Phase I-II study of combined 5-fluorouracil and cisplatin chemotherapy and altered fractionation radiotherapy for advanced squamous cell carcinoma of the cervix

Forty patients with advanced carcinoma of the cervix were prospectively treated by an intermodality approach using chemotherapy combination concomitant with split-course hyperfractionated radiation therapy (RT). Cisplatin (CDDP) (60 mg/m2) was administered before radiotherapy initiation followed by 5-fluorouracil (5-FU) (750 mg/m2) for 5 days during the first week of irradiation. The same schedule was repeated in the last week of the RT, with 5-FU administration (1,000 mg/m2) for only 3 days. RT consisted of 5,020 cGy to the pelvis, followed by two intracavitary applications for a total of 5,000-5,500 mg/h radium equivalent when possible: 140 cGy/fraction was administered in the morning and evening, with a 6-h interval. The remainder of the external beam radiation was delivered at a standard daily fractionation of 180 cGy/fraction to a total dose of 5,020 cGy. This regimen of RT with concomitant chemotherapy had minimal toxicity and did not cause significant prolongation of the treatment program. However, a high rate of late complications was noted in patients who had extended-field RT due to paraaortic lymph node involvement. Thirty-two patients had complete response (CR) (80%). 24 (75%) of whom have no evidence disease (NED), with a median follow-up of 24 months. Our study suggests that this regimen of combined chemotherapy and RT in this group of patients with poor prognosis is effective and well tolerated, with acceptable acute toxicity and late morbidity.

Intestinal absorption studies on peptide mimetic alpha-methyldopa prodrugs

Two dipeptide mimetic prodrugs, 1 and 2, and two tripeptide mimetic prodrugs, 3 and 4, of L-alpha-methyldopa were evaluated for intestinal absorption by in-situ single pass rat jejunal perfusion studies and by in-vitro uptake experiments in brush-border membrane vesicles (BBMVs) prepared from rat intestine. In the perfusion studies, compound 1 demonstrated a 3.5-fold increase in permeability (Pm* = 2.27) as compared with that of alpha-methyldopa (Pm* = 0.65), indicating that this prodrug was better absorbed in the intestine than its parent drug. Other prodrugs showed no significant improvement in intestinal permeability. The results correlated with the results of BBMV uptake studies. In the presence of an inward proton gradient, compound 1 showed Michaelis-Menton saturable kinetics of BBMV uptake with a low value of K(m) (0.06 +/- 0.13 mM) and a high value of Vmax/K(m)(36.38 nmol (mg protein)-1/30s mM-1) at a low concentration range and a linear uptake at high concentrations with Kd = 0.14 +/- 0.02 mM. Compounds 2 and 3 were mainly taken up in BBMVs via passive diffusion. Compound 4 was taken up in BBMVs basically via the carrier-mediated transport system, while the rate of uptake was much lower than that of compound 1. The uptake of compounds 1 and 4 was significantly inhibited by dipeptides L-Gly-L-Pro and L-Gly-L-Phe, and cephradine, a beta-lactam known to be transported via the dipeptide carrier system, indicating that both compounds were taken up in BBMVs via the H(+)-coupled dipeptide-mediated transport system. In contrast to the complicated uptake profile of alpha-methyldopa, the higher rate of BBMV uptake with less variation demonstrated on compound 1 suggested that the attached nonessential amino acid moiety, D-phenylglycine, is a feasible delivery tool in carrying the parent drug through the intestine.

Poliovirus chimeras replicating under the translational control of genetic elements of hepatitis C virus reveal unusual properties of the internal ribosomal entry site of hepatitis C virus

Chimeric genomes of poliovirus (PV) have been constructed in which the cognate internal ribosomal entry site (IRES) element was replaced by genetic elements of hepatitis C virus (HCV). Replacement of PV IRES with nt 9-332 of the genotype Ib HCV genome, a sequence comprising all but the first eight residues of the 5' nontranslated region (5'NTR) of HCV, resulted in a lethal phenotype. Addition of 366 nt of the HCV core-encoding sequence downstream of the HCV 5'NTR yielded a viable PV/HCV chimera, which expressed a stable, small-plaque phenotype. This chimeric genome encoded a truncated HCV core protein that was fused to the N terminus of the PV polyprotein via an engineered cleavage site for PV proteinase 3CPpro. Manipulation of the HCV core-encoding sequence of this viable chimera by deletion and frameshift yielded results suggesting that the 5'-proximal sequences of the HCV open reading frame were essential for viability of the chimera and that the N-terminal basic region of the HCV core protein is required for efficient replication of the chimeric virus. These data suggest that the bona fide HCV IRES includes genetic information mapping to the 5'NTR and sequences of the HCV open reading frame. PV chimeras replicating under translational control of genetic elements of HCV can serve to study HCV IRES function in vivo and to search for anti-HCV chemotherapeutic agents.

