A novel mechanism of bradycardia and the character of acetylcholine in the heart.

UNLABELLED: At first the aim of our study was to observe the simultaneous responses of two hearts after intraarterial (into a. femoralis) adrenaline administration, in the rat with its own heart and a transplanted one--hence non-innervated. After these, some next experiments were performed: in some rats the His bundle of the heterotopically transplanted heart was damaged before transplantation. In all experiments the heart rate was observed on ECG and simultaneously, the arterial blood pressure was recorded from femoral artery in Vetbutal-anaesthetized rats. RESULTS: 1) both the heterotopically transplanted, non-innervated heart and the animal's own heart reacted to adrenaline administeration by producing bradycardia, 2) the heterotopically transplanted heart with the damaged His bundle--hence with a ventricular block reacted to adrenaline administration by raising the heart rate, whereas at the same time and in the same animal its own heart reacted by producing bradycardia. CONCLUSIONS: 1) the cause of bradycardia after adrenaline administration does not lie in the reflex from the arcus aortae, since we observed bradycardia after adrenaline administration also in the transplanted, non-innervated heart; therefore the baroreceptor reflex is not the cause of bradycardia after adrenaline administration; 2) bradycardia after adrenaline occurs in both the proper heart and the transplanted, non-innervated one, as a result of an interaction between two cholinergic centres which must be situated above and below the point of the His bundle interruption. The role of acetylcholine in the heart results from the interaction between these two centres.

The effect of multiparity and lactation periods on the graft versus host reactivity of thymocytes and splenocytes from aging C57BL mice.

The ontogeny of graft versus host (GvH) reactivity of thymocytes and splenocytes was tested in C57BL female mice from the day of birth up to the age of 24 months. In comparison with virgin mice, the effect of a different number of pregnancies, with or without lactation, on the GvH reactivity was examined in middle-aged and aging female mice. The most striking results were obtained with suckling, aging 18-month-old multiparas. After three or more pregnancies with lactation--regardless of the number of pregnancies without suckling--the weight and cell count of the thymus and GvH reactivities on both thymocytes and splenocytes were significantly increased and were comparable with those of middle-aged, 12-month-old virgins. The present results indicate that physiological lactation periods are responsible for the long-lasting, immunoenhancing effect of multiparity, and that the maternal thymus is involved in the mechanism of this phenomenon. A possible role of prolactin rejuvenation of the thymus in suckling multiparas is suggested.

The effect of age, sex and breeding on graft versus host reactivity of spleen cells from C57BL mice.

Spleen cell graft versus host (GvH) reactivity was determined in male and female, either virgin or breeder, C57BL mice from 3 to 24 months of age. The GvH reaction was assessed by a local popliteal lymph node assay and by a splenomegaly test for a systemic reaction. Although the GvH reactivity declines progressively with age in both sexes the virgin female response was greater than that of males throughout the period of 6-18 months of age. Two-year-old mice of both sexes were practically unable to mount a GvH reaction. No differences were evident in aging female reactivity after one or two syngeneic pregnancies. On the other hand, 3 or more consecutive pregnancies resulted in enhanced GvH reactivity of 12-24-month-old females, which responded comparably to young virgin mice. This long-lasting immunopotentiating effect of multiparity was similar after 3-4 and 8-9 pregnancies. The possible role of developing foetuses on the maintenance of high GvH reactivity in breeder females is suggested.

Cytotoxic macrophage in graft-versus-host reaction.

Peritoneal macrophages of F1 hybrid mice injected with parental strain spleen cells 8-14 days previously ("early" graft-versus-host (GVH) macrophages) develop an increased ability to destroy in vitro bystanding target cells of syngeneic, allogeneic, and xenogeneic origin. At later stages of GVH reaction, the nonspecific cytotoxicity of macrophages wanes ("late" GVH macrophages) and does not differ much from that of control macrophages. Trypsinization of early GVH macrophages or iodoacetate treatment significantly reduces their cytotoxicity, whereas anti-theta serum and complement have only a moderate effect. Antimouse IgM antibody significantly enhanced the cytotoxic potential of early GVH macrophages, but had no effect either on normal or late GVH macrophages. In contrast, antimouse IgG antibody enhanced, although slightly, only the cytotoxic activity of late GVH macrophages. Two possible explanations of the increased cytotoxicity of early GVH macrophages are offered: (1) cytophilic antibody of IgM type, directed against host antigens, renders macrophages capable of damaging nonspecifically bystanding target cells upon contact with antigen; (2) IgM alloantibody produced by parental cells changes the surface properties of macrophages and contributes to the cytotoxicity of these cells.

