Dusit Jirakulsomchok

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

Saliva was elicited from rat salivary glands by terbutaline at i.p. doses of 1, 5, 10 and 25 mg/kg b.wt. but not by doses of 0.1 or 0.5 mg/kg b.wt. Dobutamine elicited no secretion at 1 or 2 mg/kg but did at 5, 10 and 25 mg/kg b.wt. At 5 mg/kg terbutaline evoked nearly maximal volumes but with dobutamine, volumes were small at this dosage. At dosages of 10 and 25 mg/kg volumes with the two agonists were similar for parotid, but with submandibular, the volumes evoked by dobutamine were nearly two times as high as those elicited by terbutaline. Mean [Ca] of parotid saliva was also similar at all dosages of dobutamine (approximately 12 mEq/liter) and generally similar at all dosages of terbutaline (11-15 mEq/liter). Mean [Ca] of dobutamine-elicited submandibular saliva was approximately 6, 7 and 8 mEq/liter at 5, 10 and 25 mg/kg b.wt, respectively. With parotid, [Ca] was approximately 10 mEq/liter at 1, 5 and 10 mg/kg b.wt. but increased to 16-18 mEq/liter at 25 mg/kg. The time course of calcium secretion is described for both agonists at each dosage. [Ca] of both glands was decreased 60 min after i.p. injection of 10 or 25 mg/kg doses of dobutamine or terbutaline but was not changed by 5 mg/kg doses. Administration of 10 mg/kg of atenolol, the selective beta 1 antagonist, 20 min prior to injection of a 10 mg/kg dose of either terbutaline (beta 2 agonist) or dobutamine (beta 1 agonist) blocked secretion from both glands, and prevented the usual agonist-induced reduction in glandular concentration of calcium. Butoxamine, on the other hand, did not modify effects of terbutaline on fluid secretion or depletion of glandular calcium; it did partially inhibit dobutamine-induced fluid and calcium secretion but not depletion of glandular calcium. The present data suggest that beta adrenoceptors of salivary glands are predominantly of the beta 1 subtype and that it is these that regulate calcium and fluid secretion. On the basis of the data with the antagonists, it is concluded that terbutaline activates beta 1 rather than beta 2 receptors since the beta 1 antagonist but not the beta 2 antagonist blocked secretory responses to terbutaline.

Total Salivary Calcium and Amylase Output of Rat Parotid with Electrical Stimulation of Autonomic Innervation

Summary Calcium levels of rat parotid saliva evoked by stimulation of the auriculotemporal nerve are high (11 mEq/1) and in fact, higher than those evoked by stimulation of the sympathetic innervation. Total calcium output in the cholinergically-evoked saliva is also very high but the depletion of gland levels is insignificant 20 or even 60 min after the initiation of stimulation. With sympathetic stimulation, there is a closer correlation between gland depletion and total output of calcium in the saliva. These findings suggest that the uptake mechanism for calcium with cholinergic stimulation is more rapid than that found with adrenergic stimulation. The high levels of calcium in the cholinergically evoked saliva are also not due to acetylcho-line-induced release of catecholamines since calcium levels of cholinergically-evoked saliva are the same whether or not adrenergic blocking agents are present. The total output of amylase in the saliva when sympathetic stimulation is employed is about five times greater than that found with cholinergic stimulation, and the reduction in gland amylase under these two conditions of stimulation reflect these same relations. The data also show that there is a parallelism between depletion of gland amylase and calcium and concentration and total output of these two moieties in the saliva when adrenergic stimulation is used but that no parallelism between secretion of these substances is seen with cholinergic stimulation. It is suggested that with adrenergic stimulation all of the amylase is packaged together with calcium and the two are secreted together; however, with cholinergic stimulation, only a fraction of the total calcium is packaged with the amylase, and the remainder is transferred from blood through the gland to the saliva. Thus, two separate routes for secretion of calcium exist with cholinergic stimulation, and the pathways with the two kinds of nerve stimulation are different.

Effects of adrenergic agonists on electrolyte transport in perfused salivary duct of rat.

The Na and Cl absorption and K secretion that occur in the main duct of rat submandibular gland are affected by adrenergic actions. The specific effects of stimulation of alpha-, beta 1- and beta 2-adrenergic receptors on net transepithelial fluxes of Na, K and Cl were investigated in microperfused main excretory duct of rat submandibular gland. Administration of methoxamine (2.5 micrograms . kg-1 . min-1, i.v.) resulted in marked decreases in net efflux (or absorption) of Na (38%) from the duct into the interstitial fluid and net influx (or secretion) of K (20%) from interstitial fluid into the ductal lumen without any effect on net efflux or reabsorption of Cl. A higher dose of methoxamine (5 micrograms . kg-1 . min-1, i.v.) produced further inhibition of net fluxes of Na and K without affecting net flux of Cl. Dobutamine (50 micrograms . kg-1 . min-1, i.v.) enhanced net effluxes of Na (40%) and Cl (300%) from the lumen but did not alter net K influx into the lumen. When the dosage of dobutamine was increased to 200 micrograms . kg-1 . min-1, an inhibition of net influx of K (28%) into ductal fluid was observed in addition to enhanced net fluxes of Na and Cl from the lumen. Administration of terbutaline (15 and 30 micrograms . kg-1 . min-1, i.v.) decreased net influx of K (30-40%) and increased net efflux of Cl (280%) without affecting net efflux of Na.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of electrical stimulation of the sympathetic nerve on the levels of β-adrenergic and cholinergic muscarinic receptors and cyclic nucleotides in rat salivary glands

