Enhancement of the adrenocortical response to metyrapone by L-dopa in the chicken (Gallus domesticus).

1. Eight-week-old chickens were treated with a single intravenous injection of saline, L-dopa (20 mg/kg body weight), metyrapone (60 mg/kg) or a combined dose of L-dopa and metyrapone. Serum corticosterone was measured by radioimmunoassay at 30, 60 and 90 min after the treatment. 2. L-dopa did not alter the corticosterone concentration during the experiment, whereas metyrapone increased it at 60 and 90 min. 3. When L-dopa and metyrapone were given together there was a gradual increase in corticosterone and the hormone concentrations were significantly greater than control values at all times. 4. It was concluded that L-dopa is not a potent stimulator of adrenocortical cells in chickens, but it enhances the response to metyrapone. This may be achieved through the release of endogenous ACTH by stimulating central dopamine receptors.