Quinaprilat increases total body vascular compliance in rats with myocardial infarction

To test whether quinaprilat, a new angiotensin-converting enzyme (ACE) inhibitor, has any venous effect, we measured its immediate effects on mean circulatory filling pressure (MCFP), intravascular volume, and total body vascular (i.e., venous) compliance in conscious rats with healed myocardial infarction induced by coronary artery ligation. MCFP was determined by inflating a right atrial balloon to arrest the circulation instantly and temporarily. Total body vascular compliance was derived from total circulatory pressure-volume relationships as determined by series measurements of MCFP with different intravascular volume status. In 8 rats with mean infarct size of 26 +/- 4%, 30-min infusion of quinaprilat (0.1 mg/kg/min) decreased both mean arterial and central venous pressures (MAP, CVP) by 8 and 0.7 mm Hg, respectively (p less than 0.02); heart rate (HR), MCFP, hematocrit, and blood volume remained unchanged. As compared with control vehicle infusion, quinaprilat increased total body vascular compliance (2.09 +/- 0.12 vs. 2.69 +/- 0.23 ml/kg/mm Hg; p less than 0.05) and decreased extrapolated unstressed circulating volume (34.96 +/- 1.10 vs. 28.53 +/- 2.55 ml/kg; p less than 0.02). These data suggest that quinaprilat produces possible venodilation through improved total body vascular compliance, thereby reducing cardiac preload in this rat model of myocardial infarction.

ANF does not increase total body venous compliance in conscious rats with myocardial infarction

To test the hypothesis that atrial natriuretic factor (ANF) increases total body venous compliance through venodilation and thereby reduces cardiac preload, we compared the systemic hemodynamic effects of ANF (99-126) with the venodilator nitroglycerin in conscious rats with myocardial infarction (mean infarct size 25%) induced by coronary artery ligation 3 wk previously. A 30-min ANF infusion (0.5 microgram.kg-1.min-1) decreased mean arterial pressure, central venous pressure, and blood volume by 11 mmHg, 0.8 mmHg, and 3 ml/kg, respectively (P less than 0.02). Nitroglycerin (10 micrograms.kg-1.min-1) similarly reduced arterial and venous pressures (7 and 0.6 mmHg; P less than 0.02) but increased blood volume by 2 ml/kg (P less than 0.05). Both ANF and nitroglycerin reduced mean circulatory filling pressure (MCFP) by 1 mmHg (P less than 0.05). Compared with vehicle infusion, nitroglycerin increased total body vascular compliance as derived from serial MCFP measurements taken during 10% blood volume changes (2.09 +/- 0.12 vs. 2.76 +/- 0.32 ml.kg-1.mmHg-1; P less than 0.05) and reduced extrapolated unstressed volume (34.96 +/- 1.10 vs. 23.79 +/- 3.80 ml/kg; P less than 0.02). In contrast, ANF had no effect on either measurement. These data suggest that ANF and nitroglycerin reduced cardiac filling pressure through different mechanisms; the lack of effects of ANF on total body venous compliance and unstressed volume does not support its venodilating effect in these rats postmyocardial infarction.

Variability and repertoire size of T-cell receptor V alpha gene segments

The immune system of higher organisms is composed largely of two distinct cell types, B lymphocytes and T lymphocytes, each of which is independently capable of recognizing an enormous number of distinct entities through their antigen receptors; surface immunoglobulin in the case of the former, and the T-cell receptor (TCR) in the case of the latter. In both cell types, the genes encoding the antigen receptors consist of multiple gene segments which recombine during maturation to produce many possible peptides. One striking difference between B- and T-cell recognition that has not yet been resolved by the structural data is the fact that T cells generally require a major histocompatibility determinant together with an antigen whereas, in most cases, antibodies recognize antigen alone. Recently, we and others have found that a series of TCR V beta gene sequences show conservation of many of the same residues that are conserved between heavy- and light-chain immunoglobulin V regions, and these V beta sequences are predicted to have an immunoglobulin-like secondary structure. To extend these studies, we have isolated and sequenced eight additional alpha-chain complementary cDNA clones and compared them with published sequences. Analyses of these sequences, reported here, indicate that V alpha regions have many of the characteristics of V beta gene segments but differ in that they almost always occur as cross-hybridizing gene families. We conclude that there may be very different selective pressures operating on V alpha and V beta sequences and that the V alpha repertoire may be considerably larger than that of V beta.

