Relative contributions of ATP and noradrenaline to the nerve evoked contraction of the rabbit jejunal artery. Dependence on stimulation parameters.

Isotonic contractions of the rabbit jejunal artery were evoked by perivascular nerve stimulation with trains of 10 or 100 stimuli at 2 Hz or 10 Hz. Short trains of stimuli elicited contractions that were totally resistant to alpha-adrenoceptor blockade (0.1 mumol/l prazosin) but blocked by alpha,beta-methylene ATP (1 mumol/l). A substantial noradrenergic component of contraction comprising about 50% of the total could be evoked by adjusting the stimulation parameters (increasing the frequency and/or number of stimuli in a train). The noradrenergic and the purinergic components are derived from sympathetic nerves as both were blocked by TTX and the adrenergic neurone blocker guanethidine (3 mumol/l). It is concluded that the contraction of the rabbit jejunal artery to short trains of stimuli is predominantly purinergic, a noradrenergic component only being revealed at higher frequencies of stimulation or during longer trains of stimuli. The purinergic component of contraction is derived from sympathetic nerves and not from a separate population of purinergic nerves.