Stretch increases inositol trisphosphate and inositol tetrakisphosphate in cultured pulmonary vascular smooth muscle cells.

There are no reports of the effect of stretch on inositol phosphates in smooth muscle. Phosphoinositide and inositol phosphate metabolism was studied in cultured rat vascular smooth muscle cells subjected to stretching. The masses of inositol trisphosphate and tetrakisphosphate increased (+34 +/- 7% and +58 +/- 12%, respectively; p less than 0.001) after 25 s of a single 20% stretch and had returned to control levels by 45 s; phosphatidylinositol, phosphatidylinositol phosphate and bisphosphate did not change. Repetitive stretch did not alter the masses of any of the compounds. A single stretch also increased 45Ca2+ efflux (+52 +/- 5%, p less than 0.01). These data suggest that stretch of cultured vascular smooth muscle can elicit a rapid, short-lived increase in inositol phosphates, which may subsequently affect Ca2+.

Effect of sodium intake on phosphoinositides and inositol trisphosphate response to angiotensin II, K+ and ACTH in rat glomerulosa cells.

To assess the impact of sodium intake on the adrenal phosphoinositide system, rats were maintained on a low or normal salt diet for 5 days, and glomerulosa cell preparations (2 x 10(5) cells) were stimulated by angiotensin II (AII; 10 nmol/l), potassium (K+; 8.7 mmol/l) or ACTH (0.1 nmol/l) for 0, 2, 4, 6, 12, 15 and 60 s. Levels of phosphatidylinositol (PtdIns), phosphatidylinositol 4-phosphate (PtdIns 4-P), phosphatidylinositol 4,5-bisphosphate (PtdIns 4,5-P2) and inositol 1,4,5-trisphosphate (Ins 1,4,5-P3) + inositol 1,3,4-trisphosphate (Ins 1,3,4-P3) were assayed by a microspectrophotometric procedure. Non-stimulated levels of PtdIns, PtdIns 4-P, PtdIns 4,5-P2 and Ins 1,4,5-P3 (+ Ins 1,3,4-P3) (means +/- S.E.M.; n = 36) in cells from rats on the low Na+ intake were 580 +/- 6.5, 187 +/- 2.6, 82 +/- 3 and 95 +/- 1.2 pmol per incubate respectively, indistinguishable from those observed in rats on a normal Na+ intake, except for the significantly (P less than 0.025) greater PtdIns 4,5-P2 level. In response to AII stimulation, all four compounds showed an earlier and greater peak response when cells were obtained from animals on a low rather than a high sodium intake. All values has returned to control levels by 12-15 s, regardless of the level of sodium intake. In contrast, with K+ stimulation there were no differences in the peak response of cells from rats on the two dietary intakes, but there was a shift of the peak to a longer time-interval (6 versus 8 s) in animals maintained on a low sodium intake.(ABSTRACT TRUNCATED AT 250 WORDS)

Mass determination of polyphosphoinositides and inositol triphosphate in rat adrenal glomerulosa cells with a microspectrophotometric method.

A method is described for the assay of subnanogram amounts of phosphorus in phospholipids and organic phosphates. The formation of a complex with a high molar absorption coefficient at 600 nm when malachite green is added to phosphomolybdate at low pH and the adaptation of a microspectrophotometer to quantify the color in 10 microliters solution have made it possible for a dose-response curve from 0.1-1.2 ng phosphorus to be developed. The method has been applied to the assay of phosphatidylinositol (PtdIns), phosphatidylinositol-4-phosphate (PtdIns 4-P), phosphatidylinositol-4,5-diphosphate (PtdIns 4,5-P2), and inositol-1,4,5-triphosphate (Ins 1,4,5-P3) in rat adrenal glomerulosa cells after stimulation with angiotensin II (AII), K+, and ACTH for 0, 2, 4, 6, 8, 10, 12, 15, and 60 sec. A control (nonstimulated) sample was incubated concomitantly for every time period. Nonstimulated cell levels (mean +/- SEM; n = 216) were: PtdIns, 577 +/- 6.4; PtdIns 4-P, 183 +/- 3.1; PtdIns 4,5-P2, 59 +/- 1.8; and Ins 1,4,5-P3, 94 +/- 1.3 pmol/incubate. Maximum increase in levels of PtdIns, PtdIns 4-P, PtdIns 4,5-P2, and Ins 1,4,5-P3 above control values was obtained after 8 sec with AII (10(-8) M) and after 6 sec with K+ (8.7 mM) stimulation. The values (picomoles per 2 X 10(5) cell incubate; n = 4) were: PtdIns, 808 +/- 28; PtdIns 4-P, 263 +/- 20; PtdIns 4,5-P2, 112 +/- 10; and Ins 1,4,5-P3, 136 +/- 4 for AII stimulation, and PtdIns, 925 +/- 76, PtdIns 4-P, 308 +/- 11; PtdIns 4,5-P2 146 +/- 28; and Ins 1,4,5-P3, 149 +/- 5 for K+ stimulation. No increase above control levels could be found at any incubation time after ACTH stimulation. Thus, both AII and K+ stimulate a short-lived increase in the mass of several elements of the phosphatidylinositol pathway. The discrepancy between these mass determinations and isotope study suggests that only some, but not all, pools are labeled by currently available techniques.

