Effect of intraventricular injection of neurotensin and other various bioactive peptides on plasma immunoreactive somatostatin levels in rat hypophysial portal blood

The role of various bioactive peptides in the control of secretion of hypothalamic somatostatin into the hypophysial portal blood was examined in anesthetized rats. Hypophysial portal blood was withdrawn at a rate of 5.0 microliter/min into a chilled tube through a cannula placed over the stump of the pituitary stalk and segmented every 20 min by air bubbles. Immunoreactive somatostatin (IRS) in the plasma was extracted with acetic acid and acetone and quantified by RIA. Basal levels (mean +/- SE) of plasma IRS in the hypophysial portal blood were 646 +/- 36 and 317 +/- 44 pg/ml in urethane- and pentobarbital-anesthetized rats, respectively. Under urethane anesthesia, injection of synthetic neurotensin into the lateral ventricle at various doses in the range of 0.016--2 microgram/rat caused a significant and dose-related increase of plasma IRS levels in the hypophysial portal blood, and this effect of neurotensin was significantly (P less than 0.05) suppressed by pretreatment with diphenhydramine (1 mg/100 g BW, iv), a histamine receptor blocker. Enhancement of IRS release by neurotensin was also observed in pentobarbital-anesthetized rats. Intraventricular injection of substance P (10 microgram/rat), beta-endorphin (1 and 5 microgram/rat), or [Met5]enkephalin had no effect on the level of somatostatin in the hypophysial portal blood of urethane-anesthetized rats. These results suggest a release of hypothalamic somatostatin into the hypophysial portal blood in response to intraventricular administration of neurotensin, probably by a histaminergic mechanism.

Interaction between thyrotropin (TSH) binding inhibitor immunoglobulins (TBII) and soluble TSH receptors in fat cells

To clarify whether TSH binding inhibitor immunoglobulins (TBII) are antibodies to the membrane site associated with the TSH receptor itself or its neighboring sites, the interactions of TSH and TBII with soluble TSH receptor were investigated with a TSH radioreceptor assay using labeled highly purified bovine TSH (bTSH) and Triton extracts from guinea pig crude fat cell membranes (800-10,000 x g fraction). Treatment of the crude fat cell membranes with 0.5% (vol/vol) Triton X-100 resulted in solubilization of membrane proteins with recoveries of 25-30%, whereas increasing the concentration of Triton X-100 in the assay medium caused a decrease of [125I]bTSH binding to the solubilized membranes. Thus, the solubilized membranes were found to retain the capacity to bind [125I]bTSH below the Triton X-100 concentration of 0.4% in the assay medium. Incubation of the solubilized membranes with [125I]bTSH for 24 h at 4 C led to a steady state of specific binding, while incubation at 37 C resulted in more rapid but less specific binding, with a shorter duration of the steady state. Maximum binding occurred within the physiological pH range. Both TSH and Graves' immunoglobulins (Igs) specifically inhibited [125I]bTSH binding to the solubilized membranes, as demonstrated by polyethylene glycol separation of the [125I]bTSH-solubilized membrane complex from unbound [125I]-bTSH. Scatchard analysis of [125I]bTSh displacement curves for both TSH and Graves' Igs indicated a single class of binding site for each, with an affinity constant of 1.8 x 10(9) M-1. In addition, Igs capable of inhibiting [125I]bTSH binding to the solubilized membranes were detected predominantly in the serum of patients with Graves' disease. These results strongly suggest that TBII are antibodies directed to the TSh receptor itself without strict organ and species specificity.

Concentration and secretion of gastric somatostatin in streptozotocin-diabetic rats

Both the release and the content of gastric somatostatin were investigated in streptozotocin-diabetic rats. Fundic and antral somatostatin contents were both increased in streptozotocin-diabetic rats compared with control animals. Basal somatostatin levels in the perfusates of streptozotocin-treated animals were not significantly different from those of the control animals. However, the peak values of somatostatin release induced by 5 x 10(-9) M glucagon in the diabetic animals were significantly higher than those of the controls. These results lead us to conclude that a hyperfunctioning state of the gastric D-Cells exists in hypoinsulinemic diabetes.

