Experimental Biology and Medicine

Abelson murine leukemia virus (A-MuLV) is an acute transforming retrovirus which induces a rapid lymphosarcoma in mice. The virus arose in one of a series of mice that were treated with prednisolone and infected with the replication-competent retrovirus Moloney murine leukemia virus (M-MuLV) (1, 2). One such mouse developed a non-thymic tumor; the cause was shown to be a virus when it was demonstrated that filtered extracts from this tumor were capable of inducing similar tumors in animals. These tumors were quite distinct from the thymic tumors normally induced by the parental M-MuLV, suggesting that a new virus had arisen in the course of the infection. This new virus, termed A-MuLV, has been the subject of intensive study in recent years. The analysis of the structure of the viral genome has had profound effects on our thinking about the mechanisms by which oncogenic gene structures can arise. This review will describe the biology of the virus, its genetic structure, current models for the origin of the virus, and the properties of the cellular gene from which it arose. Several other reviews describing these and other aspects of the virus have been published (3–8).

Biology of A-MuLV. Infection of experimental animals with A-MuLV preparations results in the rapid onset of disease. Neonatal mice injected with the virus develop an invariably fatal lymphosarcoma 3 to 5 weeks after injection; the first neoplastic cells appear in the bone marrow as early as 15 to 20 days after infection. The cells spread rapidly to the meninges and to selected lymph nodes, often resulting in localized lymphadenopathy. The tumor cells, exhibiting a characteristic lymphoblastic morphology, can be adapted to growth in vitro and cloned. These cultures have allowed a detailed characterization of the tumor cells. More importantly, primary explants from various tissues can be prepared and transformed in vitro by infection with the virus (9, 10).

Overview. In recent years nucleoside biochemistry and lymphocyte physiology have been brought together in a number of ways. Lymphocytes are particularly sensitive to the cytotoxic effects of low concentrations of nucleosides. Deficiencies in certain enzymes of nucleoside metabolism result in immune dysfunction. In addition, lymphocyte proliferation and differentiation can be stimulated by other nucleosides and numerous observations have been made of variations in the activities of the enzymes involved in nucleoside metabolism as they relate to different stages of lymphocyte activation or function. Naturally occurring purine and pyrimidine nucleosides participate in intermediary metabolism. Furthermore, many nucleoside analogs and derivatives have been synthesized, some of which have significant biological effects and serve as anticancer agents for lymphoid malignancies. The interface between different nucleosides and their effects on lymphocyte function is the topic of this issue.

Nucleosides and their phosphorylated derivatives participate in the general metabolism of lymphocytes as they do in all cells in a wide variety of biochemical reactions. ATP is the universal energy currency and adenine nucleotides are components of the major coenzymes FAD, NAD, and coenzyme A. Also, nucleotides are the building blocks for nucleic acids, both RNA and DNA. Nucleotides serve as activated intermediates in many biosynthetic reactions. Finally, nucleotides are regulator molecules for enzymes involved in their own metabolism: ribonucleotide reductase is activated or inactivated depending on the concentrations of several different nucleotides; adenylate cyclase is regulated by GTP which binds to modulatory proteins [for effects on lymphoid cells see Ref (1) and P. Insel, this issue].

Besides their overall importance in metabolism, nucleosides are highly cytotoxic, particularly for lymphocytes. Indeed, various diseases of the immune system have been correlated with a lack or reduced amounts of enzymes involved in nucleoside metabolism.

Three general questions regarding nucleosides and lymphocytes are discussed: (a) Why are so many measurements being made of adenosine deaminase activity, what do the results mean, and why is there still disagreement about some of the conclusions; (b) what do we understand about nucleosides and lymphocyte death; and (c) to what extent do we really understand nucleoside and nucleotide metabolism in lymphocytes? Experimental studies show that treatment of mice with deoxycoformycin, to produce accumulation of deoxyadenosine, leads to rapid thymus involution, elevated dATP concentrations in thymus and liver, and inhibition of adenosylhomocysteine hydrolase in these tissues. Deoxyguanosine inhibits the growth of mouse lymphoma L5178Y cells, and this toxicity is prevented by deoxycytidine plus adenine. In cells treated with deoxyguanosine, concentrations of both GTP and dGTP are elevated, and this is not affected by deoxycytidine. Adenine, however, reduces GTP concentrations to normal, and prevents most of the elevation in dGTP concentrations. Contrary to previous belief, it has been demonstrated that lymphocytes and nucleated bone marrow cells will synthesize purine nucleotides de novo if incubated in an appropriate medium; carbon dioxide is particularly important for this process.