A third type of murine T-cell receptor gene

By subtractive cDNA hybridizations, we have isolated a new species of T-cell receptor cDNA clone whose predicted amino acid sequence has homology to variable, constant, joining and diversity segments of immunoglobulins and T-cell receptors. The corresponding genomic sequence is also rearranged in several T-cell DNAs. The four potential N-linked glycosylation sites, frequency of expression and predicted molecular weight (27,800) of this molecule make it a likely candidate for the alpha-chain of the T-cell receptor. Expression data also indicate that this gene may be activated at a later stage of T-cell differentiation than the beta-chain.

Structure, expression and divergence of T-cell receptor beta-chain variable regions

Analysis of three new T-cell receptor beta-chain variable regions together with those in the literature indicates that they have both remarkable similarities and differences with those of immunoglobulin. Less than 10 V regions appear to predominate in the thymus. V beta sequences are much more heterogeneous at the amino acid level than are immunoglobulin V regions and they appear to diverge between species much more quickly, apparently the result of additional hypervariable regions. Three of these putative new hypervariable regions lie outside of the classical immunoglobulin binding site, an indication that important interactions may be occurring in these regions with polymorphic MHC determinants.

Genomic organization and sequence of T-cell receptor beta-chain constant- and joining-region genes

The genomic structure of the joining (J) and constant (C) regions of the locus encoding the beta-chain of the murine T-cell receptor has been analysed. The gene segments are arranged tandemly (J-C/J-C) within a 15-kilobase region. The two constant-region genes are almost identical, differing by only four amino acids, all in carboxy-terminal portions. Each C region comprises four exons encoding an external globular domain, a small hinge-like region, a transmembrane region and a cytoplasmic tail plus 3'-untranslated region. The two clusters of J regions each contain 7 distinct elements, 12 of which may be functional.

Localization of a T-cell receptor diversity-region element

Recently, complementary DNA clones encoding one chain of the T-cell receptor for antigen have been isolated from both murine and human cell lines. Sequence analysis of these clones indicates that they encode elements analogous to the variable (V), constant (C) and joining (J) regions of immunoglobins and that this corresponds to the beta-chain subunit of the T-cell receptor complex. These genes are rearranged in the genomes of specific T-cell lines and hybrids but not in other cell types. Analysis of the components of one such rearranged gene, 2B4, isolated from the pigeon cytochrome c-specific, H-2E-restricted T helper (TH) hybridoma, and its unrearranged (liver) counterpart, indicate that an 8-nucleotide sequence 3' to the rearranged variable region is not derived from either the germ-line V- or J-region gene segments. As this sequence lies at a similar position to the diversity (D) region in immunoglobulin heavy-chain genes, we postulated the existence of an array of germ-line D-region elements that would contribute significantly to the number of different beta-chain molecules which could be created. Here we describe the localization and sequence of one such D-region element, found approximately 650 nucleotides 5' to the first JT cluster. This element seems to be involved in both functional (V-D-J) and non-functional (D-J) rearrangements. Our observations, combined with previous results, indicate that variable-region formation (V-D-J joining) in the T-cell receptor beta-chain gene follows the 12/23-base pair (bp) rule of rearrangement established for the recombination of immunoglobulin gene segments, but that the organization of the heptamer and nonamer element found surrounding the D region is significantly different.

Virus RNA species in kirsten murine sarcoma virus-transformed mink cells

The nuclear and cytoplasmic RNAs from Kirsten murine sarcoma virus (KiMuSV)-transformed non-producer mink cells were studied for the species of virus-specific RNA by fractionation in agarose gels, transfer to diazotized aminophenylthioether paper and hybridization to complementary DNA probe. In both nuclei and cytoplasm, only genome-length KiMuSV-specific RNA was detected. No subgenomic virus RNA species was detected in poly(A+) or poly(A-) RNA fractions. The same observations were made in KiMuSV-transformed mink cells superinfected with feline leukaemia viruses. The significance of these findings is discussed.