Thromboxane A2 augments adrenergic neurotransmission.

Platelet microsomes were utilized to generate thromboxane A2 in rabbit isolated superior mesenteric arteries to assess the effects of thromboxanes on neurotransmission. The microsomes were added to rabbit isolated mesenteric arteries to determine effects of thromboxanes on the following: 1) contractile force; 2) neurogenic contractions; 3) norepinephrine-induced contractions; and 4) electrically stimulated norepinephrine release. Immunoreactive thromboxane B2 concentrations were measured and all responses of the microsomes were correlated with thromboxane production. The microsomes generated thromboxane B2, increasing bath concentrations form 529 +/- 63 pg/ml to 4249 +/- 385 pg/ml at the highest dose. Basal force was increased 0.53 +/- 0.16 g by the highest microsome dose. Neurogenic force generation was enhanced to 303 +/- 57% of control while norepinephrine release was increased to 270 +/- 98% of control. Norepinephrine-induced contractions also were enhanced by the microsomes. Exogenous thromboxane B2 augmented adrenergic neurotransmission and norepinephrine-induced contractions only at concentrations exceeding 1 microM. These results are consistent with a potentiative neuromodulatory role of thromboxane A2 which is both of a pre- and postjunctional nature.