Hepatic sinusoidal responses to intraportal injections of phenylephrine and isoprenaline in the rat

Effect of increasing liver blood flow on nanodrug clearance by the liver for enhanced antitumor therapy

A norepinephrine-loaded nano-system can serve as an effective auxiliary agent for reducing nanodrug clearance by the liver and enhancing tumor therapy.

Mechanism of hard-nanomaterial clearance by the liver

The liver and spleen are major biological barriers to translating nanomedicines because they sequester the majority of administered nanomaterials and prevent delivery to diseased tissue. Here we examined the blood clearance mechanism of administered hard nanomaterials in relation to blood flow dynamics, organ microarchitecture and cellular phenotype. We found that nanomaterial velocity reduces 1,000-fold as they enter and traverse the liver, leading to 7.5 times more nanomaterial interaction with hepatic cells relative to peripheral cells. In the liver, Kupffer cells (84.8 ± 6.4%), hepatic B cells (81.5 ± 9.3%) and liver sinusoidal endothelial cells (64.6 ± 13.7%) interacted with administered PEGylated quantum dots, but splenic macrophages took up less material (25.4 ± 10.1%) due to differences in phenotype. The uptake patterns were similar for two other nanomaterial types and five different surface chemistries. Potential new strategies to overcome off-target nanomaterial accumulation may involve manipulating intra-organ flow dynamics and modulating the cellular phenotype to alter hepatic cell interactions.

Decreased intrahepatic response to alpha(1)-adrenergic agonists in lipopolysaccharide-treated rats is located in the sinusoidal area and depends on Kupffer cell function

BACKGROUND AND AIM

Livers from lipopolysaccharide-treated rats have a decreased vascular response to alpha(1)-adrenergic agonists due to an increased production of nitric oxide. Kupffer cells play a central role in the development of intrahepatic microvascular abnormalities during endotoxemia. We investigated the role of Kupffer cells in the intrahepatic vascular tone control in normal and endotoxemic rats.

METHOD

Twenty-four hours after pretreatment with gadolinium chloride (to eliminate/inactivate Kupffer cells) or saline, rats were treated with lipopolysaccharide or a second dose of saline. Six hours later, rats (under deep anesthesia) were submitted to liver perfusion with Krebs-Henseleit solution using a system that allowed the measurement of both perfusion and sinusoidal pressures. Dose-response curves to methoxamine (alpha(1)-adrenergic agonist) were obtained in the absence or the presence of the nitric oxide synthase inhibitor N-monomethyl-L-arginine.

RESULTS

Pretreatment with gadolinium did not change the intrahepatic vascular response to methoxamine in normal livers. Livers from lipopolysaccharide-treated rats showed a decreased sinusoidal vascular response to methoxamine and a 10-fold increase in nitric oxide production during liver perfusion. Either pretreatment with gadolinium or the presence of N-monomethyl-L-arginine in the perfusate restored the response to methoxamine and decreased the nitric oxide overproduction by more than 50%.

CONCLUSIONS

Kupffer cells neither mediate nor modulate the intrahepatic vascular response to alpha(1)-adrenergic agonists in normal livers. Reduction in intrahepatic vascular response to alpha(1)-adrenergic agonists in livers from lipopolysaccharide-treated rats is located in the sinusoidal area and depends on Kupffer cell function.

Variation of incorporation of [3H]orotic acid into the nucleotide and RNA fractions of different parts of the same liver lobe in the rat

1. Anaesthetized rats were given [3H]orotic acid either intraperitoneally or via a catheter into the hepatic artery with or without degradable starch microspheres. 2. The radioactivity in the acid soluble and RNA fractions of five pieces of the left lateral liver lobes was determined. 3. A variation of the distribution of the precursor into the different parts of the same liver lobe was shown. 4. This variation was most pronounced (3000-17,000 cpm/micrograms in the acid soluble fraction) when the precursor was administered via the artery and without microspheres. 5. The correlation between the radioactivity in the acid soluble and RNA fractions within each liver piece was 0.85, 0.90 and 0.75 in the three groups respectively. 6. It is suggested that the variation of the distribution depends on circulatory differences within the liver.

