Highly potent and selective ectonucleotide pyrophosphatase/phosphodiesterase I inhibitors based on an adenosine 5'-(α or γ)-thio-(α,β- or β,γ)-methylenetriphosphate scaffold

Aberrant nucleotide pyrophosphatase/phosphodiesterase-1 (NPP1) activity is associated with chondrocalcinosis, osteoarthritis, and type 2 diabetes. The potential of NPP1 inhibitors as therapeutic agents, and the scarceness of their structure-activity relationship, encouraged us to develop new NPP1 inhibitors. Specifically, we synthesized ATP-α-thio-β,γ-CH2 (1), ATP-α-thio-β,γ-CCl2 (2), ATP-α-CH2-γ-thio (3), and 8-SH-ATP (4) and established their resistance to hydrolysis by NPP1,3 and NTPDase1,2,3,8 (<5% hydrolysis) (NTPDase = ectonucleoside triphosphate diphosphohydrolase). Analogues 1-3 at 100 μM inhibited thymidine 5'-monophosphate p-nitrophenyl ester hydrolysis by NPP1 and NPP3 by >90% and 23-43%, respectively, and only slightly affected (0-40%) hydrolysis of ATP by NTPDase1,2,3,8. Analogue 3 is the most potent NPP1 inhibitor currently known, Ki = 20 nM and IC50 = 0.39 μM. Analogue 2a is a selective NPP1 inhibitor with Ki = 685 nM and IC50 = 0.57 μM. Analogues 1-3 were found mostly to be nonagonists of P2Y1/P2Y2/P2Y11 receptors. Docking analogues 1-3 into the NPP1 model suggested that activity correlates with the number of H-bonds with binding site residues. In conclusion, we propose analogues 2a and 3 as highly promising NPP1 inhibitors.

Identification of a promising drug candidate for the treatment of type 2 diabetes based on a P2Y(1) receptor agonist

The activation by extracellular nucleotides of pancreatic P2Y receptors, particularly, the P2Y(1)R subtype, increases insulin secretion. Therefore, we developed analogues of the P2Y(1)R receptor agonist 2-MeS-ADP, as potential antidiabetic drugs. Analogue 3A was found to be a potent P2Y(1)R agonist (EC(50) = 0.038 μM vs 0.0025 μM for 2-MeS-ADP) showing no activity at P2Y(2/4/6)Rs. Analogue 3A was stable at pH 1.4 (t(1/2) = 7.3 h) and resistant to hydrolysis vs 2-MeS-ADP by alkaline phosphatase (t(1/2) = 6 vs 4.5 h), human e-NPP1 (4% vs 16% hydrolysis after 20 min), and human blood serum (30% vs 50% hydrolysis after 24 h). Intravenous administration of 3A in naive rats decreased blood glucose from 155 mg/dL to normal values, ca. 87 mg/dL, unlike glibenclamide, leading to subnormal values (i.e., 63 mg/dL). Similar observations were made for streptozotocin (STZ)-treated and db(+)/db(-) mouse models. Furthermore, 3A inhibits platelet aggregation in vitro and elongates bleeding time in mice (iv administration of 30 mg of 3A/kg), increasing bleeding time to 16 vs 9 min for Prasugrel. Oral administration of 30 mg/kg 3A to rats increased tail bleeding volume, similar to aspirin. These findings suggest that 3A may be an effective treatment for type 2 diabetes by reducing both blood glucose levels and platelet aggregation.

Boranophosphate isoster controls P2Y-receptor subtype selectivity and metabolic stability of dinucleoside polyphosphate analogues

Dinucleoside polyphosphates, Np(n)N', exert their physiological effects via P2 receptors (P2Rs). Np(n)N' are attractive drug candidates as they offer better stability and specificity compared to nucleotides, the most common P2R ligands. To further improve the agonist properties of Np(n)N', we synthesized novel isosters of dinucleoside polyphosphates where N and N' are A or U and where the Pα or Pβ phosphate groups are replaced by boranophosphate, denoted as Np(n)(α-B)N' or Np(n)(β-B)N' (n = 3, 4), respectively. The potency of Np(n)(α/β-B)N' analogues was evaluated at tP2Y(1), hP2Y(2), hP2Y(4), and rP2Y(6) receptors. The most potent P2Y(1)R and P2Y(6)R agonists were the Up(4)(β-B)A (A isomer, EC(50) of 0.5 μM vs 0.004 μM for 2-SMe-ADP) and Up(3)(α-B)U (B isomer, EC(50) of 0.3 μM vs 0.2 μM for UDP), respectively. The receptor subtype selectivity is controlled by the position of the borano moiety on the Np(n)N' polyphosphate chain and the type of the nucleobase. In addition, Np(n)(α/β-B)N' proved ∼22-fold more resistant to hydrolysis by e-NPP1, as compared to the corresponding Np(n)N' analogues. In summary, Up(4)(β-B)A and Up(3)(α-B)U are potent, stable, and highly selective P2Y(1) and P2Y(6) receptor agonists, respectively.