Canyon rim residues, including antigenic determinants, modulate serotype-specific binding of polioviruses to mutants of the poliovirus receptor

Several mouse cell lines expressing hybrid human poliovirus receptors (hPVRs) bearing mutations in the first immunoglobulin-like domain were previously characterized for their defective binding and replication of poliovirus type 1 Mahoney (G. Bernhardt, J. Harber, A. Zibert, M. DeCrombrugghe, and E. Wimmer, Virology, 203, 344-356, 1994). Here we report that these mutant hPVRs were utilized to explore differences in the binding behavior of the three serotypes of poliovirus. Type 3 polioviruses (both Sabin and the neurovirulent Leon strain) clearly bound to the hPVR mutant Q130G/GD, but were incapable of initiating infection. Also, binding at 25 degrees of poliovirus types 2 and 3 to cell lines expressing the hPVR mutants P84SYS/HPGA, L99GAE/AAAA, and D117F was greater than type 1 poliovirus. Further study of the serotype-specific interaction with mutant hPVRs was accomplished with antigenic hybrid viruses. Improved binding by antigenic hybrid viruses demonstrated that serotype-specific binding to mutant hPVRs is, in part, determined by the amino acid sequence of neutralization antigenic sites (NAgs) and the probable conformational rearrangement of amino acids adjacent to the NAg sites. Finally, site-directed mutants of poliovirus were utilized to determine the relative contributions, to hPVR interactions, of individual amino acids with solvent accessible side chains in the viral canyon. Of the 18 viable virus mutants produced, 3 (D1226A, I1089A, and VPEK1166HPGA) expressed impaired replication phenotypes on the mutant hPVR cell lines P84SYS/HYSA and D117F. A location at the rim of the poliovirus canyon was implicated for the interaction of the amino terminal domain of the poliovirus receptor with conserved and serotype-specific viral surface amino acids. The possible involvement of elements of neutralization antigenic sites in receptor binding may explain, in part, why poliovirus exists in only three serotypes.

Analysis of picornavirus 2A(pro) proteins: separation of proteinase from translation and replication functions

The poliovirus (PV) genome was manipulated by replacing its 2A-encoding sequence with the corresponding sequence of coxsackie B4 virus (CBV4) or human rhinovirus type 2 (HRV2). In vitro translation of the resulting chimeric PV genomes revealed a normal cis-cleavage activity for both heterologous 2A(pro) proteinases in the chimeric PV polyproteins. However, only the genome containing the 2A-encoding sequence of CBV4 (PV/CBV4-2A) yielded viable virus in transfected cells, producing a mixture of large and small plaques on HeLa cell monolayers. The large-plaque variants were found to contain single-amino-acid mutations at a specific site near the C terminus of the CBV4 2A(pro) protein. When the same single-amino-acid mutations were directly introduced into the parental PV/CBV4-2A genome, chimeric viruses with a large-plaque phenotype and a wild-type PV-like growth pattern were obtained upon transfection, an observation demonstrating that these point mutations alone had a drastic effect on the growth of the PV/CBV4 chimeric virus. On the other hand, the chimeric genome containing the 2A-encoding sequence of HRV2 (PV/HRV2-2A) produced a null phenotype in transfected HeLa cells, although low-level replication of this chimeric genome was evident. We conclude that only 2A(pro) of the more closely related enterovirus CBV4 is able to functionally substitute for that of PV in vivo, and a subtle genetic modification of the CBV4 2A(pro) protein results in a drastic improvement in the growth of the chimeric PV/CBV4-2A virus. In addition, this chimeric cDNA approach enabled us to dissect multiple biological functions encoded by the 2A(pro) proteins.

