Involvement of pertussis toxin-sensitive GTP-binding protein in prostaglandin F2 alpha- induced phosphoinositide hydrolysis in osteoblast-like cells

Prostaglandin F2 alpha (PGF2 alpha) stimulated the formation of inositol phosphates in a dose-dependent manner in cloned osteoblast-like MC3T3-E1 cells. This reaction was markedly inhibited dose-dependently by pertussis toxin. In the cell membranes, pertussis toxin-catalyzed ADP-ribosylation of a 40-kDa protein was significantly attenuated by pretreatment of PGF2 alpha. These results suggest that pertussis toxin-sensitive GTP-binding protein is involved in the coupling of PGF2 alpha receptor to phospholipase C in these cells.

Effect of metyrapone pretreatment on adrenocorticotropin secretion induced by corticotropin-releasing hormone in normal subjects and patients with Cushing's disease

To examine the influence of endogenous cortisol on the ACTH response to CRH, we compared ACTH secretion during CRH tests before and after metyrapone administration in 9 normal subjects and 12 patients with Cushing's disease. The administration of 4.5 g metyrapone (750 mg, orally, every 4 h) resulted in a decrease in basal (pre-CRH) plasma cortisol levels and an increase in basal plasma ACTH levels in both normal subjects and Cushing's patients. The pretreatment with metyrapone significantly blunted the increase in plasma cortisol levels and markedly enhanced ACTH secretion after iv injection of 100 micrograms human CRH. The peak ACTH levels during CRH test before and after metyrapone administration were 8 +/- 1 and 58 +/- 8 pmol/L, respectively, in normal subjects (P less than 0.01) and 26 +/- 5 and 50 +/- 11 pmol/L, respectively, in Cushing's patients (P less than 0.05). Although the basal and peak ACTH levels as well as delta ACTH (peak ACTH - basal ACTH) during the CRH test before metyrapone administration were significantly higher in Cushing's disease patients than in normal subjects (P less than 0.01), no such difference was observed between the 2 groups after metyrapone administration. The results clearly indicate that the endogenous cortisol levels greatly influence the ACTH response to CRH, and that the CRH test as commonly performed does not allow a correct evaluation of potential responsiveness of normal pituitaries and Cushing's adenomas to CRH.

Osmoregulation of plasma vasopressin in myxedema

We studied osmoregulation of plasma vasopressin (AVP) in eight patients with untreated myxedema due to primary hypothyroidism. All patients had severe thyroid hormone deficiency due to chronic thyroiditis and had been receiving no medication at the time of this study. AVP release was defined by 5% hypertonic saline infusion test in all patients, and urinary diluting capacity was estimated by the iv water-loading tests in five patients. Plasma AVP was measured by sensitive and specific RIA. The mean basal plasma AVP level in the patients (0.5 +/- 0.1 pmol/L) was significantly lower (P less than 0.01) than that in normal adults (2.5 +/- 0.5 pmol/L). During hypertonic saline infusion, the rise in plasma AVP was normal or subnormal in all patients. In two patients who showed mild to moderate hyponatremia in the basal state and mild urinary diluting defect during water loading, plasma AVP was appropriately suppressed in each case. These results indicate that inappropriate elevation of plasma AVP is not common in myxedema, and that impaired water excretion is due mainly to AVP-independent mechanisms.

Plasma osmolality and exocrine pancreatic secretion

To confirm the influence of plasma osmolality on exocrine pancreatic secretion, hypertonic saline (4% saline) was given intravenously to dogs with gastric and pancreatic fistulae. Intravenous administration of hypertonic saline caused a reduction of pancreatic juice flow and bicarbonate output, but did not alter protein output stimulated by secretin and cerulein. The changes of pancreatic juice flow(X) exhibited negative correlations with the changes in plasma osmolality(Y) (Y = -2.2X + 6.4, r = -0.74, p less than 0.01). Plasma osmolality and plasma vasopressin level were measured simultaneously. Plasma osmolality was elevated from 292 to 315 mOsm/kg with concurrent increase of plasma vasopressin level from 2.4 to 19.6 pg/mL. On the other hand, exogenous administration of vasopressin inhibited pancreatic juice flow and bicarbonate output dose-dependently. In conclusion, elevation of plasma osmolality decreased exocrine pancreatic secretion stimulated by secretin and cerulein, and vasopressin may play an important role in its mechanism.

