Cerebral vessels have the capacity to transport sodium and potassium.

The activity of Na+, K+-activated adenosinetriphosphatase and the uptake of a potassium analog, rubidium, were found to be similar in cerebral microvessels and choroid plexus when measured in vitro. This similarity suggests that sodium and potassium concentrations in the nascent brain extracellular fluid are determined by the same active process that regulates their concentration in nascent cerebrospinal fluid. The brain microvessels may thereby play on active role in brain potassium homeostasis and brain extracellular fluid formation.

In vitro demonstration of an endothelial proliferative factor produced by neural cell lines.

Cultured endothelial cells exhibit a six- to tenfold increase in thymidine labeling index in response to a soluble factor elaborated by clonal cell lines of neural origin. This factor, endothelial proliferation factor, appears to be a unique property of tumor cells and may mediate the vascularization of these neoplasms.

Effective and fibrin-specific clot lysis by a zymogen precursor form of urokinase (pro-urokinase). A study in vitro and in two animal species.

A single-chain 55,000-mol wt form of urokinase (UK), similar to that previously isolated from urine, was purified from a transformed kidney cell culture medium and characterized; and its fibrinolytic properties were evaluated. The preparation immunoprecipitated with UK antiserum, had a low intrinsic amidolytic activity that was 0.1% of its active derivative, and resisted diisopropyl fluorophosphate treatment and inactivation by plasma inhibitors. The single-chain UK was therefore designated pro-UK. In the presence of plasmin and during clot lysis, activation by conversion to two-chain, 55,000-mol wt UK (TC-UK) was demonstrated. This did not occur during blood clotting nor on incubation with purified thrombin. Clot lysis in plasma consistently occurred in 2-5 h with 50-100 IU per ml of pro-UK, whereas comparable lysis was inconsistently achieved by 500-1,000 IU of UK. Pro-UK, in sharp contrast to UK, caused no fibrinogen degradation at fibrinolytic concentrations. In the absence of a clot, pro-UK in plasma was stable for more than 2 d. When a clot was added after incubation (37 degrees C) for 50 h, activation to full lytic activity took place. The findings in vivo were comparable but the rapid clearance of pro-UK required that it be given by a constant infusion despite its plasma stability. In rabbits, a UK-resistant species, pro-UK was significantly (P less than 0.001) more efficacious than TC-UK but neither induced significant fibrinogen degradation. In dogs, a more sensitive species, the high specificity of thrombolysis by pro-UK contrasted with the defibrinogenation and uncontrollable bleeding that accompanied thrombolysis by UK. It was concluded that clot lysis by pro-UK is more effective and specific than UK. The advantage of pro-UK is in the limitation of its activation to the site of a clot. This can be explained by an activation mechanism that is dependent, under physiological conditions, on fibrin-stabilized plasmin.

Action of pancreatic polypeptide on exocrine pancreas and on release of cholecystokinin and secretin.

We have studied the effect of exogenous porcine pancreatic polypeptide (PP; 0.8 and 2.1 microgram/kg . h, iv) on endogenously stimulated pancreatic exocrine secretion in five pancreatic-fistula dogs. Plasma levels of cholecystokinin (CCK), secretin, and PP were measured in addition to pancreatic secretion of water, bicarbonate, and protein. Intraduodenal infusions of acid and a mixture of phenylalanine and tryptophan were used to stimulate hormone release. PP caused a dose-dependent inhibition of endogenously stimulated pancreatic secretion, whereas the release of CCK and secretin was not affected. Duodenal acidification and intraduodenal infusion of phenylalanine and tryptophan caused a significant release of PP. This study shows that: 1) PP suppresses pancreatic secretion by means of a mechanism that is probably direct; this effect is not mediated through inhibition of release of CCK or secretin, and 2) phenylalanine and tryptophan, both strong stimulants of CCK release, cause a substantial rise in PP in peripheral blood. The mechanism of PP release may involve CCK (in previous studies, we have shown a rise in circulating PP levels after iv CCK infusion).

Release of antral gastrin in response to an intestinal meal in dogs.

This study was designed to determine whether gastrin is released by the antrum in response to an intestinal meal in dogs. Two groups of anesthetized dogs were prepared with innervated antral pouches. The antrum and duodenum were separated by complete division at the pylorus to prevent duodenoantral reflux. The duodenum and proximal jejunum were perfused with 10% liver extract at 200 ml/hr. In one group of six dogs a significant elevation of antral vein gastrin levels was observed after 45 minutes. Gastrin levels in portal and peripheral blood were not significantly elevated. In another group of eight dogs, in which antral veins were not cannulated, a significant rise in peripheral gastrin concentration was noted after 60 minutes. We conclude that gastrin is released by the antrum during the intestinal phase of gastric acid secretion; significantly increased levels of gastrin are detected in both antral and peripheral venous blood. Duodenoantral reflux, as a possible cause of this release, is ruled out by complete surgical separation between duodenum and antrum.

