Effects of glyceryl trinitrate, nitroprusside and nitric oxide on arterial, venous and capillary functions in cat skeletal muscle in vivo

NG-nitro-L-arginine methyl ester potentiates the effect of aminophylline on the isolated rat hemidiaphragm

The effects of different concentrations of N(G)-nitro-L-arginine methyl ester (L-NAME) (0.3, 1, 3, and 10 mM), a non-selective inhibitor of NOS, on the effect of aminophylline on the isometric contraction of the isolated rat hemidiaphragm were investigated. The muscle contractions were induced by direct subtetanic electrical stimulation. Aminophylline (0.36 - 3.60 mM) produced a typical concentration-dependent increase in both parameters of the isometric contraction: tension developed (Td) and the maximum rate of rise of tension (dT/dt max). The second series of additions of aminophylline produced a more pronounced effect. L-NAME (0.3, 1, 3, and 10 mM, 30 min of incubation without stimulation) itself did not change Td and dT/dt max. However, L-NAME (1, 3, and 10 mM) produced a statistically significant potentiation of the effect of aminophylline on Td and dT/dt max.

S-nitroso-N-acetylcysteine protects skeletal muscle against reperfusion injury

The effects of a nitric oxide (NO) donor on microcirculation and contractile function of reperfused skeletal muscle were studied. Rat cremaster muscles underwent 5 hours of ischemia and 90 minutes of reperfusion and were divided into two groups systemically infused with S-nitroso-N-acetylcysteine (SNAC, 100 nmol/min) and phosphate-buffered saline (PBS), respectively. The results showed that the vessels in the SNAC group had more rapid and complete recovery than that in controls. A significant difference was found from 10 to 40 minutes and at 90 minutes in 10-20-microm arterioles, from 10 to 90 minutes in 20-40-microm arterioles, and at 10 and 90 minutes in 40-70-microm arteries. When compared to controls, SNAC-treated muscles showed larger fluorescein filling areas at 15, 30, 60, and 90 minutes and greater isometric tetanic contractile forces in response to stimulation frequencies of 40, 70, 100, and 120 Hz. The data indicate that supplementation of exogenous NO could effectively improve microcirculation and contractile function of skeletal muscle during early reperfusion.

Role of nitric oxide in skeletal muscle: synthesis, distribution and functional importance

Over the last two decades, nitric oxide (NO) has been established as a novel mediator of biological processes, ranging from vascular control to long-term memory, from tissue inflammation to penile erection. This paper reviews recent research which shows that NO and its derivatives also are synthesized within skeletal muscle and that NO derivatives influence various aspects of muscle function. Individual muscle fibres express one or both of the constitutive NO synthase (NOS) isoforms. Type I (neuronal) NOS is localized to the sarcolemma of fast fibres; type III (endothelial) NOS is associated with mitochondria. Isolated skeletal muscle produces NO at low rates under resting conditions and at higher rates during repetitive contraction. NO appears to mediate cell-cell interactions in muscle, including vasodilation and inhibition of leucocyte adhesion. NO also acts directly on muscle fibres to alter cell function. Muscle metabolism appears to be NO-sensitive at several sites, including glucose uptake, glycolysis, mitochondrial oxygen consumption and creatine kinase activity. NO also modulates muscle contraction, inhibiting force output by altering excitation-contraction coupling. The mechanisms of NO action are likely to include direct effects on redox-sensitive regulatory proteins, interaction with endogenous reactive oxygen species, and activation of second messengers such as cyclic guanosine monophosphate (cGMP). In conclusion, research published over the past few years makes it clear that skeletal muscle produces NO and that endogenous NO modulates muscle function. Much remains to be learned, however, about the physiological importance of NO actions and about their underlying mechanisms.

Effects on skeletal muscle oxygenation and capillary blood flow by adenosine-, sodium nitroprusside- and acetylcholine-induced hypotension

BACKGROUND

Adenosine (ADO)-induced hypotension during diethyl ether anesthesia has been shown to increase skeletal muscle oxygenation. Whether this beneficial effect of ADO hypotension is present also during another anesthetic technique was tested in the present study using ketamine-xylazine anesthesia, and its actions were compared with sodium nitroprusside (SNP) and acetylcholine (ACh) induced hypotension in rabbits.

METHODS

Local oxygen pressure and capillary blood flow were measured with a multiwire microelectrode which was placed on the surface of the left vastus medialis muscle. The experiments were performed in three groups, in which either ADO, SNP or ACh was infused into a central vein in a dose that produced a reduction of the mean arterial pressure by 20-25%, to approximately 60 mmHg.

RESULTS

In the ADO group (60-170 micrograms kg-1 min-1) the tissue oxygen pressures increased by 23% while capillary blood flow decreased by 38%. During SNP administration (1-3 micrograms kg-1 min-1) the oxygen pressures decreased by 21% and an increase of 31% in capillary flows was seen. When ACh was infused (1-4 micrograms kg-1 min-1) the oxygen pressures decreased by 21% and, in parallel, capillary blood flow decreased by 50%. During hypotension no low tissue oxygen pressure values (< 1.5 kPa) were found in the ADO group, whereas they were present in both the SNP and ACh group.

CONCLUSION

Compared to sodium nitroprusside and acetylcholine, adenosine appears to have an oxygen-sparing effect in the skeletal muscle during pharmacologically induced hypotension.