Modification of dobutamine- and terbutaline-induced calcium and fluid secretion from rat salivary glands by atenolol and butoxamine

Cardiac peroxisome proliferator-activated receptor δ (PPARδ) as a new target for increased contractility without altering heart rate

Background and Aims

Agents having a positive inotropic effect on the heart are widely used for the treatment of heart failure. However, these agents have the side effect of altering heart rate. It has been established that peroxisome proliferator-activated receptor δ (PPARδ) is mediated in cardiac contraction, however the effect on heart rate is unknown. Thus, we used an agonist of PPARδ, GW0742, to investigate this issue in the present study.

Methods and Results

We used isolated hearts in Langendorff apparatus and hemodynamic analysis in catheterized rats to measure the actions of GW0742 extra-vivo and in vivo. In diabetic rats with heart failure, GW0742 at a dose sufficient to activate PPARδ reversed cardiac contraction without changes in heart rate. In normal rats, PPARδ enhanced cardiac contractility and hemodynamic dP/dt_max significantly more than dobutamine. Both actions were diminished by GSK0660 at a dose enough to block PPARδ. However, GW0742 at the same dose failed to modify heart rate, although it did produce a mild increase in blood pressure. Detection of intracellular calcium level and Western blotting analysis showed that the intracellular calcium concentration and troponin I phosphorylation were both enhanced by GW0742.

Conclusion

Activation of PPARδ by GW0742 increases cardiac contractility but not heart rate. Thus, PPARδ may be a suitable target for the development of inotropic agents to treat heart failure without changing heart rate.

Relationships of beta-blockers and anxiolytics intake and salivary secretion, masticatory performance and taste perception

OBJECTIVE

Assess the influence of salivary flow on physiological parameters of the stomatognathic system in patients who take beta-blockers or anxiolytic medications.

DESIGN

Sixty patients were divided into three groups based on the following criteria: Group 1, control (n=20; no use of medication); Group 2, use of antihypertensive beta-blockers (n=20); and Group 3, use of benzodiazepine anxiolytics (n=20). Salivary flow was assessed by determining stimulated and non-stimulated flow/minute. The quantification of the sense of taste was determined on a visual analogue scale (VAS) using solutions of 0.9% NaCl (salty), 50% sucrose (sweet), 20% unsweetened coffee (bitter) and 4.2% vinegar (sour). The DMFT index (number of decayed/missing/filled teeth) was determined by a calibrated examination, following the criteria of the World Health Organization (WHO). Masticatory performance was assessed with an Optosil comminution test and Rosim-Ramler equation.

RESULTS

The results did not reveal a significant correlation between salivary flow and masticatory performance (p>0.05). We observed significant decreased non-stimulated salivary flow for Group 2 (p=0.05) when compared to controls. However, taste perception was not influenced by salivary secretion amongst groups. Furthermore, we observed a significant negative correlation between non-stimulated salivary flow and DMFT in Group 1 (p=0.02; r=-0.52).

CONCLUSIONS

Patients under beta-blockers therapy presented reduced non-stimulated salivary flow when compared to controls, without influencing the sense of taste or masticatory performance. The use of anxiolytics did not affect salivary flow and taste perception in the studied sample.

Blockade of isoprenaline-induced fluid and protein secretion by the mandibular glands of the red kangaroo, Macropus rufus, with selective antagonists

Selective and non-selective beta-adrenoceptor antagonists were used to block the increases in fluid and protein secretion caused by sympathomimetic stimulation of the mandibular gland of red kangaroos during intracarotid infusion of isoprenaline. Atenolol or ICI118551 at antagonist:agonist ratios up to 300:1 caused increasing but incomplete blockade of fluid secretion and protein release. Both selective antagonists had equal potency and both antagonists were more effective at blocking protein release than at blocking fluid secretion. Consequently, the mechanisms underpinning fluid secretion are more sensitive to beta-sympathomimetic stimulation than those causing protein release. Propranolol at antagonist:agonist ratios of 300:1 was more potent than the selective antagonists, almost totally blocking the increases in fluid secretion and protein release. The data are consistent with the acini of the kangaroo mandibular gland having both beta(1)- and beta(2)-adrenoceptors and with the increased fluid secretion and protein release by isoprenaline being mediated by both receptor subtypes.