Somatostatin release from the isolated, perfused diabetic rat pancreas: inverse relationship between pancreatic somatostatin and insulin

The changes in pancreatic somatostatin content and release were studied in streptozotocin (STZ)-diabetic rats. Male Wistar rats were treated with a graded dose of STZ (group I, 0; II, 25; III, 50; IV, 75 mg/kg), which produced various grades of diabetic rats four weeks later. The pancreatic somatostatin content increased in proportion to the dose of STZ (I, 189 +/- 31; II, 222 +/- 20, III, 343 +/- 4; IV, 515 +/- 36 ng/g wet wt), while graded reductions of insulin content were observed. Significant increases in glucagon content were found only in groups III and IV. Pancreatic somatostatin release increased during arginine infusion (19.2 mM) dose dependently, (I, 543 +/- 36; II, 946 +/- 64; III, 1229 +/- 55; IV, 2186 +/- 150 pg/15 min), and it correlated with the graded decreases of insulin release. The glucagon release induced by arginine, however, did not change significantly. These results indicate that pancreatic somatostatin content and release increased in STZ-diabetic rats in proportion to the degree of insulin deficiency.

Multiple hormone receptors in the adenylate cyclase of human adrenocortical tumors

Adenylate cyclase responses to pituitary hormones including adrenocorticotropic hormone (ACTH), biogenetic amines, prostaglandin E1 (PGE1), angiotensin II, and glucagon were evaluated in adrenocortical tumors and hyperplastic adrenal tissues, obtained from patients with Cushing's syndrome at surgery, and in normal adrenals. The adenylate cyclase of two normal adrenals was activated only by ACTH and PGE1 among the hormones tested, while that of two hyperplastic adrenal tissues due to excessive pituitary ACTH secretion was stimulated only by ACTH. Of five ACTH-responsive adrenocortical adenomas, in contrast, three were stimulated by norepinephrine, two by epinephrine, one by thyroid-stimulating hormone, and one by luteinizing hormone in addition to ACTH, indicating the presence of multiple receptors for hormones other than ACTH and PGE1 in these four tumors. The cyclase of an ACTH-unresponsive adrenocortical carcinoma ws activated only by PGE1 and not by other hormones including ACTH, whereas that of an ACTH-responsive adrenocortical nodular hyperplasia was stimulated by ACTH and glucagon but not by other hormones including PGE1. These results indicate the presence of multiple receptors for hormones other than ACTH and PGE1, the normal adrenocortical stimulants, in human adrenocortical tumors, particularly in adrenal adenomas, but not in normal and hyperplastic (of whichever an etiology) adrenocortical tissues, suggesting a functional alteration of the cellular membrane receptors in human adrenocortical tumors.

Reversal of the enhanced somatostatin release from the isolated, perfused diabetic rat pancreas after the amelioration of diabetes by whole pancreas transplantation

To investigate the pancreatic endocrine function in streptozotocin-diabetic rats before and after the whole pancreas was transplanted, pancreatic insulin, glucagon, and somatostatin content and release were measured. Highly inbred Lewis male rats were divided into the following three groups: normal control rats; streptozotocin-induced-diabetic rats; and streptozotocin-diabetic rats transplanted with whole pancreas. Studies in vivo revealed normalization of elevated blood glucose and marked improvement of the impaired arginine-induced plasma insulin release by the transplantation of a healthy pancreas into the diabetic rats. Neither basal nor arginine-induced plasma glucagon levels in the diabetic rats were significantly different from the normal group, but significantly higher plasma glucagon levels were found in the transplanted rats. Studies in vitro using the isolated perfused rat pancreas revealed a significant increase of somatostatin release from the diabetic pancreas, with a marked reduction of insulin release and almost normal glucagon release. In the transplanted rats, on the other hand, arginine-induced somatostatin release from the host pancreas was reduced to normal without a significant change in insulin or glucagon release. In addition, the endocrine function of the graft remained normal in the transplanted rats. Pancreatic somatostatin release, thus, appears to be effected by changes in circulating insulin, since pancreatic transplantation effectively corrects the circulating insulin level.

