The effect of cyclic AMP elevating agents on bradykinin- and carbachol-induced signal transduction in canine cultured tracheal smooth muscle cells.

1. The effects of the beta 2-adrenoceptor agonist, procaterol, on sympathetic neuroeffector transmission were studied in the pithed adrenal demedullated rat to determine if generation of angiotensin II was involved in its effect. Pressor responses were elicited by either electrical stimulation (20 V, 2 Hz) of the entire spinal sympathetic outflow or methoxamine (0.1 mg kg-1, i.v.). 2. Sodium nitroprusside (3 and 5 micrograms kg-1 min-1, i.v.) produced hypotension and the pressor responses to both sympathetic nerve stimulation and methoxamine were reduced. This indicates that decreasing blood pressure in pithed rats reduces pressor responses. Procaterol (10 and 30 ng kg-1 min-1, i.v.) also produced hypotension but did not alter pressor responses to sympathetic nerve stimulation. Nevertheless, procaterol (10 and 30 ng kg-1 min-1, i.v.) did reduce pressor responses to to methoxamine. Together these results suggest that procaterol may have enhanced sympathetic neurotransmitter release. This was confirmed in another series of experiments where procaterol (30 ng kg-1 min-1, i.v.) increased plasma noradrenaline levels during sympathetic nerve stimulation. 3. Captopril (5 mg kg-1, i.v.) produced hypotension and as expected reduced pressor responses to sympathetic nerve stimulation. When the hypotensive effect of captopril was abolished by concomitant vasopressin infusion (1.5-4.5 i mu kg-1 min-1, i.v.), pressor responses to sympathetic nerve stimulation were restored to pre-captopril levels. (ABSTRACT TRUNCATED AT 250 WORDS)