Stress-induced changes in muscarinic and beta-adrenergic binding sites on rat thymocytes and lymphocytes.

This study examined the effect of immobilization stress on the expression of muscarinic and beta-adrenergic receptors on thymocytes and lymphocytes obtained from 5-month-old L-E male rats. After 2 h immobilization (acute stress) there was a significant increase in specific binding of [3H]-DHA to beta-adrenergic receptors on thymocytes and on lymphocytes from the blood but not from the spleen, whereas [3H]-QNB binding to muscarinic receptors in those cells was not altered in comparison with the undisturbed control. Chronic immobilization stress (5 days, for 2 h) decreased the [3H]-QNB binding to lymphocytes collected from the spleen and blood but not from thymus; it caused neither a significant change in the 3H-DHA binding to thymocytes nor lymphocytes obtained from the blood and spleen.

Splenic suppressor cells in fetal and newborn mice.

Newborn mice are refractory to sensitization with picryl chloride and the graft versus host reaction (GvHR) in F1 fetal mice injected with parental lymphocytes is markedly reduced. Moreover, spleen cells (but not thymic lymphocytes) of fetal or newborn animals are able to suppress the cell-mediated immune responses, contact sensitivity (CS) and GvHR in a variety of experimental situations. The inhibitory cells are thy-positive and their suppressive activity wanes early after birth.

The influence of naturally occurring suppressor cells of systemic graft versus host reaction (GvHR in fetal and newborn mice.

The early symptom (splenomegaly on day 7) of a graft versus host reaction (GvHR), induced in F1 fetal and newborn mice on day 0 or +1 after birth, is significantly reduced as a result of action of suppressor cells in comparison with 3-day-old recipients. However, late symptoms of GvHR, measured by a body-weight-gain assay and mortality, are similar in the recipients injected with parental spleen cells either on day 0 or +3. An existence of contra suppressive factor(s) operating in newborn early after birth is suggested.

Local renal graft versus host reaction across H-Y barrier.

Local renal graft versus host reaction measured by the kidney enlargement index can be applied to study the H-Y transplantation antigen in mice. In cyclophosphamide-treated C57BL males this test has appeared sensitive enough to discriminate between the reactivity of spleen cells from normal, hyperimmune, and tolerant syngeneic females.

Suppression of xenogeneic local graft versus host reaction by rat fetal spleen cells.

Xenogeneic local graft versus host reaction was induced by the injection of 5 X 10(7) adult rat spleen cells under the capsule of cyclophosphamide-treated adult mice. A significant decrease in the reaction, measured by the kidney enlargement index, was obtained by adding to the reacting cells 5-20% of fetal rat spleen cells. Fetal rat thymocytes of fetal mouse splenocytes were not found to be inhibitory. The suppressive activity of rat spleen cells waned completely on day 3 of the postnatal life.

The influence of the age of donors and recipients on the regional graft-versus-host reaction in mice.

Regional graft versus host (GVH) reaction in mice induced by injection of parental strain spleen cells into the footpad of F1, recipients, was measured 7 days later by a popliteal lymph node (PLN) enlargement index. Young, 6-week-old F1 hosts can be used for studying the age- and sex-dependent GVH reactivity of parental strain donors. On the other hand, senescent, 21-24-month-old F1 recipients are able to mount a host versus graft response against parental antigens which may obscure the typical GVH reaction. The PLN enlargement in syngeneic old F1 mice points to an autoimmune mechanism of this phenomenon.

Local graft versus host reaction in the xenogeneic system.

The injection of viable rat spleen cells beneath the renal capsule of cyclophosphamide (CY)-treated adult mice produced a localized graft versus host reaction (GvHR), manifested by the kidney enlargement index (KI). The optimal xenogeneic GvHR was obtained after injection of 30-50 million rat spleen cells into mouse recipients treated 24 hr before with CY, 200 mg/kg intraperitoneally (i.p.), and killed 7 days later. Splenomegaly in recipient mice suggested systemic dissemination of the local GvHR.

Effect of immobilization stress on tumor growth in mice.

The effect of immobilization stress applied daily for 2 h on the development of MF-RSV tumor graft in mice and on survival of the hosts was studied. While a single acute stress applied to mice simultaneously with a transfer of MF-RSV cells stimulated antitumor defense, chronic stress applied both before and/or after tumor cell implantation accelerated the death of recipients. The shortest survival time was found in mice which were stressed for 3 weeks before implantation and on, until their death. Heat shock applied to MF-RSV tumor cells before implantation significantly reduced their growth ability in the hosts.