Construction and genetic analysis of dicistronic polioviruses containing open reading frames for epitopes of human immunodeficiency virus type 1 gp120

On the basis of previous studies of dicistronic (dc) polioviruses that carried two internal ribosomal entry sites (L. Alexander, H.-H. Lu, and E. Wimmer, Proc. Natl. Acad. Sci. USA 91:1406-1410, 1994; A. Molla, S. K. Jang, A. V. Paul, Q. Reuer, and E. Wimmer, Nature [London] 356:255-257, 1992), we have constructed a variety of dc polioviruses which express foreign genetic elements that were inserted either between two internal ribosomal entry site elements upstream of the poliovirus open reading frame (pPNENPO derivatives) or upstream of the open reading frame for the poliovirus proteinase 2Apro (pDI-E2A derivatives). Surprisingly, the addition of an N-terminal secretory pathway signal sequence to the open reading frame of the inserted foreign sequences (specifying either truncated versions of human immunodeficiency virus type 1 [HIV-1] gp120 or chloramphenicol acetyltransferase) resulted in a null phenotype, whereas removal of the signal sequence led to the production of viable viruses. Constructs that carried a foreign gene with a signal sequence were negative in RNA synthesis, an observation that suggested a very early block in viral replication. The insertion of transmembrane sequences downstream of the leader sequence did not reverse the replication block. Studies of dc polioviruses that encoded the truncated versions of HIV-1 gp120 showed an increase in genetic stability that correlated with a decrease in the size of the insert. A dc construct that contained a minigene encoding the principal neutralization determinant of HIV-1 produced a stable virus that retained the foreign sequence through multiple passages in cultured cells. These data indicate that dc polioviruses have potential as vaccines for the expression of small foreign epitopes.

The human poliovirus receptor. Receptor-virus interaction and parameters of disease specificity

The host range of poliovirus is determined by the expression of the hPVR, a member of the immunoglobulin superfamily. We characterized hPVR proteins biochemically and found them to be complex-type glycoproteins. The outermost V-like domain of three extracellular domains harbors the PVR function. A panel of single or multiple amino acid exchanges were introduced throughout this domain in order to localize regions involved in virus-receptor interactions. Putative contact amino acids were found to reside in the C'C"D and DE regions. Binding and uptake of poliovirus paralleled virus replication in all mutants tested suggesting that virus binding was affected without abrogating the ability to mediate subsequent events in the infection. Although the primate PVR is essential in conferring susceptibility to poliovirus infection, certain strains can induce neurological disease in rodents. Mouse neurovirulent PV isolates of divergent serotypical origin each provoked a distinctive, characteristic neurological syndrome upon intracerebral infection of wild-type mice. We analyzed clinical and histopathological features of diffuse encephalomyelitis caused by these PV strains and compared the condition with poliomyelitis in mice transgenic for the hPVR. Diffuse PV encephalomyelitis in wild-type mice could be distinguished clinically and histopathologically from hPVR-mediated poliomyelitis in trangenic mice. We localized the determinants of mouse neurovirulence of PV1(LS-a), a derivative of PV1 (Mahoney), in a portion of the viral genome encompassing parts of the capsid protein VP1 as well as the nonstructural protein 2A. Mouse neuropathogenicity could possibly be conferred by reduced particle stability of PV1(LS-a) inasmuch as we found particles to be thermolabile.

Mouse neuropathogenic poliovirus strains cause damage in the central nervous system distinct from poliomyelitis

Poliomyelitis as a consequence of poliovirus infection is observed only in primates. Despite a host range restricted to primates, experimental infection of rodents with certain genetically well defined poliovirus strains produces neurological disease. The outcome of infection of mice with mouse-adapted poliovirus strains has been described previously mainly in terms of paralysis and death, and it was generally assumed that these strains produce the same disease syndromes in normal mice and in mice transgenic for the human poliovirus receptor (hPVR-tg mice). We report a comparison of the clinical course and the histopathological features of neurological disease resulting from intracerebral virus inoculation in normal mice with those of murine poliomyelitis in hPVR-tg mice. The consistent pattern of clinical deficits in poliomyelitic transgenic mice contrasted with highly variable neurologic disease that developed in mice infected with different mouse-adapted polioviruses. Histopathological analysis showed a diffuse encephalomyelitis induced by specific poliovirus serotype 2 isolates in normal mice, that affected neuronal cell populations without discrimination, whereas in hPVR-tg animals, damage was restricted to spinal motor neurons. Mouse neurovirulent strains of poliovirus type 2 differed from mouse neurovirulent poliovirus type 1 derivatives in their ability to induce CNS lesions. Our findings indicate that the characteristic clinical appearance and highly specific histopathological features of poliomyelitis are mediated by the hPVR.(ABSTRACT TRUNCATED AT 250 WORDS)

