Effect of ligation of spleen vessels on left ventricular function and coronary blood flow in dogs injected with scorpion venom

Spleen Perfusion as an Index of Gender Impact on Sympathetic Nervous System Response to Exercise

Objective: Sympathetic nervous system (SNS) reaction to exercise is gender dependent. Nevertheless, clinically applicable methods to identify this difference are still missing. An organ largely sensitive to SNS is the spleen whose response to exercise can be easily evaluated, being included in the field of view of myocardial perfusion imaging (MPI). Here, we aimed to verify whether gender interferes with the spleen perfusion and its response to exercise. Methods: For this purpose, we evaluated 286 original scans of consecutive patients submitted to MPI in the course of 2019. Our standard procedure implies a single-day stress-rest sequence with a gap of ≥2 h between the administrations of 180 and 500 MBq of 99mTc-Sestamibi, respectively. Imaging is performed 30 min after radiotracer administration, with scan duration set at 25 and 35 s per view, respectively. Non-gated scans were reconstructed with the filtered back-projection method. A volume of interest was drawn on the spleen and heart to estimate the dose-normalized average counting rate that was expressed in normalized counts per seconds (NCPS). Results: In all subjects submitted to exercise MPI (n = 228), NCPS were higher during stress than at rest (3.52 ± 2.03 vs. 2.78 ± 2.07, respectively; p < 0.01). This effect was not detected in the 58 patients submitted to dipyridamole-stress. The response to exercise selectively involved the spleen, since NCPS in heart were unchanged irrespective of the used stressor. This same response was dependent upon gender, indeed spleen NCPS during stress were significantly higher in the 75 women than in the 153 men (3.86 ± 1.8 vs. 3.23 ± 1.6, respectively, p < 0.01). Again, this variance was not reproduced by heart. Finally, spleen NCPS were lower in the 173 patients with myocardial reversible perfusion defects (summed difference score ≥3) than in the remaining 55, despite similar values of rate pressure product at tracer injection. Conclusion: Thus, exercise interference on spleen perfusion can be detected during MPI. This effect is dependent upon gender and ischemia confirming the high sensitivity of this organ to SNS activation.

Antivenom serotherapy and volume resuscitation partially improve peripheral organ ischemia in dogs injected with scorpion venom

We tested the hypothesis that fluid resuscitation combined with antivenom serotherapy given after injection of scorpion venom may increase cardiac output (CO) and blood pressure (BP) and prevent the decline in bicarbonate, pH and gastric perfusion. Seventeen anesthetized, mechanically ventilated dogs were given 0.1 mg/kg i.v. venom of the scorpion Leiurus quinquestriatus. The dogs were randomized into three groups: six dogs were given venom alone; three dogs were given 6 ml of antivenom 1 minute before venom injection; eight dogs were given 6 ml of antivenom and 20 ml/kg of synthetic colloid solution, 20 min after venom injection. Parameters reflecting respiratory and circulatory functions were determined at baseline and 120 min after venom injection. Scorpion venom caused a decrease in CO, BP, pH and HCO3-. Gastric mucosal perfusion was severely affected as assessed by mucosal pH (pHi) and the gradient between mucosal and arterial pCO2 (delta pCO2). Antivenom given before venom injection prevented all the effects induced by the venom. Antivenom and fluid given 20 min after venom injection caused a marked increase in CO and BP, but had no effect on pH and HCO3- decline (compared with venom alone). Gastric perfusion slightly improved as the increase in delta pCO2 was attenuated. The combination therapy of antivenom and fluid in this dog model is superior to the therapy of each of them alone. The marked and long-standing improvement of CO is promising and may suggest improvement in HCO3- and pH with time.

Effect of Venom from the Scorpion Leiurus Quinquestriatus on Rat Vascular Aortic Rings

The present study was designed to examine the effects of venom from the scorpion Leiurus quinquestriatus hebraeus (Lqh) on the contractility of rat aortic rings. We first examined the effect of Lqh venom on the contractile tension of isolated rat vascular aortic rings and then whether long-term exposure to the venom reduces the contractility of vascular smooth muscle by increasing the production of nitric oxide. Following the administration of 33 microg/mL of crude Lqh venom, contractile tension increased by 18.9 +/- 11.4 percent. The administration of 2.4 x 10(-7) M noradrenaline (NA) led to a 31.6 +/- 8.2 percent increase in tension (p < 0.01). The effects induced by NA and Lqh venom were similar and additive (p < 0.01). Pretreatment with the alpha-adrenergic blocker phenoxybenzamine (0.2 microM) eliminated the effect of the venom, whereas the calcium-channel blocker verapil (8.3 microM) merely attenuated the effect. Incubation of the rings with Lqh venom for 16 to 18 h, followed by NA stimulation, led to a 15 to 20 percent decrease in tension (p < 0.001). Treatment with N-omega-nitro-L-arginine methyl ester (110 microM), a constitutional nitric oxide inhibitor, restored the tension to control values. Treatment with S-methyl-isothiourea (0.1 microM), an inducible nitric oxide synthesis inhibitor, had no effect on contractile tension. The results of the present study suggest that the effect of Lqh venom on isolated aortic rings is induced via sympathetic nerve terminals. Calcium had little effect on the smooth muscle contractility of aortic rings incubated with the venom. No evidence was found to support nitric oxide synthesis after the long-term exposure of the rings to Lqh venom.