Role of the adrenal cortex in gastric mucosal protection by prostaglandins, sulfhydryls, and cimetidine in the rat.

To investigate the possible role of hormones in gastric mucosal protection, the effect of prostaglandin F2 beta, dimercaprol, or cysteamine on ethanol-induced gastric erosions, and of cimetidine on gastric erosions caused by aspirin was studied in intact, adrenalectomized, medullectomized, ovariectomized, or thyroidectomized rats. Cimetidine was administered at a low dose that did not inhibit hydrogen ion secretion. Adrenalectomized animals failed to exhibit the usual mucosal protective response to prostaglandin F2 beta, sulfhydryls, or cimetidine. Ovariectomy or thyroidectomy did not influence mucosal protection with these agents. The inhibition by total adrenalectomy of mucosal protection was not reversed by large intragastric doses or by parenteral administration of prostaglandin F2 beta. Adrenal medullectomy alone significantly diminished (by approximately one-third) ethanol-induced gastric mucosal injury; prostaglandin F2 beta or sulfhydryl drugs produced significant additional protection. Replacement therapy with glucocorticoids (triamcinolone, corticosterone) but not with mineralocorticoids (deoxycorticosterone, 9 alpha-fluorocortisol) restored the cytoprotective effect of prostaglandin F2 beta and sulfhydryls in adrenalectomized rats. The generation of prostaglandin E2- and prostaglandin I2-like activity in the gastric mucosa was unaltered by adrenalectomy. These studies suggest a permissive role for glucocorticoids in gastric mucosal protection induced by prostaglandins, sulfhydryls, and cimetidine.

Extracellular calcium is not necessary for acute, low calcium- or dopamine-stimulated PTH secretion in dispersed bovine parathyroid cells.

Although elevated extracellular calcium concentrations inhibit PTH release, little is known about the necessity of extracellular calcium for the secretory process in this cell type. In the studies reported here, we examined the effects of low extracellular calcium concentrations on basal and agonist-stimulated immunoreactive PTH (iPTH) release in dispersed bovine parathyroid cells. There was a difference of 15% or less in the rate of iPTH release from cells exposed for 30-60 minutes to calcium concentrations varying from less than 10(-8) mol/L to 1 mmol/L. Low calcium concentrations likewise had no effect on dopamine-stimulated iPTH secretion. We employed high performance liquid chromatography (HPLC) to demonstrate directly that EGTA did not alter the degradation of PTH in the medium and that the release of intact PTH was stimulated slightly by very low extracellular calcium concentrations. Like iPTH release, both the basal and dopamine-stimulated cAMP content in parathyroid cells were unchanged by extracellular calcium concentrations as low as 10(-8) mol/L. Following exposure of cells to EGTA for two or more hours, there was a 50% to 60% inhibition of iPTH secretion. This reduction in secretory rate was not reversible, however, by the readdition of 0.1-1.0 mmol/L calcium for one hour. These results demonstrate that the secretion of PTH differs from that of many other exocytotic systems not only in that hormonal release is inhibited at high extracellular calcium concentrations but also in that extracellular calcium is not needed for acute hormonal release.

Ca-ATPase activity in bovine parathyroid cells.

