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Biomedical subjects

Z M Liu

Publications and source records attributed to Z M Liu.

66 records · Page 4Linked to original sources
PubMed1984

The effects of phentolamine and isoproterenol in experimental hemorrhagic shock in the dog.

The effects of phentolamine and isoproterenol were investigated in eight dogs versus eight control dogs. The dogs were placed into simulated hemorrhagic shock using a reservoir to maintain arterial pressure at 40 mmHg until the level of the reservoir decreased to 20% of the maximum shed volume, or for 2 hr in the isoproterenol groups. After 30 min, during which phentolamine, isoproterenol, or saline was infused, the remaining blood was reinfused. Phentolamine was given as a 5-mg intravenous bolus. Isoproterenol was infused at 2.0 micrograms/kg/min. The dogs were monitored until their arterial pressure declined to 70 mmHg (50 mm for isoproterenol) or death ensued. Phentolamine lowered peripheral resistance and the size of the vascular space increased as shown by the rapid uptake of blood, 214.0 +/- 12.5 ml, during the 30 min after injection. The control group took back only 72.5 +/- 7.5 ml. Although reinfusion of the shed blood restored blood pressure to near normal for a short period, all groups showed a progressive decline in arterial pressure. There was no evidence that phentolamine or isoproterenol significantly decreased capillary permeability or that renal or pulmonary function were significantly altered by treatment. A large increase in venous oxygen content occurred following phentolamine, and a mild inotropic and vasodilator action lasted for about 30 min. Isoproterenol also decreased postinfusion arterial pressure. Neither drug influenced the hypoglycemia seen after reinfusion.

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PubMedDate not supplied

Evidence for a direct action of melatonin on the immune system.

Pineal melatonin modulates the mammalian immune system. In vivo studies showed that melatonin enhanced the natural and acquired immunity while in vitro studies demonstrated its inhibitory influence. The mechanism of melatonin action on the immune system remains unknown. Actions through lymphokines or opioid release or via other endocrine changes have been proposed. In this paper, a direct action of melatonin on the lymphoid tissue is hypothesized. 2-[125I]Iodomelatonin binding sites have been identified in the membrane homogenates of thymus, bursa of Fabricius and spleens of a number of birds and mammals. The bindings were stable, saturable, reversible, specific and of high affinity. The Bmax ranged from 0.6 to 3.9 fmol/mg protein. The Kd was in the physiological range of circulating melatonin levels, about 30-70 pmol/l. The binding sites in the primary lymphoid organs demonstrated diurnal variation in density, with higher levels found at the middle of the light period. However, those in the spleen did not vary with the time of the day. An age-dependent decrease in the density was also found in the chicken bursa of Fabricius. In addition, when the nocturnal melatonin secretion was suppressed by constant light exposure, the density of the binding sites increased in the guinea pig spleen. Immunosuppression with cortisol injection in young ducks decreased the density of the melatonin binding sites in the thymus. The regulation of the binding characteristics by physiological variation in melatonin levels and/or immunological status of the animals provide evidence that these 2-[125I]iodomelatonin binding sites in the lymphoid tissues may be physiologically significant and represent true melatonin receptors. The melatonin receptors in the lymphoid organs may be coupled to a G protein as Guanosine 5'-0-(3-thiotriphosphate inhibited 2-[125I]iodomelatonin binding in the spleen by increasing the Kd and decreasing the Bmax.

Animals↗
PubMedDate not supplied

Binding of [125I]-labelled iodomelatonin in the duck thymus.

[125I]-labelled iodomelatonin binding sites in membrane preparations of duck thymus were studied. The specific binding of [125I]-labelled iodomelatonin in the duck thymus was stable, saturable, reversible and of high affinity. Scatchard analysis of the binding of [125I]-labelled iodomelatonin in the duck thymus collected at midlight had an equilibrium dissociation constant (Kd) of 34.8 +/- 9.4 pmol/l and a maximum number of binding sites (Bmax) of 0.98 +/- 0.07 fmol/mg protein. Two-point diurnal study demonstrated that the Bmax in samples collected at midlight was 42.0% higher (p < 0.05) than that at middark, but there was no significant difference (p > 0.05) between the midlight and middark Kd values. Competition inhibition studies showed that only melatonin, 2-iodomelatonin, 6-chloromelatonin, 6-hydroxymelatonin, N-acetylserotonin, 5-methoxytryptophol, and 5-hydroxytryptamine showed significant inhibition of the [125I]iodomelatonin binding in duck thymus membrane preparations, while the other compounds had no significant inhibition. Our results suggested a direct action of melatonin on the thymus and, thus, the cellular immune system.

Animals↗