Effect of beta-antagonists on isoprenaline-induced secretion of fluid, amylase and protein by the parotid gland of the red kangaroo, Macropus rufus

Selective and non-selective beta-adrenoceptor antagonists were used to block the increases in fluid, protein and amylase secretion caused by sympathomimetic stimulation of the parotid gland of red kangaroos during intracarotid infusion of isoprenaline. ICI118551 at antagonist/agonist ratios up to 300:1 caused increasing but incomplete blockade of fluid secretion, and protein/amylase release. Atenolol at antagonist/agonist ratios up to 300:1 was only marginally more potent than ICI118551 at blocking the fluid, protein and amylase responses. Propranolol at antagonist/agonist ratios of 30:1 was as effective at blocking fluid and protein secretion as the highest ratios of either atenolol or ICI118551. Simultaneous administration of atenolol (30:1) with ICI118551 (30:1) was not as potent as propranolol (30:1). Thus, the beta-adrenoceptor/s in the acini of the kangaroo parotid gland appear to have antagonist-binding affinities atypical of those found for eutherian tissues. The data are consistent with the gland possessing either a single anomalous beta-adrenoceptor or functional beta(2)-receptors in addition to the beta(1)-receptors which are characteristic of eutherian salivary glands.

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.

Peripheral beta-adrenoreceptors and stress-induced hypercholesterolemia in rats

Three experiments were conducted examining the contribution of beta-adrenergic receptors to stress-induced cholesterol increases. Rats were exposed to 3 90-min sessions of inescapable tailshock, or left undisturbed in their home cage. Propranolol, a nonselective beta-blocker, attenuated the stress-induced cholesterol increase when administered prior to the daily shock session. Atenolol, a beta-1 specific antagonist, also attenuated the stress-induced cholesterol increase. Butoxamine, a beta-2 specific antagonist, had no effect on the stress-induced cholesterol increases. Results are discussed in terms of catecholamine-stimulated free fatty acid (FFA) release as a potential mechanism for producing stress-induced hypercholesterolemia.

Effects on salivary flow rate and composition of withdrawal of and re-exposure to the beta 1-selective antagonist metoprolol in a hypertensive patient population

Secretion rates and composition of unstimulated and chewing-stimulated whole saliva and 3% citric acid stimulated parotid and submandibular-sublingual secretions were studied in 12 hypertensive patients during withdrawal of and re-exposure to antihypertensive pharmacotherapy. All the patients' blood pressures were well controlled by monotherapy with metoprolol, a beta 1-selective adrenoceptor antagonist. Blood pressure measurements and saliva sampling were performed at about 9:30 a.m., 2 h after intake of breakfast, on days 0 (medicated baseline), 7, 14, 28 (nonmedicated experimental values and nonmedicated baseline) and 35 (medicated experimental values). A significant increase in unstimulated whole saliva secretion rate was observed when metoprolol was withdrawn and a corresponding decrease when the drug was reintroduced. A positive correlation was found between diastolic blood pressure levels and chewing-stimulated whole saliva secretion rates. In unstimulated whole saliva and 3% citric acid stimulated submandibular-sublingual secretion, the output of total protein, amylase, potassium, calcium and phosphate was significantly increased during the withdrawal period and decreased when metoprolol was reintroduced. For chewing-stimulated whole saliva, the corresponding changes were restricted to output of total protein and amylase, while for citric acid stimulated parotid secretion, no changes in salivary composition were observed. Finally, in all secretions one or both of the ratios hexosamine/total protein and sialic acid/total protein were affected, indicating a possible effect of beta-adrenoceptor antagonists on salivary protein synthesis.

Effects of the beta-adrenoceptor antagonists atenolol and propranolol on human unstimulated whole saliva flow rate and protein composition

The effects of 1-wk medication with two beta-adrenoceptor antagonists on unstimulated whole saliva flow rate and protein composition were evaluated in 11 healthy young men in a randomized, double-blind, placebo-controlled, cross-over study. Unstimulated whole saliva was collected before each treatment period and then again after 7 days. The saliva was assessed for flow rate, total protein, and hexosamine and sialic acid concentrations and for amylase activity. No significant effect on saliva secretion rate was found. A statistically significant reduction of salivary total proteins was registered during atenolol medication. The amylase activity decreased significantly during treatment with both atenolol and propranolol. Significant changes of the calculated ratios of sialic acid/hexosamine and hexosamine/total protein indicated an alteration in glandular protein synthesis after atenolol treatment.

Effects of the beta-adrenoceptor antagonists atenolol and propranolol on human parotid and submandibular-sublingual salivary secretion

The aim of the study was to evaluate the effects of a beta 1-selective (atenolol 50 mg q.d.) and a non-selective (propranolol 80 mg b.i.d.) beta-adrenoceptor antagonists on human stimulated parotid and submandibular-sublingual (SM-SL) gland secretion. A randomized double-blind, placebo-controlled cross-over ("Latin square") design was used in 19 healthy male volunteers. Stimulated parotid and SM-SL saliva were sampled immediately before and 7 days after the start of each treatment period. Stimulation of salivary secretion was achieved by use of a 3% citric acid solution. Plasma concentrations of propranolol and atenolol were determined from blood samples. The salivary secretion of both glands was assessed for flow rate, amylase, lysozyme, and salivary peroxidase activity and for concentrations of total protein, hexosamine, sialic acid, Ca2+, Cl-, K+, Mg2+, Na+, and PO4(3-). In both parotid and SM-SL secretions, the total protein and phosphate concentrations and amylase activity were significantly decreased during the two active treatment periods. In SM-SL gland secretion, there were significant changes in potassium and calcium concentrations during active treatment as compared with baseline, with potassium showing a decreased and calcium an increased concentration. During atenolol treatment, salivary peroxidase activity decreased significantly in SM-SL secretion. In parotid secretion, the hexosamine/total protein ratio decreased and the sialic acid/hexosamine ratio increased during atenolol treatment, which may indicate an effect on protein synthesis. No significant effects on salivary secretion rates were disclosed.