A novel insulin secretagogue based on a dinucleoside polyphosphate scaffold

Dinucleoside polyphosphates exert their physiological effects via P2 receptors (P2Rs). They are attractive drug candidates, as they offer better stability and specificity compared to nucleotides, the most common P2 receptor ligands. The activation of pancreatic P2Y receptors by nucleotides increases insulin secretion. Therefore, in the current study, dinucleoside polyphosphate analogues (di-(2-MeS)-adenosine-5',5''-P(1),P(4),alpha,beta-methylene-tetraphosphate), 8, (di-(2-MeS)-adenosine-5',5''-P(1),P(4),beta,gamma-methylene-tetraphosphate), 9, and di-(2-MeS)-adenosine-5',5''-P(1),P(3),alpha,beta-methylene triphosphate, 10, were developed as potential insulin secretagogues. Analogues 8 and 9 were found to be agonists of the P2Y(1)R with EC(50) values of 0.42 and 0.46 microM, respectively, whereas analogue 10 had no activity. Analogues 8-10 were found to be completely resistant to hydrolysis by alkaline phosphatase over 3 h at 37 degrees C. Analogue 8 also was found to be 2.5-fold more stable in human blood serum than ATP, with a half-life of 12.1 h. Analogue 8 administration in rats caused a decrease in a blood glucose load from 155 mg/dL to ca. 100 mg/dL and increased blood insulin levels 4-fold as compared to basal levels. In addition, analogue 8 reduced a blood glucose load to normal values (80-110 mg/dL), unlike the commonly prescribed glibenclamide, which reduced glucose levels below normal values (60 mg/dL). These findings suggest that analogue 8 may prove to be an effective and safe treatment for type 2 diabetes.

2-MeS-beta,gamma-CCl2-ATP is a potent agent for reducing intraocular pressure

Extracellular nucleotides can modify the production or drainage of the aqueous humor via activation of P2 receptors and therefore affect the intraocular pressure (IOP). We have synthesized slowly hydrolyzable nucleoside di- and triphosphate analogues, 1, and 8-14. Analogues 8-14 were completely resistant to hydrolysis by alkaline phosphatase over 30 min at 37 degrees C. In human blood serum, analogues 8-14 exhibited high stability, e.g., analogues 9 and 10-14 were only 15% and 0% degraded after 24 h, respectively. Moreover, analogues 8-14 were highly stable at pH 1.4 (t(1/2) 1 h-30 days). Analogues 8-14 were agonists of the P2Y(1) receptor (EC(50) 0.57-9.54 muM). Ocular administration of most analogues into rabbits reduced IOP, e.g., analogue 9 reduced IOP by 32% (EC(50) 95.5 nM). Analogue 9 was more effective at reducing IOP than several common glaucoma drugs and represents a promising alternative to timolol maleate, which cannot be used for the treatment of patients suffering from asthma or cardiac problems.

Identification of hydrolytically stable and selective P2Y(1) receptor agonists

P2Y nucleotide receptors (P2YRs) are attractive pharmaceutical targets. Most P2YR agonists proposed as drugs consist of a nucleotide scaffold, but their use is limited due to their chemical and enzymatic instabilities. To identify drug candidates, we developed non-hydrolyzable P2YR agonists. We synthesized ATP-beta,gamma-CH(2) analogues 2-4, and evaluated their chemical and metabolic stabilities and activities at P2Y(1,2,4,6) receptors. Analogues 2-4 exhibited t(1/2) values of 14.5-65 h in gastric juice pH. They were completely resistant to alkaline phosphatase for 30 min at 37 degrees C and slowly hydrolyzed in human blood serum (t(1/2) 12.7-71.9 h). In comparison to ATP, analogues 2-4 were barely hydrolyzed by nucleoside triphosphate diphosphohydrolases, NTPDase1,2,3,8 (< 8% hydrolysis), and nucleotide pyrophosphatases, NPP1,3 (< or = 10% hydrolysis). Analogues 2 and 4B were selective agonists of the P2Y(1)R with EC(50)s of 0.08 and 17.2 microM, respectively. These features make analogues 2 and 4B potential therapeutic agents for health disorders involving the P2Y(1)R.

