Increases in adrenal tyrosine hydroxylase mRNA induced by 48 Hr water deprivation are prevented by splanchnic denervation in rats

It is not clear if the chronic blood volume depletion produced by water deprivation (WD) increases sympathetic activity. We previously reported that WD increases adrenal tyrosine hydroxylase (TH) mRNA levels (FASEB J. 8: A849, 1994). The hypothesis that this increase is mediated by increased sympathetic activity was tested in the present study by determining if prior adrenal denervation prevents the TH response. TH mRNA was quantitated using a sequence-specific ribonuclease protection assay. The left splanchnic nerve of 14 rats was cut a week before the experiment (SPLNX). A second group of 10 rats had no surgery (INTACT). WD for 48 hr decreased (p<0.01) body weight in SPLNX (303±8 g, n=7) and INTACT (281 ±7 g, n=5) rats compared to hydrated SPLNX (332±7 g, n=7) and INTACT (343±13 g, n=5) rats. TH mRNA levels (fg/2 Mg total RNA) were :p<0.05 between WD and hydrated): WATER DEPRIVED HYDRATED left right left right INTACT 1117±151 1287±229' 692±110 659±52 SPLNX 781±88 1079±107' 770±73 898±80 WD increased TH mRNA in both adrenals of INTACT rats. In contrast, WD increased TH mRNA only in the innervated right adrenal of SPLNX rats. These data show that increases in rat adrenal TH mRNA in response to WD are prevented by splanchnic nerve cuts. The findings support the hypothesis that the increase in adrenal TH mRNA is mediated by increased sympathetic activity.