Structural and functional studies of the effects of sympathetic nerve stimulation on rabbit submandibular salivary glands

Continuous sympathetic stimulation at 8-10 Hz caused intense vasoconstriction in the gland, so stimulation was generally given in an interrupted pattern to minimize this detrimental effect on secretion. Only a small increase in fluid secretion occurred; it became thick and tended to block the cannula; therefore in later experiments the main duct was not cannulated. After sympathetic stimulation there was substantial degranulation of acinar cells. However, as this was accompanied by little movement of water, the secreted mucosubstance distended the ductal lumina. The granular tubule cells were unchanged by sympathetic stimulation. Use of selective blocking agents revealed that the sympathetically-evoked secretion of acinar mucin was mediated mainly via beta-adrenoreceptor activation. As stimulation of the sympathetic nerves alone caused little additional formation of fluid, the effects of superimposing continuous low frequency sympathetic stimulation onto a background of low parasympathetic secretion were compared with similar parasympathetic stimulation alone of the contralateral gland. These double nerve stimulations did not augment the volume of fluid secreted, or cause morphological changes additional to those from parasympathetic stimulation alone. Nevertheless, it is likely that, under natural reflex conditions, sympathetic impulses can increase the amount of acinar mucosubstance secreted.