beta 1-Adrenergic regulation of cyclic nucleotide levels and potassium fluxes in rat parotid gland

Interaction between substance P and beta-adrenergic agonists in the modulation of the secretion of fluid and protein by the rat submandibular gland

The interactions between substance P and beta-adrenergic agonists such as isoprenaline, dobutamine and terbutaline in the control of the secretion of fluid and protein from the rat submandibular gland have been examined. Substance P elicited large volumes of saliva whereas isoprenaline, dobutamine and terbutaline elicited small volumes only. The secretion of fluid in response to substance P was markedly enhanced when substance P was administered in combination with isoprenaline or dobutamine but not when it was administered in combination with terbutaline. Isoprenaline elicited large amounts of protein, whereas substance P elicited small amounts. The secretion of protein in response to isoprenaline did not change when isoprenaline was administered in combination with substance P. The secretion of fluid and protein induced by substance P in combination with isoprenaline was antagonized by metoprolol and by spantide, but it was unaffected by pretreatment with ICI118551. These results suggest that in the rat submandibular gland stimulation of beta1-adrenoceptors but not of beta2-adrenoceptors potentiates the secretion of fluid that is induced by stimulation of tachykinin receptors, whereas stimulation of tachykinin receptors does not enhance the secretion of protein that is induced by stimulation of beta1-adrenoceptors.

Enhancement of stimulation-evoked catecholamine release from cultured bovine adrenal chromaffin cells by forskolin

Acetylcholine (ACh) increased cyclic AMP levels in cultured bovine chromaffin cells with a peak effect at 1 min after the addition. Pretreatment with forskolin (0.3 microM) enhanced the ACh-evoked cyclic AMP increase. The catecholamine (CA) release induced by ACh was enhanced by forskolin, but forskolin alone did not enhance the CA release. The effect of forskolin increased dose-dependently up to 1 microM, but decreased at higher concentrations. Dibutyryl cyclic AMP (DBcAMP) also enhanced ACh-evoked CA release, but the effect was less potent than that of forskolin. Forskolin enhanced both [3H]norepinephrine ([3H]NE) and endogenous CA release evoked by 30 mM K+ from cells that were preloaded with [3H]NE. The effects of forskolin were substantial when CA release was evoked with low concentrations of ACh or excess K+, but decreased with higher concentrations of the stimulants. Forskolin also enhanced the CA release induced by ionomycin and veratrine, or by caffeine in Ca2+-free medium. The potentiation by forskolin of the ACh-evoked CA release was manifest in low Ca2+ concentrations in the medium, but decreased when Ca2+ concentration was increased. These results suggest that cyclic AMP may play a role in the modulation of CA release from chromaffin cells.

Hypertrophy and dysfunction of parotid gland induced by chronic stimulation of beta 1-adrenergic receptors

The present study was carried out to determine the beta-receptor subtype responsible for the hypertrophy and dysfunction of parotid glands in rats chronically treated with isoproterenol (ISP). Treatment with dobutamine (DBT), a beta 1-agonist, (30 mg/kg twice a day for 4 days) produced a significant enlargement of the parotid gland just as in the ISP-treated rats. The effects of secretagogues on amylase release and ISP-induced cyclic AMP accumulation were markedly decreased in the parotid tissue of the treated rats. Co-administration of the beta 1-antagonists metoprolol and acebutolol clearly inhibited the development of parotid enlargement and its secretory dysfunction induced by ISP or DBT. Procaterol treatment (30 mg/kg, twice a day for 4 days) did not cause any dysfunction or any increase in the gland weights. These results indicate that both hypertrophy and dysfunction of the rat parotid gland, which were observed in chronic treatment with ISP, may result from chronic stimulation of beta 1-adrenoceptors.

Isoproterenol inhibition of potassium release from rat parotid gland

The mechanism of isoproterenol-induced inhibition of potassium release from rat parotid slices has been determined. Spontaneous potassium release from the slices was significantly inhibited by isoproterenol at concentrations above 10(-6) M. This isoproterenol effect was completely abolished in the presence of propranolol (10(-5) M) and ouabain (10(-3) M) and was abolished during Na+-exclusion from the incubation medium. Isoproterenol caused an enhancement of the microsomal Na+, K+-ATPase activity at concentrations above 10(-5) M, and this activity was inhibited by propranolol (10(-5) M). The stimulatory effect of isoproterenol on the Na+, K+-ATPase exhibited a strong correlation with the inhibition of potassium release on each dose of isoproterenol. Moreover, dibutyryl cyclic AMP at concentrations above 10(-4) M inhibited potassium release in a dose-dependent manner and cyclic AMP caused an enhancement of the microsomal Na+, K+-ATPase activity. These results suggest that the inhibitory effect of isoproterenol on potassium release is clearly derived from the elevated Na+, K+-ATPase activity and that it may in part be mediated by cyclic AMP.