[Effects of captopril on platelet-derived growth factor ligand and receptor gene expression of vascular wall after balloon angioplasty]

A predominant fibromuscular plaque was produced by balloon catheter denuding angioplasty of both iliac arteries and feeding cholesterol in 16 New Zealand white rabbits. Balloon angioplasty was performed in model animals. Captopril-treated (n = 8, captopril 12.5 mg.kg-1/d) group which received captopril 7 days before to 4 wk after angioplasty were examined by dot blot hybridization. The results showed that captopril can inhibit platelet-derived growth factor ligand and receptor gene expression of vascular wall after balloon angioplasty.

Mouse neurovirulence determinants of poliovirus type 1 strain LS-a map to the coding regions of capsid protein VP1 and proteinase 2Apro

Poliovirus type 1 strain LS-a [PV1(LS-a)] is a OV variant adapted to mice by multiple passages through mouse and monkey tissues. To investigate the molecular basis underlying mouse neurovirulence of PV1(LS-a), a cDNA of the viral genome containing nucleotides 112 to 7441 was cloned, and the nucleotide sequence was determined. Compared with that of the mouse avirulent progenitor PV1(Mahoney), 54 nucleotide changes were found in the genome of the PV1(LS-a) virus, resulting in 20 amino acid substitutions in the virus polyprotein. Whereas the nucleotide changes were scattered throughout the genome, the amino acid substitutions were largely clustered in the capsid proteins and, to a certain extent, in the virus proteinase 2Apro. By in vitro mutagenesis, PV1(LS-a)-specific capsid mutations were introduced into a cDNA clone of PV1(Mahoney). We show that neither the individual amino acid mutations nor combinations of mutations in the region encoding VP1 conferred to PV1(Mahoney) the mouse-adapted phenotype of PV1(LS-a). Chimeric cDNA studies demonstrated that a recombinant type 1 virus containing the PV1(LS-a) sequence from nucleotide 2470 to nucleotide 3625 displayed a neurovirulent phenotype in mice. Further dissection of this region revealed that mouse neurovirulence of PV1(LS-a) was determined by multiple mutations in regions encoding both viral proteinase 2Apro and capsid protein VP1. The mouse neurovirulent viruses, PV1(LS-a), W1-M/LS-Pf [nucleotides 496 to 3625 from PV1(LS-a)], and W1-M/LS-NP [nucleotides 2470 to 3625 from PV1(LS-a)], showed increased sensitivity to heat treatment at 45 degrees C for 1 h. Surprisingly, the thermolabile phenotype was also displayed by a recombinant of PV1(Mahoney) carrying a PV1(LS-a) DNA fragment encoding the N-terminal portion of 2Apro. This suggests that base substitutions in the region encoding 2Apro affected capsid stability, thereby contributing to the neurovirulence of the virus in mice.

Polioviruses containing picornavirus type 1 and/or type 2 internal ribosomal entry site elements: genetic hybrids and the expression of a foreign gene

A picornavirus hybrid genome was constructed in which the internal ribosomal entry site (IRES) of encephalomyocarditis virus was inserted between the 5' non-translated region and the open reading frame of poliovirus (PV), type 1 (Mahoney). Upon transfection into HeLa cells, the hybrid RNA replicated and yielded a derivative of PV (W1-PNENPO). The PV IRES could be removed from pPNENPO, which resulted in a hybrid picornavirus (W1-P108ENPO) in which the translation of the PV open reading frame normally promoted by the type 1 IRES of PV was promoted by the type 2 IRES of encephalomyocarditis virus. This result indicates that these elements are not likely to contain cis-acting elements necessary for PV replication or encapsidation. A foreign gene (bacterial chloramphenicol acetyltransferase, CAT) was inserted into pPNENPO cDNA between the PV and encephalomyocarditis virus IRES elements. The dicistronic RNA replicated in HeLa cells and yielded a derivative of PV (W1-DICAT) with a genome 17% longer than that of wild-type PV. CAT assays and immunoblot analyses showed that the viral RNA efficiently expressed the foreign gene in cell culture. The CAT activity diminished somewhat with each passage of the dicistronic virus, an observation which suggested that the inserted gene had a deleterious effect on viral replication. However, even after five virus passages, a significant quantity of the foreign gene was still expressed. Insertion of the open reading frame of luciferase (67 kDa) resulted in an RNA species that replicated and expressed luciferase for up to 20 hr after transfection. However, this elongated RNA was not encapsidated.

