Amine uptake and metabolism by endothelium of pig pulmonary artery and aorta

Pharmacological properties of serotonin receptor subtypes mediating contraction of bovine inferior alveolar arteries

OBJECTIVE

To characterise the 5-hydroxytryptamine (5-HT) receptor subtypes mediating contraction of the inferior alveolar artery. Additionally, to determine the role of cyclooxygenase products, nitric oxide, endothelium, monoamine oxidase and 5-HT uptake in modulating contraction of inferior alveolar arteries to 5-HT.

METHODS

Contractile responses to 5-HT were examined in vitro using ring segments of bovine inferior alveolar arteries. Affinity constants (K(B)'s) of subtype-selective 5-HT receptor antagonists were determined to characterise the 5-HT receptor-subtypes causing contraction of inferior alveolar arteries.

RESULTS

In 100 nM ketanserin or 30 nM spiperone, 5-HT caused a biphasic contraction best-fit by a two-site curve model, where one site was antagonist-sensitive and the other site antagonist-insensitive. 5-HT(2A) receptor-subtype selective antagonists, ketanserin and spiperone, blocked 5-HT induced contraction with K(B)'s of 1.0 and 0.16 nM, respectively. RS102221 (5-HT(2C) selective) and (S)-WAY100135 (5-HT(1A) selective) blocked 5-HT stimulated contraction with low affinities (K(B)'s=100 nM and 330 nM, respectively). GR55562, a 5-HT(1) receptor subtype antagonist with a reported affinity of 500 nM at the 5-HT(1D) receptor subtype, blocked 5-HT induced contraction with a K(B) of 470 nM. Cylooxygenase inhibition with 50 microM ibuprofen caused a 44% increase in maximal contraction to 5-HT; whereas, nitric oxide inhibition with N(G)-nitro-L-arginine, endothelium removal or inhibition of 5-HT uptake and monoamine oxidase with imipramine and iproniazid, respectively, did not affect 5-HT contraction.

CONCLUSIONS

Both 5-HT(2A) and 5-HT(1D/1B) receptor subtypes mediate 5-HT induced contraction of the bovine inferior alveolar artery. 5-HT stimulated contraction of the inferior alveolar artery is modulated by a vasodilator prostaglandin.

Low 4-aminopyridine concentration-induced contraction is mediated by neuronal noradrenaline in canine saphenous vein

4-Aminopyridine (4-AP), a known inhibitor of the voltage-dependent potassium channels, is able to increase the basal tone of different types of blood vessel preparations. In order to determine the efficiency of 4-AP in veins and to clarify its possible mechanism of action, the aim of the present study was to determine the basal tone and release of radio-labelled tissue noradrenaline (NA) after administration of low 4-AP concentrations. Experiments were performed in canine saphenous vein in the absence and presence of functional endothelium. 4-AP (0.012-5 microM) enhanced the basal tone of venous rings without and with endothelium (maximum tone at 5 microM 4-AP: 2.20 +/- 1.29 and 1.3 +/- 0.57 mN, respectively). NA stores of the venous tissue were loaded by adding 1 mM NA to the tissue for 10 min and then washed out. After loading the NA-stores of venous tissue, 4-AP-induced contractions were significantly increased both in the absence and presence of endothelium (maximum tone at 5 microM 4-AP after loading with NA: 10.51 +/- 3.64 and 10.52 +/- 4.69 mN, respectively). Following NA loading, chemical denervation of the endothelium denuded venous preparations by 0.5 mM 6-hydroxydopamine (6-OHDA) completely abolished the contractions evoked by 4-AP. After incubation of the saphenous preparations with 3H-NA, 5 microM 4-AP significantly increased tritium-efflux from the tissue. These results provide evidence for the efficiency of 4-AP on the basal tone of isolated canine saphenous vein when applied in low concentrations. Furthermore, it is suggested that this action of 4-AP may considerably depend on the release of NA from the perivascular nerve endings.

