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A three-dimensional structure of the complex of human renin and the scissile site P4 Pro to P1' Val of angiotensinogen was deduced in order to design potent human renin inhibitors rationally. On the basis of this structure, an orally potent human renin inhibitor (1a) was designed from the angiotensinogen transition state and synthesized. The inhibitor 1a contains a (2R)-3-(morpholinocarbonyl)-2-(1-naphthylmethyl)propionyl residue (P4-P3) with a retro-inverso amide bond, L-histidine, and a novel amino acid, (2R,3S)-3-amino-4-cyclohexyl-2-hydroxybutyric acid, named cyclohexylnorstatine (2a). The optically pure cyclohexylnorstatine was efficiently prepared from Boc-L-cyclohexylalaninol (3), and the stereochemistry of 1a was established by X-ray crystal analysis. The analyses of interaction between 1a and human renin using modeling techniques indicated that (1) the cyclohexyl group of P1 and the naphthyl group of P3 were accommodated in large hydrophobic subsites S1 and S3, respectively; (2) the imidazole of P2 His was hydrogen bonded to the side chain OH of Ser-233 to contribute to the selectivity of renin inhibition; (3) cyclohexylnorstatine isopropyl ester residue was accommodated in S1-S1'. The importance of the stereochemistry in the potent and specific inhibitor was clearly shown. Oral administration to monkeys of this inhibitor resulted in a drop of 10-20 mmHg in mean blood pressure and a reduction of plasma renin activity for a 5-h period.

Thyroidal radioiodine uptake and release varied somewhat from strain to strain in rats, but no abnormal elevation or depression has been reported in rats (1). Okamoto (2) isolated a new strain from Wistar rats with spontaneous hypertension and noticed that this strain of rats had bigger thyroids, adrenals, and pituitaries than those of the control strain. Since coincidence of an increase of pituitary and thyroid weights suggests an increased production and release of TSH by the anterior pituitary, the present experiment was undertaken to study TSH concentrations of the anterior pituitary and circulating blood and to measure thyroid activity in response to an increase of blood TSH. The data indicated that spontaneously hypertensive rats (SHR) had not only high blood pressure but also an abnormal increase of blood TSH.Materials and Methods. Control rats and SHR were obtained from two different sources. One substrain of SHR was obtained from NN Laboratory, and the other substrain of SHR was bred in Kyoto University. Only male rats were used for the experiments. The animals were fed laboratory chow and water ad lib. unless otherwise stated. In experiment 2, animals were fed low-iodine diets beginning 10 days before radioiodine injection. Radioiodine (1.7 pCi of l 3 I I ) was injected intraperitoneally, and autopsy was performed 24 hr later. At autopsy, blood was obtained by cardiac puncture, using heparinized syringes. Plasmas were separated and kept at -20" until use. The pituitary, thyroid, and adrenal were cleanly dissected out and weighed on a torsion balance. Thyroid and adrenal weights were expressed as mg/100 g body wt. In experiment 3, 2 pg T4 was injected intraperitoneally daily for 7 days beginning 3 days after thyroidectomy. Bloods were drawn 24 hr after the last dose of T4. Pituitary and plasma TSH concentrations were measured as reported previously (3). Plasma thyroxine (T4) concentration was measured by competitive binding assay. Plasma triiodothyronine (T3) concentration was measured by radioimmunoassay. To rule out the error associated with measurements of T4, T3 and TSH, pooled plasma was always used as the standard. Plasma PB1311 was measured as reported previously (4). Blood pressures were measured by tail-pulse pickup in unanesthetized rats. The data were analyzed for statistical significance by the Student t test.Results. Experiment I . Serum thyroxine, triiodothyronine, and TSH levels, and pituitary contents of TSH. In the first step of this experiment, rats were obtained from NN Laboratory Blood pressure of SHR was 185 =t 7 mm Hg (mean =t SE), while it was 135 =t 6 mm Hg (mean =t SE) in the controls. Plasma T4 was slightly but significantly less in SHR than in the controls. Plasma T3 concentration was the same in both SHR and control groups (Table I). However, plasma TSH concentration was significantly elevated in SHR. Also, pituitary content of TSH increased significantly in SHR.In the second part of this experiment, rats were obtained from Kyoto University. Blood pressure of SHR was 194 =t 7 ...