The effects of magnetic field on the biomechanics parameters of soleus and extensor digitorum longus muscles in rats with streptozotocin-induced diabetes.

BACKGROUND: The aim of this study was to determine the effects of the magnetic field (MF) on the isometric contractile characteristics of the soleus and extensor digitorum longus (EDL) muscles in rats both with and without diabetes. METHODS: Biomechanical parameters were recorded in vitro from Wistar rats without diabetes (Group I, n=20), rats without diabetes exposed to MF (Group II, n=20), rats with streptozotocin-induced diabetes (Group III, n=20), and rats with diabetes exposed to MF (Group IV, n=20). Muscle strips were taken from the distal tendon soleus and EDL muscles of rats killed by decapitation. The muscles were hung in organ baths containing Krebs solution (pH 7.4) with a gas mixture of 95% O2 and 5% CO2. Then the muscles were triggered to direct supramaximal stimulation with 0.05 Hz frequency square pulses for periods of 0.5 ms to obtain control values. The contractile parameters were also determined for two muscles of the four groups. Later, the tension-frequency relationship was determined by applying stimulating pulses of 10, 20, 50, and 100 Hz to the muscles. RESULTS: Diabetes caused a certain amount of decrease in the contractile force of the two muscles compared with that of control values. However, MF increased the contractile force of the two muscles in rats both with and without diabetes. The isometric contraction forces obtained by different stimulating frequencies showed a significant linear increase in the tetanic contraction (P<0.05). Diabetes increased the contraction time of the isometric twitch tension compared with that of the control group with a statistically significant difference (P<0.05). MF decreased the contraction time of the two muscles of rats without diabetes (P<0.05) but increased that of rats with diabetes (P>0.05). CONCLUSION: In our study, these results suggest that MF exposure regulates the isometric contractile characteristics of the soleus and EDL muscles of rats with diabetes, positively.

Interaction between AVP and sympathetic system in subtotal nephrectomy-saline hypertension: role of alpha and V1 receptors.

The development process of subtotal nephrectomy-salt hypertension is still unclear. The aim of the present study was to determine the role of the interaction between vasopressin and sympathetic system in the development of this hypertension by using AVP V1 antagonist and alpha blocker phentolamine under anesthesia condition. For this purpose, we carried out about 73% subtotal nephrectomy on male Wistar rats. One group of these rats (normotensive group) was given a low-salt diet and the other group (hypertensive group) was given a high-salt diet for 4 weeks. Finally, eight groups of rats were formed according to the kind(s) of the injected drug(s): (1) normotensive and hypertensive groups injected only V1 antagonist, (2) normotensive and hypertensive groups injected only phentolamine, (3) normotensive and hypertensive groups injected first V1 antagonist and then phentolamine, (4) normotensive and hypertensive groups injected first phentolamine and then V1 antagonist. Either V1 or alpha blockage separately led to a higher reduction in the mean blood pressure (MAP) of the hypertensives than, of the normotensives (p < 0.05). The combined blockage of V1 and alpha receptors, also caused a higher decrease in the MAP of hypertensive group than, of normotensive group, not depending on the order of the injections (p < 0.01). The heart rate increase recorded as a response to the phentolamine injection in normotensive group, did not develop in hypertensive group (p < 0.05). There was no significant difference between the two groups with regard to plasma electrolytes and osmolality. A positive correlation was found between systolic blood pressure and plasma osmolality in hypertensive group (r = 0.40, p < 0.05), but not in normotensive group. We conclude that the increase in V1 and alpha pressor activities contributes to the subtotal nephrectomy-saline hypertension and the augmentation of alpha pressor activity by vasopressin may participate in this contribution.