Deficiency of the enzyme purine nucleoside phosphorylase is associated with a specific depletion of T cells which is presumably mediated by its substrate, 2′-deoxyguanosine. Inhibitors of this enzyme are therefore being developed as potential immunosuppressive agents. We have compared the effects of 8-aminoguanosine, a competitive inhibitor of purine nucleoside phosphorylase, on the metabolism of 2′-deoxyguanosine by human T lymphoblasts, B lymphoblasts, and mature T-cell lines. 8-Aminoguanosine markedly potentiates the accumulation of dGTP in T lymphoblasts, but results in increased GTP levels in B lymphoblasts and mature T cells. GTP accumulation is associated with ATP depletion of a magnitude similar to that seen with an inhibitor of de novo purine biosynthesis, but does not result in inhibition of either DNA or RNA synthesis. In contrast, direct inhibition of de novo purine biosynthesis sharply decreased the incorporation of [³H]uridine into both DNA and RNA. We conclude that the mechanism of cell damage resulting from prolonged accumulation of GTP appears to involve more than inhibition of de novo purine biosynthesis and consequent ATP depletion. Perturbations in guanine nucleotide pools resulting from partial inhibition of purine nucleoside phosphorylase activity in vivo could result in cellular toxicity not limited to the target T cell population.

The ability of inosine 5′-monophosphate vs inosine or hypoxanthine to supply the total purine requirements of mitogen-stimulated human T cells or rapidly dividing human B lymphoblastoid cells was evaluated. Mitogen-stimulated human peripheral blood T cells were treated with aminopterin to inhibit purine synthesis de novo and make the cells dependent upon an exogenous purine source. Thymidine was added as a source of pyrimidines. Under these conditions, 25 μM inosine 5′-monophosphate, inosine, and hypoxanthine showed comparable abilities to support [³H]thymidine incorporation into DNA at rates equal to that of untreated control cultures. In parallel experiments with the rapidly dividing human B lymphoblastoid cell line, WI-L2, treatment with aminopterin (plus thymidine) inhibited the growth rate by >95%. The normal growth rate was restored by the addition of 30 μM inosine 5′-monophosphate, inosine, or hypoxanthine to the medium. However, in similar experiments with cell line No. 1254, a derivative of WI-L2 which lacks detectable ecto-5′-nucleotidase activity, only inosine and hypoxanthine (plus thymidine), but not inosine 5′-monophosphate (and thymidine) were able to restore the growth inhibition due to aminopterin. These results show that the catalytic activity of ecto-5′-nucleotidase is sufficient to meet the total purine requirements of mitogen-stimulated human T cells or rapidly dividing human B lymphoblastoid cells and suggest that this enzyme may have functional significance when rates of purine synthesis de novo are limited and/or an extracellular source of purine nucleotides is available.

Deficiency of either one of the subsequent purine catabolic enzymes adenosine deaminase or purine nucleoside phosphorylase results in immunodeficiency disease in humans. However, the mechanism by which impairment of purine metabolism may cause immunodeficiency is unclear. In the present work we have studied the catabolism of purine ribonucleotides and deoxyribonucleotides in T lymphocytes to better understand the role of purine nucleoside phosphorylase and adenosine deaminase in the immune function. It was found that purine deoxyribonucleotides are degraded via catabolic pathways distinctly different from those used for purine ribonucleotide degradation. Thus both adenine and guanine ribonucleotides are deaminated to IMP whereas purine deoxyribonucleotides are exclusively dephosphorylated to the corresponding deoxyribonucleosides. These findings may explain the relatively higher degradation rates of purine deoxyribonucleotides in mammalian cells as compared to purine ribonucleotides. The catabolism of purine nucleotides is tightly linked to the active purine nucleoside cycles which consist of the phosphorolysis of purine nucleosides and deoxyribonucleosides to their corresponding bases, their salvage to monophosphates and back to the corresponding ribonucleosides. The above observations also imply that a possible role of the purine nucleoside cycles is to convert purine deoxyribonucleotides into their corresponding ribonucleotide derivatives. Deficiencies of purine nucleoside phosphorylase or of adenosine deaminase activities, enzymes which participate or lead to the purine nucleoside cycles, thus result in a selective impaired deoxyribonucleotide catabolism and immunodeficiency.