Release of 3H-5-hydroxytryptamine from isolated rabbit aorta

The main aim of the present investigation was to study systematically the passive and stimulation-evoked release of 3H-5-hydroxytryptamine (3H-5-HT) from rabbit isolated aorta. This was accomplished by preloading rings of aorta with 3H-5-HT (10(-6)M) and then monitoring by fractional collection the basal 3H-outflow and stimulation-evoked 3H-overflow. The basal 3H-outflow from aorta preloaded with 10(-6)M of either 3H-5-HT or (-)-3H-noradrenaline (3H-NA) leveled off about 100 min. after the onset of wash-out and remained almost constant thereafter (100-240 min.). The basal 3H-outflow from tissue preloaded with 3H-5-HT was almost 3-fold higher (70-240 min.) than that seen after preloading with 3H-NA. Cocaine (3 x 10(-5)M) did not alter the basal 3H-outflow (15-240 min.) from tissue preloaded with 3H-5-HT, while pargyline (5 x 10(-4)M) decreased it by about 66% (100-240 min.). Electrical-field stimulation (S1-S7, 200 mA, 600 pulses, 0.5 msec., 3 Hz) were applied to the tissue. The initial stimulation-evoked 3H-overflow from aorta preloaded with 3H-5-HT was higher than the subsequent ones (S1-S7; 100, 35, 35, 35, 35, 37, and 40%). Similar results to these were obtained with tissues preloaded with 3H-NA. The stimulation (S1-S7; 200 mA). 600 pulses, 0.5 msec, 3 Hz)-evoked 3H-overflow increased in an apparent linear manner with the amount of current used (50-200 mA).(ABSTRACT TRUNCATED AT 250 WORDS)

An immunohistochemical study of endothelial cell heterogeneity in the rat: observations in "en face" Häutchen preparations

"En face" sheets of endothelium, in which cellular spatial relationships were maintained, were prepared from proximal pulmonary and femoral arteries and aortae of the Wistar rat, in order to visualise patterns of heterogeneity in populations of endothelial cells. These preparations, termed Häutchen, were immunolabelled with antibodies to angiotensin II, endothelin and Factor-VIII-related antigen, and visualised by an avidin/biotin peroxidase complex. Clusters of cells, which accounted for approximately 30% of the total endothelial cell population, and which were positively immunostained for angiotensin II, were found perpendicular to the longitudinal axis of the aorta and femoral artery. Cells in the pulmonary artery were immunonegative for angiotensin II. The majority of cells in all three vessels were immunopositive for endothelin; groups of intensely stained cells were present in both the femoral artery and aorta, but not in the pulmonary artery. Immunoreactivity to Factor-VIII-related antigen was heterogeneous, with intensely stained amorphous patches of endothelial cells present in the femoral artery and aorta. Häutchen preparations present an opportunity for the investigation of endothelial cell heterogeneity, both within and between vessels; this may provide a basis for the interpretation of the heterogeneity of endothelium-dependent responses in vessels of differing origin.

Modulation of cultured pulmonary microvessel and arterial endothelial cell barrier structure and function by serotonin

Pulmonary microvessel endothelial cell and pulmonary artery endothelial cell monolayers in tissue culture were treated with serotonin (5-hydroxytryptamine; 5-HT) alone or in conjunction with histamine, bradykinin, the thromboxane analog U-46619, and the actin modulating agent cytochalasin B. After agent treatment, cross-sections through endothelial cell (EC) monolayers were examined by light microscopy and the percentage and widths of intercellular openings were quantitated. To correlate structural changes in the endothelial barrier with an alteration in permeability, EC monolayers cultured on micropore filters were assayed for transit of Evan's blue albumin (EBA) following treatment with vasoactive mediators. 5-HT was found to decrease the patency of endothelial junctions by up to 94%, compared to untreated monolayers, and to prevent or reverse the appearance of interendothelial gaps induced by histamine, bradykinin, U-46619, and cytochalasin B. The 5-HT effect was dose and time dependent, with a maximal increase in junctional apposition observed at a concentration of 10(-6) M for 30 min. This response was significantly blocked by the 5-HT antagonists LSD and ketanserin. The formation or reduction of interendothelial gaps by histamine, bradykinin, and U-46619 and by 5-HT, respectively, was positively correlated to changes in monolayer permeability to EBA. These results suggest that pulmonary edema caused by inflammatory mediators in part may be a consequence of transient increases in pulmonary EC junctional gaps, and that 5-HT may contribute to the homeostatic maintenance of endothelial barrier integrity.

