Issue published December 1, 1968

M ost of the information concerning secretion changes in follicle-stimulating hormone (FSH) in humans has been gained with relatively insensitive bioassays of concentrates of pools of urine. We have developed a sensitive and specific radioimmunoassay for FSH that is 500-1000 times more sensitive than the rat ovarianweight augmentation assay and which is capable of quantifying FSH in small volumes of serum. Anti-FSH was prepared by immunizing rabbits with an impure FSH preparation. The majority of antisera showed complete inability to distinguish LH, TSH, and FSH, illustrating the immunological similarities of these hormones. One antiserum was specific when used in a radioimmunoassay. Potency estimates by bioassay were in good agreement, with a single exception, with those obtained with the radioimmunoassay for 10 FSH-containing preparations. Highly purified LH gave a higher potency by immunoassay than by bioassay.Sera from eugonadal men contained 5-25 mIU/ml; sera from castrate men contained over 30 mIU/ml. Sera from eugonadal women contained 7-25 mIU/ml during the follicular phase and 5-15 mIU/ml during the luteal phase of the menstrual cycle. Sera from castrate or postmenopausal women contained 40-250 mIU/ml. FSH was measured throughout the menstrual cycle in 19 women. The general pattern that emerged is summarized as follows: there is a small early follicular phase rise in FSH, and then FSH is relatively constant until mid-cycle; in the majority of women a mid-cycle rise of FSH occurs coincidentally to the mid-cycle LH ovulatory peak; during the luteal phase FSH levels are relatively constant and lower than during the follicular phase. Nonsequential oral contraceptives containing estrogen and progestogen abolish these changes and FSH concentrations remain low throughout treatment. Treatment of castrate men and castrate or postmenopausal women with high doses of oral estrogens results in a fall of FSH to levels found in eugonadal men or women, but not to undetectable levels. Children less than 5 yr of age had undetectable FSH (< 5 mIU/ml).

T he excretion of mucopolysaccharides normally found in urine (chondroitin, chondroitin sulfates A and C, keratosulfate, and heparitin sulfate) is increased approximately twofold in patients with progresive exophthalmos. A threefold elevation of total serum mucopolysaccharides is also found. These increases are unrelated to thyroid function.

A irway conductance is known to increase with an increase in the lung volume at which it is measured, owing to a change in transpulmonary pressure and lung tissue tension. We investigated the effect of surgical resection of lung tissue on functional residual capacity and airway conductance in patients with localized lung disease (i.e., carcinoma or tuberculosis) and in patients with lung cysts or bullous emphysema. In four out of five of the patients who had resection of one or more lobes of the lung to remove localized disease there was a reduction both in the airway conductance and in the functional residual capacity with relatively little change in the conductance volume ratio.By contrast, in all patients who underwent bullectomy, there was a decrease in functional residual capacity but an increase in airway conductance, and an increase in the conductance/volume ratio. This change was sustained in patients who had had localized cysts removed. However, the measurements gradually reverted toward preoperative values in those patients who had generalized emphysema.The increase in airway conductance after resection of blebs and bullae presumably was due to improved lung elastic pressure causing the airways to increase in diameter and conductance. In addition, some patients may have experienced relief of compression of neighboring airways.

C alcium balances and calcium kinetic studies using ⁴⁷Ca were performed in nine male patients with idiopathic hypercalciuria and in three normal male subjects. A sharp reduction in calcium intake in eight patients with idiopathic hypercalciuria caused a decrease in urinary calcium excretion, the latter remaining elevated above that reported for normal subjects on a low calcium diet. The hypercalciuric patients had an enlarged miscible calcium pool size, an increased calcium turnover rate, increased bone formation and bone resorption rates, and an elevated true intestinal calcium absorption rate, the increase of the latter three parameters being proportional to the increase of the turnover rate. The fraction of the calcium turnover rate excreted in the urine was elevated whereas that constituted by the endogenous fecal calcium excretion was decreased. Arguments are presented for the concept that the primary abnormality in idiopathic hypercalciuria is neither renal calcium hyperexcretion nor intestinal calcium hyperreabsorption, but a more fundamental disturbance in calcium metabolism of as yet unknown cause, leading to a high calcium turnover.