Interleukin-1beta enhances nucleotide-induced and alpha-secretase-dependent amyloid precursor protein processing in rat primary cortical neurons via up-regulation of the P2Y(2) receptor

The heterologous expression and activation of the human P2Y(2) nucleotide receptor (P2Y(2)R) in human 1321N1 astrocytoma cells stimulates alpha-secretase-dependent cleavage of the amyloid precursor protein (APP), causing extracellular release of the non-amyloidogenic protein secreted amyloid precursor protein (sAPPalpha). To determine whether a similar response occurs in a neuronal cell, we analyzed whether P2Y(2)R-mediated production of sAPPalpha occurs in rat primary cortical neurons (rPCNs). In rPCNs, P2Y(2)R mRNA and receptor activity were virtually absent in quiescent cells, whereas overnight treatment with the pro-inflammatory cytokine interleukin-1beta (IL-1beta) up-regulated both P2Y(2)R mRNA expression and receptor activity by four-fold. The up-regulation of the P2Y(2)R was abrogated by pre-incubation with Bay 11-7085, an IkappaB-alpha phosphorylation inhibitor, which suggests that P2Y(2)R mRNA transcript levels are regulated through nuclear factor-kappa-B (NFkappaB) signaling. Furthermore, the P2Y(2)R agonist Uridine-5'-triphosphate (UTP) enhanced the release of sAPPalpha in rPCNs treated with IL-1beta or transfected with P2Y(2)R cDNA. UTP-induced release of sAPPalpha from rPCNs was completely inhibited by pre-treatment of the cells with the metalloproteinase inhibitor TACE inhibitor (TAPI-2) or the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002, and was partially inhibited by the MAPK/extracellular signal-regulated kinase inhibitor U0126 and the protein kinase C inhibitor GF109203. These data suggest that P2Y(2)R-mediated release of sAPPalpha from cortical neurons is directly dependent on a disintegrin and metalloproteinase (ADAM) 10/17 and PI3K activity, whereas extracellular signal-regulated kinase 1/2 and PI3K activity may indirectly regulate APP processing. These results demonstrate that elevated levels of pro-inflammatory cytokines associated with neurodegenerative diseases, such as IL-1beta, can enhance non-amyloidogenic APP processing through up-regulation of the P2Y(2)R in neurons.

Src homology 3 binding sites in the P2Y2 nucleotide receptor interact with Src and regulate activities of Src, proline-rich tyrosine kinase 2, and growth factor receptors

Many G protein-coupled receptors activate growth factor receptors, although the mechanisms controlling this transactivation are unclear. We have identified two proline-rich, SH3 binding sites (PXXP) in the carboxyl-terminal tail of the human P2Y(2) nucleotide receptor that directly associate with the tyrosine kinase Src in protein binding assays. Furthermore, Src co-precipitated with the P2Y(2) receptor in 1321N1 astrocytoma cells stimulated with the P2Y(2) receptor agonist UTP. A mutant P2Y(2) receptor lacking the PXXP motifs was found to stimulate calcium mobilization and serine/threonine phosphorylation of the Erk1/2 mitogen-activated protein kinases, like the wild-type receptor, but was defective in its ability to stimulate tyrosine phosphorylation of Src and Src-dependent tyrosine phosphorylation of the proline-rich tyrosine kinase 2, epidermal growth factor receptor (EGFR), and platelet-derived growth factor receptor. Dual immunofluorescence labeling of the P2Y(2) receptor and the EGFR indicated that UTP caused an increase in the co-localization of these receptors in the plasma membrane that was prevented by the Src inhibitor PP2. Together, these data suggest that agonist-induced binding of Src to the SH3 binding sites in the P2Y(2) receptor facilitates Src activation, which recruits the EGFR into a protein complex with the P2Y(2) receptor and allows Src to efficiently phosphorylate the EGFR.