We have studied the turnover and synthesis of purine nucleoside phosphorylase by using a polyclonal rabbit antiserum to this protein. The turnover of purine nucleoside phosphorylase was studied in the B lymphoblast cell, WI-L2, by specific immunoprecipitation of [³H]leucine-labeled proteins. The half-lives for total protein and purine nucleoside phosphorylase were 14.5 and 14.1 hr, respectively. For cells cultured in the presence of inosine the half-life of purine nucleoside phosphorylase was reduced to 11.2 hr. The synthesis of purine nucleoside phosphorylase was analyzed during phytohemagglutinin-stimulated T cell transformation by pulse labeling cells with [³⁵S]methionine. Purine nucleoside phosphorylase synthesis increased greater than 10-fold during the first 12 hr of transformation and continued to a maximum of 30-fold. The relative rate of purine nucleoside phosphorylase labeled to total proteins was 0.04% in unstimulated T cells and increased to 0.18% 12 hr after stimulation. These studies identify some preferential synthesis of purine nucleoside phosphorylase during the early stages of T cell transformation.

Deoxyadenosine and its nucleotides are thought to be involved in the pathogenesis of the immunodeficient state associated with inherited adenosine deaminase (ADA) deficiency (1–3) and in the lymphotoxicity that occurs during the treatment of leukemia with deoxycoformycin, an ADA inhibitor (1–3). Lymphotoxicity can be simulated in vitro by treating lymphoid cells with deoxyadenosine in the presence of an ADA inhibitor. Such a treatment of lymphoblasts results in intracellular accumulation of deoxy-ATP (dATP), inhibition of DNA synthesis, ATP depletion, leading to cell toxicity; different lymphoid cells display very different sensitivity to this deoxyadenosine cytotoxicity (4, 5).

The mechanism of dATP-induced cytotoxicity is still poorly understood; one of the first hypotheses was the blockade by dATP of ribonucleotide reductase which would result in an inhibition of DNA synthesis due to the shortage of deoxynucleotide precursors (4–6). More recently it was claimed that a dATP-induced inhibition of RNA synthesis could provide an alternative explanation for deoxyadenosine toxicity in lymphoid cells (7). Both hypotheses appear correlated to the cell capacity to accumulate dATP; nevertheless, as suggested by Sylwestrowicz (8), this cytotoxicity depends not only on intracellular dATP synthesis but also on the capacity of the cell to degrade accumulated dATP.

Both AMP-deaminase (AMP-DA), which deaminates AMP and dAMP, and cytosolic 5′-nucleotidase (c5′N), which hydrolyzes intracellular mononucleotides, are involved in nucleotide catabolism. Contrary to other enzymes of nucleotide metabolism, these enzymes have scarcely been studied in lymphoid cells. It was only reported that T lymphoblasts display AMP-DA activities 5- to 10-fold lower than those of B lymphoblasts and that different AMP-DA isoenzymes could be expressed in these lymphoblasts (9). It was also shown that AMP-DA activity is greatly altered during the in vitro differentiation of muscle cells (10).

