1,25-Dihydroxyvitamin D3 stimulates 45Ca2+ uptake by cultured adult rat ventricular cardiac muscle cells

Overall tolerance and safety of quinapril in clinical trials

A comprehensive analysis of the reporting of adverse events, withdrawals due to adverse events, and serious adverse events has been conducted on 2,010 patients treated with quinapril hydrochloride. An analysis of all events (from both double-blind and open label studies combined) showed no increase in the incidence of events reported in congestive heart failure (CHF) patients compared to hypertensive patients. When the data for all studies were combined, an age analysis showed no increase in the total reporting of adverse events in the 379 elderly patients studied. The incidence of events was lower in those patients who did not take concomitant diuretic therapy. A comparison of the double-blind phases showed quinapril to have a lower incidence of adverse events than captopril, enalapril, or chlorthalidone. An analysis of the onset of events, or withdrawals, did not show an increase with time on quinapril therapy, and no dose-relationship. A review of serious adverse events did not reveal an unexpected occurrence or a high incidence of serious events considered to be related to quinapril therapy. The proportion of patients who experienced "first-dose" hypotension, or symptomatic hypotension was similar to captopril or enalapril. Quinapril, a nonsulfhydryl ACE inhibitor, has been extensively studied and is equally well tolerated in the young and elderly for the treatment of hypertension and CHF.

Multiple sites of action of the vitamin D endocrine system: FSH stimulation of testis 1,25-dihydroxyvitamin D3 receptors

1,25-Dihydroxyvitamin D [1,25(OH)2D] receptors exist in numerous unexpected tissues. These include, for example, rat lung, heart, testis, and uterus, but not prostate and bladder. The issues of 1,25(OH)2D effects on and receptor location in the testis were addressed by (a) physiological and pharmacological manipulations of tubule cell types and (b) histological examination of testes of vitamin D-deficient rats. FSH treatment in hypophysectomized adult rats increased 1,25(OH)2D receptor levels by 135% (P less than 0.01). Busulfan treatment reduced testis receptor levels by 35% (P less than 0.05) after 35 days (maximum effect), and the effect was reversed after recovery (85 d). Cryptorchidism for 5 or 50 days resulted in modest (33%, P less than 0.05) or substantial (79%, P less than 0.001) reductions in receptor levels. Only the FSH treatment and 50 days cryptorchidism reduced receptor levels in the residual tissue. The testes of vit. D-deficient rats showed incomplete spermatogenesis and degenerative changes. Although interpretation is complicated by the intricate communication among testis cell types, these data suggest that the Sertoli cell is a primary site of action of 1,25(OH)2D in the testis. Moreover, these data indicate that 1,25(OH)2D receptor function in the testis relates to germ cell division/maturation, although this may be an indirect effect via the Sertoli cells.

Involvement of 1,25-dihydroxyvitamin D3 in regulating myocardial calcium metabolism: physiological and pathological actions

The role of the prohormone vitamin D3 in regulating calcium and phosphate metabolism in the intestine, kidney, and bone has been known for several decades. Recent studies have provided evidence that vitamin D3, may also play an important role in regulating metabolism in other organs, including heart. This role has been suggested by the identification of a specific receptor for 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], the active metabolite of vitamin D3, in these tissues, as well as the presence of a 1,25(OH)2D3-dependent calcium binding protein. Although administration of excessive quantities of vitamin D3 has been shown in many studies to produce myocardial calcinosis and heart failure, the importance of vitamin D3 in regulating myocardial metabolism under normal conditions has only recently been demonstrated. The purpose of the present review is to assess the current status of research regarding the pathological and physiological actions of vitamin D3 on the heart. The initial section of this report will focus on the pathological effects of excessive vitamin D3 on cardiovascular function, while the latter sections will describe recent studies related to the involvement of 1,25(OH)2D3 in regulating calcium homeostasis in ventricular cells and the relationship between vitamin D3 and myocardial contractility.

