Influence of splanchnic nerve on reserpine action in avian adrenal medulla

Reserpine at three doses (0.05, 0.2, and 0.8 mg/100 g body wt) has been injected intraperitoneally to seven unilaterally splanchnic denervated avian species, in order to ascertain the neural regulation of its action in avian adrenal medulla. The adrenomedullary catecholamines (CA) were estimated at 24 hr after reserpine injection. The findings revealed that reserpine at high doses caused 66-92% depletion of total CA from both the innervated and the denervated glands in all the species investigated. The low dose of reserpine in the passerine (common myna and bulbul) birds resulted in 40-84% reduction of both norepinephrine (NE) and epinephrine (E) from the adrenal glands irrespective of its nerve supply. As a contrast, it depleted 60-80% of both NE and E from the innervated glands as compared to 17-43% reduction from the denervated glands in nonpasserine (woodpecker, parakeet, and koel) birds. Interestingly, in other nonpasserine (pigeon and duck) birds, the low dose of reserpine depleted 66-71% of NE from the innervated glands as compared to only 2-13% reduction from the denervated glands. But in these birds, 60-85% depletion of E, however, occurred independent of neural regulation. The findings suggest that at high doses depletion of CA by reserpine is controlled by some nonneurogenic mechanisms. Generally speaking, at a low dose of reserpine, the splanchnic nerve probably modulates depletion of CA from the adrenal medulla of the nonpasserine birds while the same is governed by some nonneurogenic mechanisms in the passerine birds.