ABSTRACT
Royal jelly (RJ) is known to have abundant nutritional properties and a variety of biological activities. To investigate the effects of RJ on insulin resistance, 10-week-old Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a type 2 diabetic model, were treated for 4 weeks with RJ (10, 30, and 300 mg/kg, p.o.). RJ treatment tended to decrease systolic blood pressure and significantly decreased serum levels of insulin and the Homeostasis Model Assessment ratio, an index of insulin resistance. In isolated and perfused mesenteric vascular beds of OLETF rats, RJ treatment resulted in significant reduction of the sympathetic nerve-mediated vasoconstrictor response to periarterial nerve stimulation (PNS) and potentiation of the calcitonin gene-related peptide (CGRP) nerve-mediated vasodilator response to PNS, compared with that in untreated OLETF rats. However, RJ treatment did not significantly affect norepinephrine-induced vasoconstriction and CGRP-induced vasodilation. These results suggest that RJ could be an effective and functional food to prevent the development of insulin resistance.
Subject(s)
Diabetes Mellitus, Type 2/physiopathology , Diabetes Mellitus, Type 2/therapy , Fatty Acids/administration & dosage , Fatty Acids/pharmacology , Insulin Resistance , Animals , Calcitonin Gene-Related Peptide/physiology , Disease Models, Animal , In Vitro Techniques , Insulin/blood , Mesenteric Arteries/drug effects , Mesenteric Arteries/innervation , Rats , Rats, Long-Evans , Sympathetic Nervous System/physiology , Systole/drug effects , Vasoconstriction/drug effectsABSTRACT
Adrenomedullin (AM) is a potent vasodilator peptide whose major source is the vascular wall. In the present study, the mechanism of release of AM was investigated in the rat mesenteric resistance artery. The isolated mesenteric vascular bed was perfused with Krebs solution at a constant flow rate (5 ml/min) and AM in the perfusate was measured by a highly sensitive enzyme immunoassay (Immunoenzymometric assay; IEMA) method. In preparations without endothelium, spontaneous release of AM was detected in the perfusate (68.7+/-5.8 fmol/ml, n=45). Periarterial nerve stimulation (PNS, 4 and 8 Hz) caused 11.4+/-3.9% (4 Hz) and 9.1+/-3.5% (8 Hz) decreases in the spontaneous release of AM. Removal of Ca2+ from the medium did not affect the spontaneous AM release, but abolished the PNS-induced inhibition of spontaneous AM release. Perfusion of 10nM calcitonin gene-related peptide (CGRP) or 0.1 microM capsaicin (inducer of CGRP release) inhibited significantly the spontaneous AM release. PNS (8 Hz)-induced inhibition of spontaneous AM release was antagonized by CGRP(8-37) (CGRP receptor antagonist). These results suggest that AM is mainly released from vascular smooth muscle cells of the rat mesenteric artery and endogenous or exogenous CGRP inhibits AM release.
