to be overcome before this can be done. The present findings certainly provide an impetus for such undertakings. Acknowledgement-A
Queensland University of Technology grant to M. F. Capra supported this project. REFERENCES
Axelsson J. and Holmberg B. (1969) The effects of extracellularly applied ATP and related compounds on electrical and mechanical activity of the smooth muscle taenia coli from the guinea-pig. Acra Physiol. stand. 75, 149-156. Bowden B. F., Co11 J. C., Heaton A., Konig G., Bruck M. A., Cramer R. E., Klein D. M. and Scheuer P. J. (1985) The structures of four isomeric dihydrofurancontaining cembranoid diterpenes from several species of soft coral. J. Nat. Prod. 50, 650-659. Burnstock G., Dumsday B. and Smythe A. (1972) Atropine resistant excitation of the urinary bladder: the possibility of transmission via nerves releasing a purine nucleotide. Br. J. Pharmac. 44, 451-461.
681
Chapman D. M. (1974) Cnidarian histology. In Coelenterate Biology Reviews and New Perspectives (Edited by Muscatine, L. and Lenhoff, H. M.), pp. l-92. Academic Press, New York. Co11 J. C.. Bowden B. F.. Heaton A.. Scheuer P. J.. Li M. K. w., Clardy J., Schulte G. K. and Finer-Moore J. (1989) Structures and possible functions of epoxypukalide and pukalide: diterpenes associated with the eggs of Sinularian soft corals (Cnidaria, Anthozoa, Cktocorallia, Alcyonacea, Alcyoniidae). J. them. Ecol. 15, 1177-l 191. Grimmelikhuijzen C. J. P. and Graff D. (1986) Isolation of Glu-Gly-Arg-Phe-NH, (Antho-RFamide), a neuropeptide from sea anenomes. Proc. natn. Acad. Sci. U.S.A. 83, 98 17-9821.
Heaton A. (1988) Chemical Studies of Soft Corals. PhD Thesis, James Cook University of North Queensland, Townsville, Qld., Australia. Horridge G. A. (1956) The response of Heteroxenia (Alcyonaria) to stimulation and to some inorganic ions. J. exp. Biol. 33, 604-614.
Lewis J. B. (1982) Feeding behaviour and feeding ecology of the Gctocorallia (Coelenterata: Anthozoa). J. Zool. Lond. 196,371-384.