Charlotte A. Schneyer

Accelerated development of salivary glands of early postnatal rats following isoproterenol.

Summary Chronic administration of the sympathetic amine isoproterenol to early postnatal rats (1–4 days old at time of first injection) for selected periods results in marked increases in the size of the submaxillary and parotid glands, and to a less extent, in the size of the heart. The sublingual salivary gland is unaffected. Other organs are reduced in size, especially after 3 to 5 weeks, when a retardation in body size and weight also becomes pronounced. A clear effect on differentiation of the parotid and submaxillary gland has been observed with isoproterenol treatment. The effect is most marked in parotid, where acini develop much earlier than in the litter-mate controls and striated ducts earlier become more abundant. The effects of isoproterenol on differentiation are separable from the influence of the drug on cell size.

Ultrastructural changes of rat parotid glands induced by a diet of liquid Metrecal.

SummaryThe ultrastructure of parotid glands was studied in rats fed a diet of liquid Metrecal for two weeks and compared with that of parotid glands of control rats which received a diet of Purina lab chow. The liquid diet induced major alterations of acinar cells, but other parenchymal components were apparently unaffected.Most acinar cells of experimental rats were atrophic and some of these were undergoing necrosis. Lipid droplets and dense bodies (believed to be lysosomes) were numerous in atrophic cells. The Golgi apparatus, quantity of secretory granules, and intercellular canaliculi were smaller than in acinar cells of control rats.Such findings suggest that the secretory process was impaired and support the conclusion that parotid glands of rats maintained on a liquid diet are physiologically less active than those of chow fed rats. The decreased activity, as previously reported, may result from reduced masticatory activity.

REGULATION OF SALIVARY GLAND AMYLASE ACTIVITY

Secretory activity by digestive glands is characteristically periodic. This periodicity is distinguishable even in such glands as rat pancreas and human submaxillary and parotid, which exhibit a tendency toward continuous basal secretion. During periods of activity several of the digestive glands discharge relatively large quantities of hydrolytic enzymes into carrier secretory fluid and, perhaps, into the blood. In such cases a relationship between secretory discharge and ensuing reconstitution of secretory protein stores in the gland has frequently been assumed; the clearest exposition of this has been that of Langstroth et a1.I Langstroth and his co-workers selected the pancreas as their biological experimental system. Here, initial secretion in response to an appropriate stimulating agent involves depletion of preformed gland stores of secretable protein, for example, hydrolytic enzymes and enzyme precursors. Cessation of stimulation leads eventually to replenishment of gland protein stores as a result of synthesis of new protein by the pancreas cells. This replenishment process is unaffected by blockage of parasympathetic influences. Langstroth and his co-workers postulated that intermediate reactions in the synthesis process are reversible. Adherence to the law of mass action would then link synthesis rate to degree of depletion. The assumptions are simple and, in the light of newer work on amino acid activation and incorporation, they are also plausible. Additional information concerning actual synthesis rates a t various stages of the secretion cycle is, however, urgently needed. In contrast to the sequence of events described for the pancreas and characteristic also of the parotid gland-that is, stimulation, depletion and then synthesis-the pattern of active enzyme accumulation in the submaxillarysublingual gland of the rat is wholly different. Stimulation of this gland, instead of depleting the tissue of amylase, a secretory enzyme, leads to a rapid, progressive, and appreciable rise in gland amylase level. This rise is dependent on continuing parasympathomimetic influence. Evidence indicates that amylase accumulation in the submaxillary-sublingual gland of the rat is the result, as in the pancreas, of synthesis of new enzyme. In the case of the submaxillarysublingual gland, however, this synthesis is subject to relatively direct regulation by the parasympathetic branch of the autonomic nervous system.

The influence of the sympathetic nervous system on the development of β-adrenergic receptors in the rat submandibular salivary gland

During the development of the rat submandibular gland (SMG) there is a clearly-defined sequence in the maturation of the beta-adrenergic receptor/adenylate cyclase-linked stimulus-secretion coupling system. The sympathetic nervous system does not become functionally linked to the exocrine process in the SMG until approximately six days after birth. The temporal correlation of the ingrowth of catecholamine-containing nerve processes, the appearance of beta-adrenergic receptors and the functional coupling of the stimulus-secretion system suggested the possibility of a cause and effect relationship between the appearance of the catecholamine-containing nerves in the gland and the maturational increase in the number of beta-adrenergic receptors. Chemical sympathectomy in neonates did not effect the time of appearance or the number of beta-adrenergic receptors seen in the developing gland. However, chronic isoproterenol treatment resulted in accelerated maturation of the gland with a concomitant premature appearance of the beta-receptors. These data suggest that the increase in the number of beta-adrenergic receptors which normally occurs in the developing gland at 5-6 days after birth is a specifically-programmed step closely associated with the degree of maturation attained by the cells and is independent from the ingrowth of catecholamine-containing nerves.

Role of Autonomic Pathways in Disuse Atrophy of Rat Parotid

Summary Selective section of the auriculotemporal nerve and removal of the superior cervical ganglion in rats fed Metrecal or chow resulted in differing degrees of parotid weight reduction. The maximum reduction (50%) in weight occurred with PxSx glands of rats fed Metrecal or chow and with Px glands of rats fed Metrecal. The weight reduction in normally innervated glands of rats fed Metrecal was about 17% less than this maximal reduction. This residual autonomic influence was found to be mediated by the parasympathetic innervation and may represent a trophic effect. The sympathetic innervation, nonetheless, played a role in mediating effects of activity on parotid size. About 13% of the 33% reduction in parotid weight (disuse atrophy) induced by liquid diet was attributed to the sympathetic innervation and about 20% to the parasympathetic innervation. In view of the altered physiological status of the gland with surgical denervation, liquid diet remains a more effective and convenient means of producing disuse atrophy of parotid gland than denervation. This work was supported in part by grants from the U.S. Public Health Service, HD00174 and DE 02110. The authors thank Mead Johnson Co. for supplying the Metrecal.

