Biochemical Pharmacology, Vol. 53, pp. 1867-1871, 1997. Copyright 0 1997 Elsevier Science Inc. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA ELSEVIER ISSN 0006-2952/ 97/ $17.00 + 0.00 PII SOOOS-2952(97)00012-9 Dietary Calcium Supplementation and Dopamine+- hydroxylase in Spontaneously Hypertensive Rats Edem Nuglozeh* and Andre’e G. Roberget zyxwvutsrqponmlkjihgfedcbaZYXWV UNIVERSITY DU QUEBEC, INSTITUT NATIONAL DE LA RECHERCHE SCIENTIFIQUE, POINTE-CLAIRE, QUEBEC, CANADA H9R lG6 A BSTRA CT. Spontaneously hypertensive 4-week-old male rats w ere fed, before and after the onset of hypertension, with either commercial chow (control) or commercial chow combined with different forms of milk proteins with or without calcium supplementation. After 40 weeks, rats were still hypertensive, and dopamine-p-hydroxylase enzyme activity measured simultaneously in serum and adrenal was found to be higher than in the controls. The enzyme activity in rats fed diets with milk proteins was increased significantly in both serum and adrenal compared with the control, and such enhancement was significantly higher than that observed in animals fed the commercial diet supplemented with calcium (1.2%), suggesting that dietary calcium intake associated with dietary protein of high digestibility, such as casein, potentiates the endogenous mechanisms regulating the homeostasis of calcium more than calcium supplementation itself. Moreover, the selective and additive effect of diets supplemented with milk proteins and calcium on adrenal enzyme activity clearly suggests a relationship between cardiovascular diseases involving the genesis of hypertension and stress mechanisms through the hypothalamo-pituitary adreno-sympathetic axis. BlOCHEM PHARMACOL 53;12: 1867-1871, 1997. 0 1997 Elsevier Science Inc. KEY WORDS. dopamine-p-hydroxylase; dietary intake; SHR rats; calcium supplementation DBHS [3,4 dihydroxyphenylethylamine ascorbate:02 oxi- doreductase (P-hydroxylating), EC 1.14.17. l] catalyses the conversion of 3,4-dihydroxyphenylethylamine into nor- adrenaline and, as a constituent of the chromaffin granules of the adrenal medulla and of the nerve granules of the sympathetic nervous system [I, 21, is released with nor- adrenaline into the circulation during sympathetic trans- mission processes [3-51. Several studies have demonstrated a sharp elevation in human serum DBH enzyme activity following various stressful situations [6-81. It was found that serum enzyme activity in animals was influenced by nutrient deficiencies including those of copper, zinc, and calcium [9, lo] as well as by dietary proteins with or without stress [ll-141. Moreover, Fujita et al. [15] clearly demon- strated that stress induces a pronounced elevation of DBH activity in adrenal, serum, and brain, but not in heart of SHR compared with normotensive rats, thus suggesting a close relationship between hypertension and catechol- amine release. The purpose of this study was to compare the effects of calcium supplementation on serum and adrenal DBH en- * Present address:Jackson Laborarory, 600 Main St., Bar Harbor, ME 04609. Tel. (207) 288-6368; FAX (207) 288-6078. t Corresponding author: And&e G. Roberge, Ph.D., Universitk du Quebec, lnstitut national de la recherche scientificme, 245, boulevard Hymus, Pointe-Claire, Quebec, Canada H9R 106. Tel. (514) 630-8839; FAX (514) 630-8850. $ Abbrewiations: DBH, dopamine+hydroxylase; SHR, spontaneously hypertensive rats; and HPAS, hypothalamo-pituitary adreno-sympathetic. Received 24 April 1996; accepted 26 December 1996. zyme activity in SHR fed prior to the onset of hypertension and for the 40 weeks that followed with either commercial chow (control) or commercial chow combined with differ- ent forms of milk proteins. MA TERIA LS AND METHODS zyxwvutsrqponmlkjihgfedcba Chemicals Bovine serum albumin, fumaric acid, pargyline HCl, ascor- bic acid, catalase, tyramine, octopamine, sodium m-perio- date, and Dowex 5OW-4X were purchased from the Sigma Chemical Co. (St. Louis, MO, U.S.A.). Trichloroacetic acid, sodium bisulphite, and monobasic and dibasic sodium phosphate were obtained from Fisher Scientific (Ste-Foy, Quebec, Canada). Sodium acetate and N-ethylmaleimide were purchased from BDH (Ville St-Laurent, Quebec, Canada). Whole milk and skim milk were furnished by “ la Cooperative de la C&e-sud,” Bellechasse, Quebec, Canada. Animals Thirty-six male SHR weighing 50-55 g, obtained from Charles River (St-Constant, Quebec), were adapted to the environmental conditions and fed with Purina Chow for 1 week. Rats were housed six per group in a room controlled at constant room temperature (22” ) and humidity (55%), with fluorescent lights and background music from 7:00 a.m. to 7:00 p.m.