Bretylium and the degeneration contraction of the sympathetically innervated periorbital smooth muscle in the rat.

Abstract

AbstractThe ability of bretylium to delay the start of the degeneration contraction of the sympathetically innervated periorbital muscle has been studied in conscious rats. The sympathomimetic and neuron blocking action of bretylium at the doses most frequently used were also tested. A low dose, 0.5 mg/kg, that induced no measurable neuron block still delayed. The delay caused by local injection into the muscle exceeded the duiation of the neuron block. These findings indicate that the bretylium‐induced delay is not caused by neuron block and that the delaying action mainly is exerted on the terminal parts of the neurons. Bretylium given repeatedly postponed the onset of the degeneration contraction at least 6 to 10 hrs. Later the processes responsible for the degeneration contraction appeared to develope despite the treatment. Within 4 hrs preceding or just including the start of the degeneration contraction the time of injection was very critical for the effect of bretylium on the time course of the contraction. An injection of bretylium during an ongoing degeneration contraction interrupted the contraction and displaced the latter part for several hrs. Before the interruption the drug seemed to enhance the transmitter release. It appeared that early during the degeneration contraction there are nerve endings at different stages of degeneration on which bretylium acts differently.