Exercise training causes skeletal muscle venular growth and alters hemodynamic responses in spontaneously hypertensive rats.

OBJECTIVE: To investigate whether training changes skeletal muscle venular profile and hemodynamic responses to exercise we studied spontanesouly hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats submitted to training programme (T = 50-60% of VO2max). DESIGN: Training (T) was performed on a treadmill over a period of 13 weeks. Age-matched control groups were kept sedentary (S). T and S rats were chronically instrumented for hindlimb flow (HLF) and arterial pressure (AP) measurements at rest, during dynamic exercise and recovery in two different situations: control and after extensive intravenous blockade (hexamethonium + losartan + Nomega-nitro-L-arginine methyl ester + hydralazine). For morphometric analysis, skeletal muscle samples (gracilis) were obtained after transcardiac perfusion with fixative. RESULTS: T caused a significant reduction of resting mean arterial pressure (MAP) (-11%) only in the SHR group without changing basal HLF. In the sedentary SHR (SHRs), basal relative hindlimb resistance was increased by 45%, but was significantly reduced after T (P < 0.05). During dynamic exercise, MAP increased similarly (10-20 mmHg) in all groups. HLF increases were similar for the four groups up to 0.8 km/h; at higher workloads, HLF was higher in trained SHR (SHRT) versus trained WKY (WKYT) (3.9- versus 2.9-fold increase over basal HLF, respectively). After blockade (and pressure correction with IV phenylephrine infusion), steady-state exercise was performed with similar hindlimb vasodilation in all groups and was accompanied by MAP reduction (-17 +/- 8 mmHg) only in SHRT group. Skeletal muscle venular profile (density, diameter and lumen cross-sectional area) was similar in WKY(T), WKY(S) and SHR(S), but significantly increased in SHR(T). In this group the two-fold increase in venule density was correlated with both the reduction in baseline MAP and the increase in HLF during dynamic exercise. CONCLUSIONS: The results suggest that increased venule density is a specific adaptation of SHR skeletal muscle to training. Venular growth may contribute to both the pressure-lowering effect and the large HLF at high exercise intensities observed in the trained SHR.

Effects of Tityus serrulatus scorpion venom and one of its purified toxins (toxin gamma) on the isolated guinea-pig heart.

1. The effects of Tityus serrulatus scorpion venom and its most important toxin (toxin gamma) were investigated on isolated guinea-pig hearts, perfused with Locke solution, by the Langendorff's method. 2. The cardiac contraction, the coronary flow and the electrocardiogram (ECG) were simultaneously recorded. 3. Bolus injections of 25, 50 or 100 micrograms of scorpion venom and 2.5, 5 or 10 micrograms of toxin gamma in the heart evoked complex effects which were divided into 3 phases: an initial phase (tachycardia or bradycardia associated with an increase in contractile force), an intermediate phase (oscillations of cardiac rate, contractile force and coronary flow, due to wandering pacemakers) and a third phase (sinus tachycardia). 4. The bradycardia and the oscillations of rhythm were prevented by atropine, whereas the tachycardia and the increase in contractile force were prevented either by reserpine or propranolol. 5. Scorpion venom or toxin gamma induced a ST segment displacement in the ECG, explained by a transitory myocardial hypoxia, due to an increase in the contractile force and a simultaneous decrease of the coronary flow. 6. Perfusion of the heart with Locke solution containing 2% scorpion antivenom prevented almost totally the effects elicited by the venom. 7. It is concluded that the complex effects induced by scorpion venom and toxin gamma are due to the simultaneous release of acetylcholine and catecholamines from postganglionic nerve fibers in the heart.