The selective toxicity of purine deoxynucleosides against lymphoid cells appears to be mediated by a preferential accumulation of the corresponding triphosphates in these cells. We report a study of the metabolism and toxicity of arabinonucleosides of guanine and cytosine toward human T- and B-lymphoblastoid-cell lines. Both compounds inhibited the growth of T lymphoblasts at concentrations < 2 μM. However, only ara-G exhibited a strong selectivity for T lymphocytes as indicated by a 100-fold greater toxicity to T than B cells. ara-G is not significantly degraded to guanine but is metabolized to the triphosphate. In common with the other arabinonucleoside, cytotoxicity by ara-G was associated with specific inhibition of DNA synthesis in cells. The capacity of T cells (CCRF-CEM) to accumulate ara-GTP was dependent primarily on deoxycytidine kinase. The level of intracellular ara-GTP accumulated after incubation with the corresponding nucleoside was 20- to 40-fold higher in T cells than either of two B-lymphoblast-cell lines, WI-L2 or PF-2S. The levels of phosphorylating activity for ara-C in extracts of T- and B-cell lines were approximately equal; in contrast, ara-G phosphorylating activity was four- to fivefold higher in B lymphoblasts. After removal of arabinonucleosides from the culture medium, ara-GTP levels in B lymphoblasts declined at a rate that was two to four times faster than that of ara-CTP. In marked contrast, no catabolism of the arabinonucleoside triphosphates was detected in T lymphoblasts. These results suggest that the selectivity of arabinonucleosides to human lymphoid cells of various phenotypes can be correlated with their nucleotide metabolism. The selectivity of ara-G for T and B cells can be correlated with their differential ability to catabolize ara-GTP.

From a mutagenized population of wild-type S49 T lymphoblasts, cells were selected for their ability to survive in semisolid medium containing 0.5 mM hypoxanthine, 0.4 μM methotrexate, 30 μM thymidine, 30 μM deoxycytidine, and 30 μM p-nitrobenzyl-6-thioinosine (NBMPR), a potent inhibitor of nucleoside transport. Unlike wild-type parental cells, two mutant clones, KAB1 and KAB5, were still sensitive to nucleoside-mediated cytotoxicity in the presence of NBMPR. Comparisons of the abilities of wild-type cells, KAB1, and KAB5 cells to incorporate exogenous nucleoside to the corresponding nucleoside triphosphate indicated that nucleoside incorporation was much less sensitive to inhibition by NBMPR in the mutant cells. Rapid transport studies indicated that the mutant cell lines, unlike the wild-type parent, had acquired an NBMPR-insensitive nucleoside transport component which was similar to the NBMPR-sensitive wild-type transporter with respect to affinities for nucleosides and sensitivities toward N-ethylmaleimide and dipyridamole. Binding studies with [³H]NBMPR indicated that KAB5 cells were 70–75% deficient in the number of NBMPR binding sites, whereas KAB1 cells possessed a wild-type complement of NBMPR binding sites with wild-type binding characteristics. These data suggest that the NBMPR binding site in wild-type S49 cells is genetically distinguishable from the nucleoside carrier site and that the former may be a regulatory site.

We have examined several features of the regulation of cyclic AMP accumulation in lymphoid cells isolated from peripheral blood of human subjects and in the murine T-lymphoma cell line, S49. S49 cells are unique because of the availability of variant clones with lesions in the pathway of cyclic AMP generation and response. We found that human lymphoid cells prepared at 4°C showed substantially greater cyclic AMP accumulation in response to histamine and the β-adrenergic agonist isoproterenol than did cells prepared at ambient temperature. The muscarinic cholinergic agonist carbamylcholine and peptide hormone somatostatin failed to inhibit cyclic AMP accumulation in human lymphoid cells and treatment with pertussis toxin (which blocks function of G_i, the guanine nucleotide binding protein that mediates inhibition of adenylate cyclase) only minimally increased cyclic AMP levels in these cells. Thus the G_i component of adenylate cyclase appears to play only a small role in modulating cyclic AMP levels in this mixed population of lymphoid cells. Incubation of whole blood with isoproterenol desensitized human lymphocytes to subsequent stimulation with β agonist. This desensitization was associated with a redistribution of β-adrenergic receptors such that a substantial portion of the receptors in intact cells could no longer bind a hydrophilic antagonist. Wild-type S49 lymphoma cells showed a similar redistribution of β-adrenergic receptors after a few minutes'incubation with agonist. Based on studies in S49 variants, this redistribution is independent of components distal to receptors in the adenylate cyclase/cyclic AMP pathway. By contrast, a more slowly developing, agonist-mediated down-regulation of β-adrenergic receptors was blunted in variants with defective interaction between receptors and G_s, the guanine nucleotide binding protein that mediates stimulation of adenylate cyclase. Unlike results in human lymphoid cells, S49 cells show a prominent inhibition of cyclic AMP accumulation mediated by G_i; this inhibition is promoted by somatostatin and blocked by pertussis toxin.

