In Vivo Studies of Individual Mucous Glands in the Frog

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Abstract
Individual mucous glands in the toe web were studied in curarized decerebrate frogs using vital microscopy in combination with still or motion photomicrography. By changing the focus position to different levels various structures in the gland could be identified and their changes during glandular activation studied. The first visible effect of nerve stimulation was a contraction of the myoepithelium and probably also structural changes of the secretory epithelium resulting in a narrowing of the glandular lumen. Following this, the tricuspid valve opened and secretion was ejected. The latency and time course of the contractile response to nerve stimulation were determined and the influence of the number of stimuli on the duration of the contraction and relaxation phases was analyzed. Comparisons were made with reflex activation of the gland as well as with neurohormonal stimulation. The myoepithelial contraction was found to be under adrenergic control. Of the smooth‐muscle stimulants tested only Substance P induced contractions. The time course of the ionic outflow from the toe web was determined by conductance measurements in the fluid surrounding the web and compared with the visually observed phenomena. The initial outflow was concomitant with the phasic myoepithelial contraction but a continued secretion could also be observed and recorded from glands kept in a steady state of contraction by iterative nerve stimulation. The functions of the toe web glands were found to be critically dependent on a maintained circulation in the surrounding capillary network.