Internalization and intracellular processing of an anti-B-cell lymphoma monoclonal antibody, LL2

The successful clinical experience with antibody LL2 (an IgG2a, anti-B-cell lymphoma antibody) in radioimmunodetection and radioimmunotherapy suggests that this antibody may have potential as a carrier of cytotoxic agents. The internalization, cellular trafficking, and catabolism of this antibody in target human Burkitt lymphoma cells (Raji) were investigated. Internalization of intact antibody as well as of the F(ab')2 and Fab' fragments was detected by an FITC-labeled anti-mouse second antibody probe, and evaluated by fluorescence microscopy. Internalization of intact IgG (or the fragments) was observed as early as 5 min after incubation at 37 degrees C. Initially, the internalized antibodies were present as micro-particles inside the cell membrane, and were translocated to the lysosomal compartment within 2 hr. The anatomic location of the internalized antibody, before translocation to the lysosomal compartment, was deduced by comparing the fluorescence images obtained with the antibody to those obtained with fluorescent probes with known cellular distribution in a co-internalization study. A Golgi-like compartment was found to be involved in the translocation of the antibody. Cellular catabolism of the bound antibody was studied by using 125I-labeled antibody on the target cells. At 21 h, 40% of the radioactivity was released into the supernatant as degraded fragments. The observation suggested that the antibody was degraded mainly in the lysosomes, since the degradation was significantly inhibited in the presence of lysosomal inhibitors such as ammonium chloride or leupeptin. Subcellular fractionation of Raji cells after the binding of 125I-labeled LL2 indicated that the antibody was translocated to lysosomes as evidenced by SDS-PAGE. The rate of internalization (Ke) of LL2, and the re-expression of the antigen were determined. The rapid internalization of LL2 and the re-expression of the antigen suggest that this antibody may have potential as a therapeutic immunoconjugate, since it could deliver a higher accumulation of cytotoxic agents into lymphoma cells.

Assessment of Nd:YAG laser via metal cap and sapphire tip delivery system. An experimental and clinical investigation

Sixteen segments of normal human aorta were irradiated by Nd:YAG laser beam delivered via domestically made metal cap and sapphire tip fibre systems. It was found that the metal tip fibre caused more target tissue damage and adhesion than the sapphire tip fibre. The sapphire tip fibre caused an ablation crater with a smoother edge, less carbonization layer and smaller thermal necrotic zone than the metal tip did. The metal cap and sapphire tip fibre were applied to 2 cases of iliac artery stenosis and 5 cases of coronary stenosis, all showing an immediate ablation.

Intestinal water and solute absorption studies: comparison of in situ perfusion with chronic isolated loops in rats

The effects of lumenal glucose on jejunal water transport and the influence of glucose-induced water absorption on solute uptake from single-pass perfusions are compared in anesthetized rats in situ and isolated chronic loops in unanesthetized rats in vivo. While the magnitudes of solute membrane permeabilities are consistently higher in the chronic loop system, the effects on water transport and its promotion of jejunal solute uptake are comparable between the two experimental systems. The effect of glucose-induced water absorption on the enhanced/baseline jejunal uptake ratio of the hydrophilic drug, acetaminophen, is greater than that for the lipophilic drug, phenytoin, in both experimental systems. The fact that chronic loop effective solute permeabilities were equivalent to solute membrane permeabilities in situ is consistent with greater lumenal fluid mixing in vivo. In addition, in situ body temperature affects the uptake of phenytoin but not acetaminophen, water, or glucose. This suggests that active and paracellular solute transport is not compromised in situ, while membrane partitioning and diffusion of lipophilic species are more sensitive to experimental conditions.

