Antidiuretic hormone involvement in the release of α-melanocyte-stimulating hormone by hyperosmotic stimuli

Summary In the normal Wistar rat, the plasma -MSH level was raised by hypertonic saline injection (as compared with control rats injected with isotonic saline). No such rise in -MSH followed hypertonic saline administration in the Brattleboro (hereditary diabetes insipidus) animal (compared to isotonic saline injected controls). It is suggested that, in the rat, endogenous antidiuretic hormone is involved in the secretory response of the pars intermedia to osmotic stimuli.     

The role of volume expansion,of prostaglandins and catecholamines in the development of acute renal failure

Summary A single injection either of isotonic or hypertonic saline solutions protected rats against acute renal failure (ARF) induced with glycerol. This protection was accompanied by increased urinary prostaglandin E (PGE) concentration. On the contrary, a single s.c. injection either of hypotonic saline or isotonic glucose solution, which did not increase urinary PGE concentration, or depletion of the endogenous catecholamines, using reserpine, did not protect the animals against acute renal failure.The authors wish to thank Miss Sylvie Bompis and Miss Ermione-Loukia Ghikas for their technical assistance and Mr Richard Irvine B.A. for his help with the English.     

Influence de différents types de diurèse sur l'excrétion rénale de l'urée étudiée chez le rat, à l'aide des microponctions rénales

Summary The renal tubular fate of urea, as studied in the rat by free-flow micropunctures of cortical tubules, is shown to vary with different types of diuresis (urea overloading, iso- or hypertonic saline diuresis). Under certain experimental conditions, the renal tubular handling of urea appears to differ in the cortical and the juxtamedullary nephrons.

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Ce travail bénéficie du soutien du Fond National suiss de la Recharche Scientifique (crédit Nos. 4495 et 4983).     

Influence of alpha-MSH and ACTH on cortical bone remodelling in hypophysectomized rats.

Hypophysectomy increases both periosteal resorption and endosteal apposition along the femur diaphysis in rat. Administration of alpha-MSH decreased the periosteal resorption but had no effect on the endosteal apposition. ACTH had only minor effects on the endosteum. Thus, alpha-MSH and ACTH, in the doses used, have different effects on cortical bone in rat. The effect of alpha-MSH on cortical bone could be an effect of the hormone alone or by its stimulation of other factors.     

Distribution of thyrotropin releasing hormone (TRH), alpha-melanocyte-stimulating hormone (alpha-MSH) and somatostatin in the skin of the green frog (Rana esculenta)]

High concentrations of Thyrotrophin-Releasing Hormone (TRH) have been found in the dorsal skin of the Frog Rana esculenta, lower levels being measured in the ventral skin. alpha-MSH and somatostatin were undetectable in these tissues. Nor was TRH detected in the blood of these animals. The concentration of somatostatin in the pancreas was similar to that of the hypothalamus and twice or one hundred times higher than in the intestine or stomach respectively.     

High salt effect on RNA synthesis in Krebs ascites tumor cells

The incubation of Krebs ascites tumor cells in medium with a high salt concentration resulted in a partial inhibition of nuclear RNA synthesis. The residual RNA polymerase activity in such nuclei was only slightly inhibited by low concentrations (50 nM) of alpha-amanitin. This finding suggested an inhibition of RNA polymerase II activity under conditions of medium hypertonicity. Indeed, RNA polymerase II, isolated from the nuclei of cells exposed to hypertonicity, revealed only half of the control activity. On the other hand, RNA polymerase I was not affected by hypertonicity. Moreover, chromatin fractions isolated from cells incubated in hypertonic or isotonic medium were equally template-active in RNA synthesis.     

Dissociation of digoxin-like immunoreactivity and Na+,K+-ATPase inhibitory activity in rat plasma

We measured endogenous digitalis-like factor (EDF) in rat plasma during acute saline infusion by two different procedures. Na+,K+-ATPase inhibitory activity in the rat plasma significantly increased during saline loading (7.8 +/- 2.2 vs 2.5 +/- 0.9%, with and without acute saline loading, respectively, p less than 0.05). On the other hand, the plasma digoxin-like immunoreactivity significantly decreased during acute saline loading (16.9 +/- 1.6 vs 32.0 +/- 2.8 pg digoxin equivalents/ml, with and without acute saline loading, respectively, p less than 0.01). These results indicate that the major substances detected by digoxin-like immunoreactivity and direct Na+,K+-ATPase inhibitory activity are completely different, at least in rat plasma.     