Measurement of hepatic blood flow

Measurement of hepatic blood flow is fundamental to understanding hepatic physiology and biochemistry, quantitating drugs metabolized in the liver, and describing pathophysiologic states such as portal hypertension. However, the dual blood supply, altered handling of labels during disease states, and the relative inaccessibility of the portal system have made precise measurements of hepatic blood flow difficult. A variety of techniques can be utilized in both laboratory animals and patients; the more invasive techniques are generally available for animal studies, while semi-invasive and noninvasive methodologies yield information from patients. Each method has its inherent strengths and weaknesses, and may be utilized in a particular circumstance to accurately assess hepatic blood flow. It is therefore critical to select a measurement technique which yields the desired accuracy without interfering with the physiologic conditions under study. The methodology is presently available to achieve this end.

Hepatic microvascular effects of terbutaline in experimental cardiogenic shock in rats

1. Experimental myocardial infarction was produced in rats by direct electrical cauterization of the myocardium of left ventricle. This produced cardiogenic shock with the accompanying haemodynamic changes of low cardiac output, low mean arterial pressure, raised central venous pressure and an absence of cardiac arrhythmias. 2. The liver microcirculation was observed using in vivo television microscope method. The diameter and erythrocyte flow velocity in the liver sinusoids were measured quantitatively. 3. During experimental cardiogenic shock 80% of the liver sinusoids were constricted; the remaining 20% showed dilatation. In all these liver sinusoids the erythrocyte flow velocity was only 50% of the pre-shock level. 4. Intravenous injection of the selective beta 2-adrenoceptor agonist terbutaline (0.15 mg/kg) restored the systemic arterial pressure to pre-shcok levels and partially raised the cardiac output. In the liver microcirculation terbutaline restored both constricted and dilated liver sinusoids to pre-shock calibres, but only partially raised erythrocyte flow velocity. 5. It is proposed that during experimental cardiogenic shock, terbutaline produces dilatation in the terminal liver microcirculation by opening sphincters of liver sinusoids and restores sinusoid diameters to pre-shock calibres. Therefore, terbutaline has the capacity to decrease peripheral resistance and unload the circulation during cardiogenic shock.

beta 2-Adrenoceptors in rat liver microcirculation

1. Rat liver sinusoids were observed by a microscopic in vivo transillumination method. The diameter of liver sinusoids and intrasinusoid erythrocyte flow velocities were measured quantitatively by a close-circuit television technique. 2. Both isoprenaline and the selective beta 2-adrenoceptor agonist terbutaline produced a concentration-dependent dilatation of liver sinusoids and slowed erythrocyte flow velocity. The effects of isoprenaline and terbutaline were antagonized by propranolol but not by the selective beta 1-adrenoceptor antagonist atenolol. Propranolol alone produced constriction of the liver sinusoids and increased erythrocyte flow velocity; these effects were not produced by atenolol. 3. The percentage dilatations produced by isoprenaline alone, isoprenaline in the presence of phenoxybenzamine and isoprenaline in the presence of phenylephrine-induced constriction were similar. 4. It is proposed that the beta-adrenoceptors in liver sinusoids are of the beta 2-type, and their physiological role was to counteract constrictor responses produced by alpha-adrenoceptor activity.

Stimulation and blockade of cholinergic receptors in terminal liver microcirculation in rats

This study was designed to establish the existence of cholinergic vascular receptors in the terminal portion of the rat liver microcirculation. The liver microcirculation was observed in vivo by a transillumination technique through a television microscope. The changes in the caliber of the liver sinusoids were measured directly on the television screen. Infusion of the parasympathetic neurotransmitter acetylcholine into the portal venous circulation caused a concentration-dependent dilation of liver sinusoids. Similar dilatation effects were observed for other cholinergic receptor agonists. Atropine, the specific cholinergic receptor blocker, inhibited this dilator effect, displacing the acetylcholine concentration-effect curve to the right. In contrast, physostigmine, the cholinesterase inhibitor, caused displacement of the curve to the left. In conclusion, cholinergic receptors are present in the terminal portion of the liver microcirculation, subserving the functional role of vasodilatation.