NAD+-induced inhibition of phosphate transport in canine renal brush-border membranes Mediation through a process other than or in addition to NAD+ hydrolysis

We previously demonstrated inhibition of Na⁺-dependent ³²P_i transport in canine renal brush-border membranes in association with NAD⁺-induced ADP ribosylation of membrane protein(s) and postulated that NAD⁺ inhibits P_i transport across the brush-border membrane via ADP ribosylation. Recently it was shown that incubation of rat brush-border membrane with NAD⁺ resulted in release of P_i which was prevented by EDTA. It was proposed that NAD⁺-mediated inhibition of ³²P_i transport might occur through this mechanism. To determine whether NAD⁺ inhibited ³²P_i transport by a mechanism other than or in addition to release of P_i, we compared Na⁺-dependent ³²P_i counterflow in brush-border membrane equilibrated with P_i or with P_i generated from NAD⁺. Release of P_i from NAD⁺ incubated with brush-border membrane was confirmed. The increased uptake of ³²P_i which was demonstrated in brush-border membrane equilibrated with P_i was not measured when intravesicular P_i was generated from a concentration of NAD⁺ which effected ADP-ribosylation of brush border membranes (100 μM NAD⁺). In contrast, increased uptake of ³²P_i was demonstrated when intravesicular P_i was generated from 1 μM NAD⁺ which did not effect ADP ribosylation. Mg²⁺-dependent ADP ribosylation of brush-border membrane incubated with NAD⁺ was demonstrated which persisted during the time interval of ³²P_i uptake measurements. Our findings are compatible with the hypothesis that NAD⁺-induced ADP ribosylation of brush-border membrane protein(s) results in inhibition of P_i transport across the membrane in vivo. EDTA may act to prevent this inhibition in brush-border membrane by chelation of Mg²⁺ and decreased ADP ribosylation.     

Cerebroside and Sulfatide Biosynthesis in the Brain of Snell Dwarf Mouse: Effects of Thyroxine and Growth Hormone in the Early Postnatal Period

Snell dwarf mice (dw/dw) and normal mice (+/?) were injected with thyroxine (T₄) (1 μg/animal, four injections) and growth hormone (GH) (20 μg/animal, four injections) from the 5th to the 15th day of life. In the untreated dw/dw mouse brain, the specific activities of UDP-galactose:ceramide galactosyltransferase (CGalT), PAPS:cerebroside sulfotransferase (CST), and 2′,3′-cyclic nucleotide 3′-phosphohydrolase (CNP) were decreased by 28, 25, and 37%, respectively, compared with the control untreated +/? mice. The major effect of T₄ was an increase of the brain CNP in the +/? mice (+40%) and dw/dw mice (+111%). The treatment with T₄ also brought to normal the level of CGalT in dw/dw brain; a somewhat less marked effect on CST was observed. The treatment with GH had a great stimulatory effect on CNP: the specific activity of this enzyme increased by 40 and 69% in +/? and dw/dw mouse brain, respectively. On the contrary, no effect of GH on the CGalT activity was observe in this study. Our results suggest that T₄ and GH may have both independent and complementary actions on the myelin-associated enzymes during the early postnatal period of brain development.     

Precocene causes male determination in the aphid Myzus persicae

When adult apterous viviparous females of Myzus persicae, reared in short night conditions at 21–23°C, are treated with the precocene analogue 6-methoxy-7-ethoxy-2,2-dimethylchromene, they deposit males towards the end of their reproductive lives. The first-born normal daughters of the treated females also deposit some males at various times in their reproductive lives. Karyotypic analysis was used to investigate the sequence of male and female embryos in the ovarioles of precociously metamorphosed aphids. The experiments support the hypothesis (Mittler et al., 1979) that juvenile hormone level controls the sex determination process in aphids. Since male aphids have an XO sex chromosome constitution, this implies that juvenile hormone level influences the behaviour of the X-chromosomes at or before the single maturation division of the egg. At this division one X-chromosome is eliminated from eggs which will develop as males. Aphids provide the first example of a specific endocrine influence on chromosome behaviour in sex determination.     

Effects of decapitation and ovariectomy on the regulation of juvenile hormone synthesis in the cockroach, Diploptera punctata

Corpora allata from Diploptera punctata females at adult ecdysis or at the end of the last-larval stadium, when implanted into decapitated females, underwent a cycle of juvenile hormone synthesis similar in timing and magnitude to that of glands implanted into control animals which had been starved and allatectomized. Starvation did not alter the cycle in rates of juvenile hormone synthesis of sham-operated animals.Decapitation of ovariectomized animals resulted in no cycle in rates of juvenile hormone synthesis by implanted adult corpora allata; however, implantation of an ovary along with the corpora allata into decapitated, ovariectomized hosts resulted in a cycle of juvenile hormone synthesis. In control animals, which retained their heads but were starved and allatectomized as well as ovariectomized, the implanted corpora allata showed a cycle of juvenile hormone synthesis only when implanted with an ovary. The maximal rates of juvenile hormone synthesis by the corpora allata in both experimental and control conditions were lower than normal, likely due to the repeated trauma of surgery. However, at no time from eclosion to the end of the first gonotrophic period was the brain necessary for the cyclic response of the corpora allata to the presence of the ovary.     