C arbonate-¹⁴C was used to label the hepatic intracellular arginine pool and direct measurement of albumin synthesis was made in six rabbits before and after an 18-36 hr fast. 18 perfusion studies were performed with livers derived from fed and fasted rabbits (18-24 hr). Microsomal amino acid-incorporating ability with leucine-³H and phenylalanine-¹⁴C was compared in 17 studies, using microsomes isolated from livers taken from fed and fasted rabbits and from isolated perfused livers whose donors were fed and fasted.Albumin synthesis is rapidly inhibited by fasting. Albumin synthesis decreased 33% in vivo and 53% in the perfused liver. The microsomes from perfused livers taken from fed animals did not demonstrate a significantly reduced capacity to incorporate leucine-³H or phenylalanine-¹⁴C into protein. Microsomes derived from perfused and nonperfused livers whose donors were fasted incorporated 32-54% less tracer than microsomes obtained from fed donor rabbits. Microsomes separated from perfused livers removed from fed and fasted rabbits responded to polyuridylic acid stimulation and phenylalanine-¹⁴C incorporation rose from 58 to 171%.An 18-36 hr fast inhibits albumin production in vivo and in the perfused liver. The microsomal system is less active in the fasted state and perfusion per se does not inhibit the microsomal response.

I n response to intraluminal challenge with crude cholera exotoxin, canine Thiry-Vella duodenal loops consistently produced isotonic fluid for a 24-36 hr period. Isotonic fluid production generally began within 15 min after challenge. Mean bicarbonate concentration of fluid produced by duodenal loops was 24±6 (SD) mEq/liter. Perfusion of exotoxin-treated duodenal loops with an isotonic electrolyte solution containing glucose 60 mOsm/liter caused a significant decrease in exotoxin-induced isotonic fluid output. The net effects of glucose on isotonic fluid absorption by perfused duodenal loops were not significantly different before and after administration of crude cholera exotoxin.The response of canine duodenal loops to challenge by cholera exotoxin differs from responses of jejunal and ileal loops in a) absence of a detectable “lag period” between administration of exotoxin and initiation of net fluid output; b) a longer period of fluid production following exotoxin administration; and c) a significantly greater net fluid output per unit length of gut. The mean bicarbonate concentration of the fluid produced by duodenum is less than that produced by ileum, but is not significantly different from that produced by jejunum. The duodenal response is similar to that of the more distal small bowel segments in that an effect on isotonic fluid movement is observed shortly after exotoxin administration and the maximum rate of exotoxin-induced isotonic fluid production is not reached until 4-5 hr after exotoxin administration. The basis for the consistent delay of 4-5 hr between intraluminal exotoxin administration and maximum gut fluid production has not yet been determined.Current data are consistent with the hypothesis that the rate of secretion of isotonic fluid induced by cholera exotoxin is not significantly different per unit length, in duodenum and ileum and that the lesser net fluid output in the ileum is due to the greater capacity for isotonic fluid absorption by the more distal small bowel segment.

P urified acid-soluble and insoluble human collagen accelerated the clotting of plateletpoor plasma in silicone-treated tubes. The clot-promoting effect did not appear to be due to thromboplastic activity since the collagen preparations did not activate factor X in the presence of factor VII and calcium. Instead, collagen appeared to accelerate clotting by activating Hageman factor (factor XII) on the basis of the following findings: collagen increased the clot-promoting activity of partially purified Hageman factor but exerted no further effect in the presence of kaolin, a known activator of Hageman factor; clot-promoting eluates were obtained from collagen exposed to normal, hemophilic, or PTC-deficient plasma but not from collagen exposed to Hageman or PTA-deficient plasma. The collagen molecule itself appeared to be required for the clot-promoting activity since digestion with collagenase or thermal denaturation at pH 2.5 (about 35°C) resulted in very marked reduction in clot-promoting activity. Since thermal denaturation is associated with transformation of collagen structure from triple helical to random coil form, it is suggested that the native form of collagen is essential for the ability to activate Hageman factor.Blockage of the free amino groups by treatment with nitrous acid or dinitrofluorobenzene only slightly reduced the clot-promoting activity of collagen. In contrast, since addition of cationic proteins to collagen markedly reduced pro-coagulant activity it is suggested that negatively charged sites on the collagen molecule are critical for Hageman factor activation. This suggestion is supported by the finding that pepsin treatment of collagen, which removes the predominantly negatively charged telopeptides, results in significant decrease in coagulant activity. Esterification of collagen, which neutralizes 80-90% of the free carboxyl groups, reduced coagulant activity by over 90% and it is suggested that the free carboxyl groups of glutamic and aspartic acids provide the negatively charged sites critical for Hageman factor activation.