Localization of vasopressin, serotonin and angiotensin II in endothelial cells of the renal and mesenteric arteries of the rat

The localization of vasopressin, serotonin and angiotensin II in the endothelial cells of renal and mesenteric arteries was investigated using the pre-embedding peroxidase-antiperoxidase technique for electron microscopy. Vasopressin- and serotonin-positive endothelial cells were present in both renal and mesenteric arteries while angiotensin II-positive cells were observed in the mesenteric artery exclusively. Both arteries showed less than 10% immunoreactive cells. The lack of angiotensin II in the endothelial cells of the renal artery suggests that there may be subtle physiological differences between the renal and mesenteric arteries with respect to the local control of blood flow.

Dissipation mechanisms for 5-hydroxytryptamine in the coronary circulation of the isolated perfused heart of the rat

1. The contribution of uptake into vascular endothelial cells, of neuronal uptake and of extraneuronal uptake in the dissipation of 5-hydroxytryptamine (5-HT) perfused through the coronary circulation of the rat heart was examined. 2. Hearts from reserpine-pretreated rats were isolated and perfused in vitro with 5-HT, in the absence or presence of inhibitors, and rates of appearance of the deaminated metabolite, 5-hydroxyindoleacetic acid (5-HIAA), in the venous effluent were measured using an h.p.l.c. assay. 3. The steady-state rates of 5-HIAA appearance in the venous effluent in hearts perfused with 1 microM 5-HT (422 +/- 8.48 pmol g-1 min-1, n = 12) were reduced by pretreatment of the rats with 6-hydroxydopamine (22% inhibition), and by inclusion in the perfusion solution of 30 microM cocaine (28% inhibition), 100 microM 3-O-methylisoprenaline (64% inhibition), 100 microM corticosterone (58% inhibition), or 30 microM cocaine and 100 microM 3-O-methylisoprenaline (87% inhibition). 4. The extraneuronal deamination of 5-HT in the heart was saturable (Km = 101 microM, Vmax = 31.2 nmol g-1 min-1). The neuronal deamination of 5-HT was saturated by about 50 fold lower concentrations of 5-HT than was extraneuronal deamination, but Km and Vmax values could not be determined. 5. In the coronary circulation of the rat heart, 5-HT was dissipated by the uptake processes for catecholamines, extraneuronal uptake (predominantly) and neuronal uptake, and subsequent metabolism by monoamine oxidase. There was no evidence that a cocaine-sensitive uptake of 5-HT into vascular endothelial cells made any significant contribution to 5-HT dissipation in the heart.

Tannin induces endothelium-dependent contraction and relaxation of rabbit pulmonary artery

The effects of tannin purified from cotton bracts were studied on pulmonary artery rings isolated from rabbit lungs. Tannin (2 to 50 micrograms/ml) caused concentration-dependent contractions of resting vessels, and maximal responses averaged 25% of the contraction induced by 10(-4) M exogenous norepinephrine. Tannin-induced contractions were blocked by removal of the endothelium and by pretreatment of intact tissues with either indomethacin or SQ 29,548, a thromboxane A2 receptor antagonist. In contrast, tissues contracted with 3 x 10(-7) M norepinephrine relaxed by 49 +/- 8% in response to 50 micrograms/ml tannin. Tannin-induced relaxations were unaltered by pretreatment of tissues with indomethacin but were significantly reduced by pretreatment with hemoglobin. We conclude that tannin causes the release of both smooth muscle contracting and relaxing factors from pulmonary artery endothelial cells. Thromboxane A2 is the contracting factor, whereas an endothelium-derived relaxing factor such as nitric oxide appears to be the primary relaxing factor that is released.

Chylomicron metabolism by normal and injured isolated rat lungs

Since the lung is the first highly vascularized organ to which chylomicrons are exposed, we sought to determine whether the lung vasculature is capable of metabolizing triglyceride contained in circulating, native chylomicrons. In addition, since acute lung injury can depress other endothelial cell associated metabolic functions, we determined whether acute injury due to alpha-naphthylthiourea (ANTU) changed chylomicron triglyceride metabolism by lungs. We compared the hydrolysis of radiolabelled chylomicrons from rat mesenteric lymph by perfused lungs isolated from rats pretreated with ANTU; with the vehicle, Tween 80, alone; or untreated control rats. In all groups of lungs, we found that perfusate content and concentration of triglyceride decreased over 30 minutes of perfusion, while that of free fatty acid increased, indicating that isolated lungs are able to hydrolyze chylomicron triglyceride. Despite enhancement of hydrolysis by perfusates containing 6 gm/100 ml of bovine serum albumin, there were no differences among the groups of lungs in the extent or rate of triglyceride metabolism. The [1-14C]-oleate from chylomicron triglyceride was taken up into lung tissue during 30 minutes of perfusion and incorporated into neutral lipid, phosphatidylcholine, and phosphatidylethanolamine to a similar degree by ANTU-injured and control lungs. Lipoprotein lipase activity in homogenates of lungs from ANTU and Tween treated rats did not differ. We conclude that lungs are capable of hydrolysis of triglyceride contained in chylomicrons and that this endothelial cell associated metabolic function is not altered by acute lung injury caused by ANTU.

