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A neutral protease with angiotensin I-forming activity which could readily be separated from acid proteases and plasma and renal renin was obtained from extracts of dog brain. This enzyme has an apparent mol wt of 40,000 by Sephadex chromatography. On chromatofocusing, it displays isoelectric points of 7.92, 7.73, and 7.42, and thus, it is a basic protein, in contrast to either renal or plasma renin which are acidic proteins. This brain enzyme does not react with antibodies specific for dog kidney renin. Since the brain enzyme forms angiotensin I from renin substrate at neutral pH, yet can be separated from and has isoelectric points different from renal renin, it is an isoenzyme of the kidney counterpart. The majority of the renin-like activity of dog brain is due to this isoenzyme. (Endocrinology 114: 2210, 1984)

During the study of an inbred strain of Wistar rats which spontaneously develop hypertension when they reach a weight of approximately 150 g, it was found that these animals also develop an erythrocytosis. A significant increase in red cell count was observed in spontaneously hypertensive (SH) rats (8-11 x 10(6) RBC/mm(3)) when compared with normotensive rats (6-7 x 10(6) RBC/mm(3)) of the same strain. This increase in red cell count paralleled the increase in body weight and the rise in blood pressure. Since the plasma volume, as measured with labeled albumin was normal, there was an absolute increase in red cells. The hematocrit and hemoglobin content of the blood measured in SH rats were only slightly greater than those found in normotensive rats. However, the mean cell volume (MCV) of the red cells in the SH rats was 45-47 mu(3) as compared with 51-53 mu(3) in normotensive rats.A fourfold increase in 24 hr (59)Fe incorporation into the red cells was found in the SH rats when compared with normotensive controls. The bone marrow of the SH rats showed erythroid hyperplasia. When the SH rats were treated with alpha-methyldopa (Aldomet 200 mg/kg daily, i.p.) the red cell count fell in parallel with the drop in blood pressure. No change in red cell count or blood pressure was observed in normotensive rats treated in the same manner. The erythropoietin titer was high in SH rats, and was undetectable in normotensive rats. These observations suggest a direct relationship between the hypertension and the erythrocytosis mediated by erythropoietin; both are genetically controlled.

[1-N-Methylisoasparagine,8-isoleucine]- (I), [1-sarcosine,4-N-methyltyrosine,8-isoleucine]- (II), [1-sarcosine,5-N-methylisoleucine,8-isoleucine]- (III), [1-sarcosine,8-N-methylisoleucine]- (IV), [1-sarcosine8k-N-methylisoleucine,8-N-methylisoleucine]- (V), [1-sarcosine,8-O-methylthreonine]- (VI), [1-sarcosine,8-methionine]- (VII), and [1-sarcosine,8-serine]angiotensin II (VIII), synthesized by Merrifield's solid-phase procedure, possess respectively 0.8, 0.3, 0.5, 1.0, 0.0, 0.5, 3.7, and 0.7% pressor activity of angiotensin II (vagotomized, ganglion-blocked rats). They caused an initial rise in blood pressure (30 min of infusion, 250 ng/kg/min in vagotomized, ganglion-blocked rats) of 16.57, 9.80, 22.80, 32.00, 7.00, 15.06, 32.50, and 11.42 mmHg and showed secretory activity (isolated cat adrenal medulla) of 1.0, 0.1, 0.01, 0.1, less than 0.01, 0.1, less than 0.01, and 0.05% of angiotensin II. On isolated organs pA2 values (rabbit aortic strips) of 8.74, 7.44, 7.64, 7.85, 7.89, 8.76, 8.63, and 8.08, and pA2 values (cat adrenal medulla of 8.16, 9.16, 9.31, 8.00, 8.00, 7.00, 9.16, and 9.33 were obtained. Dose ratios (ratio of ED20 of angiotensin II during infusion of the antagonist and before infusion of the antagonist) in vagotomized, ganglion-blocked rats, infused at 250 ng/kg/min, were 33.43, 2.14, 3.26, 2.99, 0.62, 62.52, incalculable, and 11.15, respectively. The results obtained suggest that (a) analogs I and VI are potent antagonists of the pressor response of angiotensin II in normal rat, VI being the most potent antagonist thus far synthesized; (b) replacement of position 4 (Tyr) with MeTyr or position 5 and/or 8 (Ile) with Melle in [1-sarcosine,8-isoleucine]angiotensin II reduced the antagonist activity of this peptide (rabbit aortic strips and rats), indicating that steric hindrance imposed due to N-methylation in positions 4, 5, or 8 was not favorable in eliminating the initial pressor activity or prolonging the duration of action of [Sar1, Ile8]angiotensin II without reducing its antagonistic properties; (c) except II, none of the analogs showed any enhanced duration of action, suggesting that N-methylation in positions 5 or 8 did not afford protection against proteolytic enzymes; and (d) perfusion studies in cat adrenals indicated that all of these analogs are only very weak secretagogues. With the exception of [Sar1,Thr(ObetaMe)8]angiotensin II, which gave lower antagonistic properties, all other analogs had either similar antagonistic properties or were better antagonists in adrenal medulla than in smooth muscle.

Male Sprague-Dawley rats were maintained on either a normal or low-sodium diet for 5 weeks to examine whether dietary sodium restriction alters angiotensin II (Ang II) receptors. The receptor sites in the hypothalamus-thalamus-septum (H-T-S) region of the brain, the adrenal glands and bladder visceral smooth muscle were measured by saturation isotherm binding assays using 125I-Ang II. Compared to control rats, the low-sodium diet group showed a smaller weight gain, reduced water intake, elevated hematocrit, and decreased urinary sodium concentration. In addition, sodium-depleted rats had a 10-fold elevation in plasma renin activity. However, neither binding affinity of 125I-Ang II to the brain H-T-S region nor its density was significantly different between the two groups. In contrast, both the 125I-Ang II binding density and dissociation constant in the adrenal gland were significantly elevated, while the binding density of 125-I-Ang II in the bladder smooth muscle was significantly decreased in the sodium-restricted group. These results suggest that dietary sodium depletion does not alter Ang II receptors in the rat brain areas wherein Ang II exerts the majority of its central actions.