Effects of acetylcholine and monensin on 22Na uptake and cytosolic Ca2+ in rat submandibular salivary cells

Cells isolated by enzymatic digestion of gland fragments were incubated in solutions with or without Ca2+ or Na+ and exposed to monensin (10 microM) or acetylcholine (1 microM). Effects on accumulation of 22Na and on cell Ca2+ (measured with fura-2) were compared. In Ca2(+)-containing medium, accumulation of 22Na was increased by the 2 drugs (23 and 20%, respectively) and their effects were additive. Tracer accumulation was also increased by the ionophore A23187. The effect of monensin was not inhibited by 1 mM amiloride, but partially inhibited by 1 mM furosemide. Acetylcholine caused a rapid increase (peak) in cell Ca2+, followed by a gradual decline, while monensin caused a gradual increase with no initial peak. In Ca2(+)-free medium, acetylcholine failed to enhance 22Na accumulation, but still caused a rapid peak in cell Ca2+, followed by a more rapid decrease to resting levels. Monensin enhanced 22Na uptake 16% and caused a gradual increase in cell Ca2+ in this medium. In a medium with no Na+ but containing 1 mM Ca2+, acetylcholine increased cell Ca2+ but no initial peak was observed; monensin caused a slight decrease in cell Ca2+ and then an increase to resting levels. These results suggest important interactions between Na+ and Ca2+ movements in salivary cells. Ca2+ mobilization may activate Na+ uptake and changes in cell Na+ may, in turn, influence Ca2+ mobilization from cell pools. Some of these interactions may involve a Na/Ca co- or counter-transport system.

Amiloride inhibits 22Na uptake and [3H]QNB binding in rat submandibular cells

Dispersed acini isolated by collagenase digestion of the rat submandibular gland were used to compare the effects of amiloride and furosemide on the uptake of the isotopic tracer 22Na and on the binding of [3H]quinuclidinyl benzylate ([3H]QNB). In mM concentrations, both inhibitors reduced 22Na uptake in resting cells 34 and 25-29%, respectively. Acetylcholine (1 microM) enhanced uptake 23% and this effect was reduced 45% by amiloride and 26% by furosemide. Amiloride inhibited the binding of [3H]QNB to crude membranes prepared from fresh submandibular glands in a dose-dependent fashion (IC50 = 8 x 10(-6) M). Furosemide (3 x 10(-8) to 10(-3) M) did not inhibit radioligand binding. Na influx into resting salivary acini thus appears to occur by both amiloride-sensitive and furosemide-sensitive transport systems. The similar inhibition by furosemide of unstimulated and stimulated uptake of 22Na suggests that acetylcholine does not significantly activate the cotransport system within the time frame (i.e., 2 min) of the experiments. Acetylcholine appears to activate an amiloride-sensitive Na/H antiport, but amiloride blocks cholinergic receptors and may thus affect Na transport by receptor blockade. Other actions of amiloride, such as its ability to penetrate into cells and to act as a weak base which alters intracellular pH, may also contribute to the inhibition of Na entry into salivary cells.

Ca2+ mobilization and Cl efflux in submandibular salivary cells of adult and newborn rats

These cells were isolated by enzymatic digestion from glands of 1-day-old and fully mature rats. The effects of exposure to acetylcholine on cytosolic Ca2+ and Cl efflux were studied by, respectively, spectrofluorimetry of fura-2 and the net efflux of the isotopic tracer 36Cl from preloaded cells. In both types of cells, when incubated in Ca2+-containing solutions, acetylcholine initially caused a rapid, significant increase in cytosolic Ca2+ (from approx. 90 to 480-570 nmol), followed by a slower decrease to a plateau value of 280-290 nmol. The initial peak persisted (315-339 nmol) in Ca2+-free solutions but the cytosolic Ca2+ concentrations decreased rapidly to levels below prestimulation values (30 nmol). 36Cl efflux in tracer preloaded cells incubated in Ca2+-containing medium in the presence of acetylcholine was 18% in cells of new born animals and 35% in adult cells. In Ca2+-free medium, mature cells showed a transient but significant (26%) efflux of 36Cl. Cells of 1-day-old rats did not show a net efflux of 36Cl under these conditions, but subsequent addition of Ca2+ caused a 15% reduction (i.e. efflux) in tracer content. The antagonist 3,4,5-trimethoxybenzoate-8(N,N-dithylamino)octyl ester (TMB 8), which blocks internal Ca2+ release, inhibited both the initial increase in cell Ca2+ in both types of cells and the transient efflux of 36Cl seen in mature cells when incubated in Ca2+-free solutions. At high concentrations (5 mM), LaCl3 inhibited efflux of 36Cl in mature cells but not in those of newborn rats. However, at lower concentrations (0.1 mM), which do not interfere with fluorescence spectra, LaCl3 did not inhibit the effect of acetylcholine on cell Ca2+. These results suggest that Cl efflux in adult submandibular cells is regulated by an increase in cell Ca2+ arising from release of internal Ca2+ and from influx of external Ca2+. Both of these responses are evident in cells of newborn animals but Cl efflux is either decreased or absent. This is likely to be associated with a deficiency in the Cl channels or in the coupling between Ca2+ and the channel substrate through regulatory molecules associated with phosphorylation of the channel protein.