I n studying some of the properties of collagen responsible for the ability to aggregate platelets it was found that thermal treatment at pH 2.5 of acid-soluble human collagen resulted in a sharp reduction in relative viscosity and platelet aggregating activity at about 35°C. The reduction in viscosity is known to be associated with structural transition from triple helical to random coil form and it is postulated that the native structure of collagen is essential for its platelet aggregation effect. Blockage of the free amino groups by deamination, N-acetylation, or treatment with dinitrofluorobenzene resulted in over 90% reduction in platelet aggregating activity. Addition of cationic proteins to collagen, removal of the negatively charged telopeptides by treatment with pepsin, or acetylation of the free carboxyl groups did not significantly affect the platelet aggregating activity of collagen. On the basis of these findings it is suggested that the free amino groups and specifically the epsilon amino groups of lysine are critical for the platelet aggregating activity of collagen whereas the carboxyl groups are of relatively little importance.

T his report suggests a mechanism for collagen degradation mediated by human granulocytic leukocytes. A specific collagenase, which is extractable from human granulocytes, has been partially purified by DEAE chromatography. This collagenolytic enzyme is operative at physiological pH and is inhibited by EDTA, cysteine, and reduced glutathione but not by human serum. The enzyme cleaves the collagen molecule into two specific products, without loss of helical conformation. Electron micrographs of segment long spacing aggregates indicate that the cleavage occurs one-quarter of the length from the carboxy terminal end of the molecule. Experiments with crude extracts from granulocytes suggest that the specific products of granulocyte collagenase activity are then degraded by other proteases present in the human granulocyte.

T he in vitro incorporation of inorganic ³²P into erythrocyte phospholipids has been studied in normal subjects and in splenectomized patients with hereditary spherocytosis (HS). Phosphatidic acid (PA) was the only lipid measurably labeled in both kinds of cells. The actual turnover rate of PA phosphate was determined by simultaneously isolating inorganic phosphate (P_i) and adenosine triphosphate (ATP) and determining their specific activities. This turnover is very small: 1.3 μmoles P/liter of erythrocytes per hr in normal cells and 4.0 μmoles P in HS erythrocytes when either ATP or cellular P_i is considered the immediate precursor. This value represents less than 0.1% of the total membrane lipid phosphate. Incorporation of added ³²P_i into the other phosphatides, including phosphatidyl serine, was essentially zero in both kinds of cells.The effects of stimulation and inhibition of active cation transport, metabolic depletion, and extracellular phosphate concentration on both the degree of labeling and the actual turnover of PA phosphate were studied. In any given experiment, the degree of labeling of PA depended on the specific activities of the other intracellular phosphates (P_i and ATP). The actual turnover rate of PA phosphate, however, did not vary with active transport or metabolic depletion. The greater turnover of PA phosphate in HS erythrocytes may be due to the somewhat younger age of these cells. The results suggest that the very low turnover of PA phosphate in erythrocytes is mediated by nonspecific enzyme reactions, and that it is quantitatively insignificant in both normal and HS erythrocytes. The results also emphasize the importance of measuring intracellular phosphate precursors in any study evaluating cellular phospholipid turnover from added ³²P_i.

F ragments of synovium from patients with rheumatoid arthritis survive in defined tissue culture medium in the absence of added serum and, after 3-4 days, release into the medium enzyme capable of degrading undenatured collagen. Maximal activity is observed at pH 7-9 but the enzyme is inactive at pH 5. At temperatures of 20° and 27°C, collagen molecules in solution are cleaved into 3/4 and 1/4 length fragments with minimal loss of negative optical rotation, but with loss in specific viscosity of approximately 60%. Above 30°C the fragments begin to denature and denaturation is complete at 37°C. If the enzyme is not inhibited at this stage the large fragments are broken down further to polypeptides of low molecular weight. Reconstituted collagen fibrils and native fibers at 37°C are cleaved to the low molecular weight fragments, although the fibrils are resistant to breakdown at lower temperatures (20°-27°C). It is proposed that the production of such an enzyme by inflamed and proliferating rheumatoid synovium may be responsible for some of the destruction of collagenous structures that accompanies rheumatoid arthritis.

