Binding of catecholamines to connective tissue and the effect upon the responses of blood vessels to noradrenaline and to nerve stimulation

1. Quantitative estimates have been made of the binding of catecholamines to purified collagen and elastin, and the factors influencing this binding have been investigated. 2. Collagen shows no specificity towards the binding of either the (−)‐ or (+)‐isomer of adrenaline or noradrenaline, at low concentrations. Elastin binds the (−)‐isomer of adrenaline and noradrenaline to twice the extent of the (+)‐isomer. 3. Tetracyclines inhibit the binding of catecholamines to collagen and elastin. Oxytetracycline 10⁻⁴ M produces a maximum inhibition of the binding of (−)‐noradrenaline to collagen of 68·4%. 4. The responses of perfused blood vessels to the administration of pulses of catecholamines or to adrenergic nerve stimulation have been measured. 5. Oxytetracycline (10⁻⁴ M) potentiates the amplitude of the response of the rabbit ear artery to noradrenaline and to nerve stimulation, ten‐ and sixfold respectively. 6. Those preparations with a high content of collagen and elastic tissue, the rabbit ear artery and the rat tail, are more susceptible to the potentiating effects of oxytetracycline than one with a low content, the rat anococcygeus. 7. The results of the study suggest that in tissues with a high content of collagen and elastin, binding to extracellular sites is the major mechanism for terminating the response to noradrenaline or to adrenergic nerve stimulation.