Ca2+ influx stimulated by vasopressin is mediated by phosphoinositide hydrolysis in rat smooth muscle cells

The mechanism of Ca2+ influx stimulated by arginine vasopressin (AVP) was studied in cultured rat smooth muscle cells. AVP stimulated 45Ca2+ influx even in the presence of nifedipine, a Ca2+ antagonist that inhibits voltage-dependent Ca2+ channel. NaF, a GTP-binding protein activator, mimicked the AVP-stimulated 45Ca2+ influx. The 45Ca2+ influx stimulated by a combination of AVP and NaF was not additive. The affinity of AVP receptor was decreased by guanosine 5'-O-(3-thiotriphosphate). Pertussis toxin failed to affect the AVP-stimulated 45Ca2+ influx. AVP did not stimulate cAMP production, but increased inositol trisphosphate generation. Both AVP-stimulated 45Ca2+ influx and inositol trisphosphate generation were inhibited by neomycin, a phospholipase C inhibitor, in a dose-dependent manner, and the patterns of both inhibitions were similar. These results suggest that, in rat smooth muscle cells, AVP-stimulated Ca2+ influx is mediated exclusively through phosphoinositide hydrolysis.

[Radioimmunoassay of vasopressin in unextracted random urine; clinical application for screening of central diabetes insipidus]

The concentration of unextracted urinary arginine vasopressin (UAVP) was directly measured by high-sensitive radioimmunoassay (AVP-RIA Kit, Mitsubishi Petrochemical Co., Ltd.). Urine was diluted to eliminate interference of nonspecific substance without prior extraction. When urine aliquots were diluted in 4 to 32 fold in assay buffer, the relationship between UAVP concentration and dilution ratio corresponded exactly in a linear regression line. The elution pattern on Sephadex G-25 of UAVP immunoreactivity was identical with that of synthesized AVP. The AVP concentration in unextracted urine was not significantly different from that of extracted urine by Sep-Pak C18 column (Water Associates, Milford MA). The mean recovery of added AVP to urine specimens was 101.1 +/- 9.8% (mean +/- SD). The immunoreactivity of UAVP was not modified by either albuminuria (50 and 100 mg/dl) or glycosuria (1000 g/dl). Mean coefficients of variance between-assay and within-assay were 8.3% and 6.6% respectively. In normal subjects (n = 28), significant correlation was observed between UAVP concentration and simultaneously measured plasma AVP (r = 0.701, p less than 0.001). Moreover, AVP concentration in random urine was significantly correlated with AVP excretion in 24 hr-urine (r = 0.703, p less than 0.05, n = 9), and this suggested that random UAVP concentration may indicate daily UAVP secretion. In normal subjects, AVP concentration in random urine was widely scattered from 9.2 to 470.6 pg/mg Cr (89.5 +/- 76.4 pg/mg Cr, n = 211). In patients with diabetes insipidus (DI), UAVP concentration (1.6 to 13.0 pg/mg Cr, 6.94 +/- 2.77 pg/mg Cr, n = 25) was significantly lower (p less than 0.001) than that of normal subjects. UAVP concentration in a patient with primary polydipsia (43.2 pg/mg Cr) was not similar to that of ID but to that of normal subjects. UAVP concentration in 2 patients with SIADH was not more than that of normal subjects, indicating that random UAVP concentration is not suitable for detecting inappropriate AVP secretion. In this study, it is suggested that patients of random UAVP concentration below 13.0 pg/mg Cr should be recommended other intensive examination to diagnose DI, even though 2 normal subjects (0.9%) were incorrectly estimated as DI. In conclusion, radioimmunoassay of AVP in unextracted random urine is easy to sample and assay, and useful in screening polyuric patients.

Neurohypophyseal function in postpartum hypopituitarism: impaired plasma vasopressin response to osmotic stimuli

We studied neurohypophyseal function in 12 women with postpartum hypopituitarism (Sheehan's syndrome) by measuring plasma arginine vasopressin concentrations during 5% hypertonic saline infusions. All patients had a history of obstetric shock or massive bleeding, and were receiving cortisol and/or L-T4 replacement therapy. None had any symptoms of diabetes insipidus. The mean basal plasma vasopressin level in the patients [0.6 +/- 0.1 (+/- SE) pmol/L] was significantly lower (P less than 0.01) than that in normal adults (2.5 +/- 0.5 pmol/L; n = 12), whereas mean plasma osmolality values were similar in the two groups. During hypertonic saline infusion, the 10 hypopituitary patients had varying degrees of subnormal arginine vasopressin responses to the increase in plasma osmolality. Urine-concentrating ability after dehydration also was lower in the patients, although overt polyuria was absent at the time of this study. These results indicate that the osmoregulation of arginine vasopressin secretion is frequently impaired in postpartum hypopituitarism, suggesting neurohypophyseal damage.