Poliovirus antigenic hybrids simultaneously expressing antigenic determinants from all three serotypes

We have constructed six hybrid polioviruses (PVs) modified to express PV type 2 and type 3 antigenic determinants on a PV type 1 (Mahoney) capsid. The hybrids were modified in neutralizing antigenic site (NAg) I and/or NAgII. They were viable, but impaired for growth in comparison to PV1 (Mahoney). Some hybrids modified to express type 2 and type 3 NAgI determinants simultaneously displayed some type 2 but no type 3 antigenicity (in addition to type 1 antigenicity associated with other antigenic sites). Hybrids modified to express a type 2 NAgI determinant and a type 3 NAgII determinant, or vice versa, displayed antigenic characteristics of all three serotypes, although expression of the modified NAgII determinant was weak. We conclude that it is possible to construct a viable hybrid PV simultaneously modified in NAgI and NAgII which expresses antigenic determinants of all three serotypes.

Influence of D-glucose-induced water absorption on rat jejunal uptake of two passively absorbed drugs

The intestinal absorption of D-glucose is coupled to transepithelial sodium transport and this process generates intestinal water absorption. In situ jejunal perfusions were performed in rats to determine the extent of water transport as a function of perfusion flow rate, perfusate osmolality, and D-glucose concentration. Jejunal perfusions of iso-osmolar D-glucose, at flow rates and concentrations representative of the fed state, increased the dimensionless membrane permeabilities of the analgesic acetaminophen from 0.6 to 1.4, and that of the corticosteroid prednisolone from 1.6 to 2.2. This increase is less important for the more hydrophobic prednisolone since its baseline permeability (1.6) is indicative of complete uptake from solution, while the lower baseline permeability (0.6) of the more hydrophilic acetaminophen represents incomplete membrane uptake. The results suggest that nutrient-induced water transport can enhance jejunal uptake of small hydrophilic solutes. This phenomenon may contribute to variability in the absorption of drugs in this physicochemical class during the fed state.

Adrenergic receptors and increased reactivity of aortic smooth muscle in renal hypertensive rats

The contractile responses of aortic smooth muscle and the dissociation constant (Ka) of the norepinephrine (NE) acting on alpha-adrenergic receptors in isolated thoracic aorta from normotensive and renal hypertensive rats were studied. Male Wistar rats were made hypertensive by uninephrectomy with figure-of-eight ligatures around the contralateral kidney. Two to three weeks after operation, the arterial systolic pressure for sham-operated rats was 123 +/- 2, and that for hypertensive rats was 164 +/- 4 mm Hg. Spontaneous rhythmic contractions of aortic rings, which were potentiated by low [Na]o and abolished by nifedipine (10(-6) - 10(-5) M), were observed in 4 out of 18 hypertensive rats. Aortic rings from normotensive rats showed no spontaneous rhythmicity. Although rhythmic phasic contractions could be induced in normotensive tissues by NE or caffeine in the presence of NE, tissues of hypertensive rats responded more readily. Furthermore, the threshold and the ED50 for tonic contractile response to NE was lower in hypertensive aortic rings than in the rings obtained from normotensive aortas. The Ka of NE acting on alpha-adrenergic receptors was derived from concentration-response data for NE before and after irreversible blockade of a fraction of the receptors with dibenamine (1-2 X 10(-7) M) in the presence of cocaine and propranolol. Mean Kas obtained were 5.58 +/- 0.42 X 10(-7) and 2.12 +/- 0.28 X 10(-7) M for normotensive and hypertensive rats, respectively. The increased contractile responses of the hypertensive aorta may be explained, at least partially, by a higher resting [Ca]i and a greater affinity of NE acting on the alpha-adrenergic receptors.

Shifts in pacemaker dominance within the sinoatrial region of cat and rabbit hearts resulting from increase of extracellular potassium

Simultaneous recording of action potentials from cells in different parts of sinoatrial preparations from cat and rabbit hearts confirms the suggestion by Meek and Eyster that the dominant pacemaker site shifts during treatment with high [K + ]. The direction of the shift can be either upward or downward depending upon the location of the original dominant pacemaker site. In the majority of cases, the original dominant site is located in the upper part of the preparation, consequently the shift is from above downward. In environments with high [K + ], both true and latent pacemaker cell action potentials show a decrease in both maximal diastolic potential and the slope of the prepotential but these changes seem to be more marked in the true pacemaker cell. It is suggested that the shift of dominant pacemaker site in response to high [K + ] is due to the difference in sensitivity to K + between these two types of pacemaker cells.