["Hormone receptor diseases" in Japan: A nation-wide survey for testicular feminization syndrome, pseudohypoparathyroidism, nephrogenic diabetes insipidus, Bartter's syndrome and congenital adrenocortical unresponsiveness to ACTH (author's transl)]

A nation-wide survey for five "hormone receptor diseases" was carried out. For the first survey, an inquiry was sent to all hospitals in Japan having more than 200 beds, in order to determine how many patients there were between 1968-1977. A further detailed survey was carried out on patients who were reported in the first survey. The approximate numbers of patients in Japan estimated from these surveys are the following: testicular feminization syndrome (TFS), 390; pseudohypoparathyroidism (PHP), 220, nephrogenic diabetes insipidus (NDI), 280; Bartter's syndrome, 90; congenital adrenocortical unresponsiveness to ACTH (CAUA), 18. In 73 cases of TFS, partial virilization was observed in 23% (the incomplete form). Testes were found in all cases and the epididymis in 84%, whereas none of the patients had seminal vesicles. PHP consisted of 38 Type-I cases, 6 Type-II cases and 25 unclassified cases. There were 27 males and 42 females. Skeletal anomalies were found in two-thirds of the patients. Grades of hypocalcemia and soft tissue calcification were more prominent in Type I. After treatment, none of the Type-I patients showed normal urinary cyclic AMP response to parathormone, although urinary phosphate response was normalized in one and markedly improved in 4. In 78 patients with NDI, there were 67 males and 11 females. The age of the onset of NDI ranged from 0 to over 50, but 22 out of 29 cases of hereditary NDI had the onset at age 0. There seemed to be at least two subtypes; one beginning in the neonatal period or early childhood, and the other having the onset in late childhood or adult. The important initial symptoms were fever and anorexia in the early onset type. Growth retardation was remarkable in early childhood. Diuretics were effective in most of the cases. There were 22 male and 12 female patients with Bartter's syndrome. Indomethacin was effective in 9 out of 10 patients studied.

High molecular weight forms of immunoreactive ACTH in a human pituitary and ectopic ACTH-producing tumors

High molecular weight forms of immunoreactive ACTH (IR-ACTH) were studied in a human pituitary gland and 4 ectopic ACTH-producing tumors in man. Both the pituitary and tumor extracts contained "big" IR-ACTH, which eluted near the void volume, and a small amount of "intermediate" IR-ACTH components, which eluted between the void volume and 125I-alpha h1-39 ACTH, in addition to "little" ACTH which coeluted with 125I-alpha h1-39ACTH by Sephadex G-100 gel filtration. A significant amount of the "big" IR-ACTH applied bound to the concanavalin A-agarose column and was eluted with 0.2 M alpha-methyl-D-mannopyranoside, indicating the glycoprotein content of "big" IR-ACTH fractions. When the "big" and "intermediate" fractions were further analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, they were resolved into 4 molecular forms of IR-ACTH with apparent molecular weight of 37,000, 24,000 , 18,000 and 4,500, respectively. These results indicate that 3 high molecular forms of IR-ACTH are present in the human pituitary and the ectopic ACTH-producing tumors.

Qualitative and quantitative analyses of human chorionic gonadotropin and its subunits produced by malignant tumors

Human chorionic gonadotropin (hCG) and its subunits in plasma, urine, ascites, and tumor extracts from four patients with hCG-producing tumors (undifferentiated cell carcinoma and choriocarcinoma of the bladder, malignant teratoma of the retroperitoneum, and pancreatic carcinoma) were measured by the radioimmunoassays specific to each component. While both free alpha and beta subunits as well as the whole molecule of hCG were found in all these samples, the proportion of beta subunit was much higher in these tumor extracts than in the placental extracts. Since the alpha and beta subunits are known to be translated from separate mRNAs, such increase of subunit is probably due to the predominant increase of mRNA encoding beta subunit of hCG in the hCG-producing tumors. Gel filtration of the extracts of these four tumors on Sephadex G-100 and G-150 columns demonstrated a heterogeneity of hCG, alpha, and beta subunits in these tumor extracts, and the elution profiles of plasma, urine and tumor extracts were slightly different. Lower molecular weight forms of hCG and its beta subunit were present in all urine samples. The significance of these heterogeneities remains to be elucidated.