Possible involvement of protein kinase C in proliferation and differentiation of osteoblast-like cells

In cloned osteoblast-like cells, MC3T3-E1, 12-O-tetradecanoylphorbol-13-acetate (TPA), a protein kinase C activating phorbol ester, and 1-oleoyl-2-acetylglycerol (OAG), a specific activator for protein kinase C, stimulated DNA synthesis in a dose-dependent manner. Both TPA and OAG acted synergistically with insulin-like growth factor I to stimulate DNA synthesis. TPA as well as OAG suppressed the increase in alkaline phosphatase activity of MC3T3-E1 cells induced by parathyroid hormone. These results suggest that protein kinase C is involved in the process which directs osteoblast-like cells toward proliferation.

Effect of the opioid kappa-receptor agonist U50488H on the secretion of arginine vasopressin. Study on the mechanism of U50488H-induced diuresis

The effect of U50488H, a potent opioid kappa-receptor agonist, was investigated on the urine volume and on the secretion of arginine vasopressin (AVP) in response to dehydration or hyperosmolar or hypovolemic stimulation in conscious rats. This agonist markedly increased the urine volume in normally hydrated rats and suppressed plasma AVP in a dose-dependent manner in rats given hyperosmolar saline. This suppression of plasma AVP was completely reversed by concurrent injection of naloxone. U50488H also inhibited the release of AVP in dehydrated or hypovolemic rats. These findings indicate that the diuresis induced by U50488H is mainly caused by the suppression of plasma AVP. They also suggest that the kappa-opioid receptor plays an important role in regulating the secretion of AVP.

[Impaired vasopressin secretion in patients with myotonic dystrophy]

Hypernatremia has occasionally been observed in patients with myotonic muscular dystrophy (MyD). To elucidate the possibility of osmoregulatory dysfunction, we investigated hypothalamo-posterior pituitary function as well as serum electrolytes in eight patients with MyD. Blood samples were obtained early in the morning after overnight dehydration. Renal function was estimated by blood urea nitrogen, serum creatinine and creatinine clearance. Posterior pituitary function was evaluated by direct measurement of plasma vasopressin (AVP) during a 5% hypertonic saline infusion. Plasma AVP concentrations were determined by sensitive radioimmunoassay. In five patients, circulating blood volume (CBV), plasma renin activity (PRA) and serum aldosterone (S-Aldo.) were also measured. The mean serum sodium level (143.9 +/- 1.7mEq/1: Mean +/- SD) was significantly higher than in the controls (139.4 +/- 2.2mEq/1). A 5% hypertonic saline infusion showed a subnormal increase in AVP and diminished thirst, despite sufficient elevation of plasma osmolality, in all patients as compared with healthy adults. Renal function was intact. Biochemical evidence of dehydration, estimated by PRA, S-Aldo and CBV, was unremarkable in four of the five patients. These findings suggest that patients with MyD have neurogenic disorders of osmoregulation in addition to previously reported endocrine abnormalities. Impaired AVP secretion in response to osmotic stimuli and reduced thirst might be responsible for such failure.

Influence of thyroid function on serum bone Gla protein

The serum BGP level was assayed in patients with hyperthyroidism (untreated and remittent cases) and hypothyroidism. The mean serum BGP concentration was 9.7 +/- 0.90 ng/ml in 30 patients with untreated hyperthyroidism which was significantly higher than the 2.7 +/- 0.38 ng/ml in 15 remittent patients and 1.3 +/- 0.31 ng/ml in 13 patients with hypothyroidism (p less than 0.001, p less than 0.001). Serum BGP had a significant positive correlation with the concentrations of free triiodothyronine and alkaline phosphatase in the serum, while it had a significant negative correlation with serum PTH. In the patients with hypothyroidism, serum BGP increased significantly in parallel with increases in serum free triiodothyronine with thyroxine therapy. In the patients with hyperthyroidism, serum free triiodothyronine decreased significantly after the first month of methimazole treatment, and fluctuated within the normal range after two months. Serum alkaline phosphatase and BGP did not show significant changes during the first six months of treatment, although they were eventually reduced significantly at the end of one year. These results suggest that thyroid hormone directly stimulates the synthesis and secretion of BGP in existent osteoblasts and also acts on the bone remodeling cycle, therapy accelerating the rate of bone formation; the latter action may occur over a long period.