Renal response to acute saline loading in Sabra hypertension-prone and -resistant rats

The renal handling of an oral isotonic saline load was studied in hypertension-prone (SBH), hypertension-resistant (SBN) and the parental Sabra (SB) rats. The diuretic and natriuretic response of SBH rats was unequivocally diminished, thus lending further support to the concept of impaired salt handling in hypertension.     

Acute effect of hypophysectomy on the natriuresis following saline infusion in dogs.

The natriuresis following an i.v. isotonic saline loading corresponding to 10% of body wt. was markedly decreased after acute hypophysectomy, due to lowered urinary sodium concentration, in anaesthetized dogs. A role of the pituitary in such a homeostatic natriuresis is suggested.     

Control of pituitary secretion of melanotropin in an anuran amphibian by thyrotropin releasing factor (TRH). Study in vitro]

Intermediate lobes from Rana esculenta pituitary glands were continuously superfused for 7 hrs at 28 degrees C with amphibian culture medium. alpha-MSH release was measured by use of a sensitive double antibody radio-immunoassay system. alpha-MSH secretion was inhibited by low temperatures. A large increase in alpha-MSH release was observed when Thyrotropin Releasing Hormone (TRH) at doses ranging from 10(-9) to 10(-7) molar was added to the superfusion medium. Since large amounts of TRH are to be found in the hypothalamus of amphibians but have no effect over pituitary TSH secretion, the action of TRH over alpha-MSH release may have a physiological significance.     

Naloxone prevents the analgesic action of alpha-MSH in mice

alpha-MSH (0.1, 1, 10 micrograms) was administered intracerebroventricularly and its action on pain sensitivity was investigated by the hot-plate method in mice. alpha-MSH produced dose-dependent analgesia and this analgesic effect was prevented by naloxone (1 mg/kg, s.c.). It is possible that alpha-MSH may play a role in the mechanism of pain through endogeneous opioid systems.     

Abdominal vagotomy attenuates drinking induced by intravenous infusion of various osmotic loads in the rat

Summary Male rats were subjected to sham surgery or total abdominal vagotomy and then subsequently received a chronic i.v. cannula. Vagotomy attenuated the dipsogenic effects of infusions of hypertonic saline and sucrose that were observed in the control rats.     

Renal response to acute saline loading in Sabra hypertension-prone and-resistant rats

Summary The renal handling of an oral isotonic saline load was studied in hypertension-prone (SBH), hypertension-resistant (SBN) and the parental Sabra (SB) rats. The diuretic and natriuretic response of SBH rats was unequivocally diminished, thus lending further support to the concept of impaired salt handling in hypertension.This work was supported in part by a grant from Bayer AG, FRG.     

High salt effect on RNA synthesis in Krebs ascites tumor cells

Summary The incubation of Krebs ascites tumor cells in medium with a high salt concentration resulted in a partial inhibition of nuclear RNA synthesis. The residual RNA polymerase activity in such nuclei was only slightly inhibited by low concentrations (50 nM) of -amanitin. This finding suggested an inhibition of RNA polymerase II activity under conditions of medium hypertonicity. Indeed, RNA polymerase II, isolated from the nuclei of cells exposed to hypertonicity, revealed only half of the control activity. On the other hand, RNA polymerase I was not affected by hypertonicity. Moreover, chromatin fractions isolated from cells incubated in hypertonic or isotonic medium were equally template-active in RNA synthesis.This investigation was supported by the Turkish Scientific and Technical Research Council (TÜBITAK), Project No. TAG 339.     