Effect of progesterone on the metabolism of noradrenaline in rabbit uterine endometrium and myometrium

The metabolism of (-)-3H-noradrenaline was examined in the endometrium and the myometrium from rabbits which had received 17 beta-oestradiol, either alone (oestrogen-dominated) or with progesterone (progesterone-dominated). The progesterone treatment resulted in a 2.5-fold increase in 3H-NMN formation in the endometrium, with no change in 3H-DOPEG, 3H-DOMA or 3H-OMDA formation. In the myometrium, progesterone caused a 5-fold increase in 3H-NMN formation and a 2.5-fold increase in 3H-OMDA formation, but did not affect 3H-DOPEG or 3H-DOMA formation. In the progesterone-dominated endometrium, both 3H-NMN and 3H-OMDA formation were strongly inhibited by cocaine 30 mumol/l. When O-methylation was inhibited by a COMT inhibitor, cocaine prevented the resultant increases in deamination of noradrenaline to 3H-DOPEG and in the accumulation of 3H-noradrenaline by the tissue. The 3H-noradrenaline which accumulated in endometria, in which both MAO and COMT were inhibited, was firmly bound; desipramine 3 mumol/l and (+)-amphetamine 10 mumol/l were equieffective with cocaine 30 mumol/l in inhibiting the accumulation. Cocaine 30 mumol/l was without effect on 3H-NMN and 3H-OMDA formation in the progesterone-dominated myometrium, nor did it prevent the increase in 3H-DOPEG formation produced by COMT inhibition. Fluorescent histochemical analysis of the endometrium indicated that the epithelial cells of the endometrial glands were the site of cocaine-sensitive noradrenaline accumulation. It is concluded that progesterone stimulates O-methylation in the endometrium and myometrium in different ways.(ABSTRACT TRUNCATED AT 250 WORDS)

Antioxidant enzyme content of pulmonary artery endothelial cells: effects of subculture

The activities of glutathione peroxidase, superoxide dismutase and catalase, enzymes which play a critical role in protection of the vascular endothelium from oxygen free-radical injury, were determined in large vessel endothelial cells obtained under three different growth conditions: from freshly isolated from bovine pulmonary arteries, in the first (primary) subculture and after six serial subcultures (6.5 population doublings). The endothelium was obtained by mechanically scraping the vascular lumen. Endothelial cell monolayers were detached mechanically from the substratum prior to passage. No proteolytic enzymes were used in either procedure. The activities of catalase, superoxide dismutase and glutathione peroxidase determined in freshly isolated endothelial cells were, respectively, 39.9 +/- 10.3, 2.2 +/- 0.8 and 3.0 +/- 0.5 X 10(2) units per mg protein. After primary culture there was no change in superoxide dismutase activity, but a significant decrease in glutathione peroxidase activity to 1.4 +/- 0.4 X 10(2) was observed, and catalase activity dropped significantly to 18.6 +/- 5.0 units per mg protein. After 6.5 population doublings, the activity of all three enzymes returned to values similar to those of the freshly isolated cells. A fourfold increase in the protein to DNA ratio occurred in cells in primary culture and was maintained in sixth-passage cells. This increase in endothelial cell size upon culture was reflected in the electron microscopic evidence of cellular hypertrophy. Measurement of the rate of transport of 5-hydroxytryptamine by endothelial cell monolayers revealed a substantial loss upon multiple passage. Transport in the sixth-passage cells was decreased to one-half the rate of primary cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of hyperoxia on biochemical indexes of pig aortic endothelial function