Effect of parathyroid function on serum bone Gla protein

The serum bone Gla protein (BGP) level was measured in patients with idiopathic hypoparathyroidism, and primary hyperparathyroidism, and normal volunteers. The mean serum BGP level was 4.5 +/- 0.20 micrograms/l in 40 normal volunteers. It was significantly lower in 12 patients with idiopathic hypoparathyroidism (1.6 +/- 0.21 micrograms/l, p less than 0.001) and significantly higher in 33 patients with primary hyperparathyroidism (13.0 +/- 1.3 micrograms/l, p less than 0.001). When a single intravenous injection of 30 micrograms of human PTH 1-34 was administered to the patients with idiopathic hypoparathyroidism, there was no significant change in serum BGP within the next 24 hours. Following a therapeutic oral dose of alfacalcidol, serum BGP was appreciably increased (p less than 0.001) from the preadministration value of 1.6 +/- 0.21 micrograms/l to 3.9 +/- 0.34 micrograms/l. In patients with primary hyperparathyroidism, the surgical excision of parathyroid adenoma led to a sharp decrease in serum PTH but a gradual decrease in serum BGP. The latter approximately paralleled the decline in serum alkaline phosphatase. Thus, serum BGP is a marker that reflects bone turnover status in parathyroid disease. It appears that the active form of vitamin D directly increases the secretion of BGP in existing osteoblasts and PTH mainly affects serum BGP to stimulate the bone remodeling cycles with its long term effect.

Determination of enolase isozymes in various adrenal gland tumours

Enolase isozymes (alpha enolase and gamma enolase) in the extracts of adrenal tumours (phaeochromocytoma, adenoma of primary aldosteronism and Cushing's syndrome, and neurinoma) were determined by means of enzyme immunoassay systems. The mean +/- SEM, respectively, of alpha and gamma enolase levels were 2.5 +/- 0.37 microgram/mg protein and 3.2 +/- 0.69 micrograms/mg protein for 9 phaeochromocytomas, 15.2 +/- 3.1 microgram/mg protein and 0.65 +/- 0.18 microgram/mg protein for three adenomas with primary aldosteronism, 10.8 +/- 3.0 micrograms/mg protein and 0.23 +/- 0.02 micrograms/mg protein for five adenomas causing Cushing's syndrome, and 3.8 +/- 0.88 micrograms/mg protein and 0.30 +/- 0.15 micrograms/mg protein for three neurinomas. Thus, the gamma enolase concentration in the extract of phaeochromocytoma was higher than that of other adrenal tumours. The serum level of gamma enolase was determined in 36 patients with adrenal tumours and 26 normal controls by radioimmunoassay. The mean +/- SEM for gamma enolase level was 5.4 +/- 0.3 ng/ml in normal controls, 9.1 +/- 0.9 ng/ml for 10 patients with phaeochromocytoma, 6.3 +/- 0.3 ng/ml for 11 with primary aldosteronism, 5.5 +/- 0.4 ng/ml for 11 with Cushing's syndrome, and 5.1 +/- 0.7 ng/ml for four with neurinoma. Thus, patients with phaeochromocytoma had a significantly higher serum gamma enolase levels than did those with tumours derived from adrenal cortex and normal controls. In patients with phaeochromocytoma, serum gamma enolase levels showed a significant positive correlation with urinary adrenaline levels (P less than 0.05), and after resection the elevated level of gamma enolase fell significantly (P less than 0.05) and returned to normal.(ABSTRACT TRUNCATED AT 250 WORDS)

[Clinical assessment of posterior pituitary function by direct measurement of plasma vasopressin levels during hypertonic saline infusion]

