Presence of immunoreactive β-endorphin and enkephalin-like material in the retina and other tissues of the frog, Rana pipiens

Substantial quantities of immunoreactive (IR)-β-endorphin have been demonstrated in the retina of Rana pipiens in amounts not affected by exposure to constant light or constant darkness. IR-β-endorphin has also been measured in blood, pituitary, hypothalamus, and extrahypothalamic brain of this species, while lower concentrations of IR-Met-enkephalin and IR-Leu-enkephalin have also been found in these tissues. The significance of the widespread distribution of opioid peptide-like material in amphibian tissues remains to be determined.