After 30 and 60 min of stimulation, there were decrease of 16 to 19 per cent in beta-adrenoceptors in rat submandibular and parotid glands; a 10-min stimulation caused no change. Pre-incubation of the reaction mixtures (stimulated glands) with atenolol, a beta 1-antagonist, prevented most dihydroalprenolol (DHP) binding, but with butoxamine, a beta 2-antagonist, DHP binding was nearly complete. Thus the beta-receptor was of the beta 1-subtype. Muscarinic receptors of parotid gland showed no change after 10 min stimulation; after 30 min there was an increase of 12 per cent, and after 60 min, of 28 per cent. With submandibular gland, there was also no change at 10 min but, at 30 min, there was a 25 per cent increase, and at 60 min, a decrease of 18 per cent. Cyclic-AMP levels of parotid gland were markedly elevated after 10 min of stimulation (9-fold increase above controls) but, at 30 and 60 min, there was only a 1.6-fold increase. In submandibular gland, cyclic-AMP increased 10-fold at 10 min; at 30 min it was 2.5 times control levels and at 60 min, 1.9 times. Cyclic-GMP levels of parotid gland increased 34-fold after 30 or 60 min of nerve stimulation, but only 1.6-fold at 10 min. With submandibular gland, there was a 22-fold increase at 10 min, but at 30 and 60 min this was 15- and 12-fold, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Secretory responses to autonomic stimulation of rat salivary glands following reserpine treatment

The response to stimulation of the parasympathetic innervation to parotid or submandibular glands of reserpinized rats was altered from that of untreated rats. Thus, acute reserpinization, like other types of sympathectomy, resulted in increase in volume of parasympathetically-evoked parotid or submandibular saliva when comparison was made with evoked saliva from untreated glands. As norepinephrine is depleted by reserpine, there was no response to stimulation of sympathetic nerves to these reserpinized glands. Adrenergic receptors were normally activated by administration of autonomic agonists. Thus a single high dose of reserpine can cause the same effects as those induced by chronic administration of low doses of reserpine, i.e. a 3-fold increase in calcium (Ca) concentration of submandibular gland but no change in Ca concentration of parotid gland. Although sympathetic stimulation caused no change in Ca concentration of submandibular or parotid glands of reserpine (acute)-treated rats, stimulation with isoproterenol (25 mg/kg, i.p., 60 min) produced a 32-35 per cent decrease in glandular Ca concentration from that of unstimulated reserpinized glands. Glands of untreated rats showed a 52 per cent depletion after 60 min of isoproterenol stimulation; however, Ca output in parotid saliva from reserpinized rat for 60 min of stimulation was not changed from that of untreated rats, but that of submandibular saliva was two times greater. Ca concentration of submandibular saliva was unchanged during 60 min-stimulation of reserpine-treated rats, but that of untreated rats decreased.

Calcium concentration of salivary glands and saliva after chemical or surgical sympathectomy.

Calcium concentration of the submaxillary (SM) gland of adult rat was increased to 2-3 times control levels 24 h after a single high dose of reserpine (RES) (5 mg/kg body weight), 6-hydroxydopamine (6-OHDA) (20 mg/kg body weight), or surgical removal of a superior cervical ganglion (Sx). The increase could also be induced within 24 h after a single injection of lower doses of RES (0.05, 0.5 mg/kg body weight). Increase in calcium concentration in the parotid (PA) was not found under any of the above conditions, but did occur transiently at times within 24 h. The increase in glandular calcium concentration was found to be temporally related to depletion of norepinephrine (NE). The time frame for initiation of calcium changes was not the same for chemical and surgical sympathectomy (Sx). Increase in calcium concentration occurred after onset of sympathectomy-induced degeneration secretion; the onset varied with the kind of sympathectomy, and was seen 1 h after drug administration with either RES or 6-OHDA, but not until about 13 h after surgical Sx. Similarly, NE was markedly depleted, but later with surgical than with chemical Sx. Furthermore, with both kinds of sympathectomy, depletion of NE occurred earlier with PA than with SM, since normal basal levels of NE of SM are 3 times as great (3400 ng/g wet weight), compared with PA levels (1300 ng/g wet weight). The fact that NED was the neurotransmitter eliciting the degeneration secretion was confirmed physiologically by examination of the composition of this secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of sympathetic nerve stimulation in the presence of specific adrenergic antagonists on Na, K, and Cl transport in perfused rat submandibular duct