Clinical usefulness of a radioimmunoassay of plasma arginine vasopressin concentration (AVP) during hypertonic saline infusion for the assessment of posterior pituitary function was studied in comparison with the conventional water deprivation test. Infusion of 5% saline at a rate of 0.05 ml/kg/min for 120 min in 15 normal subjects induced an elevation of plasma osmolality (Posm) from 290.3 +/- 0.7 to 307.5 +/- 2.1 mOsm/kg with a resultant increase in AVP from 2.4 +/- 0.4 to 9.9 +/- 2.2 pg/ml. During the infusion, a highly significant correlation between AVP and Posm was observed with a regression line expressed as AVP = 0.40 (Posm - 283.0). In 22 polyuric patients, on the other hand, the infusion induced a marked elevation of Posm from 302.6 +/- 2.5 to 321.3 +/- 2.9 mOsm/kg, but caused a slight (less than 5.8 pg/ml) or no increase in AVP from the basal levels (0.5 +/- 0.1 pg/ml). A conventional water deprivation test was carried out in ten patients with neurogenic diabetes insipidus, including one who had coincidental nephrogenic diabetes insipidus. As would be expected, urine osmolality (Uosm) did not rise beyond Posm in seven of them. However, two of three other patients, who had a complete lack of AVP response to the hypertonic saline, were able to concentrate their urine with a maximal Uosm/Posm of 1.3 and 1.1 respectively. The concurrent decrease in creatinine clearance to 49 and 57% of the initial values, respectively, indicated that a marked reduction in glomerular filtration rate due to severe dehydration was responsible for the unexpected concentration of urine in the patients with totally impaired AVP secretion. Based on these results, we conclude that the direct measurement of AVP during hypertonic saline infusion is an essential procedure for the accurate evaluation of posterior pituitary function.

Clinical significance of serum bone Gla protein and urinary gamma-Gla as biochemical markers in primary hyperparathyroidism

The serum bone Gla-protein (BGP) and urinary gamma-carboxyglutamic acid (gamma-Gla) levels were determined in patients with primary hyperparathyroidism (PHP). The mean serum BGP and urinary gamma-Gla levels were 18.6 +/- 2.34 ng/ml and 65.5 +/- 4.62 nmoles/mgCr, respectively, for the 11 patients with the skeletal type of PHP, 5.13 +/- 0.85 ng/ml and 45.2 +/- 1.33 nmoles/mgCr for the 4 with the chemical type, and 7.91 +/- 2.43 ng/ml and 43.2 +/- 3.47 nmoles/mgCr for the 5 with the renal type. Thus, patients with skeletal-type PHP had significantly higher serum BGP and urinary gamma-Gla levels than those with the other type of PHP. Serum BGP levels had significant positive correlations with serum Ca (r = 0.64, P less than 0.005), serum A1-p (r = 0.77, P less than 0.001) and serum PTH (r = 0.45, P less than 0.005). Urinary gamma-Gla levels also had significant positive correlations with serum Ca (r = 0.50, P less than 0.05), serum A1-p (r = 0.67, P less than 0.005), serum 1,25(OH)2D (r = 0.62, P less than 0.02), and serum BGP (r = 0.72, P less than 0.001). Mineral content in the left radius had significant negative correlations with serum BGP levels (r = -0.73, P less than 0.001) and urinary gamma-Gla levels (r = -0.59, P less than 0.01). As these data show, serum BGP and urinary gamma-Gla levels clearly reflect the abnormal bone metabolism and can therefore be useful biochemical markers in PHP.

Follow-up study on treatment in 27 patients with Cushing's disease: adrenalectomy, transsphenoidal adenomectomy and medical treatment

27 patients with Cushing's disease were treated over a period of 18 years at the Departments of Medicine and Surgery, Nagoya University School of Medicine and the following results were obtained. 1) Adrenalectomy. 21 of 27 patients with Cushing's disease underwent adrenalectomy. 19 patients had total bilateral adrenalectomy and 2 patients unilateral adrenalectomy. 4 patients died, the cause of death not being related directly to adrenalectomy. 9 of 15 bilaterally adrenalectomized patients had hyperpigmentation even though they had been given substitution therapy with cortisol 20-30 mg daily. They had elevated plasma ACTH levels, which were not completely suppressed by 2 mg of dexamethasone or 2.5 mg of bromocriptine per day. 2) Adenomectomy, 5 patients had adenomectomy via the transsphenoidal approach. 3 patients were cured but one of them has required postoperative substitution therapy with cortisol for hypopituitarism for one year until today. 2 of 5 adenomectomized patients had a recurrence of Cushing's syndrome after remission for 6-8 months. One of these recurrent cases has been subsequently treated successfully with bromocriptine, a dopaminergic drug. 3) Medical treatment. 2.5 mg per day of bromocriptine has been effective in 2 patients without a pituitary adenoma and ineffective in the other 4 patients with a pituitary adenoma. 24 mg per day of cyproheptadine, an antiserotoninergic drug was not effective in any of the 4 patients with a pituitary adenoma.