The contribution of T cells to potentiation of humoral immunity by the C8-substituted guanine ribonucleosides and the origin of the increased numbers of antigen-responsive B cells generated consequent to their action have been investigated. Augmentation of the antigen-specific antibody response by these nucleosides, exemplified by 8-mercaptoguanosine (8MGuo), can be separated into T-cell-dependent and T-cell-independent components, both by use of the T-cell tropic immunosuppressive agent, cyclosporin A, and by experiments using separated populations of T and B cells. Augmentation of adjuvanticity by T cells is hypothesized to involve a B-cell subpopulation not otherwise subject to the action of 8MGuo. This subpopulation could potentially arise by either of two mechanisms, one whereby preexisting antigen-specific B cells undergo clonal expansion, and one in which cells not normally participating in the response are recruited in the absence of clonal expansion. Although the former mechanism makes a minor contribution to adjuvanticity, the latter mechanism appears to be the dominant one, insofar as models in which 8MGuo-induced proliferation fails to occur (such as after irradiation, or in the SJL mouse) nonetheless exhibit strong adjuvant effects. Analysis of precursor frequency of antigen-specific B cells indicates that for each mature, antigen-responsive B cell present in adult murine spleen, an average of four additional cells can be recruited by the conjoint actions of antigen and 8MGuo. One group subject to such recruitment is the immature antigen-specific B cell, whose degree of functional maturity is accelerated in the presence of antigen and 8MGuo.

Detergent soluble DNA from splenocytes of immunologically stimulated mice has been shown to incorporate [³H]dThd more rapidly than detergent insoluble DNA. In this report we compare the incorporation of other ³H-labeled nucleosides and ³H-labeled deoxynucleosides and the distribution of ³H in the different size classes of detergent soluble DNA. The order of incorporation into DS DNA is [³H]dThd > [³H]dCyd > [³H]Ado > [³H]dGuo ≈ [³H]Cyd > [³H]dAdo > [³H]Guo. We also show that the previously reported slight enrichment in Gua + Cyt content is not due to preferential incorporation of dGuo or of dCyd into any one size class.

The observed enhancement of B-lymphocyte activation by 8-bromoguanosine and 8-mercaptoguanosine is hypothesized to occur via a “binding protein” which requires a guanine nucleoside as the syn conformer for productive interaction. In addition, because of the 7-substituent, Q nucleoside also is hypothesized to bind as the syn conformer and, therefore, to be a potential B-lymphocyte activator.

Human promyelocytic leukemia (HL-60) cells were used to begin to evaluate the role in hematopoiesis of inosine biosynthesis in the tRNA anticodon wobble position; a reaction involving the enzymatic insertion of preformed hypoxanthine. Dimethyl sulfoxide (DMSO) and hypoxanthine were found to induce the differentiation of HL-60 cells in a synergistic manner, and the induced differentiation was independent of changes in the purine catabolic enzymes adenosine deaminase and purine nucleoside phosphorylase. The short-term exposure of HL-60 cells to DMSO plus hypoxanthine resulted in enhanced leucine incorporation, and a model is presented showing how the inosine modification reaction in tRNA may be involved. A means by which hypoxanthine insertion into tRNA may modulate the synthesis of regulatory proteins (e.g., lymphokines and cell surface receptors) is also outlined.

Sera from mice which have been injected iv with either poly(A) · poly(U) or poly(I) · poly(C) 1 1/2 hr prior to bleeding were found to suppress the mixed lymphocyte reaction. This effect was reduced considerably by 18 hr. Characterization of the suppressive sera revealed it (a) was stable to heating at 56°C for 1 hr and freezing at −20°C for 1 month; (b) had a molecular weight greater than 30,000; (c) could be induced in sera from athymic nude mice; and (d) was present to a lower degree in sera from aging mice.