The role of beta 1- and beta 2-adrenoceptors in the modification of Na, K, and Cl transport in submandibular main duct of rat perfused with bicarbonate saline solution was studied with direct sympathetic nerve stimulation (4 V, 5 ms, 20 Hz) in the presence of specific adrenergic antagonists. Nerve stimulation in the presence of phenoxybenzamine (3 mg/kg b. wt., i.p.) and butoxamine (3 mg/kg b. w.t., i.p.) enhanced Na (44%) and Cl (35%) absorption but inhibited K (24%) secretion. On the other hand, the nerve-evoked response in the presence of phenoxybenzamine and metoprolol (3 mg/kg b. wt., i.p.) decreased K (19%) secretion without any changes in Na and Cl absorption. Therefore, the data suggest that beta 1- and beta 2-adrenoceptors may be present in the duct cells and activation of these receptors can modify electrolyte transport. Furthermore, prior administration of phenoxybenzamine, butoxamine, and metoprolol suppressed the effects of sympathetic nerve stimulation on transductal fluxes of Na, K and Cl; this indicates that the dosages of antagonists used were sufficiently high to block a nerve-evoked response.

Effects of α, β1, and β2 adrenergic antagonists on the Na and K concentrations of sympathetic-nerve stimulated rat saliva

Abstract Selective α and β 1 and β 2 adrenergic antagonists were used with electrical stimulation of the sympathetic innervation to parotid and submandibular glands of rats in order to delineate the role of the β 1 and β 2 adrenoceptors in regulation of salivary flow rate, Na reabsorption and K secretion from these glands. In parotid gland, [Na] of sympathetically evoked saliva in the presence of phentolamine (3 mg/kg, i.p.) was not different from that of nerve-evoked saliva in the presence of phentolamine and butoxamine (3 mg/kg, i.p.), except for the last 20 min of stimulation when [Na] of nerve-elicited saliva was higher.[K] of saliva with sympathetically evoked stimulation was the same in the presence of phentolamine alone as it was or in the presence of phentolamine and butoxamine. Again, there was no difference in salivary flow rate induced by either kind of stimulation, except for the first 10 min of stimulation, during which salivary flow rate of nerve-evoked saliva in the presence of phentolamine was lower than under the other conditions indicated. On the other hand, with submandibular gland, [Na] and [K] of nerve-elicited saliva in the presence of phentolamine were generally higher than levels of sympathetically evoked saliva in the presence of phentolamine and butoxamine. However, salivary flow rate of nerve-evoked saliva in the presence of phentolamine was generally lower than that of sympathetically evoked saliva in the presence of phentolamine and butoxamine. Thus, it is possible to conclude that β 1 and β 2 adrenoceptors are present on acinar cells as well as on duct cells, and activation of β 1 and β 2 adrenoceptors can alter primary acinar secretion rate, Na reabsorption and K secretion of the duct cells.

α- and β-Adrenergic Effects on Na, K, Cl, and HCO3 Transport in Perfused Salivary Duct during Sympathetic Nerve Stimulation

Summary Effects of stimulation of α- and β-adrenergic receptors on transport of Na, K, and Cl by ductal epithelial cells were studied in luminally perfused main excretory duct of rat submaxillary gland with isotonic bicarbonate-saline solution. Either phenoxybenz-amine or propranolol (5 mg/kg body wt) was given i.p. 25 min prior to the stimulation of the sympathetic innervation to the gland. Stimulation of the sympathetic nerve in the presence of phenoxybenzamine decreased net Na and K fluxes by 26 and 39%, respectively, while net efflux of Cl was increased by 70% and net influx of HCO3 about 65%. Stimulation of the sympathetic nerve in the presence of propranolol caused a decrease of 39% in net efflux of Na and a decrease of 32% in net influx of K; no changes in net flux of Cl and HCO3 were observed. Stimulation of the sympathetic nerve modifies electrolyte transport by duct cells, and present work shows that a reduction in net fluxes of Na and K can be induced by either α- or β - adrenergic stimulation. There was, however, a distinct difference between effects of α- and β-adrenergic receptors on net fluxes of Cl and HCO3. Thus, activation of β-adrenergic receptors enhanced net Cl efflux, and net HCO3 influx, whereas no changes in net flux of Cl and HCO3 were oberved with α-adrenergically evoked responses.

Effects of Saliva from Chronically Reserpinized Rat on Na and K Transport in Perfused Main Excretory Duct of Submandibular Gland of Normal Rat

Abstract Reserpine (RES) (0.5 mg/kg body wt, ip) was administered to rats for 7 days. On Day 8 saliva was evoked from these animals by intraperitoneal injection of pilocarpine nitrate (10 mg/ kg body wt) and saliva from submandibular and parotid glands was collected separately. These collected salivas were used to perfuse through the main ducts of the submandibular glands of normal rats. After a control period of perfusion of the main duct with bicarbonate saline solution, parotid saliva from RES rats was perfused through the duct followed by regular perfusion. There was inhibition of Na absorption (22%) and K secretion (23%). Moreover, when submandibular saliva from treated rat was perfused through the main duct prior to regular perfusion, there was a decrease in Na absorption (31%) and K secretion (28%). In contrast, perfusion of the main duct with either parotid or submandibular saliva from normal rats caused no significant changes in Na and K transport. The present experiments confirm previous studies that there is some Na-inhibitory factors) present in saliva of the chronically RES-treated rat.