Effect of intravenous and intracerebroventricular adrenomedullin injections on cardiovascular and some renal functions in rats

To investigate the effect of intravenous and intracerebroventricular adrenomedullin injections on cardiovascular and some renal functions in rats. 30 male rats were used. They were divided into 3 groups each of ten rats: Group I; rats were injected intravenously with human adrenomedullin 1 -52 [1000 P mole/kg], Group II; rats were injected intracerebroventricularly with human adrenomedullin [300 P mole] and Group Ill; rats were subjected to alpha - sympathetic blockade with phentolamine [10 microg/kg] then dealt with as in group II. The following parameters were measured: arterial blood pressure, heart rate, plasma renin activity, plasma and urinary sodium, urine volume per 24 hours and creatinine clearance. Intravenous adrenomedullin produced hypotension concomitant with tachycardia and increased plasma renin activity. Diuresis, natriuresis and increased creatinine clearance were also observed. In contrast, intracerebroventricular adrenomedullin injection resulted in hypertension which was completely abrogated by alpha - sympathetic blockade. Diuresis and tachycardia were also demonstrated after central administration of the peptide. Intravenous adrenomedullin had clear hypotensive. diuretic and natriuretic effects suggesting a role in regulation of cardiorenal homeostasis. On the other hand, intracerebroventricular adrenomedullin had hypertensive effect through alpha - adrenergic stimulation and a diuretic effect suggesting a role in neural integration of afferent information detailing pressure and volume status of the animal or counter balancing the volume unloading actions of the peptide in the periphery