Osteomalacia has been noted following in vivo aluminum (Al) loading in the rat by some investigators but not by others. To determine whether the response of bone to Al differs as a function of the skeletal site examined, quantitative histology of cortical and trabecular bone was done in the tibiae from control (C, n = 10), Al-treated (AL, n = 9), nephrectomized control (NX-C, n = 7), and nephrectomized Al-treated (NX-AL, n = 8) rats given 2 mg/day of Al for 4 weeks. Bone Al content was determined by histochemical methods. In cortical bone, osteoid seam width, osteoid volume, and percent osteoid area were similar for all groups. In contrast, for trabecular bone, both forming surface (x ± SD) (5.2 ± 3.4 vs 1.8 ± 1.1%, P < 0.05) and osteoid volume (1.7 ± 0.7 vs 1.0 ± 0.4%, P < 0.05) increased from control values in AL, although osteoid seam width did not differ. In NX-AL, trabecular forming surface (20.2 ± 6.7 vs 6.2 ± 2.4%, P < 0.01), osteoid area (13.2 ± 5.7 vs 3.5 ± 0.8%, P < 0.01), and osteoid width (18.7 ± 5.7 vs 9.7 ± 2.3 μm, P < 0.01) all were greater than in NX-C. Deposits of Al were undetectable in C and NX-C, were minimal in cortical bone in AL and NX-AL, but were present at 40.5 ± 11.5 and 71.1 ± 6.5% of trabecular surfaces in AL and NX-AL, respectively. Osteoid area and osteoid surface each correlated with trabecular bone Al. Thus, (a) osteoid accumulates in trabecular, but not in cortical, bone after 4 weeks of Al loading; (b) the extent of osteoid accumulation correlates with the bone Al content; and (c) the histologic response to Al in cortical and trabecular bone is related to local differences in the uptake of Al into bone.

Experiments were conducted in trained, conscious dogs fitted with an indwelling portal catheter. Radioenzymatic methods were employed for the quantitative measurement of plasma-free serotonin and catecholamines. An injection of ovine growth hormone (GH, 100 μg/kg) or an equimolar amount of somatostatin (somatotropin release inhibitory factor, SRIF, 7.5 μg/kg) into a saphenous vein led, within the first 15 min, to a transient but significant increase in plasma serotonin and a decrease in the concentrations of dopamine, norepinephrine, and epinephrine. The changes were frequently in excess of 40% of baseline values, and were found only in the portal and not in the peripheral circulation. When the animals were pretreated with an antiserum specifically directed against SRIF, GH surges no longer caused alterations in the portal levels of biogenic amines. Thus, the effects of spike concentrations of GH on plasma serotonin and catecholamines are apparently mediated by SRIF, a novel and unexpected function for a hormone that is known as an inhibitor of GH secretion.

Conventional and germfree mice ingested a suspension of 2-μm latex particles in drinking water for a 15-day period. Number and distribution of intestinal Peyer's patches did not differ significantly in the two types of mice. Cleared Peyer's patches were compared with regard to size and particle content. The location of particles within Peyer's patch follicles of germfree mice was similar to that of conventional mice, but the latter had significantly larger follicles and greater accumulations of latex particles. Latex concentration varied with patch location. Proximal patches contained the majority of particles in germfree mice, whereas particles were most abundant in distal patches of conventional mice. The results show that particle uptake into Peyer's patches takes place even in the complete absence of bacteria in the gut.