Ca-ATPase is thought to function as a calcium extrusion pump that may regulate cytosolic calcium concentration. Because the parathyroid gland is among the few tissues that are directly regulated by extracellular calcium and because cytosolic calcium may be a mediator of the effects of extracellular calcium on parathyroid hormone secretion, we have investigated the presence of this enzyme in homogenates of parathyroid cells. High performance liquid chromatography (HPLC) was used to quantify the formation of ADP from ATP following incubation of ATP with cellular homogenate in a buffer containing ethylenedioxy- (diethylenedinitrilo) tetra acetic acid (EGTA), ouabain, and calcium. Enzyme activity was calcium-dependent, with Ca-ATPase showing two Km (Ca) values, 31 and 853 nM. High affinity Ca-ATPase activity was reduced by the calmodulin inhibitor, trifluoperazine (TFP), with half-maximal inhibition occurring at 7 X 10(-5) M. Monovalent cations stimulated high affinity Ca-ATPase activity (K+ greater than Na+ greater than Rb+ greater than Li+) in the presence of calcium. Magnesium (0.8 mM) also stimulated cleavage of ATP. Sodium increased Ca-dependent ATPase activity by 82% but had no significant effect on Mg-stimulated activity. Furthermore, azide, an inhibitor of mitochondrial ATPase(s), had a significantly greater inhibitory effect on Mg-dependent than on Ca-dependent activity. In summary, a high affinity Ca-ATPase is present in bovine parathyroid cells which has a Km in the range of the cytosolic calcium concentration that is found in other cells. Ca-ATPase(s) may be of importance in regulating the cytosolic calcium concentration and, therefore, hormonal secretion in this cell type.

Is the adrenal angiotensin receptor angiotensin II--or angiotensin III like?

In order to determine whether the adrenal receptor is primarily directed at angiotensin II (AII) or angiotensin III (AIII) the following in vitro experiments were performed examining aldosterone responsiveness in isolated glomerulosa cells. 1) Cells exposed to increasing doses (2.4 X 10(-10)M - 2.4 X 10(-6)M) of AII or AIII were found to be significantly more responsive to AII (AII's ED50 was 6.3 X 10(-10) M vs AIII's 4.6 X 10(-9)M P less than 0.001). 2) Octapeptide analogues (Sar1 Ala8 and Asn1 Ala8), while demonstrating different inhibitory potencies relative to each other, were equally effective in blocking AII vs AIII stimulation. 3) The heptapeptide analogues (des1 Ala8 and des1 Ile8) however, inhibited AIII stimulation preferentially (P less than 0.01). 4) The 8 alanine octapeptide analogues were better inhibitors of both AII and AIII stimulation than the 8 alanine heptapeptide analogue. 5) HPLC analysis indicated that AII and AIII were being degraded at the same rate during the incubation procedure. These results, taken together, strongly suggest that the angiotensin adrenal receptor is an AII receptor.

Influence of exogenous glucocorticoids and ACTH on experimental adrenal autografts.

Minced adrenal autografts under the renal capsule in adrenalectomized rats were studied by means of serial plasma corticosterone determination and histologic examination. The effect of daily treatment with dexamethasone with or without daily porcine adrenocorticotropic hormone (ACTH) gel was determined. Control autografted rats regained normal corticosterone levels by the 2nd week and at 80 days showed full regeneration of adrenal grafts. Dexamethasone treatment completely suppressed corticosterone and resulted in striking atrophy persistent at 80 days. Porcine ACTH plus dexamethasone resulted in full regeneration with cellular hypertrophy exceeding that of controls, but the corticosterone levels in samples drawn just before the scheduled ACTH injections were very low because the effect of ACTH gel lasted only 12 hr and endogenous ACTH was suppressed. Plasma levels at 40 days were 22.8 +/- 5.9 (SD) for controls, 3.8 +/- 6.1 for dexamethasone, and 5.1 +/- 4.8 for dexamethasone plus porcine ACTH. The results indicate that ACTH is necessary for the optimal regeneration of implanted adrenal autografts.

Renin-angiotensin-aldosterone system, electrolyte homeostasis and blood pressure in alloxan diabetes.

