There is increasing evidence that dopamine (DA) inhibits aldosterone production, but the source of DA for this dopaminergic influence is not known. In the present study we examined the adrenal's zona glomerulosa for the presence of DA. Rats maintained on an intake of regular food were killed by decapitation and the adrenal capsule (containing zona glomerulosa) and the remainder of the gland (containing both cortex and medulla) were examined for their content of DA and also for norepinephrine (NE) and epinephrine (E). DA was found in adrenal glomerulosa in substantial quantity, 1.92 +/- 0.17 (SEM) ng/mg wet weight, representing an approximate concentration of DA of 1-100 microM. DA in adrenal capsule represented 12.2% of the total adrenal content of DA. NE and E were also present in glomerulosa, 3.46 +/- 0.32 and 18.7 +/- 2.1 ng/mg respectively, but, unlike DA, about 98% of the total adrenal content of NE and E was contained in adrenal medulla. The NE/E ratio in capsule and medulla were similar, although slightly higher in adrenal medulla, suggesting that the medulla is the source of the NE and E found in glomerulosa. On the other hand, the DA/E ratio was several-fold higher in glomerulosa than medulla--suggesting that glomerulosa DA was derived at least partially from a source other than adrenal medulla. We also found that short-term culturing of the adrenal reduced DA levels to 1/3 that observed in fresh tissue. This could explain in part why cultured glomerulosa has been shown to be more responsive to administered stimuli. In summary, the findings indicate a significant concentration of DA in adrenal glomerulosa, and suggest that the effects of DA on aldosterone production are mediated locally within the adrenal.