Role Of Intermedin/adrenomedullin-2 In Essential Hypertension

Adrenomedullin-2(ADM2) and intermedin(IMD) are new familial members of calcitionin and calcitonin gene-related peptide (CGRP). They are regarded as identical substance because of their same nucleotide and amino acid sequence (intermedin/ adrenomedullin 2, IMD/ADM2). A study applying cytobiology and molecular biology methods was designed to explore the physiological and pathological significance of IMD/ADM2 in the occurrence and development process of essential hypertension. This study was divided into three parts.1. Study about IMD/ADM2 for levels in blood plasma and tissues, recipient variation and genetic expression in SHRObjective: To observe changes of IMD/ADM2 in the levels of blood plasma and tissues, relationship between regulations of recipient or genetic expression and blood pressure, heart function. Methods: There were 8 male SHR of 11 weeks old in experiment group, 8 male WKY of the same age in control group. The protein amount of of ADM and IMD/ADM2 in blood plasma and tissue were obtained by radioimmunoassay. mRNA expression of CRLR and RAMPs were measured by RT-PCR method. The protein levels of CRLR and RAMPs were measured by Western blot. Data of blood pressure and heart function were obtained with cardiac catheterization. Results: 1. In SHR group, levels of IMD in blood plasma, myocardium and aorta were higher than that in WKY group (P<0.01). 2. mRNA levels of IMD/ADM2, ADM, CRLR and RAMP1, RAMP2, RAMP3 increased respectively in both myocardium and aorta in SHR (P<0.01). 3. In SHR group, IMD/ADM2 of blood plasma had significant negative correlation with SBP (P<0.05). In SHR group, levels of IMD/ADM2 in blood plasma had correlation with mRNA levels of recipient system including CRLR, RAMP1, RAMP2, RAMP3. Conclusions: These results suggest that IMD/ADM2 may have important physiological and pathological significance during the occurrence anddevelopment process of essential hypertension.2. Effect on blood pressure/heart function of SHR by applying mini-osmotic pump with IMD/ADM2 and possible mechanismObjective: To study the effect of IMD/ADM2 on SHR blood pressure/heart function and possible mechanism. Methods: Applying mini-osmotic pump implanted subcutaneouly, after two weeks, the levels of cAMP were measured by radioimmunoassay. Data including CRLR and RAMPs in left ventricle cardiac muscle and aorta, mRNA expression of BNP and atrial natriuretic peptide ANP were measured by semiquantitative RT-PCR method. Results: 1. Compared with that in SHR group, SBP, ±LV dp/dtmax, LVSP and heart rates in IMD group were decreased significantly (P<0.01). 2. The levels of ANP mRNA and BNP mRNA in cardiac muscle were higher in IMD group compared with that in WKY and SHR groups (P<0.01). 3. Results in acceptor study showed that CRLR mRNA expression increased by 22% in IMD group than that in SHR group (P<0.05). In aorta, expression of RAMPs and CRLR were significantly lower in IMD (P<0.05). Conclusions: 1. IMD/ADM2 could decrease SHR blood pressure significantly and improve heart function. 2. IMD/ADM2 can work with some other cardiovascular active factors like ANP and BNP in body, which will lead to depressurization and heart function protection. 3. Eectogenic IMD/ADM2 can affect acceptor expression of RAMPs and CRLR in their acceptor system.3. Signal conduction effect of IMD/ADM2 on blood vesselsObjective: To explore how IMD/ADM2 affects the second messenger cAMP to adjust blood vessel secretion in SHR. Methods: SHR and WKY were executed by decapitation, then aorta blood vessel in chest and abdomen were taken out and sliced.Different doses of IMD, IMD+ADM_22-52, IMD+CGRP_8-37 and ADM were added into sample one by one. After incubation, sample was boiled and homogenated. Level of cAMP in cells was measured by radioimmunoassay methods. Results: 1. After incubation and given different doses of IMD, levels of cAMP in ex vivo cardiac muscle in SHR group were decreased compared with that in WKY group (P<0.05) and increased in aorta (P<0.05).2. In SHR group,levels of cAMP were increased after ADM_22-52 were added into ex vivo aorta (P<0.01), and in cardiac muscle, decreased after CGRP_8-37 were added into these samples. But there was no statistics significance for these changes. Conclusions: 1. IMD/ADM2 can induce blood vessel in SHR to produce cAMP similar with the way in normal rat. On the other hand, secretory volume of cAMP is higher significantly than that in WKY group. The sensitivity to change in SHR for IMD maybe is the reason of that. 2. No matter was it ADM_22-52 or CGRP_8-37, neither of them could block alone IMD/ADM2 to stimulate cardiovascular tissue in SHR producing cAMP. These results suggested that IMD/ADM2 could produce a marked effect of vasodilatation through acceptor of CGRP1, ADM1 and ADM2 no-selectively.