The suggested role of the kidney in protecting against the development of hypertension through release of depressor substances may also be applicable ( 13). Thus, a depletion or exhaustion of these materials in chronic renal hypertension might lead to increased responsiveness to pressor agents. In addition, impairment of the ability of the sympathetic nervous system to buffer a pressor response in the chronic hypertensive state could account for the data.Summary. Renal hypertensive rats were found to have a pressor response to angiotensin which exceeded that of normal rats in both magnitude and duration. The results would appear to be in keeping with an intrinsic increase in pressor reactivity of the hypertensive organism, but are not compatible with the production of a specific angiotensinase as an adaptive mechanism to prevent chronic angiotensinemia.
The fact that magnesium is essential for growth has been known for some time. Leroy' was the first to demonstrate that growth was arrested after [9][10][11][12][13][14][15] Irving,6 Becks and Furuta,7 and Yamana and Singer5 have described the changes in the dentin of rats and hamsters. Typical striations occurred in the dentin, which appeared to be imperfectly calcified. The present investigation was undertaken to determine by various histochemical reactions the components of bone and dentin that were affected by the magnesium deficiency.
Materials and MethodsIntact male Holtzman rats weighing 120-140 gm. were selected for this investigation.
The isolation and structure of a-corticotropin, a polypeptide of 39 amino acid residues, derived from sheep pituitary glands and possessing an adrenocorticotropic (ACTH) activity of 150 I.V. per rag., have been reported from this laboratory (1-3). The present paper is concerned with various biological properties of the peptide hormone.
A. Stimulation of the Adrenal Glands in Normal and Hypopkysectomized RatsExperiments witk Normal Rats.--The increment of adrenal weight in 21-dayold normal male rats induced by the administration of ACTH preparations has been suggested by Moon (4) as a criterion for the assay of ACTH potency. Because various substances and conditions will produce adrenal hypertrophy in the intact animal, this criterion is not specific, and hence, as has been discussed elsewhere (5), this type of assay does not furnish a reliable index of degree of biological potency. It is, however, useful for detecting activity in a preparation, since adrenocorticotropicaUy active preparations should be capable of increasing the adrenal weight in normal animals.The hormone peptide was suspended in peanut oil and S per cent beeswax according to the procedure described by Bruce, Parkes, and Perry (6). Male rats, 28 days of age, of the Long-Evans strain were injected intraperltoneally with 0.1 ml. of the hormone suspension once daily for 4 days, and the --|reals were autopsied 24 hours after the last injection. As Table I reveals, 1 a daily dose of 1S/zg of a-corticotropin for 4 days produced an increase in * Present address:
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