Conjugated HVA increase in rat urine after insulin-induced hypoglycemia: involvement of central dopaminergic structures but not of adrenal medulla.

To examine the possible contribution of Rat adrenal medulla to urinary DOPAC and HVA, we have studied these compounds in adrenals and urine under insulin-induced (5 IU/kg) hypoglycemic stimulation. In the urine samples collected over 16-hour-period following the intravenous insulin injection, there was a great increase in E, NE and their methoxylated derivatives MN and NMN, without change in DA, DOPAC, MHPG and free HVA excretion. In addition, there was a pronounced increase in urinary HVA conjugates (glucuronide and sulfate). Only very low amounts of DOPAC (10 +/- 2 ng/gland; 0.05% of catechols) and no detectable amounts of HVA (less than 3 ng/gland) were found in adrenal glands, without no significant change two hours after insulin, thus suggesting that Rat adrenal glands are not meaningful sources for urinary HVA and DOPAC. Since free HVA and total MHPG excretion remained unchanged, HVA contribution from sympathetic neurons seems unlikely in our study. In contrast, highly increased levels of conjugated HVA--and at a lesser extent of conjugated DOPAC--have been found in the striatum, which appears to be the most likely source of urinary HVA increment. The dopaminergic activation following insulin affected too the hypothalamus but not the nucleus accumbens. The role of such central dopaminergic activation has been discussed in terms of feeding behavior.