The rat costo-uterine muscle: a preparation of smooth muscle containing a homogeneous population of beta-adrenoreceptors.

This paper describes some histological features of the costo-uterine muscle of the rat together with the effects of some sympathomimetic amines upon contractions evoked by field electrical stimulation of isolated preparations. Light and electron microscopy confirmed that the costo-uterine muscle of the rat consists of smooth muscle bundles, arranged longitudinally and interspersed with collagen. There were close contacts between individual cells within bundles. No axon profiles were observed. Histochemical techniques revealed only sparse catecholamine fluorescence at the border of the tissue in association with blood vessels. Isoprenaline, fenoterol, adrenaline, noradrenaline, salbutamol and phenylephrine consistently inhibited contractions evoked by field stimulation (40V, 30Hz, 2 ms for 5 sec every 200 sec). In contrast, tyramine was without effect upon electrically evoked contractions in concentrations of up to 200 mumol/l. The slopes of the log concentration-response curves of effective amines were similar, and all of these were capable of producing 100% inhibition of contraction. The potencies of the amines relative to isoprenaline = 100 were: fenoterol 135; salbutamol 16; adrenaline 16; noradrenaline 0.7; phenylephrine 0.1; tyramine less than 0.001. Propranolol, added to preparations in the absence of inhibitors of amine uptake and alpha-adrenoreceptors, competitively antagonised the effects of the amines. Schild plots had slopes which did not differ significantly from minus one, and the mean pA2 values fell within a narrow range, e.g. 8.65 with salbutamol; 9.20 with fenoterol. Mean pA2 values for propranolol with noradrenaline and isoprenaline were unaffected by the combined presence of phentolamine (10 mumol/l), cocaine (10 mumol/l), and corticosterone (10 mumol/l). The potencies of the agonists were also unaffected by the presence of these drugs.(ABSTRACT TRUNCATED AT 250 WORDS)