A controlled silver impregnation method to characterize cultured cardiomyocytes

A morphological characterization of cultured cardiomyocytes was attempted using a modification of a silver impregnation technique originally described for connective tissue. Cardiac cells, obtained from newborn rats and grown as dissociated cultures on plastic surfaces, were fixed in methanol plus 5% glacial acetic acid, treated with potassium permanganate, decolorized in oxalic acid, sensitized with potassium bichromate, impregnated with a silver-ammonium complex, reduced in gelatin-formalin preparation, toned with gold chloride and fixed in sodium thiosulfate. The cultured cardiac cells tended to form a monolayer, although many myocytes remained isolated. Spherical nuclei, sharply stained with silver, were centrally located and surrounded by relatively plentiful cytoplasm packed with well delineated myofibrils. Contaminating fibroblasts were readily distinguished by their spindle-shaped nuclei and the presence of overstained collagen fibers, as well as the absence of myofibrils. In the absence of specific antibody for immunocytochemical identification of cardiomyocytes, morphological characterization of cell type and degree of differentiation by the controlled silver impregnation procedure described here provides a viable alternative, both in short- and long-term studies.

1,25-Dihydroxyvitamin D3 stimulates 45Ca2+-uptake by cultured vascular smooth muscle cells derived from rat aorta

We have recently shown the presence of receptors for 1,25-dihydroxyvitamin D3 and that 1,25-dihydroxyvitamin D3 stimulates Ca-ATPase in vascular smooth muscle cells presumably via receptor mediated mechanism. These data suggest that the sterol may directly be involved in the regulation of cellular calcium homeostasis. To further define action of vitamin D in smooth muscle cells, we studied effect of the sterol on cellular uptake of calcium. 1,25-dihydroxyvitamin D3 stimulated 45Ca2+ uptake by cultured cells, A7r5, derived from fetal rat aorta, when the cells were incubated with the sterol for 18 hr. The effect was dose-dependent at 10(-10) to 10(-9) M, and three orders of magnitude higher concentration of 25-hydroxyvitamin D3 or 24,25-dihydroxyvitamin D3 was needed to obtain similar effects. Furthermore, the effect of 1,25-dihydroxyvitamin D3 was abolished by cycloheximide (10(-5) M), a protein synthesis inhibitor. These data clearly suggest that 1,25-dihydroxyvitamin D3 may directly regulate cellular calcium homeostasis in vascular smooth muscle cells presumably via receptor mediated mechanism.

1,25-Dihydroxyvitamin D3 stimulates Ca-ATPase in a vascular smooth muscle cell line

I have recently shown that a vascular smooth muscle cell line has receptors for 1,25-dihydroxyvitamin D. To examine a possible role of 1,25-dihydroxyvitamin D in the regulation of cellular calcium homeostasis, effect of the sterol on Ca-ATPase activity was studied. 1,25-dihydroxyvitamin D3 stimulated the enzyme activity in a dose dependent manner at 10(-10) and 10(-9) M when the cells were incubated with the sterol for 10 hours. By contrast, 60 minutes incubation of the cells with 1,25-dihydroxyvitamin D failed to stimulate the enzyme activity. Both 25-dihydroxyvitamin D3 and 24,25-dihydroxyvitamin D3 did stimulate the enzyme activity, but at three orders of magnitude higher concentrations. Cycloheximide, at 10(-5)M, abolished the action of 1,25-dihydroxyvitamin D3. These data suggest that 1,25-dihydroxyvitamin D3 stimulates Ca-ATPase activity probably via its receptor and may play a role in regulating cellular calcium homeostasis.

Effect of 1,25(OH)2 vitamin D3 and ionized Ca2+ on 45Ca uptake by primary cultures of aortic myocytes of spontaneously hypertensive and Wistar Kyoto normotensive rats

The effect of several regulators of whole animal Ca2+ homeostasis on 45Ca uptake by primary cultures of aortic myocytes isolated from spontaneously hypertensive (SHR) and normotensive Wistar Kyoto (WKY) rats was examined. Exposure of confluent cells to 1.0, 1.25 or 1.50 mM ionized Ca2+ in serum-free medium for seven days resulted in increased 45Ca uptake at the higher concentrations of Ca2+ in cells of the SHR but not the WKY. 1,25 (OH)2 vitamin D3 (1 ng/ml) for 7 days caused enhanced influx in cells from both the SHR and WKY while parathyroid hormone (1-34) (1 ng/ml) was without effect. The data indicate that humoral factors that serve to regulate whole animal Ca2+ homeostasis may also play a role in the regulation of Ca2+ metabolism of the vascular smooth muscle cell.