Endothelial growth factor present in tissue culture of CNS tumors.

Human endothelial cells obtained from postpartum umbilical veins and placed in primary tissue cultures were treated with media from cultures of human and experimental central nervous system tumors. Endothelial proliferation was determined by the uptake of 3H thymidine with autoradiography and represented as the thymidine labeling index (TI), which is the proportion of 3H thymidine-labeled endothelial cells to total number of cells counted. There was a marked increase in the TI when tumor-conditioned medium was added to endothelial cultures (range 28.7% to 98.3%) when compared to controls (2.1%) and endothelium with conditioned media from fibroblasts (4.5%). This study demonstrates the presence of a chemical substance produced by tumor cells which results in endothelial proliferation. The system described provides a useful assay technique for the further characterization of this endothelial growth factor.

Uptake of neurotransmitters and precursors by clonal lines of astrocytoma and neuroblastoma: III. Transport of choline.

Clonal lines of glial, neuronal, and nonneural origin accumulate choline via a high-affinity carrier-mediated transport system withK m in the range of 10-14 µM. These cell lines also accumulate choline by a second system that is not saturable at 10 mM choline, and that may represent diffusion. The transport of choline in glial cells differs from that seen in neuronal cells with respect to its Na(+) requirement. The omission of Na(+) from the incubation medium reduces high-affinity choline transport in neuronal cells and enhances it in glial cells. Kinetic analysis of the data indicates that reversible cholinesterase inhibitors and hemicholinium-3 (HC-3) inhibit the high-affinity transport system for choline. On the other hand, the diffusional or low-affinity component of choline transport in either cell type appears to have no Na(+) requirement and is unaffected by either cholinesterase inhibitors or 10(-4) M HC-3. The neuronal-glial differences in the Na(+) requirement of choline transport may be related to the coupling of transport to choline metabolism, which differs in the two cell types. The presence of a high-affinity transport system for choline in clonal glial lines used as models of normal glia suggest that glia may modulate the availability of choline for acetylcholine synthesis at cholinergic synapses.

Stability, potency, and preservative effectiveness of epoetin alfa after addition of a bacteriostatic diluent.

The stability, potency, and preservative effectiveness of two dilutions of epoetin alfa containing a bacteriostatic diluent were studied. Epoetin alfa 10,000 units/mL in single-use vials was diluted 1:1 and 1:1.5 with bacteriostatic 0.9% sodium chloride injection. USP tests of preservative effectiveness were performed on samples from two batches each of the 1:1 and the 1:1.5 dilutions. Appearance assessment, Western blot analysis, radioimmunoassay, and bioassay were used to determine the stability or potency of samples from three batches of each dilution that were stored at 5 degrees C or at 30 degrees C for 12 weeks. Both batches of the 1:1.5 dilution (epoetin alfa 4,000 units/mL with 0.54% benzyl alcohol) met the USP criteria for preserved solutions, while one batch of the 1:1 dilution (epoetin alfa 5,000 units/mL with 0.45% benzyl alcohol) did not. Epoetin alfa 10,000 units/mL diluted either 1:1 or 1:1.5 with bacteriostatic 0.9% sodium chloride injection and stored at 5 degrees C or at 30 degrees C remained stable and potent for 12 weeks. The addition of 1.5 mL of bacteriostatic 0.9% sodium chloride injection to a vial containing 1 mL of epoetin alfa 10,000 units/mL makes a solution of epoetin alfa 4,000 units/mL that meets the USP criteria for preservative effectiveness and remains stable and potent for 12 weeks at 5 degrees C.

Release of pancreatic polypeptide in humans by infusion of cholecystokinin.

Plasma levels of pancreatic polypeptide were measured after a test meal and after infusion of graded doses of 99% pure cholecystokinin in 6 healthy volunteers. Initial attempts at sterilization of 99% pure cholecystokinin resulted in complete inactivation. Successful sterilization was accomplished by filtration by using specially treated silver-coated filters. Biologic activity of sterilized material was confirmed with cholecystokinin bioassay, and plasma levels of sterilized cholecystokinin achieved by exogenous infusions were measured with a specific cholecystokinin radioimmunoassay. Significant increases in plasma levels of pancreatic polypeptide were found with a test meal and with infusions of 0.25 and 0.5 micrograms/kg-hr of 99% pure cholecystokinin. Integrated values of pancreatic polypeptide released by the low-dose and the high-dose infusions of 99% pure cholecystokinin were 59% and 50% of that obtained by food, respectively. Integrated levels of cholecystokinin after 45 min of infusion of 0.25 micrograms/kg-hr were equal to those after a standard meal. Cholecystokinin, therefore, is an effective humoral releaser of pancreatic polypeptide in humans and may play an important role in the intestinal phase of release of pancreatic polypeptide.