Isolation and biological activity of a novel kinin ([Thr6] bradykinin) from the turtle, Pseudemys scripta

Incubation of plasma from the red-eared turtle with glass beads in the presence of the kininase inhibitor 1,10-phenanthroline resulted in activation of the kallikrein-kinin system and generation of bradykinin-like immunoreactivity. The immunoreactive material comprised a single molecular form that was purified to homogeneity by reverse phase HPLC. The primary structure of the peptide was determined by automated Edman degradation and fast atom bombardment mass spectrometry. The amino acid sequence of the turtle kinin Arg-Pro-Pro-Gly-Phe-Thr-Pro-Phe-Arg contains the substitution Thr for Ser at position 6 compared with mammalian bradykinin. [Thr6] bradykinin was synthesized using solid phase methodology, and bolus injections of the peptide into the left atrium of the anaesthetized turtle produced rapid vasodilation. A dose-dependent increase in blood flow in the left aortic arch was accompanied by a decrease in peripheral vascular resistance, so that systemic blood pressure did not change. The data suggest that the kallikrein-kinin system may play an important physiological role in the regulation of cardiovascular function in reptiles.     

Cardiorespiratory effects of temperature in the turtle, Pseudemys floridana

Weight specific VO2 of resting Pseudemys floridana at body temperatures (BT) between 12 to 38 C was studied in relationship to VE, VT, f, pulmonary and systemic blood flow, and blood PO2, PCO2, pH and O2 content. The slope of the curve for VO2 against body mass was similar to that for mammals and differed from that of lizards. VE increased with BT while VE/VO2 fell, resulting in an elevation of arterial PCO2 and a decline in arterial pH of 0.013 unit/degrees C [HCO-3] and total CO2 remained constant. Increments in VE were achieved by decreasing apneic time and increasing VT up to VT of 18 ml.kg-1 when further rise in VE was exclusively on account of breathing frequency. Mean pulmonary and arterial blood flows were incremented in direct proportion to VO2, and no net intracardiac shunts was demonstrable. Ventilation-perfusion ratio fell with BT while EO2 increased. Arterial hemoglobin saturation varied inversely with BT while the arteriovenous O2 difference remained constant. EO2 was found to be highly dependent on the constant blood convection requirement as VE/VO2 fell. At similar BT, VE/VO2 was similar to that for man while Qpul/VO2 was in inverse proportion to maximum O2 capacity of the blood for the two species.     

Oxidative cost to ventilation in a turtle, Pseudemys floridana

Estimates of oxidative cost of ventilation for Pseudemys floridana were obtained by comparison of mean resting VO2 with that obtained while artificially ventilating the lungs with a constant air flow in excess of the normal VE, a circumstance during which the animals remained apneic due to reduction in alveolar PCO2. At a body temperature of 22 degrees C, the oxidative cost attributable to ventilation was 0.0047 ml O2/ml gas ventilated, a value about 10 times that of man. This cost of ventilation is then related to values of VO2 and VE at various body temperatures. The oxidative cost of ventilation, expressed as a percentage of resting VO2, is given by the equation: cost = 0.47 VE/VO2. Relative cost declines with body temperature since VE/VO2 (resting) declines according to the equation: VE(BTPS)/VO2 = -0.017 BT -0.025 log Wt + 2.01 where units are in ml, kg and min. At body temperatures of 10 and 37 C relative costs were 30 and 10% VO2, respectively. While the inverse relation between VE/VO2 and body temperature has important implications for regulation of arterial pH through influencing arterial PCO2, it has the additional meaning of reducing the relative oxidative cost of ventilation as VO2 increases.     

Functional venous admixture in the lungs of the turtle, Chrysemys scripta

Pulmonary functional venous admixture was determined during forced, unidirectional ventilation with pure O2 and air. At a normal lung volume of 140 ml X kg-1, anatomical shunts (physical bypass of gas exchange surface by the blood) averaged 10% of pulmonary blood flow but it increased to 28% as lung volume declined to 30 ml X kg-1. Diffusion limitation and possibly inhomogeneity in ventilation: perfusion ratio also contributed to a total functional venous admixture of about 25% at normal lung volume.     

Central noradrenergic regulation of cerebral blood flow and vascular permeability.

Anatomical studies employing the immunofluorescence localization of dopamine-beta-hydroxylase [= dopamine beta-monooxygenase; 3,4-dihydroxyphenylethylamine, ascorbate:oxygen oxidoreductase (beta-hydroxylating); EC 1.14.17.1] have demonstrated in brain central noradrenergic nerve fibers on small intraparenchymal blood vessels, including capillaries. This system is distinct from the peripheral noradrenergic system inervating the large extraparenchymal blood vessels. From these anatomical findings evolved the working hypothesis that the central noradrenergic system is analogous to the peripheral sympathetic system except that it is specialized for performing specific functions related to the brain microvasculature. To test this hypothesis cerebral blood flow and the brain vascular permeability of water (H215O) were measured in four adult rhesus monkeys (three with bilateral superior cervical ganglionectomies) with stereotaxically placed cannulae permanently located in the lateral ventricles and the locus coeruleus for the injection of drugs. Our data demonstrate that stimulation of the noradrenergic cell bodies in the locus coeruleus with carbachol (8 mug) produces a prompt reduction in hemispheric cerebral blood flow and an increase in brain vascular permeability of water. The intraventricular administration of the alpha-adrenergic blocker phentolamine (25--50 mug) has the opposite effect. These preliminary data support the hypothesis that the central noradrenergic system is analogous to the peripheral sympathetic system with the special function of regulating brain vascular permeability as well as blood flow.     

内皮素系统在缺血性卒中后脑血流调节中的作用

脑血流自动调节是脑组织维持脑血流量恒定的主要机制,对于缺血性卒中的发生、发展和转归均具有重要意义.文章对内皮素系统在缺血性卒中后脑血流调节中的作用和机制进行了综述.