Determination of Some Molecular Parameters of Tyrosine Hydroxylase From Rat Adrenal, Rat Striatum, and Human Pheochromocytoma

The molecular parameters of tyrosine hydroxylase (EC 1.14.16.2) from rat adrenal, rat striatum, and human pheochromocytoma were determined by combined gel filtration and sucrose gradient ultracentrifugation. The enzyme from rat adrenal has a calculated molecular weight of 228,000, a Stokes radius of 60.9 A, a sedimentation coefficient of 9.10S, and a frictional ratio of 1.39. The enzyme from rat striatum has a calculated molecular weight of 210,000, a Stokes radius of 54.3 A, a sedimentation coefficient of 9.38S, and a frictional ratio of 1.28. Tyrosine hydroxylase from human pheochromocytoma tissue has a calculated molecular weight of 255,000, a Stokes radius of 68.2 A, a sedimentation coefficient of 9.08S, and a frictional ratio of 1.50. These results indicate that the tyrosine hydroxylases from central and peripheral tissue in the rat are quite similar although the human enzyme appears to be significantly larger.     

Molting in a parasitic nematode, Phocanema decipiens—VII. The mode of action of the ecdysial hormone

The cycle of aminopeptidase activity demonstrated by histochemical methods in the activated excretory gland could not be detected in homogenates. In the electron microscope, the secretory granules in dormant glands were dense and irregular in shape and the mitochondria elongate, relatively dense, and with a crenellated outer membrane. The excretory gland was activated when the neuroendocrine system was stimulated by farnesyl methyl ether. In activated glands the secretory granules became larger, less dense and the membranes began to fuse with membranes of the ductules which ramify through the gland. The mitochondria became swollen. Aminopeptidase activity was displayed by a large uniformly less dense granules but not by the denser granules, and was seen in the endoplasmic reticulum, Golgi apparatus and in the lumen of the ducts. It is suggested that the ecdysial hormone from the neurosecretory cells sets in train a sequence of events which leads to entry of water into the gland and consequent activation of the enzyme in the granules, and to changes in the membranes of the granules which facilitate fusion with the membrane lining the ducts.     

The ACTH-interrenal axis in the freshwater stickleback,Gasterosteus aculeatus form leiurus

Summary The ACTH-interrenal axis of the freshwater stickleback has been examined with the fish in a variety of physiological conditions. A morphometric analysis of ACTH cell ultrastructure in spring animals revealed that the only change from the winter condition was a significant decrease in the amount of perinuclear RER. The interrenal gland responded to metopirone treatment by an increase in both nuclear and cell size, although only a high dose of metopirone could degranulate the ACTH cells. Morphometry of the ACTH cells from metopirone-treated animals showed a significant increase in the amount of RER and a significant decrease in the number of free ribosomes and secretory granules, compared with control animals maintained in freshwater. Such ultrastructural changes may be expected of a cell that is stimulated to increase its secretion of polypeptide hormone. The ACTH-interrenal axis also responded to 70% seawater, as this treatment increased the interrenal cell and nuclear sizes.     

Correlation between microtubular number and transport activity of hypothalamo-neurohypophyseal secretory neurons

Summary The lower pituitary stalk has been studied in rats given hypertonic saline for four days and in rats with congenital diabetes insipidus (GDI), that is, in two groups of animals in which there is evidence of an increase in the transport of polypeptides down the axons of the tractus hypophyseus.A quantitative ultrastructural analysis of this tract, the first yet made, has demonstrated that in normal animals it is composed of unusually small axons, over half of which are less than 300 nm in diameter.In this tract there is a significant increase in axonal diameter and microtubular content in animals given hypertonic saline for four days. In adult rats with CDI, these changes are even more marked, a feature which is correlated with the fact that in these animals the transport of polypeptides has probably been abnormal since birth.An alteration in the microtubular content of neurons has not previously been observed either in physiologically stressed animals or in diseased animals; such alterations suggest the participation of microtubules in polypeptide transport. The narrow diameter of axons in the tractus hypophyseus of the normal animal raises the possibility of the extravesicular transport of such polypeptides.Abbreviations used ADH antidiuretic hormone - AF aldehyde fuchsin - CDI congenital diabetes insipidus - HNS hypothalamo-neurohypophysiel system - NSM neurosecretory material - NSV neurosecretory vesicle - PVN paraventricular nucleus - SON supraoptic nucleus This paper is dedicated to Professor W. Bargmann.We are grateful to Miss Pauline Chapman for technical assistance.This project is supported by the Medical Research Council.     

Direct control by calcium of 25-hydroxycholecalciferol-1-hydroxylase activity in chick kidney mitochondria

Kidney mitochondria were isolated from rachitic chicks and their activity in the metabolism of 25-OH-D₃ was studied in relation to the amount of calcium added $\text{in vitro}$. The addition of 0.050.2 mM calcium to a mitochondrial suspension caused a marked and dose-related stimulation of 1-hydroxylation. A sharp decline in the activity was induced by higher concentrations (0.3-0.5 mM) of calcium. The rate of 24-hydroxylation was not influenced by calcium. In these effects, calcium was relatively specific among various divalent cations. These data strongly suggest that calcium is directly involved in the regulation of the vitamin D activation in kidney mitochondria.