Age-related changes in graft-versus-host reactivity of spleen cells from male, virgin, or multiparous female Long-Evans rats.

Spleen cell graft-versus-host (GVH) reactivity was determined in male and female, either virgin or breeder, Long-Evans (LE) rats from 3 to 24 months of age. The tests of a regional (popliteal lymph node enlargement index) and a systemic (splenomegaly index, mortality assay) GVH reaction was used. Although the GVH reactivity declined with age in both sexes, the onset of this decline was significantly delayed in 18-month-old virgin females in comparison with 12-month-old males. Moreover, 6 or 7 consecutive pregnancies resulted in significantly enhanced GVH reactivity of 18-24-month-old females. This long-lasting effect of multiparity was observed in females mated either syngeneically or allogeneically. The possible role of neuroendocrine factors in delaying the age-related process of thymic involution in multiparous females is suggested.

Non-specific decrease of cell-mediated immunity in female mice during syngeneic and allogeneic pregnancy.

Cell-mediated immunity is non-specifically reduced in the second half of H-2 incompatible pregnancy compared with syngeneic mating. Significant difference between syngeneic and allogeneic mated female mice was obtained using two independent tests: contact sensitivity to oxazolone (P smaller than 0.001) and local graft-versus-host reaction (P smaller than 0.01).

Reduction of the graft-versus-host reactivity of mouse and rat spleen cells by 5alpha-androstane-3,17-dione.

The local graft-versus-host reaction as evaluated by the popliteal lymph node enlargement was used for studying the immunosuppressive potency of placental steroid 5alpha-androstane-3,17-dione. Spleen cells from virgin female mice and rats injected subcutaneously with this steroid compound produced in appropriate F1 recipients a significantly weaker reaction (P less than 0.001) than spleen cells from untreated or medium-treated control animals. On the other hand, the pretreatment of cell donors either with 5beta-androstane-3,17-dione or testosterone, the compounds which are not present in the mouse and rat placenta, did not influence the normal graft-versus-host reactivity.

The role of prostaglandin E in the natural suppressor activity of spleen cells from newborn rats.

Spleen cells from newborn to 2-day-old, but not 3-day-old or older, rats suppress the activity of cells from adult animals in xenogeneic local graft-versus-host (GVH) assay. The duration of neonatal suppressor cell activity can be significantly prolonged by treating newborn rats with exogenous prostaglandin E2 (PGE2), and the suppression was completely abolished by administration of PGE inhibitor indomethacin. The results thus demonstrate an involvement of PGE2 in the mechanism of action of neonatal suppressor cells and may explain some discrepancies concerning the nature of natural suppressor cells present in newborn animals.

Immunoreactivity of ageing C57BL female mice rendered tolerant to the H-Y antigen.

Transplantation tolerance to the H-Y antigen, induced in neonatal or young adult C57BL female mice, beneficially affected their immunoreactivity during the process of ageing. The tolerance acquired in 2-month-old females significantly increased their splenocyte graft-versus-host (GVH) reactivity and the production of interleukin-2 (IL-2) at the age of 18 months. The neonatally induced tolerance also resulted in a higher weight of the thymus and a significantly enhanced GVH reactivity of thymocytes in 18-month-old females compared to control mice of the same age.

Modulation of cell-mediated immunity by lithium chloride.

Immunomodulation of cell-mediated immunity was studied in mice treated with either lithium chloride (LiCl), anti-CD8 monoclonal antibody or their combination. While 6-day LiCl treatment decreased the ability of their splenocytes to induce a local graft-versus-host reaction--anti-CD8 abolished this effect. The proliferative response of spleen cells from those three groups of mice to concanavalin A stimulation in vitro was significantly increased. The natural killer (NK) cell toxicity of the mice was decreased by over 43% after the 6-day LiCl treatment, but was x 2.5 higher then the control value after a longer 21-d treatment. These results indicate that the immunomodulatory capacity of lithium is dependent on the type of cell population studied, and on the schedule of administration.

Ontogenic development of immunoregulation in rats.

Suppressor activity of newborn rat spleen cells is totally inhibited on day 3 after birth by immunoregulatory cells of thymic origin. Contrasuppression represents a necessary, evolutionary step in the ontogenic development of the immune system.

Effect of neonatal spleen and thymus implants on H-Y incompatible skin grafts.

The transplantation reactivity of adult splenectomized C57BL females to H-Y incompatible skin grafts was significantly reduced by the implantation of spleen and thymus from foetal or 0-1-day-old syngeneic female donors. The thymus implant served as a possible source of natural suppressor cell precursors and the spleen implant as a microenvironment for their maturation.