Regulation of thyrotropin-releasing hormone secretion from frog skin

The regulation of TRH secretion from skin fragments of the leopard frog, Rana pipiens, was examined under various conditions. TRH secretion is under dual neurotransmitter control with stimulatory noradrenergic and inhibitory dopaminergic components; other neurotransmitters were generally without effect. Membrane-depolarizing conditions required the presence of calcium to cause TRH release consistent with a stimulus-secretion coupling mechanism. However, the norepinephrine-stimulated response appeared to be independent of external Ca++. TRH secretion was unresponsive to somatostatin, T3, and dibutyryl cAMP, substances which may affect TRH secretion in the mammalian hypothalamus. Anuran skin is a complex secretory tissue, but the presence of large quantities of TRH and other biologically active neuropeptides makes this tissue an attractive model to study the regulation of neuropeptide secretion.