Thyrotropin-releasing hormone and serotonin secretion from frog skin are stimulated by norepinephrine.

Abstract

TRH was found to be concentrated in the cutaneous poison gland of the leopard frog, Rana pipiens. In this gland, concentrations of TRH are 50–100 times greater than those present in the rat median eminence. When small pieces of skin containing dense populations of these glands were placed in vitro and observed microscopically, norepinephrine (NE) but not epinephrine or acetylcholine minimally stimulated gland secretion at 10−8 m. Observable gland secretion was maximally stimulated by 10−4 m NE. NE (10−6−10−4 m) evoked the doserelated release of both TRH and serotonin into the medium and caused corresponding reductions in their tissue contents. Phenoxybenzamine but not propranolol antagonized NE stimulation of TRH and serotonin release, indicating that an α-adrenergic receptor mediates the noradrenergic responses. Since previous studies have shown that NE stimulates TRH secretion from mammalian hypothalamus in vitro and pituitary TSH in vivo, the present findings can be interpreted as evidence of a phyloge...