Effects of glucagon, secretin, and vasoactive intestinal polypeptide on gastric somatostatin and gastrin release from isolated perfused rat stomach

To investigate the role of gastric somatostatin on gastrin secretion, glucagon, secretin, and vasoactive intestinal polypeptide (VIP) were perfused in the isolated pancreas-spleen-duodenum deprived preparation of rat stomach. After a preperfusion with 4.6% dextran Krebs-Ringer bicarbonate buffer containing 5.5 mM glucose, glucagon, secretin, and VIP at the concentrations of 10(-8), 10(-7), and 10(-6) M were infused into the left gastric artery at a constant flow of 2 ml/min for 15 min. All glucagon, secretin, and VIP evoked dose-dependent increases of somatostatin secretion with a simultaneous dose-related decrease of gastrin release. Furthermore, a significant correlation was found between the increase of somatostatin release and the decrease of gastrin secretion induced by glucagon, secretin, and VIP. These results raise the possibility that the suppression of gastrin secretion induced by glucagon, secretin, and VIP may, at least in part, be mediated by local action of gastric somatostatin.

Clofibrate-induced myopathy in patients with diabetes insipidus

Clofibrate has been considered to be a relatively safe antidiuretic in the treatment of diabetes insipidus. However, we have recently had four cases of clofibrate-induced myopathy in patients with diabetes insipidus due to hypothalamic lesions. Physicians should therefore be aware of its occurrence and carefully monitor serum levels of CPK, GOT and GPT during the treatment of diabetes insipidus with clofibrate, especially in patients with associated hypothyroidism, latent or overt, which possibly favors the development of myopathy.

Effects of insulin and pancreatic polypeptide on gastric somatostatin release

Effects of arginine and such pancreatic hormones as insulin and pancreatic polypeptide on gastric somatostatin release from the isolated perfused rat stomach were studied. The stomach was isolated from a fasted rat by a modification of the method of Lefébvre and was perfused with 4.6% dextran Krebs-Ringer biocarbonate buffer containing 5.5 mM glucose. Both insulin and pancreatic polypeptide (10(-10), 10(-9), and 10(-8) M) caused a significant decrease in gastric somatostatin secretion. Insulin (10(-10) M), furthermore, inhibited the glucagon (5 x 10(-8) M)-induced somatostatin response. Arginine (10 and 19 mM) failed to elicit any significant change of somatostatin release. These results suggest that gastric somatostatin release is affected by pancreatic hormones.

Concomitant production of beta-endorphin in ectopic ACTH/beta-LPH-producing tumors

It is generally accepted that ectopic ACTH-producing tumors produce not only ACTH but beta-MSH or beta-LPH as well. Using a sensitive radioimmunoassay for beta h-endorphin, we have demonstrated the presence of beta-endorphin immunoreactivity with size heterogeneity according to Sephadex gel chromatography and sodium dodecyl sulfate polyacrylamide gel electrophoresis in 6 ectopic ACTH/beta-LPH-producing tumors, providing further evidence for the role of a common precursor to ACTH and beta-LPH/beta-endorphin in the peptide biosynthesis in these tumors, in a manner similar to the biosynthetic events in the pituitary gland of several species.