T he relationship between oxygen dissociation and 2,3-diphosphoglycerate (2,3-DPG) in the red cell has been studied in subjects moving from low to high altitude and vice versa. Within 24 hr following the change in altitude there was a change in hemoglobin affinity for oxygen; this modification therefore represents an important rapid adaptive mechanism to anoxia. A parallel change occurred in the organic phosphate content of the red cell. While this study does not provide direct evidence of a cause-effect relationship, the data strongly suggest that with anoxia, the observed rise in organic phosphate content of the red cell is responsible for increased availability of oxygen to tissues.

T he mean half-life of dicumarol in the plasma of seven sets of identical and seven sets of fraternal twins after a single oral dose of 4 mg/kg was 43.6±SD 17.9 hr. Half-lives ranged from 7 to 74 hr in these 28 normal adults not receiving other drugs for 2 wk preceding dicumarol administration. Large differences among unrelated individuals in dicumarol half-life disappeared almost completely in identical twins, but persisted to some extent in most sets of fraternal twins. These results indicate that marked differences among subjects in dicumarol half-life are under genetic rather than environmental control. Reproducibility of values for dicumarol half-life was demonstrated. A direct relationship between the dose and the half-life of dicumarol occurred in unrelated volunteers administered progressively larger doses at 10-day intervals. Dose dependence of the half-life of a drug results in increased variability of half-life and hence in greater risks of toxicity on long-term therapy. Risks of toxicity on the one hand and of failure to anticoagulate adequately on the other can be reduced by determining dicumarol half-life before starting long-term therapy. Half-lives for dicumarol and phenylbutzone tended to be correlated in the 28 twins, but no correlation occurred between dicumarol and antipyrine half-lives.

T he mechanisms of hemoglobin precipitation into Heinz bodies and hemolytic anemia that characterize congenital Heinz body hemolytic anemia (CHBHA) were studied in patients with the unstable hemoglobins, Köln (β-98 valine → methionine) and Hammersmith (β-42 phenylalanine → serine). The cysteines in the 93rd position of the β-chains of CHBHA hemoglobins bound glutathione excessively in mixed disulfide linkage. The resulting diminished “free” GSH within the cell accelerated hexose monophosphate shunt metabolism. The unique precipitability of CHBHA hemoglobins when heated at 50°C could be induced in normal hemoglobin A by artificially blockading its sulfhydryl groups with paramercuribenzoate (PMB).Reflecting the previously reported excessive flux of hemes from hemoglobin Köln, the expected heme/globin ratio in this hemoglobin was reduced by 30%. The further increment in heme loss that occurs with heat (50°C) underlies the unique heat precipitability of CHBHA hemoglobins; it was retarded if detachment of heme was inhibited by cyanide or carbon monoxide.Heinz bodies were attached to red cell membrane thiol groups presumably through mixed disulfide bonds, being released by mercaptoethanol. Binding of hemoglobin Köln-⁵⁹Fe to red cell ghosts, which was markedly enhanced when Heinz bodies were generated at 50°C, was inhibited if membrane thiols were preblockaded by PMB. The depletion of membrane thiols by their reaction with Heinz bodies rendered CHBHA red cells hypersusceptible to membrane sulfhydryl inhibitors, as manifested by inordinate cation leakage, osmotic fragility, and autohemolysis.We conclude that both cellular and membrane thiols bind β-93 sulfhydryls of CHBHA hemoglobins as mixed disulfides. Concomitantly, heme avidity to β-92 lessens, suggesting that degradation of the resulting excessively freed heme may produce the pigmented dipyrroluria of this syndrome. Heinz bodies, reflecting the heightend precipitability of heme-deficient globin, attach to, thereby depleting, membrane sulfhydryl groups. This, as shown previously, could underlie the hemolytic anemia of this syndrome by causing membrane hyperpermeability, premature splenic entrapment, and ultimately osmotic destruction of red blood cells.