Activity of neurones in the paraventricular nucleus of the hypothalamus and its control

1. Activity of the paraventricular nucleus neurones was recorded by micro-electrodes during resting conditions and while various osmotic, chemical, direct and indirect neural stimuli were applied. This activity was correlated with evidence of oxytocin release by recording milk ejection responses.2. Seventy-four per cent of all paraventricular nucleus neurones were osmosensitive in that firing was augmented following close arterial injection of hypertonic solutions (1 ml. 1 M-NaCl in 10-15 sec). A very few neurones showed decreased activity and in twenty-two per cent no change at all occurred following injection. Evidence indicated that the observed depressions of cellular firing rate were due to other than osmotic stimulation.3. In post-partum cats an osmotically-induced neurone discharge increase was accompanied by a milk ejection response equivalent to that produced by 2-3 m-u. of oxytocin.4. Paraventricular neurones were also sensitive to acetylcholine. Intracarotid injections of 40-80 mug of acetylcholine greatly increased discharge rates and caused a very definite milk ejection response.5. Stimulation of the nipples by gentle suction, but not by electrical shock, and distension of the uterus in post-partum cats increased unit discharge in the paraventricular nucleus and evoked a milk ejection response.6. Neurones of the paraventricular nucleus, unlike those of the supraoptic nucleus, did not appear to be specifically responsive to electrical stimulation of skin and muscle afferent or of central nervous structures. Such stimuli did cause slight augmentations or depressions in firing rates of cells within and adjacent to the paraventricular nuclei, but many neurones were unaffected. Stimuli such as those applied appeared to have a general central effect involving paraventricular as well as many other neurones.7. Direct electrical excitation of the pituitary stalk produced a milk ejection response in post-partum cats. Electrical pulses applied to the paraventricular nuclei were less effective for reasons discussed.

Factors controlling pacemaker action in cells of the sinoatrial node

Rapid drive of isolated pacemaker tissues from cats resulted in a post-drive depression followed by a late acceleration to supernormal rates of pacemaker activity. These effects were similar to those occurring after drive of the pacemaker in situ . Lower SA nodal pacemakers discharged more slowly and irregularly than did upper SA nodal pacemaker cells. They were more readily depressed by rapid imposed drive. The balance between depression and acceleration varied in different preparations. Drive at only slightly above the intrinsic rate resulted frequently in acceleration not preceded by depression. Within limits, the greater the frequency and duration of drive, the greater the intensity and duration of both the depression and the late acceleration.

Prostigmin augmented and atropine reduced post-drive depression. Cocaine potentiated the late acceleration. Excess potassium reduced post-drive depression and, in concentrations used, caused some acceleration.

Pacemaker cells could be driven less rapidly than could other SA nodal cells. Drive generally shifted pacemaker action to a distant site; the first post-drive propagated responses originated from other pacemaker cells and dominance by the original unit was reestablished slowly. Rapid drive reduced amplitudes of action potentials and prepotentials. It also raised threshold potentials and during the post-drive period the durations of pacemaker cell action potentials were temporarily prolonged. In some preparations membrane potentials remained at a subnormal value after drive. Subthreshold potentials occurred at a somewhat subnormal rhythm but gradually developed an effective amplitude.

Conduction block was observed in isolated SA nodal tissue. This was augmented during the post-drive period of depression.

This work lends support to the hypothesis 1 that dominating action by pacemaker cells influences the pacemaker activity in other potential pacemaker tissues.

Production and abolition of alternation in mechanical action of the ventricle

Persisting alternation in mechanical response of the ventricle, pulsus alternans, develops when the heart is driven above certain rates. This critical rate varies, but tends to occur between rates of 200 and 300 beats/min. The ventricle can be driven slightly faster (10–20 beats/min) by direct than by indirect drive, through atrial electrodes, without showing pulsus alternans. There is a rate "threshold" for persisting alternation which represents the rate limits of compensation. Alternation appears at lower rates but the contractile process can gradually accelerate and alternation disappears even in denervated hearts and after adrenalectomy. Slower progressive accelerations delay onset of pulsus alternans and compensation occurs more quickly than when stepwise rate changes are made. Fast drives above the threshold for pulsus alternans can produce some additional acceleration of the contraction-relaxation process: if the rate is reduced to a level which previously produced a persisting alternation, pulsus alternans does not occur for a number of seconds. The resemblances of these phenomena to "treppe" and "postextrasystolic potentiation" and implications relative to catecholamine release and action are discussed.