Effects of acetylcholine and transport inhibitors on K content in dispersed submandibular salivary cells of newborn and adult rats

These isolated cells were used to measure uptake of the radioactive tracer 86Rb as an index of changes in K+ content. There was time-dependent tracer uptake in the absence of secretagogue in both one-day-old and adult cells. Kinetic analysis of this uptake revealed two components, a fast one during the first 5 min of incubation and a slower one between 5 and 30 min. The early (fast) component was slower in the newborn cells (0.084 nmol mg-1 min-1) than in adult cells (0.116 nmol mg-1 min-1). Values for the second component of uptake were, respectively, 0.015 and 0.009 nmol mg-1 min-1. Basal uptake of K+ was inhibited by both ouabain and furosemide (at 1 mM concentrations) but, after 5 min of incubation, the effect was more pronounced in adult cells. The K+ content (i.e. K+ uptake) was increased after exposure to 1 microM acetylcholine in both cell types, but the effect was larger in those from one-day-old rats after 5 min incubation (16 per cent increase, compared to 9 per cent increase in adult cells). The secretagogue-induced increase in K+ uptake or content was inhibited by ouabain (57 per cent in adult cells, 24 per cent in newborn cells), and by furosemide (25 and 37 per cent, respectively). These findings suggest that K+ uptake in submandibular cells occurs by both an ouabain-sensitive Na, K pump and a diuretic-sensitive transport system. Both appear to have lower resting activities in the cells of newborn rats but can be significantly stimulated cholinergically.(ABSTRACT TRUNCATED AT 250 WORDS)

Na, K ATPase activity during early postnatal development of the rat submandibular gland

The activity of the ouabain-sensitive Na, K ATPase was measured in membrane fractions of the submandibular gland of 1-, 7-, 14- and 21-day-old rats. This activity increased with age and reached adult levels by 21 days.

36Cl fluxes in dispersed-cell aggregates of the submandibular salivary gland of early postnatal rats

Salivary cells were isolated from the gland of rats (1, 7, 14 and 21 days old) by enzymic digestion. They formed small aggregates with typical morphological characteristics and were functional units with characteristic 36Cl fluxes. The rates of isotopic uptake in the absence of secretagogue (basal uptake) were similar at all ages. Uptake was time-dependent, leading to a steady-state isotope content of 6.7-8.9 nmol/mg protein after 3-5 min of incubation. 36Cl accumulation (uptake) in the unstimulated condition was inhibited 33-39 per cent by exposure to 1 mM furosemide at all ages, but was reduced significantly less (50 per cent) by 1 microM acetylcholine in cells of 1-day-old animals than in older ones. In aggregates exposed to 36Cl for 12 min (preloaded with tracer), acetylcholine caused a net efflux of isotope which was significantly less in cells of 1-day-old rats (18 versus 35 per cent in cells of older animals). Thus it was shown (1) that functional cell aggregates can be obtained from early postnatal rats; (2) that when not stimulated, their time-dependent Cl accumulation is partially inhibited by loop diuretics, and so likely to involve a cation/anion cotransport system; and (3) that Cl efflux, which may occur by way of membrane channels, is significantly reduced early in the postnatal period. The putative Cl channels are therefore either not fully developed, or they do not become responsive to stimulation until later. This reduced Cl efflux could be related to differences in Ca2+ mobilization at early and late phases of postnatal glandular development as Cl efflux is a Ca2+-dependent phenomenon in salivary cells.

