Tissue distribution & elimination of capsaicin, piperine & curcumin following oral intake in rats.

Background & objectives: Curcumin, capsaicin and piperine - the bioactive compounds present in spices-turmeric (Curcuma longa), red pepper (Capsicum annuum) and black pepper (Piper nigrum) respectively, have a considerable portion of structural homology. Tissue distribution and elimination of these three structurally similar bioactive compounds was examined following their oral intake in rats. Methods: Separate sets of animals (150 - 160 g) were orally administered the three spice principles at dosages of 30 mg (capsaicin), 170 mg (piperine) and 500 mg (curcumin) / kg body weight. The tissue concentrations of administered spice compounds were determined by HPLC. Results: Maximum distribution of 24.4 per cent of administered capsaicin was seen at 1 h, while no intact capsaicin was detectable after 4 days. Absorption of capsaicin was about 94 per cent and very rapid relative to other two compounds. A maximum of 10.8 per cent of administered piperine was seen in tissues at 6 h. Absorption of the administered piperine was about 96 per cent. Curcumin concentration was maximum in the intestine at 1 h; maximum in blood at 6 h and remained at significantly higher level even at 24 h. About 63.5 per cent of the curcumin dose was absorbed. Only a small portion of the administered dose of capsaicin (< 0.1%) and curcumin (0.173 %) was excreted in urine, whereas piperine was not detectable in urine. Enhanced bioavailability of curcumin was evidenced when the same was orally administered concomitant with piperine. Intestinal absorption of curcumin was relatively higher when administered concomitantly with piperine, and it stayed significantly longer in the body tissues. Intact curcumin was detected in brain at 24, 48 and 96 h with a maximum at 48 h. Conclusions: Considerable difference exists in the bioavailability of the three test compounds. Curcumin could be traced in the brain following its administration. Bioavailability of curcumin can be improved by co-administration with piperine.

Anandamide injected into the lateral ventricle of the brain inhibits submandibular salivary secretion by attenuating parasympathetic neurotransmission

Our objective was to determine the effect of arachidonylethanolamide (anandamide, AEA) injected intracerebroventricularly (icv) into the lateral ventricle of the rat brain on submandibular gland (SMG) salivary secretion. Parasympathetic decentralization (PSD) produced by cutting the chorda tympani nerve strongly inhibited methacholine (MC)-induced salivary secretion while sympathetic denervation (SD) produced by removing the superior cervical ganglia reduced it slightly. Also, AEA (50 ng/5 µL, icv) significantly decreased MC-induced salivary secretion in intact rats (MC 1 µg/kg: control (C), 5.3 ± 0.6 vs AEA, 2.7 ± 0.6 mg; MC 3 µg/kg: C, 17.6 ± 1.0 vs AEA, 8.7 ± 0.9 mg; MC 10 µg/kg: C, 37.4 ± 1.2 vs AEA, 22.9 ± 2.6 mg). However, AEA did not alter the significantly reduced salivary secretion in rats with PSD, but decreased the slightly reduced salivary secretion in rats with SD (MC 1 µg/kg: C, 3.8 ± 0.8 vs AEA, 1.4 ± 0.6 mg; MC 3 µg/kg: C, 14.7 ± 2.4 vs AEA, 6.9 ± 1.2 mg; P < 0.05; MC 10 µg/kg: C, 39.5 ± 1.0 vs AEA, 22.3 ± 0.5 mg; P < 0.001). We showed that the inhibitory effect of AEA is mediated by cannabinoid type 1 CB1 receptors and involves GABAergic neurotransmission, since it was blocked by previous injection of the CB1 receptor antagonist AM251 (500 ng/5 µL, icv) or of the GABA A receptor antagonist, bicuculline (25 ng/5 µL, icv). Our results suggest that parasympathetic neurotransmission from the central nervous system to the SMG can be inhibited by endocannabinoid and GABAergic systems.