The involvement of the renin-angiotensin system in the regulation of cell proliferation in the rat endometrium

Oestrogens are known to enhance angiotensin biosynthesis by increasing the elaboration of its precursor, angiotensinogen. On the other hand, we found that inhibition of angiotensin-converting enzyme (ACE) suppressed the proliferative response of the rat anterior pituitary gland to oestrogens. To answer the question whether the angiotensin system is involved in the control of the cell proliferation of the uterine epithelium, the effects of an ACE inhibitor, enalapril maleate, and of angiotensins II and IV, alone or together with losartan, an antagonist of angiotensin receptor type 1 (AT1), on endometrial epithelial cell proliferation have been studied. The experiments were performed on ovariectomized female Wistar rats. In the first experiment the animals were injected with a single dose of oestradiol benzoate or received an injection of solvent only. Half of the oestrogen-treated rats were injected additionally with enalapril maleate (EN, twice daily). The incorporation of bromodeoxyuridine (BrDU) into endometrial cell nuclei was used as an index of cell proliferation. It was found that oestradiol alone dramatically increased the BrDU labelling index (LI) of endometrial cell nuclei, and this effect was partially blocked by the simultaneous treatment with EN. In the second experiment, the animals were injected intraperitoneally with angiotensin II (AII), angiotensin IV (AIV) or saline, alone or together with losartan. It was found that AIV induced an increase in the LI in uterine epithelium, and this effect was not blocked by the simultaneous treatment with losartan. The increase in LI in uterine epithelium was also observed in the rats treated with AII and with losartan. These findings suggest an involvement of angiotensin IV in the control of uterine epithelium cell proliferation. Received 12 October 1998; received after revision 6 January 1999; accepted 2 February 1999     

The effect of alkaloids from Tabernanthe iboga H. Bn. on the response of isolated organs to catecholamines and the possible role of calcium exchange. Case of Ibogaine]

On isolated Rat duodenum, ibogaine (70 mumoles/l) increases the hypertonic effect following the addition of Calcium ions to the organ previously decalcified. Moreover, this alkaloid increases the hypotomic effect resulting from decalcification of the normal organs. These actions are taken into account with the potentiating effects of ibogaine on noradrenaline and dopamine responses observed on rat vas deferens.     

Intact teratogenic immunoglobulins may reach the rat embryo

It is known that heterologous antiserum against rat kidney homogenate may induce congenital malformations when injected into pregnant rats during the period of organogenesis. Teratogenic rabbit antibodies against a purified rat renal tubular glycoprotein were isolated, labelled with 125I and injected into pregnant rats on the 10th day of gestation. Extracts of visceral yolk-sacs (VYS) and embryos were obtained 16 h later and chromatographed separately on a Sephacryl S-300 gel filtration column. The resultant chromatograms showed several radioactive peaks, one of which coincided with the eluate of intact rabbit immunoglobulins G (IgG). We interpret the result as an indication that some undigested intact teratogenic IgG were present in VYS and the embryo.     

Immunofluorescence identification of cells with corticotropic and alpha-melanotropic activity in the hypophysis of the grass snake Natrix natrix L.]

The use of anti ACTH (17-39) and alpha-MSH allowed us to detect by immunofluorescence in the Pituitary gland of Grass Snake the site of elaboration of ACTH and alpha-MSH. Corticotropic cells are located in the rostral part of the Pars Distalis and in the Pars intermedia. Melanotropic cells occupy the whole part of the Pars intermedia.     

Diuretic and antifeedant actions byManduca sexta diuretic hormone in lepidopteran larvae

Neuroendocrine disruption of water balance in insect larvae was evaluated as the basis for a new approach to pest insect control. Effects on water balance and food consumption were measured for larvae ofHeliothis virescens (cotton budworm) treated with syntheticManduca sexta diuretic neurohormone (MasDH). Synthetic MasDH (50–250 nM) caused dose-dependent increases in fluid secretion by larval Malpighian tubules in vitro; higher concentrations resulted in lower fluid secretion. Last instar larvae injected with 20–100 pmol MasDH exhibited increasing weight loss. Larvae injected with 500 pmol MasDH dramatically reduced both water excretion and food consumption by 70%. These latter results indicate that high titers of diuretic hormone can suppress feeding damage by larval insects by depressing water excretion and food consumption.     

Comparative morphometric study of the cells of the third proximal segment of the rat kidney under different conditions of fixation.

The morphometric study of the P3 segment of rat proximal tubule has shown that neither the method of fixation, nor the fixative itself, significantly change the relative and absolute volumes of the cell compartments, provided that the fixation media are made approximately isotonic.