The effect of a chronic glucose osmotic diuresis on electrolyte homeostasis was evaluated in alloxan diabetic rats with urine volumes greater than 150 ml/day and glycosuria of 4 to 10 gm/day. Results were compared with control rats for periods up to 84 days. Sodium and potassium intake and urinary losses were significantly higher in diabetic animals throughout the study periods. Negative Na balance, however, persisted for only four days, and negative K balance for only 18 days. Blood volumes were elevated probably secondary to the osmotic effect of hyperglycemia (serum glucose greater than 600 mg %). Plasma renin activity decreased progressively, in part because of an early decrease in renin substrate at a time when renin concentration was normal. Despite hyperkalemia, mean plasma aldosterone was not increased compared with that in control rats, suggesting diabetic rats had relative hypoaldosteronism. Although three diabetic rats became hypertensive, no significant difference in mean blood pressure was observed between the groups. The results suggest that diabetic rats have losses of Na and K early in their diabetes, following which mechanisms to conserve Na and K are activated preventing further electrolyte depletion despite continuation of the osmotic diuresis. Decreased renin activity with inadequate stimulation of aldosterone would contribute to K conservation. Maintenance of Na balance must be explained by increased Na intake and other renal Na conserving mechanisms.

Pathophysiology of spironolactone-induced gynecomastia.

Peripheral blood levels of testosterone, estradiol, luteinizing hormone, and follicle-stimulating hormone and the metabolic clearance rates of testosterone and estradiol, as well as the peripheral conversion of testosterone into estradiol, were measured in 16 patients with hypertension. Six of these patients were treated with spironolactone and developed gynecomastia. The other 10 patients served as control subjects. The blood testosterone level in the spironolactone-treated group (2.7 +/- 0.5 ng/ml) was significantly less (P less than 0.02) than in the control group (4.4 +/- 0.4 ng/ml). On the other hand, blood estradiol levels in the spironolactone group (30 +/- 4 pg/ml) were significantly greater (P less than 0.01) than in the control group (13 +/- 2 pg/ml). These changes were primarily due to significant increases in the metabolic clearance rate of testosterone (P less than 0.02) and in the rate of peripheral conversion of testosterone into estradiol (P less than 0.001) in the spironolactone-treated group. Thus, spironolactone does alter the peripheral metabolism of testosterone resulting in changes in the ratio of testosterone to estradiol, which could contribute to the production of gynecomastia.

The regulation of plasma 18-hydroxy 11-deoxycorticosterone in man.

18-hydroxy 11-deoxycorticosterone (18-OH DOC), a weak mineralocorticoid, was estimated by a radioimmunoassay procedure after purification in 49 patients with hypertension and 38 normal control subjects. The sensitivity of the method was 2-4 pg; there was no detectable blank, and the precision was 9-10%. In normal subjects the absolute plasma levels were similar to those of aldosterone. ACTH administration produced a 23-fold increase, and sodium restriction resulted in a 4-fold increase (5.4+/-0.7-20.5+/-3.0 ng/dl). On the other hand, the plasma levels of 18-OH DOC declined by nearly 50% with upright posture or angiotensin II infusion. During both of these procedures, plasma aldosterone levels significantly increased. Patients with normal and low renin hypertension had similar changes in plasma 18-OH DOC levels with sodium restriction. However, the mean high sodium level in the normal renin essential hypertension group (11.6+/-1.6 ng/dl) was significantly greater (P is less than 0.001) than in the control group (5.4+/-0.7 ng/dl). In addition, at least 22% and perhaps as high as 37% of the hypertensive subjects had levels greater than the upper limits of normal on a high sodium intake. Differences between the groups were less impressive in the sodium-restricted studies. There were no significant differences in age, duration of hypertension, sodium balance, serum sodium, potassium, or blood urea nitrogen in those patients who had elevated levels of plasma 18-OH DOC. Patients with primary aldosteronism had levels within the normal range on both dietary intake. However, in contrast to the other groups there were no significant changes in the plasma levels with sodium restriction. Thus, a significant number of patients with essential hypertension presumably have an alteration in 18-OH DOC secretion.

Testosterone metabolism in benign and malignant breast lesions.

Tissues from a variety of breast lesions were incubated with 14C-testosterone (17beta-hydroxy-4-androsten-3-one). Conversion to 14C-5alpha-dihydrotestosterone (17beta-hydroxy-5alpha-androstan-3-one) and 14C-androstenedione (4-androsten-3,17-dione) was measured. Normal breast tissue showed formation of 14C-androstenedione but no formation of 14C-5alpha-dihydrotestosterone. Fibroadenomas showed a high degree of testosterone metabolism forming both 14C-androstenedione and 14C-5alpha-dihydrotestosterone. The adenocarcinomas of the breast, contrary to a previous report in the literature, showed no conversion to 14C-5alpha-dihydrotestosterone. The data suggest that formation of 5alpha-dihydrotestosterone is a predominant metabolic pathway in fibroadenoma.