To determine what biochemical indexes might be useful in measuring the endothelial response to hyperoxia in vitro we exposed endothelial cell monolayers (ECM) from pig aortas to either hyperoxic (95% O2:5% CO2, 1 atm) or control conditions (95% air:5% CO2) and made the following measurements: (a) DNA and protein contents remaining in the ECM; (b) lactate dehydrogenase (LDH) activity in the medium; (c) the net uptake of rubidium (Rb+), adenine, and adenosine; and (d) cellular ATP and medium lactate. Twelve hours of hyperoxic exposure did not cause significant changes. After 24 or 48 h of hyperoxia, DNA and protein contents were decreased; LDH activity and the protein-to-DNA ratio were increased; adenosine uptake was decreased per ECM but was unchanged when corrected for culture DNA and protein contents. Adenine uptake was unaltered as were cellular ATP content and medium lactate concentration. The net Rb+ uptake-to-DNA ratio was increased after 24 h but not after 48 h of hyperoxia. The extent of the DNA and LDH changes indicated that the cellular disturbance caused by hyperoxia was progressive from 12 to 48 h. Presence of superoxide dismutase (250 U/ml) prevented both the increase of LDH activity and the decrease of protein after 48 h but did not affect the decrease of DNA. These results suggest that the cells remaining in the ECM after hyperoxia have normal biochemical function and may represent a subpopulation of cells more resistant to oxygen toxicity than the damaged cells.

Central control of vasopressin release and thirst

The effects of changes in the composition and/or the volume of the extracellular fluid on central receptors involved in the regulation of water balance are discussed. A review of results obtained in adults is given, followed by a discussion of possible roles for vasopressin during the neonatal period.

Catecholamine transport in isolated lung parenchyma of pig

1 Lung parenchyma strips of the pig incubated at 37 degrees C with [(3)H]-(-)-noradrenaline ([(3)H]-NA) or [(3)H]-(+/-)-isoprenaline ([(3)H]-Iso), accumulated radioactivity via saturable, high affinity uptake processes. Apparent saturation constants (K(m)) for [(3)H]-NA and [(3)H]-Iso were 1.34 x 10(-6) M and 1.63 x 10(-6) M respectively, while apparent transport maxima (V(max)) were 4.86 and 1.63 x 10(-9) mol min(-1) g(-1) respectively.2 Cellular accumulation of radioactivity from radiolabelled catecholamines was greatly reduced by lowering the temperature to 7 degrees C, pretreatment with ouabain (100 muM), phentolamine (15 muM) or phenoxybenzamine (80 muM). However, accumulation of radioactivity derived from ((3)H]-NA was inhibited selectively by cocaine (10 muM) and desipramine (1 muM), while normetanephrine (80 muM) and 3-O-methylisoprenaline (50 muM) caused much greater reductions in cellular radioactivity from [(3)H]-Iso than from ((3)H]-NA. Taken together with information from kinetic studies, the results indicate that these amines are transported by separate uptake processes.3 Cocaine (50 muM) which selectively reduced [(3)H]-NA transport, had no significant effect on the sensitivity (EC(50)) of isolated parenchyma lung strips of the pig to the contractile effects of cumulative concentrations of NA. The catechol-O-methyl transferase (COMT) inhibitor, U-0521 (60 muM), also failed to alter the potency of NA, while normetanephrine (80 muM) caused a 2 fold decrease in potency.4 Phentolamine (15 muM), which reduced the cellular accumulation of radioactivity derived from [(3)H]-Iso by 64%, caused a small potentiation of Iso-induced relaxations of porcine lung strips. Normetanephrine (80 muM) and 3-O-methylisoprenaline (50 muM), which also depressed the accumulation of cellular radioactivity from [(3)H]-Iso by > 50%, caused rightward shifts in Iso concentration-effect curves as a result of beta-adrenoceptor blockade. In sharp contrast, cortisol (80 muM) and U-0521 (60 muM), which caused smaller reductions in the cellular accumulation of radioactivity derived from [(3)H]-Iso, both caused an approximately 9 fold potentiation of responses to Iso in isolated lung strips.5 The results indicate that the major sites of uptake and metabolism of NA in porcine parenchyma strip are remote from alpha-adrenoceptors mediating NA-induced contraction. Similarly, some major sites of uptake of Iso are remote from beta-adrenoceptors mediating Iso-induced relaxation. However, beta-adrenoceptors are apparently in close proximity to a compartment containing COMT activity.

