Stimulation of Somatostatin Release from Median Eminence Tissue Incubated in Vitro by Taurine and Related Amino Acids*

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Abstract
To determine if the putative amino acid transmitter taurine could affect the release of somatostatin (SRIF) from median eminence fragments [rat], median eminence were incubated in vitro in the presence of various concentrations of taurine and its precursors, hypotaurine, cysteamine, cysteic acid and L-cysteine sulfinic acid. Taurine was effective in releasing SRIF at doses of 50 .mu.M and higher. Surprisingly, cysteic acid was the most potent stimulant of SRIF release, with a minimal effective dose of 0.1 .mu.M. Cysteamine was effective at a dose of 50 .mu.M, hypotaurine was effective only at 200 .mu.M and cysteine sulfinic acid was ineffective in stimulating SRIF release at any of the doses tested. To determine if the effect of taurine was mediated by the dopaminergic system, the dopamine receptor blocker pimozide (1 .mu.M) was added to the medium containing either taurine or cysteic acid. Pimozide did not prevent the stimulatory effect of the amino acids. Apparently, taurine and related amino acids may be involved in SRIF release by a nondopaminergic pathway. In view of the high concentrations of taurine in the hypothalamus, it must be considered a putative transmitter releasing SRIF.