Involvement of NO-cGMP pathway in anti-hyperalgesic effect of PDE5 inhibitor tadalafil in experimental hyperalgesia

The association of elevated level of cyclic guanosine monophosphate (cGMP) with inhibition of hyperalgesia and involvement of nitric oxide (NO)-cGMP pathway in the modulation of pain perception was previously reported. Phosphodiesterases 5 (PDE5) inhibitors, sildenafil and tadalafil (TAD) used in erectile dysfunction, are known to act via the NO-cGMP pathway. TAD exerts its action by increasing the levels of intracellular cGMP. Hence, the present study investigated the effect of TAD 5, 10, or 20 mg/kg, per os (p.o.) or L-NAME 20 mg/kg, intraperitoneally (i.p.) and TAD (20 mg/kg, p.o.) in carrageenan- and diabetes-induced hyperalgesia in rats using hot plate test at 55 ± 2 °C. In carrageenan- and diabetes-induced hyperalgesia, TAD (10 and 20 mg/kg, p.o.) significantly increased paw withdrawal latencies (PWLs) as compared to the control group. L-NAME significantly decreased PWLs as compared to the normal group and aggravated the hyperalgesia. Moreover, significant difference in PWLs of L-NAME and TAD 20 was evident. Co-administration of L-NAME (20 mg/kg) with TAD (20 mg/kg) showed significant difference in PWLs as compared to the TAD (20 mg/kg), indicating L-NAME reversed and antagonized TAD-induced anti-hyperalgesia. This suggested an important role of NO-cGMP pathway in TAD-induced anti-hyperalgesic effect.

Antihypertensive and Diuretic Effects of the Aqueous Extract of Colocasia esculenta Linn. Leaves in Experimental Paradigms

Colocasia esculenta Linn (CE) is traditionally used for the treatment of various ailments such as high blood pressure, rheumatic pain, pulmonary congestion, etc. Hence in present study, the effect of aqueous extract of CE leaves (AECE) was evaluated for antihypertensive and acute diuretic activity in rats. Preliminary phytochemical evaluation revealed the presence of carbohydrate, saponins, tannins, and flavonoids in AECE. The animals did not show any sign of toxicity and mortality after the administration of AECE 2000 mg/Kg in acute oral toxicity study. The administration of AECE (100, 200, and 400 mg/Kg/day, p.o.) for six weeks and AECE (10, 20, and 40 mg/Kg, IV) on the day of experiment in renal artery-occluded hypertensive rats and AECE (20 and 40 mg/Kg, IV) in noradrenalin-induced hypertension in rats produced significant (p < 0.05) anti-hypertensive effects. AECE (400 mg/Kg, p.o.) showed positive diuretic activity at 5 h. AECE (200 and 400 mg/Kg, p.o.) significantly increased sodium and chloride content of urine in 5 h and 24 h and additionally potassium in 24 h urine. Hence, the results of the present study revealed the antihypertensive and weak diuretic activity of AECE. These effects may be attributed due to the ACE inhibitory, vasodilatory, β-blocking, and/ or Ca(2+) channel blocking activities, which were reported for the phytoconstitunts, specifically flavonoids such as vitexin, isovitexin, orientin, and isoorientin present in the leaves of CE.