Neural Regulation of Calcium and Amylase of Rat Parotid Saliva

Summary The course of amylase and calcium secretion into saliva is described under diverse conditions of autonomic stimulation of parotid. Of special importance is the fact that for the first time calcium levels of saliva were measured under conditions of nerve stimulation. Initial levels of calcium with stimulation of the parasympathetic innervation were as high as those evoked by stimulation of the sympathetic innervation. While calcium and amylase levels were characteristically high with adrenergic stimulation (either following drug administration or nerve stimulation), amylase levels following stimulation of the parasympathetic nerve were characteristically low. In fact, a parallelism between secretion of calcium and amylase was not observed under conditions of cholinergic nerve stimulation, but was observed with adrenergic nerve stimulation. It is suggested that with cholinergic nerve stimulation mediation of calcium and amylase secretion may differ from that observed with adrenergic stimulation.

Inhibition of isoproterenol-induced DNA and RNA synthesis in rat parotid and pancreas following removal of submandibular-sublingual glands

Summary[3H] thymidine incorporation into DNA of the parotid (PA) gland of adult and 20-day-old rats and into DNA of the pancreas (PANC) of 20-day-old rats was increased markedly following a 2-day regimen of isoproterenol (ISO) administration. However, when the submandibular-sublingual (SM-SL) glands had been removed just prior to initiation of the ISO injections, the [3H] thymidine incorporation into PA and PANC was inhibited, and cpm/mg protein of these organs was even lower than that of organs of untreated rats with SM-SL glands present. Removal of the PA glands just prior to initiation of the ISO regimen had no effect on the ISO-induced [3H] thymidine incorporation into DNA of PANC but partially inhibited that of the submandibular (SM) gland. It is suggested that the inhibitory effects on DNA and RNA synthesis that follow removal of SM-SL glands are attributable to the growth factors (epidermal growth factor and nerve growth factor) found in the rat SM gland. These factors appear to regulate normal DNA synthetic activity of exocrine glands as well as β1-adrenoceptor mediated DNA synthesis. Cellular hypertrophy induced by the ISO was less markedly affected by absence of the SM glands, but a partial inhibition of [3H] uridine incorporation into RNA of PA of adult rats also occurred when SM-SL glands were removed prior to initiation of the ISO-regimen.

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.

Effect of postganglionic sympathectomy on the ultrastructure of the rat parotid gland

SummaryFollowing two weeks of superior cervical ganglionectomy, the parotid glands of adult rats were removed and studied by electron microscopy. Sympathectomy induced striking alterations of acini, resulting in a heterogeneous population of acinar cells, but it had no obvious effect on the duct system. Most of the altered cells could be classified on a cytological basis as “dark cells” or “light cells.” Dark cells predominated and contained more secretory granules, less granular endoplasmic reticulum, fewer Golgi membranes, and smaller lumina and intercellular canaliculi than normal acinar cells. The synthesis and extrusion of secretory products appeared to be minimal in these cells. Light cells possessed ultrastructural features, such as dilated cisternae of granular endoplasmic reticulum and prominent Golgi membranes, which were opposite to those of dark cells and indicative of a high degree of secretory activity.The heterogeneous population of cells following sympathectomy indicates that the sympathetic nervous system may play an important role in regulating the secretory synchrony of acinar cells.

Effect of α- and β-adrenergic agonists on fluid and calcium secretion by rat salivary glands

Abstract The separate roles of ga- and β-adrenergic receptors in regulating fluid and calcium (Ca) secretion by rat salivary glands were examined using phenylephrine (PE), an adrenergic agonist that acts predominantly on ga-receptors, isoproterenol (ISO), an adrenergic agonist that acts predominantly on β-receptors, and PE and ISO in combination with β-adrenergic antagonist propranolol (PROP) and α-adrenergic antagonist phentolamine (PHENTO), respectively. PE evoked a greater volume of saliva from submandibular (SM) gland than from parotid (PA) gland, whereas ISO evoked a similar volume of saliva from both glands during 60-min of drug stimulation. PE even at a low dose had β-adrenergic effects on flow rate of salivary glands because pretreatment of rats with PROP (1 mg/kg) 20 min before PE (5 mg/kg, i.p.) stimulation resulted in a 4-fold reduction in total volume of PE-evoked PA saliva. Thus α-adrenergic receptors play a major role in fluid secretion by SM glands but play only a minor role in PA glands. ISO evoked SM and PA saliva with Ca concentration higher than that evoked by PE. ISO (25 mg/kg, i.p.) also had an effect on α-adrenergic receptors as well as β-adrenergic receptors. Although PHENTO did not significantly alter flow rate and volume of ISO-evoked PA or SM saliva, Ca concentration of ISO-evoked saliva was greatly potentiated by PHENTO. Total Ca output of ISO-evoked saliva from either gland was not significantly altered by PHENTO. Thus, in both salivary glands, activation of β-adrenergic receptors evoked saliva with a high concentration of Ca. ISO caused a marked decrease in glandular Ca concentration of both PA and SM whereas PE caused a marked depletion of glandular Ca concentration of SM but no depletion of Ca concentration of PA. PROP or PHENTO only slightly decreased ISO or PE-induced glandular depletion of Ca concentration of both glands. Thus, use of ISO or PE to delineate the specific role of α- or β-adrenergic receptors must take into account the affinities ISO and PE have for both types of adrenergic receptors of salivary glands.