Sympathetic and β ‐Adrenergic Stimulation of Parotid Salivary Secretion in Sheep

The effects of sympathetic and β ‐adrenergic stimulation (with isoprenaline) on the secretion of parotid saliva were examined in anaesthetized and totally pithed preparations of sheep. This was studied against a background of spontaneous secretion or of secretion augmented by pilocarpine. In addition to the previously established α‐ adrenergic sympathetic motor effect causing mechanical expulsion of saliva, a β ‐ adrenergic secretory response has now been identified. Characteristically, the secretory effect was obtained from electrical stimulation of the cervical sympathetic nerve trunk when lower frequencies or shorter pulse durations were used. This secretory effect and similar responses to isoprenaline were blocked by propranolol. Two phenomena confirmed that the β ‐adrenergic responses to sympathetic stimulation were secretory: namely there were nett increases in the amount of fluid formed (by as much as 128% or as great as 93·9 mg saliva.gm gland ‐1 .min ‐1 ), and they were accompanied by increases in the protein content of the parotid saliva (up to 8–9 fold). The amounts of protein rose from resting levels of 10–170 µg.ml ‐1 (expressed as equivalents of bovine serum albumin) to as high as 840µg.ml ‐1 in response to single i.v. injections of 2 µg.kg ‐1 of isoprenaline, and to 1240µg.ml ‐1 with cervical sympathetic nerve stimulation. It is concluded that there is a sympathetic secretory innervation in parotid salivary glands of sheep that is mediated by β ‐adrenergic mechanisms.