The chemistry and pharmacology of a central nervous system stimulant from the sea anemone, Stoichactis kenti

Abstract

A central nervous system stimulant has been isolated from the sea anemone, Stoichactis kenti. A chromatographically homogeneous fraction has been obtained from the crude extract by dialysis and gel filtration on Sephadex G-50. Attempts were made to purify the active fraction further by ion exchange column chromatography, but the specific activity of the active fraction was not increased. The active substance was found to be water soluble, heat and acid labile and stable to alkali. It showed a positive color reaction with ninhydrin on paper (circular) chromatography, using n-butanol: acetic acid:water (4:1:5) system. Steroids, steroidal glycosides, nucleic acids, lipids and carbohydrates were found to be absent in the active fraction, when tested with specific reagents. The active fraction has a characteristic u.v. maximum at 277.5 nm. Determination of protein by Lowry's method and estimation of nitrogen by Kjeldahl's method indicated the active fraction was rich in protein. An acid and alkaline hydrolysis of the active fraction was carried out and hydrolysates were analyzed both by two dimensional chromatography and Technicon auto aminoacid analyzer. The following amino acids were identified by comparing with standard aminoacids: cysteine, aspartic acid (asparagine), threonine, serine, glutamic acid (glutamine), proline, glycine, alanine, valine, cystine, isoleucine, leucine, tyrosine, phenylalanine, lysine, histidine and arginine. From these results it was concluded that the active fraction was a polypeptide containing seventeen different aminoacids. Based on behavior on Sephadex G-50, the approximate molecular weight of the active fraction was estimated to be in the range of 2,500 - 3,000. Signs of central nervous system stimulatory activity produced by the active fraction in male mice included fighting episodes, increased motor activity and clonic convulsions. The ED50 of the active fraction based on fighting episodes was 6.4 mg/kg. The fighting episodes occurred at a frequency of 2-3 times/minute. After the administration of the active fraction intraperitoneally, the fighting episodes started within 4-6 minutes, peaked at 15 minutes and waned within about 30 minutes. The LD50 dose of the active fraction was 12.2 mg/kg. Toxic symptoms such as ataxia, catalepsy and tonic convulsions were observed before death. Phenobarbital sodium, chlorpromazine and methocarbamol completely blocked the fighting response of the active fraction even at the ED100 dose level but did not change the LD50. The antagonism of the active fraction induced stimulant activity (as measured by fighting episodes) by these drugs suggests that this activity was probably mediated centrally. Reserpine and tetrabenazine pretreatment markedly increased the stimulant effect of the active fraction by decreasing the ED50 of the active fraction by 50%. Such treatment increased toxicity twofold. a-methyl p-tyrosine methylester Hel (α-MPT) pretreatment did not alter the ED50, while the LD50 was significantly decreased. When α-MPT treatment was incorporated in reserpine or tetrabenazine treated animals, the stimulatory activity of the active fraction was completely blocked even at the ED100 (9.3 mg/kg) dose level. The active fraction produced a significant decrease in brain norepinephrine content at the ED50 and the ED100 doses during the stimulation period. Both the active fraction and reserpine produced a hyperthermic response in mice. DL-dopa treatment restored the active fraction induced stimulant action (fighting episodes) which was abolished after combined treatment with a-MPT and reserpine and reserpine and disulfiram. DL-dopa also increased the LD50 of the active fraction. The active fraction at the ED50 dose significantly decreased brain dopamine content. Pretreatment with p-chlorophenylalanine did not alter the ED50 and the LD50 of the active fraction. No change in brain serotonin content was observed after administration of the active fraction at the ED50 dose. The active fraction at the ED50 dose significantly inhibited the re-uptake mechanism of norepinephrine during the stimulation period. It also elevated normetanephrine levels at the ED50 dose. Propranolol but not phentolamine treatment completely blocked the stimulatory action of the active fraction, with no change in the LD50. Atropine treatment decreased the toxicity, with no change in the ED50. On the other hand physostigmine blocked the stimulatory action and increased toxicity by twofold. In conclusion, the results suggest that the active fraction causes stimulant action by releasing active norepinephrine from functional pools and inhibiting its re-uptake, thus making more norepinephrine available at adrenergic receptors.