42K spaces in submandibular gland of early postnatal rats: effects of carbachol and transport inhibitors

Equivalent spaces of 42K were measured in fragments of the submandibular gland of 1-, 7-, 14- and 21-day-old and adult rats in the absence and presence of carbachol and the transport inhibitors ouabain and furosemide. The results indicate that the 42K space was increased by carbachol in an ouabain-sensitive manner at all ages studied and that part of the secretagogue-stimulated K uptake occurred by way of a furosemide-sensitive transport system in the latter part of the postnatal period and in the adult.

Temporal dissociation in the ability of ouabain and furosemide to inhibit K+-transport in rat submandibular salivary gland slices at various postnatal ages

Slices of glands from 1, 7, 14 and 21-day-old rats were perfused with a physiological salt solution in a lucite chamber; acetylcholine-induced release and uptake of K were compared to that of adult glands, in the absence and presence of the ion-transport inhibitors, ouabain and furosemide. Without inhibitors, peak K efflux from the glands of 1-day-old rats was 50 per cent of that in 7, 14 and 21-day-old rats, and 33 per cent of that in adults. Maximum K+ uptake was 72 per cent of that in 7, 14 and 21-day-old rats and 61 per cent of that in adults. However, K+ uptake was a larger part (78 per cent) of the preceding efflux in glands of 1-day-old rats than in adult glands (43 per cent) or in glands of 7, 14 and 21-day-old rats (55 per cent). Ouabain (10(-3) M) immediately after a 3-min pulse stimulation with 10(-5) M acetylcholine abolished K uptake at all ages. Furosemide (10(-3) M) inhibited K uptake throughout but its effect increased with age. Thus K+ uptake was 21 per cent less than in the absence of inhibitor in slices from 1-day-old rats but 73 per cent less in adult glands. Similar, but smaller, effects were observed when exposure to furosemide followed acetylcholine. Both K efflux and uptake can thus be elicited in rat submandibular glands from the first day of life and the increased response with age correlates with morphological development and with the progressive, postnatal appearance of acinar cell. The large uptake:efflux ratio suggests that a Na, K pump, responsible for a large portion of K+ uptake, is already present and active in the glands of 1-day-old rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Volume and composition of pilocarpine- and isoproterenol-stimulated submandibular saliva of early postnatal rats

Submandibular saliva was collected from early postnatal rats by cannulation of the main excretory duct of individual glands after i.p. injections of pilocarpine (10 mg/kg body weight) or isoproterenol (10 mg/kg body weight). With this method of saliva collection, a secretory response to pilocarpine was observed at two wk of age. The average weight of 40 glands was 35.6 +/- 1.6 mg, and the average volume of saliva secreted in 60 min was 32 +/- 2.2 microliters. By three wk of age, the gland had approximately doubled in size (average weight of 39 glands = 61.9 +/- 3.1 mg), and the average total volume of saliva secreted in 60 min was more than three times larger (120.4 +/- 10.5 microliters) than that secreted by two-week-old rats. The relationship between electrolyte (Na+, K+, Ca++) and protein concentrations and rate of flow was similar to that observed in pilocarpine-stimulated adult saliva, and did not differ appreciably in the saliva of two- and three-week-old animals. A measurable secretory response to isoproterenol was observed at three wk of age when saliva was collected by duct cannulation. The average total volume of saliva secreted in 60 min was 48 +/- 3.1 microliters, and salivary Na+ and K+ concentrations, and their relationship to flow rate, were similar to those of isoproterenol-stimulated adult saliva. Saliva Ca++ and protein concentrations were also generally similar to those of isoproterenol-stimulated adult saliva. Total protein output (in 60 min) was 2 1/2 times greater in three-week-old rats with isoproterenol stimulation (compared to pilocarpine stimulation), but was significantly smaller than that of isoproterenol-stimulated adult glands. It is concluded that the submandibular gland of early postnatal rats is capable of secreting saliva in vivo following cholinergic and beta-adrenergic stimulation, and that this ability corresponds with the appearance of the corresponding autonomic receptors, but precedes cytodifferentiation. Ductal transport of electrolytes is well-developed at this stage of postnatal development, but fluid and protein output is smaller than in adult glands and requires full morphological maturation of acinar cells.

