Royal jelly (RJ) produced by honey bees is known to contain three major nutrients including amino acids, vitamins and minerals.1) Additionally, RJ has various biological activities such as a hypotensive effect, insulin-like action and antitumor activity.2-4) Therefore, it is possible that RJ may have some effects on insulin resistance, which is considered to be a cause of various lifestyle-related diseases. Many clinical studies have shown a possible relationship between hypertension and insulin resistance, since patients with type 2 (noninsulin dependent) diabetes mellitus frequently have insulin resistance associated with hypertension. 5-7)Chronic administration of fructose to rats has been reported to cause insulin resistance, which is characterized by increased serum insulin and euglycemia.8) Especially, a hyperinsulinemic state associated with hypertension was more prominently induced by fructose drinking than by fructose feeding.9) Previously, we reported that rats with chronic hyperinsulinemia, which was induced by giving a 15% fructose solution in drinking water for 10 weeks (fructose-drinking rats, FDR), showed deficient neuronal regulation of vascular tone, and this leads to hypertension. 10,11) Recently, we demonstrated that chronic administration of RJ prevented development of insulin resistance in Ohtsuka Long-Evanse Fatty (OLETF) rats, which is a spontaneous type 2 diabetic model. 12)Thus, in the present study, we investigated the effects of RJ on the insulin resistance in FDR. We also examined whether RJ prevents hypertension and altered vascular responsiveness induced by insulin resistance using isolated mesenteric vascular beds of rats. MATERIALS AND METHODS AnimalsSix week-old male Wistar rats were used in this study. They were given 15% fructose solution as drinking water ad libitum for 8 weeks. The control group was given tap water instead of 15% fructose solution. Three rats were housed in each cage (W 220ϫL 320ϫH 135 mm; Natsume Seisakusho, Tokyo, Japan), and given normal rat chow (Oriental Yeast, Tokyo, Japan). They were housed in the Animal Research Center of Okayama University at a controlled ambient temperature of 22Ϯ2°C with 50Ϯ10% relative humidity and with a 12-h light/12-h dark cycle (lights on at 8:00 a.m.). This study was carried out in accordance with the Guidelines for Animal Experiments at Okayama University Advanced Science Research Center, Japanese Government Animal Protection and Management Law (No. 105) and the Japanese Government Notification on Feeding and Safekeeping of Animals (No. 6). Every effort was made to minimize the number of animals used and their suffering.Long-Term Administration of RJ RJ, which was enzymatically treated and supplied by Yamada Apiculture Center, Inc. (Okayama, Japan) (Lot No. 020605), was used in this study. RJ was diluted by adding distilled water and orally administered at doses of 100 mg/kg/d and 300 mg/kg/d for 8 weeks from 6 to 14 weeks of age. Each animal was lightly anesthetized with ether and orally administrated RJ solution at a volum...

Propolis, a honeybee product, contains a variety of biologically active substances. The present study was designed to investigate the eŠects of propolis on insulin resistance induced by fructose-drinking rats (FDR; type 2 diabetic animal model). Male Wistar rats (6 weeks old) received 15％ fructose solution in drinking water for 8 weeks. FDR showed signiˆcant increases in plasma levels of insulin, Homeostasis Model Assessment ratio (HOMA R, an index of insulin resistance), body weight, and systolic blood pressure but not blood glucose levels, when compared with control rats. Brazilian propolis extract (100 and 300 mg/kg, p.o.) treatment for 8 weeks signiˆcantly decreased the plasma level of insulin, HOMA-R, and body weight, increased plasma triglyceride levels without aŠecting blood glucose and total cholesterol levels, and tended to decrease systolic blood pressure. In isolated and perfused mesenteric vascular beds of FDR, propolis treatment resulted in a signiˆcant reduction of sympathetic nerve-mediated vasoconstrictor response to periarterial nerve stimulation (PNS; 8 Hz) and tended to increase the calcitonin gene-related peptide (CGRP) nervemediated vasodilator response to PNS, compared with those in untreated FDR. However, propolis treatment did not signiˆcantly aŠect norepinephrine-induced vasoconstriction and CGRP-induced vasodilation. These results suggest that propolis could be an eŠective functional food to prevent the development of insulin resistance.