T otal nonsuppressible insulin-like activity (ILA) of human plasma (measured by the adipose tissue assay) results from the additive effects of at least two distinct components. They differ in molecular size, solubility in acid-ethanol, and in thermostability. More than 90% of nonsuppressible ILA of human plasma is insoluble in acid-ethanol. Its molecular size of 100,000-150,000 remains unchanged by treatment with acid-ethanol, 5 M acetic acid-0.15 M NaCl, urea, and EDTA. It is inactivated by heat.Approximately 5% of total nonsuppressible serum ILA is soluble in acid-ethanol. The molecular weight is 6000-10,000 after partial purification on Sepadex G-75 (acetic acid-NaCl). This molecule is thermostabile for 3 hr at 80°C.When the acid-ethanol soluble molecule with nonsuppressible ILA is chromatographed on Sephadex G-100 at neutral pH, it is eluted in a broad peak corresponding to a molecular weight of approximately 50,000-70,000. When rechromatographed on Sephadex G-75 (acetic acid-NaCl) its mol wt is irreversibly converted from 70,000 to 6000.Most of the insulin-like activity retained on Dowex-50 (“bound insulin”) is eluted off Sephadex G-75 (acetic acid-NaCl) at the same column volume as the small molecular weight nonsuppressible ILA. The latter molecule is retained on Dowex-50, whereas big molecular weight nonsuppressible ILA is not.

T he disappearance of bacteria from the normal urinary bladder is apparently a function of two host defense mechanisms: the mechanical clearance of organisms by voiding, and the antibacterial activity of the bladder wall. This study quantified the relative contribution of each of these mechanisms to the resistance of the bladder to bacterial infection.³²Phosphorus-labeled E. coli. S. aureus, and P. mirabilis were each injected into the urinary bladders of unanesthetized female guinea pigs. At intervals after voiding, the bladders were removed, washed, homogenized, and assayed for residual radioactivity and viable bacteria. Mechanical clearance was measured by the changes in total radioactive count. Antibacterial activity was quantified by comparing the bacterial to radioactive ratios of the original bacterial inoculum with similar ratios in the bladder homogenates.More than 99.9% of the bladder inoculum was rapidly excreted and about 0.1% (10⁴-10⁵) organisms remained attached to the bladder wall. Of those E. coli attached to the bladder, rapid sequential reduction in viability occurred and reached a level of 85% loss at 30 min after inoculation. 4 hr after challenge, less than 10% of those organisms still attached to the bladder mucosa remained viable. P. mirabilis was handled with equal facility, but S. aureus showed a reduction in viability of only 46% at 1 hr and 67% at 4 hr after inoculation. 6 hr after infection with S. aureus, 6 of 12 guinea pig bladders showed multiplication of the organisms still attached to the bladder wall; only 1 of 12 animals challenged with E. coli had comparable multiplication.The mechanism whereby the bladder wall kills bacteria is unclear, but it did not appear to be related to an antibacterial activity of urine, clumping of organisms on bladder mucosa, phagocytosis by leukocytes, or serum levels of bactericidal antibody. Although it is clear that the bladder exhibits intrinsic antibacterial properties, the role of this defense mechanism in the pathogenesis of urinary tract infection requires further clarification.

T he toxic effects associated with rapid lipid mobilization and a high plasma free fatty acid (FFA) concentration produced by glucagon were evaluated. Glucagon (0.5 mg/kg of body wt) was injected intravenously into nonfasting geese. The geese developed rapid respirations and high plasma FFA levels within 15 min after the glucagon injection; three of eleven died. Control geese, injected with saline, did not exhibit toxic signs. Peak FFA concentrations developed 15 min after glucagon and high levels persisted for over 90 min. Geese injected with glucagon frequently developed electrocardiographic abnormalities that included supraventricular tachycardia, premature ventricular contractions, and signs of myocardial ischemia. Light and electron microscopy revealed acute myocardial degeneration and fatty infiltration of the liver. The increase in plasma FFA concentrations and toxic effects were not prevented by pretreatment with nicotinic acid or propranolol.