Ouabain-sensitive K+ uptake in submandibular salivary gland slices of rats of different post-natal ages

Slices of submandibular glands of newborn and early post-natal rats took up K+ when incubated in vitro in an enriched, oxygenated Krebs-Ringer bicarbonate solution. This uptake of K+ was observed when the slices were transferred to K+-containing medium after pre-incubation in K+-free medium, when the previously stimulated cholinergic or alpha-adrenergic receptors were blocked with appropriate antagonists or when the Ca2+ in the medium was chelated with EGTA 2 min after stimulation with carbamylcholine. The extent of K+ uptake was larger in the youngest (1-day-old) animals in all these experiments. Uptake of K+ was inhibited by 1 mM ouabain. This inhibition was not immediate and varying rates of K+ uptake were observed for 2-5 min after addition of the glycoside. It is concluded that: (1) K+ uptake can be elicited in the developing submandibular glands of newborn and early post-natal rats; (2) this response is sensitive to ouabain and is likely to depend, therefore, on the presence of a Na+, K+ ATPase in the immature gland; (3) changes in ouabain-sensitive K+ uptake with age suggests that the activity of the Na, K ATPase varies as the gland matures in the immediate post-natal period. As the Na+, K+ ATPase is thought to provide a driving force for the transport of ions underlying salivary secretion, the findings suggest that this mechanism is present in the early stages of post-natal development of the rat submandibular gland.

In-vitro release of K+ from the developing submandibular gland of early postnatal rats

The release studied by incubating tissue slices in an enriched, oxygenated medium in the presence and absence of secretagogues indicated that slices from 1-day-old rats released K+ in response to carbamylcholine, but not in response to epinephrine. The response to carbamylcholine was dose-related, with a 12.6 +/- 1.3 per cent release at a concentration of 2 X 10(-5) M. Epinephrine did not induce K+ release in concentrations from 2 X 10(-7) to 2 X 10(-4) M. Glands from 7- and 14-day-old rats released a similar amount as those of newborns in response to carbamylcholine and by 21 days of age the glands released 21.5 +/- 1.9 per cent of their K+ content upon exposure to 2 X 10(-5) M carbamylcholine. A response to epinephrine (2 X 10(-5) M) was first detected at 14 days of age, when the slices released 8.3 +/- 1.2 per cent of their K+. Slices of 21-day-old rats showed a 17.9 +/- 1.3 per cent K+ release in response to this dose. As in adult glands, the net amount of K+ released by the developing postnatal gland seems to be the result of two opposing mechanisms, a passive efflux and an active re-uptake which depends on the activation of an ouabain-sensitive Na+ -K+ -ATPase. The passive efflux component was similar in glands from different postnatal ages and was enhanced by secretagogues. The extent of active uptake, on the other hand, decreased with increasing postnatal age. As in the adult, the net release of K+ depended on the presence of Ca2+ in the incubation medium, but the sensitivity of the response to Ca2+ omission varied in accord with the age of the animals and with the stimulant used. It is speculated that proacinar and terminal tubular cells may be involved in K+ release in the early postnatal period.

Inhibition of Na+ reabsorption in the rat parotid gland by prostaglandin E1 and kallidin: implications for cystic fibrosis

Prostaglandin E1 caused a dose-related inhibition of sodium reabsorption in the rat parotid gland when injected by retrograde perfusion into the glandular ducts. The extent of inhibition ranged from 11.7 +/- 2.4% at a dose of 2.5 micrograms to 63.8 +/- 8.9% at a dose of 31.2 micrograms. Both phospholipase A2, an enzyme involved in prostaglandin synthesis, and arachidonic acid, a precursor of prostaglandins, also increased the Na+ concentration of parotid saliva in a dose-dependent fashion. With phospholipase A2 the inhibition ranged from 21.6 +/- 4.4% at a dose of 3 micrograms to 73.5 +/- 8.2% at a dose of 30 micrograms. With arachidonic acid, the degree of inhibition was 5.1 +/- 3.0% at a 10(-5) M dose and 57.7 +/- 10.2% at a dose of 10(-3) M. Lysine bradykinin (kallidin), a peptide present in salivary and other exocrine glands and their secretions, also caused a 30% inhibition of Na+ reabsorption when retroperfused at a concentration of 12.5 micrograms, as did kallikrein (176 micrograms) and trypsin (33.3 micrograms). These results indicate that prostaglandins and kinins can inhibit Na+ reabsorption in the rat parotid duct when present in the luminal side of the cells. Since they are normally present in exocrine glands and can presumably be secreted, they may have a role as luminal factors in the regulation of transductal transport of Na+. The possibility that they may be increased in the exocrine secretions of patients with cystic fibrosis and that they may act as the so-called cystic fibrosis "factors" is also raised by the findings of this study.