Background and purpose: The vascular endothelium regulates vascular tone by releasing various endothelium-derived vasoactive substances to counteract excess vascular response. We investigated whether the vascular endothelium regulates vasodilatation via released endothelium-derived contracting factors (EDCFs), by examining the effect of endothelium removal on responses to periarterial nerve stimulation (PNS) and various vasodilator agents. Experimental approach: The rat mesenteric vascular bed was perfused with Krebs solution. Vasodilator responses to PNS and 5 min perfusion of vasodilator agents in preparations with endothelium were compared with those in the same preparations without endothelium. The endothelium was removed by 30 s perfusion with sodium deoxycholate. Key results: Endothelium removal significantly augmented vasodilator responses to PNS and calcitonin gene-related peptide (CGRP), isoprenaline (b-adrenoceptor agonist), SNP and 8-bromo-cGMP (8-Br-cGMP; cGMP analogue) but not BAY41-2272 (soluble guanylate cyclase activator). The augmentation of SNP-induced vasodilatation after denudation was much greater than that of CGRP-or isoprenaline-induced vasodilatation. In the preparations with an intact endothelium, L-NAME (nitric oxide synthase inhibitor) significantly augmented vasodilator responses to PNS and CGRP, isoprenaline, SNP and 8-Br-cGMP, but not BAY41-2272. Indomethacin (cyclooxygenase inhibitor) and seratrodast (thromboxane A 2 receptor antagonist), but not phosphoramidon (endothelin-1-converting enzyme inhibitor) or BQ-123 (selective endothelin type A receptor antagonists), significantly augmented vasodilator responses to PNS and CGRP, isoprenaline, SNP and BAY41-2272. Conclusion and implication: These results suggest that the endothelium in rat mesenteric arteries regulates and maintains vascular tone via counteracting not only vasoconstriction through releasing endothelium-derived relaxing factors, but also vasodilatation, in part by releasing an EDCF, thromboxane A 2 .

Abstract. Lafutidine is a histamine H 2 -receptor antagonist with gastric antisecretory and gastroprotective activity associated with activation of capsaicin-sensitive nerves. The present study examined the effect of lafutidine on neurotransmission of capsaicin-sensitive calcitonin gene-related peptide (CGRP)-containing vasodilator nerves (CGRPergic nerves) in rat mesenteric resistance arteries. Rat mesenteric vascular beds were perfused with Krebs solution and vascular endothelium was removed by 30-s perfusion with sodium deoxycholate. In preparations preconstricted by continuous perfusion of methoxamine (α 1 adrenoceptor agonist), perfusion of lafutidine (0.1 -10 µM) concentration-dependently augmented vasodilation induced by the periarterial nerve stimulation (PNS, 1 Hz) without affecting vasodilation induced by exogenous CGRP (10 pmol) injection. Perfusion of famotidine (H 2 -receptor antagonist, 1 -100 µM) had no effect on either PNS-induced or CGRP-induced vasodilation. Perfusion of lafutidine concentration-dependently augmented vasodilation induced by a bolus injection of capsaicin (vanilloid-1 receptor agonist, 30 pmol). The presence of a vanilloid-1 receptor antagonist, ruthenium red (10 µM) or capsazepine (5 µM), abolished capsaicin-induced vasodilation and significantly decreased the PNS-induced vasodilation. The decreased PNS-induced vasodilation by ruthenium red or capsazepine was not affected by perfusion of lafutidine. These results suggest that lafutidine facilitates CGRP nerve-mediated vasodilation by modulating the function of presynaptic vanilloid-1 receptors located in CGRPergic nerves.

We reported that vasodilator responses to various vasodilator agents were augmented by endothelium removal. To explain this mechanism, we hypothesized that endothelium removal eliminates the release of endothelium-derived contracting factor EDCF, which counteracts the vasodilation. However, the underlying mechanism is unknown. Therefore the present study investigated the second messenger system further to investigate the mechanisms underlying enhanced vasodilator response after endothelium removal in rat mesenteric resistance arteries. Mesenteric vascular beds isolated from Wistar rats were perfused and perfusion pressure was measured. The vascular endothelium was removed by 30-s perfusion of sodium deoxycholate. Vasodilator responses to sodium nitroprusside (SNP) perfusion were markedly augmented and prolonged by endothelium removal. In preparations with intact endothelium and active tone, 5-min perfusion of sodium azide (non-speciˆc guanylate cyclase (GC) activator), ANP (membrane-linked GC activator), and 8-Br-cGMP (cGMP analogue) caused a concentration-dependent vasodilation that was markedly augmented by endothelium removal. However, vasodilation induced by YC-1 and BAY41-2272 (selective soluble GC activator) was not augmented by endothelium removal. When methylene blue (soluble GC inhibitor) was present in the medium, SNP caused a concentration-dependent vasodilation in the preparation with intact endothelium, which was less augmented by endothelium removal compared with control (preparation without methylene blue). Theseˆndings suggest that endothelium removal aŠects intracellular cGMP-mediated signal transduction system in vascular smooth muscle cells.