Electrical stimulation of the sciatic nerve (2 Hz, 1 ms, 3 v, 40 pulses at 5 minrnintervals) increased hind limb vascular resistance in rabbits. However, whenrnguanethidine was applied the nerve stimulation induced a decrease in hind limbrnresistance and an increase in hind limb blood flow which was pulse duration-,rnfrequency- and voltage dependent. The nerve induced responses were not affectedrnby cholinergic or adrenergic blockade.rnThe nerve induced vasodilatory responses were mimicked by local intraarterialrninfusions of substance P, both of which could be diminished by L-NAME (arnnitric oxide synthesis blocker). In another set of experiments, CP-96, 345, a highlyrnselective antagonist of neurokinin- l receptor, diminished both the nerve-induced asrnwell as the substance P-induced decreases in hind limb vascular resistance. NeitherrnL-NAME nor CP-96,345 affected the vasodilatory responses elicited by adenosine.rnIn another set of experiments in sheep, L-NMMA (another nitric oxidernsynthesis blocker) was infused into the lateral ventricles. NO blocking centrally wasrnassociated with an increase in free water clearance and a decrease in plasma AVPrnlevels during the infusion. Blood pressure decreased and heart rate increasedrnduring the infusion. O-NMMA had little effect.rnIn a similarly prepared sheep, as the previous experiment, water deprivationrnfor 96 hours resulted in a significant increase in plasma A VP and ANG-II levels asrnwell as a significant increase in the levels of cerebrospinal fluid ANG-I/, NPYandrnCGRP levels all of which paralleled to an increase in plasma osmolality. The levelsrnof the neuropeptides decreased when water was allowed and animals hydrated.rnThe last study was conducted in thirteen children with moderate to severerndegree of dehydration secondary to diarrhoea who were admitted to the ORT centrernat Ethio-Swedish Paediatric hospital for rehydration with DRS. Plasma samplesrntaken before the start of DRS therapy and another sample col/ected after fu llrnhydration were compared for various variables. Plasma osmolality, sodium andrnpotassium were lower than controls before DRS therapy all of which increa sed afterrnfull hydration was achieved. Tota l plasma protein, measured to assess the state ofrnhydration, decreased after the DRS therapy.rnThe results suggest the importance of the above mentioned neuropeptidesrnin hydromineral balance and blood flow control in mammals. The involvement of thernL-arginine/ NO pathway in blood flow is also demonstrated and the possible centralrnin volvement of this pathway in hydromineral balance and release of somernneuropeptides is suggested