LOCALIZATION, IDENTIFICATION, AND ACTION OF GALANIN IN THE FROG ADRENAL-GLAND

The distribution of galanin-like immunoreactivity was studied in the a drenal gland of the frog Rana ridibunda using the indirect immunofluor escence technique. A dense network of varicose fibers immunoreactive t o galanin was found in the adrenal tissue. A combination of HPLC analy sis and RIA detection was used to characterize galanin-like immunoreac tivity in frog adrenal gland extracts. The elution profile revealed th e existence of a single form of galanin exhibiting the same retention time as synthetic frog galanin. The possible involvement of galanin in the regulation of corticosteroid secretion was investigated in vitro using a perifusion system for frog adrenal slices. For concentrations ranging hom 10(-9) to 3 x 10(-6) M, synthetic frog galanin induced a d ose-dependent inhibition of corticosterone and aldosterone release. Re peated pulses of galanin (10(-6) M), given at 90-min intervals, result ed in a reproducible inhibition of corticosteroid secretion without an y apparent tachyphylaxis. During prolonged administration of galanin ( 10(-6) M), the steroidogenic effect of ACTH (10(-9) M) was significant ly reduced. In contrast, galanin did not attenuate the stimulation of corticosteroid secretion induced by the angiotensin II analog [Sar(1), Val(5)]angiotensin II. These results show the occurrence of galanin in fibers innervating the frog adrenal gland. The data also demonstrate that synthetic galanin inhibits spontaneous and ACTH-induced corticost eroid release. Taken together, these findings suggest that galanin, re leased by nerve fibers in the adrenal tissue, can act locally as a mod ulator of steroid secretion.