ENHANCED DEPRESSOR EFFECT OF CENTRALLY ADMINISTERED HIGH-CALCIUM SOLUTION IN SALT-LOADED EXPERIMENTAL-HYPERTENSION

The depressor effect by oral calcium supplementation is known to be mo re pronounced in salt-dependent than in renin-dependent hypertension. This study was conducted to investigate the role of central calcium on two different pathophysiologic subtypes of experimental hypertension; (a) salt-dependent, deoxycorticosterone acetate-salt hypertensive rat s (DOCA), and (b) renin-dependent, 2-kidney, 1 clip (2-K, 1C) hyperten sive rats. In DOCA (n = 10), high-calcium solution (Ca2+, 65.2 mM, 10 mu l) given centrally (i.c.v.) elicited a marked decrease in mean bloo d pressure (MBP; 170 +/- 4 to 138 +/- 5 mm Hg, p < 0.01) with a decrea se in heart rate (HR; 390 +/- 18 to 344 +/- 17 beats/min, p < 0.05) la sting for 30 min. In 2-K, 1C (n = 10), high-Ca2+ i.c.v. showed a lesse r decrease in MBP (178 +/- 4 to 171 +/- 5 mm Hg) and HR (419 +/- 10 to 395 +/- 12 beats/min) with shorter duration (for 20 min) than in DOCA . This significant depressor and bradycardic response to Ca2+ i.c.v. o bserved in DOCA was dose dependent at Ca2+ concentrations between 65.2 and 130.4 mM. In DOCA, high Ca2+ i.c.v. reduced the plasma noradrenal ine (Nad) concentration significantly (479 +/- 81 to 319 +/- 62 pg/ml, p < 0.05). These results suggest that central Ca2+ plays a more impor tant role in regulating sympathetic nerve activity and BP in salt-depe ndent than in renin-dependent experimental hypertension.