Localization, identification, and action of galanin in the frog adrenal gland

The distribution of galanin-like immunoreactivity was studied in the adrenal gland of the frog Rana ridibunda using the indirect immunofluorescence technique. A dense network of varicose fibers immunoreactive to galanin was found in the adrenal tissue. A combination of HPLC analysis and RIA detection was used to characterize galanin-like immunoreactivity in frog adrenal gland extracts. The elution profile revealed the 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 from 10^-9 to 3 x 10^-6 M, synthetic frog galanin induced a dose-dependent inhibition of corticosterone and aldosterone release. Repeated pulses of galanin (10^-6 M), given at 90-min intervals, resulted in a reproducible inhibition of corticosteroid secretion without any apparent tachyphylaxis. During prolonged administration of galanin (10^-6 M), the steroidogenic effect of ACTH (10^-9 M) was significantly reduced. In contrast, galanin did not attenuate the stimulation of corticosteroid secretion induced by the angiotensin II analog [Sar¹,Val⁵]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 corticosteroid release. Taken together, these findings suggest that galanin, released by nerve fibers in the adrenal tissue, can act locally as a modulator of steroid secretion.