T he present investigation was intended to evaluate myocardial inert gas desaturation curves for manifestations of heterogeneous coronary perfusion. The test gas was hydrogen (H₂) and blood H₂ analyses were performed with a gas chromatograph capable of detecting small but prolonged venous-arterial H₂ differences produced by areas of reduced flow. Curves were initially obtained after 4-min left ventricular infusions of H₂-saturated saline in six patients with arteriographically proven coronary artery disease, three patients with normal coronary arteries, and nine closed-chest dogs. The dogs were studied before and after embolic occlusion of a portion of the left coronary artery. Although the slopes of their semilogarithmically plotted venous desaturation curves varied with time before embolization, they showed more distinct deviations from single exponentials after embolization (after H₂ concentrations had fallen below 15% of their initial values). The human curves divided similarly, those from coronary artery patients deviating appreciably from single exponentials. A similar separation was also evident in studies of coronary venous-arterial H₂ differences after 20 min of breathing 2% H₂: data were obtained in four dogs before and after coronary embolization, and in three normal patients, and five patients with coronary artery disease. Additional data indicated that the findings were not the result of right atrial admixture in sampled coronary venous blood, although admixture occurred frequently when blood was sampled in the first 2 cm of the coronary sinus (as seen in the frontal projection). Finally, average coronary flows calculated from a given set of data varied significantly with different methods of calculation. Areas of below-average flow seemed likely to be overlooked when single rate constants of desaturation, relatively insensitive analytical techniques, or relatively short periods of saturation and (or) desaturation are employed.

T echniques are described in detail for a radioimmunoassay of plasma adrenocorticotropin (ACTH) that is capable of detecting hormone in unextracted normal human plasma at 1:5 dilution under the conditions described. The sensitivity of the assay is at the level of 1 μμg/ml (equivalent to 0.014 mU/100 ml).In normal subjects ACTH concentrations averaged 22 μμg/ml (equivalent to 0.308 mU/100 ml) plasma at 8-10 a.m. In a smaller group the concentrations averaged 9.6 μμg/ml (equivalent to 0.134 mU/100 ml) at 10-11 p.m. Although a circadian rhythm in normal subjects was not always well marked throughout the daytime hours, plasma ACTH usually fell to its lowest value in the late evening. In hospital patients who were not acutely ill, concentrations were infrequently above 100 μμg/ml in the morning and usually fell to significantly lower levels in the late evening. Severely ill hospital patients occasionally exhibited a.m. concentrations above 200 μμg/ml.In a group of subjects showing frequent spiking of plasma 17-OHCS concentrations throughout the day parallel spiking of plasma ACTH as well was generally observed.Metyrapone produced marked increases in plasma ACTH within 24 hr in all cases and generally within 3-6 hr except when started late in the day. Dexamethasone brought about a persistent reduction in plasma ACTH in a patient under continued treatment with metyrapone.Hypoglycemia, electroshock, surgery under general anesthesia, histalog and vasopressin administration were usually followed by significant increases in plasma ACTH concentration. Prior administration of dexamethasone blocked the response to hypoglycemia.Marked elevations in plasma ACTH were observed in patients with adrenal insufficiency off steroid therapy, in Cushing's disease after adrenalectomy even in the presence of persistent hypercortisolemia, and in some untreated patients with Cushing's disease.Umbilical cord blood contained higher plasma ACTH concentrations than maternal blood at delivery in seven of eight cases.After suppression of ACTH secretion by dexamethasone or cortisol. ACTH disappeared from plasma with half-times ranging from 22 min to 30 min in three cases studied.

P revious studies have demonstrated that electrically induced seizures in rat result in an increased brain intracellular sodium which can be decreased by treatment with sodium diphenylhydantoin (DPH). The correlation of cation transport with membrane-oriented sodium-potassium-adenosine triphosphatase (Na-K-ATPase) prompted an investigation of the effect of DPH upon ATPase enzyme activity.Rat cerebral cortical synaptosomes isolated in Ficoll gradients were employed as the source for Na-K-ATPase. With 50 mM Na, 10 mM K, 7.5 mM Mg, and 1.8 mM ATP, the specific activity of the preparation was 70 μmoles P_i released/mg synaptosomal protein per 30 min. The ionic and substrate concentrations yielding one-half maximal velocity were 0.5 mM K, 5 mM Na, and 8.5 × 10^-5 M ATP, respectively.At 50 mM Na and 0.2 mM K, DPH produced an average of 92% stimulation of P_i release above control. The ratio of Na:K rather than the absolute levels of the ions was critical in determining the effect of DPH. DPH produced significant stimulation of enzyme activity under conditions of a high Na:K ratio (25-50:1). At ratios of 5-10:1, DPH produced little or no effect, and at low Na:K ratios (less than 5:1), DPH was inhibitory. Under all ionic conditions examined, DPH produced no apparent change in enzyme affinity for ATP.Assuming the proposed association of Na-K-ATPase with cation transport in brain, the data suggest the possibility that DPH may control seizures by its stimulation of Na-K-ATPase activity.