Effects of the beta-adrenoceptor antagonists atenolol and propranolol on human whole saliva flow rate and composition

The effects of beta-adrenoceptor antagonists on salivary secretion have been extensively studied in animals but not in man. The aim here was to compare salivary flow rate and composition in man during 1 week of treatment with a non-selective (propranolol 80 mg b.i.d.) and a beta 1-selective (atenolol 50 mg o.d.) antagonist with that of placebo. The randomized, double-blind, cross-over ("Latin square") design was used and 42 healthy male volunteers were recruited to the study. The treatment periods were separated by a wash-out period of 2 weeks. Whole saliva was sampled on day 0 (before) and on day 7 during each treatment. The plasma concentration of propranolol and atenolol was determined from blood samples obtained on day 7. Resting saliva was assessed for flow rate, amylase activity and concentration of total protein, hexosamine and sialic acid. Stimulated saliva was assessed for flow rate, pH, buffer pH, amylase activity and concentration of total protein, Ca2+, Mg2+, Na+, K+, Cl- and PO4(2-). In resting as well as stimulated whole saliva both the total protein concentration and the amylase activity were significantly decreased during the active treatment periods (p less than 0.05-p less than 0.001). At lunchtime during atenolol treatment the hexosamine/total protein and the sialic acid/total protein ratios were significantly increased (p less than 0.05-p less than 0.01), suggesting a possible effect on protein synthesis. In addition, the concentrations of Ca2+, PO4(2-), Cl- and Mg2+ were significantly altered during the active treatment periods (p less than 0.05-p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Introduction of cyclic AMP phosphodiesterase into rat submandibular acini prevents isoproterenol-stimulated cyclic AMP rise without affecting mucin secretion

Cyclic AMP phosphodiesterase has been incorporated into isolated rat submandibular acini by hypotonic swelling. This resulted in complete inhibition of the cyclic AMP rise stimulated by isoproterenol (10 microM), but had no effect on the stimulation of mucin secretion. Acini swollen in the absence of cyclic AMP phosphodiesterase showed similar cyclic AMP and mucin secretion responses to those of unswollen acini. The dissociation between cyclic AMP rise and mucin secretion was not due to stimulation of different beta-receptor subtypes since both responses to isoproterenol were inhibited by the beta 1 antagonist atenolol, but not by the beta 2 antagonist, butoxamine. The results are the first to directly demonstrate that a maximally effective concentration of isoproterenol can increase mucin secretion in the absence of a detectable increase in cyclic AMP.

Calcium levels in rat submandibular gland and saliva after sympathetic nerve stimulation in the presence of alpha, beta 1 and beta 2-adrenergic antagonists

Calcium concentration was reduced by 51 per cent compared with unstimulated contralateral glands after 60-min of electrical stimulation to the sympathetic nerve. When the alpha-adrenergic antagonists, phentolamine or phenoxybenzamine, were given 20 min before stimulation, the decrease in glandular calcium concentration (45-47 per cent) was similar to that after nerve stimulation alone; with the selective beta 2-adrenergic antagonist added to the phentolamine, the percentage decrease was similar to that found after phentolamine and sympathetic nerve stimulation only. When atenolol, a beta 1-adrenergic antagonist, was given with phentolamine, there was no secretion after subsequent nerve stimulation, nor was calcium concentration different from that of unstimulated glands. When propranolol (3 mg/kg, body wt), or atenolol + butoxamine (3 mg/kg, body wt), was given prior to stimulation there was a decrease of 21-22 per cent in gland-calcium concentration. Calcium concentration of nerve-stimulated saliva was nearly 6 m-equiv./l, and twice as high with phentolamine prior to stimulation; for butoxamine together with phentolamine the change was similar to that with phentolamine alone. When beta-adrenergic antagonists were given prior to nerve stimulation, concentration of the saliva was either unchanged (propranolol) from that with nerve stimulation alone or somewhat decreased (atenolol + butoxamine). Thus sympathetic stimulation results in activation of alpha and beta 1-adrenoceptors; calcium secretion is principally regulated by the beta-adrenoceptors, and beta 1-receptors have the principal role.