Effects of culture conditions and hyperoxia on antioxidant enzymes in pig pulmonary artery and aortic endothelium

Because hyperoxia induces early injury to lung endothelial cells and since tolerance to hyperoxia is correlated with increased lung antioxidant enzyme activity, we measured superoxide dismutase, catalase and glutathione peroxidase in both fresh isolates and primary cultures of endothelial cells from pig pulmonary artery and aorta. Cultured endothelial cells were studied at confluency and up to 5 days thereafter under control or hyperoxic conditions. In both types of confluent cell, total and cyanide-insensitive superoxide dismutase increased when compared to fresh cells. The most conspicuous postconfluency change in both types of endothelial cell was a marked decrease in glutathione peroxidase, which could be prevented by the addition of selenomethionine to culture media. A 5-day exposure to hyperoxia resulted in a 2-fold increase in cyanide-insensitive superoxide dismutase in both aortic and pulmonary artery endothelial cells. In view of a similar decrease in DNA in both types of cells despite some differences in enzyme levels, oxygen cytotoxicity could not be related to a particular antioxidant enzyme profile.

Uptake and release of 14C-morphine by pulmonary endothelium and cultured pulmonary endothelial cells

1. Isolated perfused rabbit lungs and cultured pulmonary endothelial cells take up radiolabeled [14C]morphine in proportion to the amount of labeled drug in the medium. 2. The accumulated label is readily released from the isolated lungs by perfusion with unlabeled morphine or naloxone, but not by perfusion with Krebs-Ringer solution, sucrose or thiopental. 3. Thiourea also enhances efflux of radioactivity, suggesting that the release is not related to interaction with specific opiate receptors. 4. Uptake of [14C]morphine by cultured rabbit or human endothelial cells is unaffected by morphine or naloxone, and the release of radioactivity is not enhanced by these agents. 5. None of the drugs used caused pulmonary edema in the isolated lung preparation, and they did not cause the release of lactic dehydrogenase from cultured endothelial cells. 6. It is concluded that morphine can be taken up by pulmonary endothelium, but it is probably not bound to specific receptors, and it does not injure the endothelial cells.

Stimulation of cyclic AMP production by vasoactive agents in cultured bovine aortic and pulmonary artery endothelial cells

The ability of selected vasoactive agents to influence cyclic AMP levels of confluent, early-passaged bovine calf aortic and pulmonary artery endothelial cells was investigated. Among the agents tested, only the catecholamines (isoproterenol, epinephrine, norepinephrine) and prostaglandins (PGE1, PGE2, PGF2 alpha) resulted consistently in increased cyclic AMP production in both cell populations. The degree of cyclic AMP stimulation obtained with other vasoactive compounds (angiotensins I and II, bradykinin, and serotonin) tended to be either very small or difficult to reproduce. Isoproterenol stimulation was blocked completely by propanolol, a beta-blocking agent, but not by phentolamine, and alpha-blocking agent. These results reveal that bovine calf aortic and pulmonary artery endothelial cells are responsive to catecholamines and prostaglandins, and therefore presumably possess both sensitive adenylate cyclases and plasma membrane receptors for these compounds.

Intracerebroventricular osmosensitivity in the Pekin Duck. Properties and functions in salt and water balance

Pekin ducks were implanted with devices allowing intracerebroventricular (i.c.v.) microinfusions at rates of 0.1--0.4 mul/min during 15 min in the conscious animals. When hydrated by intragastric infusion of 1 ml/min tap water, i.c.v. infusion of hypertonic NaCl solutions reduced urine flow and increased osmolality, presumably due to increased ADH release. Osmotically equivalent Li+ salts (Cl-, Br-, So24-) caused a slightly prolonged antidiuresis, while Ca2+ and Mg2+ salts caused a more protracted antidiuresis. Urea solution osmotically equivalent to 4.8% NaCl had no effect on diuresis, while osmotically equivalent mannitol solution slightly enhanced diuresis. Angiotensin II (0.5--2.5 pmol in 15 min) and Carbachol (3.0 pmol in 15 min) infused in 0.9% saline caused antidiuresis. The results suggest that the central control of ADH release in birds is similarly organized as in mammals, with receptive elements reacting to ionic rather than osmotic changes and with Na+ as the naturally involved cation. In ducks with their salt glands activated by i.v. infusion of 800 mosmol NaCl/kg H2O at 0.2 ml/min, salt gland secretion was not augmented by i.c.v. microinfusion of hypertonic NaCl but inhibited by i.c.v. infusion of osmotically equivalent mannitol solution. The supraorbital salt glands, when activated appear to be little stimulated further by a rise but may be inhibited by a fall of i.c.v. Na+ concentration.