Eight experiments were conducted to determine effects of a phenolic polymer (Kraft wood lignin, Indulin), phenolic glycosides (cane molasses and wood molasses), and phenolic monomers (vanillin, vanillic acid, ferulic acid, and p-coumaric acid) on liver cytochromes P-450, cytochrome b ₅, and NADPH cytochrome c reductase in chicks and rats. Chicks fed 6.0% lignin had a higher (P < 0.01) cytochromes P-450 content than did chicks fed 0% fiber, 6.0% wood cellulose (Solka Floc), or 6.0% arenaceous flour. NADPH cytochrome c reductase activity was not affected by treatment. Chicks fed 12.0% wood molasses had a higher (P < 0.06) cytochromes P-450 level than did chicks fed 0% fiber or 6.0% wood molasses. Cane molasses incorporated at both 6.0 and 12.0% of the diet induced (P < 0.05) cytochromes P-450 content over those of control-fed birds. Chicks fed 6.0% lignin, with or without antibiotic (bacitracin:neomycin sulfate, 2:1), had a higher (P < 0.01) cytochromes P-450 level than did chicks fed control diets, with or without antibiotic. Additionally, chicks fed 6.0% lignin had lower (P < 0.01) intestinal diaminopimelic acid (DAP) levels than did chicks fed 0% fiber. Rats fed 0% fiber, 6.0% wood cellulose, 6.0% arenaceous flour, or 6.0% lignin exhibited no difference in cytochrome level or activity among treatments. Chicks fed 0.5% vanillin, 0.5% vanillic acid, 0.5% ferulic acid, or 0.5% p-coumaric acid had comparable cytochromes level and activity compared with chicks fed no phenolics. Chicks fed 0.5% p-coumaric acid had lower (P < 0.05) rates of gain than did chicks fed control or other phenolic-containing diets. Rats fed these phenolics had similar cytochromes P-450 content among treatments.

Conscious one-kidney, one-clip hypertensive rats and their normotensive controls were infused during 7 days with synthetic ANF (Arg 101-Tyr 126) at 100 ng/hr/rat (35 pmol/hr/rat) by means of osmotic minipumps. The basal blood pressure of 193 ± 6 mmHg gradually declined to 145 ± 6 mmHg at day 4 after the infusion was started. No changes in blood pressure were observed in ANF-infused normotensive rats. A significantly higher diuresis and natriuresis was observed in ANF-infused hypertensive rats when compared to the non-treated hypertensive group. No such changes were observed in ANF-treated normotensive animals. No differences in PRA were seen in any group. Atrial immunoreactive ANF was significantly lower in one-kidney, one-clip rats than in the normotensive animals, but whether this is the reflection of an increased release in the circulation remains to be elucidated. It is suggested that the hypotensive response of one-kidney, one-clip animals to ANF may be secondary to a dual mechanism, vasodilatation and volume depletion.

Chronic, as well as acute, exercise increases circulating PRL in females. The response of males to repeated exercise, however, is unknown. The purpose of the present study was to examine the effects of acute and chronic exercise on plasma PRL levels in untrained males. Eight male subjects performed cycle ergometer exercise at 50% of their maximal oxygen uptake on 10 consecutive days. The subjects exercised in an environmental chamber maintained at 39°C and 30% relative humidity. PRL levels were measured on days 1, 5, and 10 before exercise, and after 20 and 45 minutes of exercise. Acute exercise increased PRL levels. However, plasma levels did not significantly increase during exercise on days 5 and 10. This suggests a similarity in the PRL response to acute exercise in males and females, but a sex difference in the response to chronic exercise.

Keloid tissue has been implanted in the athymic nude mouse in order to develop an experimental animal model for the study of human keloids and hypertrophic scars. Untreated keloid tissues maintained essentially the same morphological patterns and glycosaminoglycan distributions for at least 60 days after implantation in the athymic mice. Normal human skin implanted in the same way was maintained without change in glycosaminoglycan distribution or morphologic characteristics. We suggest that this model may be useful for basic research of keloids and hypertrophic scars in that it will allow studies of morphologic, biochemical and therapeutic interrelationships under controlled Conditions.

The effect of streptozotocin-induced diabetes during pregnancy in rats on prostacyclin synthesis in aorta and heart of offsprings was investigated. Although the aortic and heart syntheses of 6-keto-PGFl_α in the offsprings of diabetic rats were not altered at birth, a significant rise in aorta and a decrease in the heart were evident at weaning. At weaning, offsprings of diabetic rats also show a significant rise in plasma cholesterol. These studies show that maternal diabetes might cause effects in the offspring which might become evident in later life.