In-vitro synthesis of androgen from pregnenolone in the testes of the goat (Capra hircus) and identification of 5-pregnene-3beta,17alpha,20alpha-triol as an intermediate in the metabolic pathway of pregnenolone

When [4(-14)C]pregnenolone was aerobically incubated in vitro in the presence of NAD+ and NADPH with cell-free homogenates of testicular tissue of adult domestic goats (Capra hircus), progesterone, 17alpha-hydroxypregnenolone, 17alpha-hydroxyprogesterone, 17alpha,20alpha-dihydroxy-4-pregnen-3-one, dehydroepiandrosterone, androstenedione and testosterone were identified as its known metabolites. Time-course studies on this metabolism showed that the production of 17alpha,20alpha-dihydroxy-4-pregnen-3-one and testosterone constantly increased up to the end of incubation, suggesting that these are both end-products of pregnenolone metabolism in this system. The other metabolites behaved as intermediates and were ultimately converted, in part, to testosterone by the testicular homogenates, indicating that testosterone was synthesized through both 4-ene and 5-ene-pathways. Furthermore, besides these metabolites, 5-pregnene-3beta,17alpha,20alpha-triol was also identified as an intermediary metabolite, formed from pregnenolone through 17alpha-hydroxypregnenolone in the presence of NADPH, and further convertible into 17alpha,20alpha-dihydroxy-4-pregnen-3-one by the microsomal fraction and into 17alpha-hydroxypregnenolone by the cytosol fraction in the presence of NAD+ and NADP+. It was not, however, significantly transformed into C19-steroids. Furthermore, 17alpha,20alpha-dihydroxy-4-pregnen-3-one, which was formed either from 5-pregnene-3beta,17alpha,20alpha-triol or from 17alpha-hydroxyprogesterone, remained almost unchanged without conversion to C19-steroids when incubated with the caprine testicular homogenates.

Effects of [Asu1,7]-eel calcitonin on gastric somatostatin and gastrin release

Effects of [Asu1,7]-eel calcitonin on gastric somatostatin and gastrin secretion were studied by using the isolated perfused rat stomach. [Asu1,7]-eel calcitonin (10(-9)--10(-7)M) caused a simultaneous dose-dependent increase of gastric somatostatin release and decrease of gastrin secretion, with a significant correlation between these two. The demonstration of calcitonin stimulation of gastric somatostatin release raises the possibility of somatostatin-mediated suppression of gastrin secretion by calcitonin.

Effect of adrenergic blocking agents on plasma gastrin and secretin levels in man

The effect of adrenergic blocking agents on gastrin and secretin secretion before and after a bolus arginine injection (arginine pulse) was investigated in normal subjects. Repeated arginine pulses given at 30-minute intervals caused abrupt and almost identical rises of plasma gastrin with each pulse. On the other hand, plasma secretin levels were unchanged by repeated injections of arginine. The increase in plasma gastrin induced by arginine pulse was significantly suppressed by the infusion of beta-adrenergic blocking agent, propranolol, while the infusion of alpha-adrenergic blocking agent, phentolamine tended to enhance the arginine-induced gastrin secretion slightly but not significantly. Whereas, the infusion of neither phentolamine nor propranolol had significant influence on secretin secretion. These results suggest that alpha- and beta-adrenergic receptors play an important role in the regulation of arginine-induced gastrin secretion.

Effects of various gastrointestinal peptides on gastric somatostatin release

Effects of various gastrointestinal peptides on gastric somatostatin release from the isolated perfused rat stomach were studied. After isolation of the stomach in a fasted rat by the method of Lefébvre and preperfusion with 4.6% dextran-Krebs-Ringer bicarbonate buffer containing 5.5 mM glucose, each peptide was infused into the left gastric artery at a constant rate for 15 min. Secretin and bombesin caused a significant increase of gastric somatostatin release in a dose-related manner (10(-8)-10(-6) M). Gastric somatostatin release was also stimulated after the administration of pentagastrin (10(-8)-10(-6) M). In contrast, both methionine-enkephalin and substance P decreased gastric somatostatin release in a dose-related manner (10(-8)-10(-6) M), whereas neurotensin (10(-8)-10(-6) M) failed to change it significantly. The present results suggest that these various gastrointestinal peptides may regulate gastric somatostatin secretion.