Competition between platelets and lung for 5-hydroxytryptamine uptake

The pulmonary endothelial cell removes 5-5-hydroxytryptamine (5-HT) from the circulation by a process of uptake and metabolism. The platelet, the major source of 5-HT in the circulation, represents another potential site of uptake for this amine. Platelet uptake of 5-HT infused into the pulmonary circulation was evaluated using isolated ventilated rat lungs. Lungs were perfused with buffer, platelet-poor, platelet-rich, or thrombin-treated platelet-rich plasma followed by an infusion of (14C) 5-HT. Platelet counts, aggregation response to adenosine diphosphate, and in vitro uptake of 55-HT were unchanged after circulation through the lung. In the presence of buffer or platelet-poor plasma, the lung removed 65.5 +/- 1.4% and 67.8 +/- 0.8%, respectively, of the infused (14C) 5-HT. In the presence of platelet-rich plasma, the lung removed 51.3 +/- 3.0 and platelet fraction 30.1 +/- 1.4% of the infused (14C) 5-HT. Recently aggregated platelets removed 24.4 +/- 1.8%, whereas platelets exposed to low oxyygen tensions removed 14.7+/- 0.6% of the (14C) 5-HT. These results indicate that 5-HT released inot the pulmonary circulation is either taken up by the endothelium and metabolized or taken back up by the platelet and stored.

Uptake and metabolism of adenosine by pig aortic endothelial and smooth-muscle cells in culture

1. Adenosine, a potent vasodilator, is transported very efficiently by pig aortic endothelium in monolayer culture (approx. 50pmol/min per 10(6) cells at 2 micrometer). Uptake proceeds by diffusion at high (millimolar) substrate concentrations, and by two discrete transport processes (Km approx. 3 micrometer and 250 micrometer) at lower concentrations. Over 90% of the adenosine taken up at 10 micrometer or 100 micrometer is rapidly converted into adenine nucleotides (mainly ATP). 2. The high-affinity process is selectively inhibited by dipyridamole and by nitrobenzylthioinosine. Adenine preferentially inhibits the lower-affinity process, papapaverine inhibits both transport processes, and inosine has no significant effect. 3. Pig aortic smooth-muscle cells in culture show no high-affinity transport system for adenosine; uptake is much slower at low concentrations than that by endothelium (approx. 5pmol/min per 10(6) cells at 2 micrometer). Over 80% of the incorporated adenosine at 10 micrometer or 100 micrometer is rapidly converted into adenine nucleotides. 4. The uptake of adenosine by smooth-muscle cells is powerfully inhibited by adenine, but dipyridamole is much less potent than in endothelium. 5. We conclude that endothelial cells are mainly responsible for the removal of circulating adenosine.

CNS regulation of salt and water intake

The brain has evolved a number of mechanisms to maintain body fluid balance. They include the sensation of thirst, which stimulates water intake, the secretion of vasopressin, which helps prevent water loss, and the secretion of aldosterone, which helps prevent sodium depletion. In the research described here, all three mechanisms are shown to be mediated by the actions of angiotensin on the brain.

Converting enzyme activity in endothelial cells isolated from pig pulmonary artery and aorta

Converting enzyme activity was studied in endothelial cells, isolated from pig pulmonary arteries and aorta by exposure to collagenase. The measure was based on the release of His-Leu from Z-Phe-His-Leu was related to the DNA content of the cellular suspension. The same activity was found in the two types of endothelium: 1 nmol His-Leu/mug DNA per 30 min. Subendothelial cells showed a very low activity, amounting to 10% of the value found for the endothelium. The enzyme activity was 2inhibited by the nonapeptide SQ 20881, EDTA, and the lack of Cl- in the same fashion for the two types of endothelium. The presence of another enzyme hydrolyzing His-Leu was detected in both endothelial populations. Isolated fragments of plasma membrane, however, exhibited only converting enzyme activity. It can be concluded that endothelial cells isolated from large vessels of the pulmonary and the systemic circulations have similar properties when dipeptidyl carboxypeptidase activity is measured.