Postnatal changes in lambs of two pathways for thyroxine 5'-monodeiodination in brown adipose tissue

We have recently shown that ovine fetal brown adipose tissue (BAT) contains two distinct iodothyronine 5'-monodeiodinase (5'MDI) activities, one with a high Km (type I) and another with a low Km (type II). Both activities increased to maximum levels near term (150 days gestation). BAT plays a major role in neonatal temperature regulation in lambs, and available evidence suggests that BAT 5'MDI activity is closely linked to thermogenic capacity. To better characterize the changes in 5'MDI after birth, we studied both type I and type II 5'MDI in lamb BAT from the time of birth to 30 days of postnatal age. Type I 5'MDI activity [pmol 3,5,3'-triiodothyronine (T3).mg protein-1.h-1] showed no significant changes during the first 11 days after birth [newborn (NB), 95 +/- 16; 1 day, 83 +/- 20; 3-4 days, 80 +/- 11; 10-11 days, 92 +/- 28]. Activity decreased significantly at 30 days (24 +/- 8.9, P less than 0.05). On the other hand, the type II 5'MDI activity (fmol I- released.mg protein-1.h-1) increased significantly (P less than 0.01) during the first 4 days, (NB, 348 +/- 23; 1 day, 679 +/- 37; 3-4 days, 785 +/- 199), decreased toward NB values (401 +/- 87) at 10-11 days of age, and fell to 66 +/- 31 at 30 days (P less than 0.05 vs. NB). Kinetic analysis of BAT type II thyroxine 5'MDI revealed a rise in maximum velocity from NB to 1 and 3-4 days of age without a change in the enzymatic activity Km.(ABSTRACT TRUNCATED AT 250 WORDS)

High salt intake attenuates the development of hypertension in two-kidney, one-clip Goldblatt rats

Effects of high salt intake on the early onset of hypertension were examined in two-kidney, one-clip rats. They were divided into high salt and control groups which were supplied with 1.0% NaCl and tap water, respectively, as a drinking solution for 12 days after clipping the left renal artery. The high salt group showed a lower plasma renin concentration and a higher plasma atrial natriuretic peptide (ANP) along with an attenuation of the magnitude of early hypertension, as compared with the control group. A significant positive correlation between blood pressure and plasma renin concentration and an inverse correlation between plasma renin concentration and ANP were shown. Cortical renal renin content was comparable between the two groups. In another two groups of sham-clipped rats, the high salt group did not differ from the tap water-drinking group in any of the parameters examined, except that ANP was significantly higher. These results demonstrate that high salt intake attenuates the developmental phase of hypertension in two-kidney, one-clip rats by increasing the ANP and suppressing the release of renin.

Purinergic stimulation of astroblast proliferation: guanosine and its nucleotides stimulate cell division in chick astroblasts

A highly active fraction that was mitogenic for astroblasts but which contained no amino acids was identified during the purification of peptides from chick embryo brains. This material was purified by ultracentrifugation, ultrafiltration through Diaflo PM-30 and YM-2 membranes and retention on Diaflo YC-05, followed by ion exchange chromatography and reversed phase high performance liquid chromatography (HPLC) on a C18 Deltapak column. On thin layer chromatography and HPLC the material co-chromatographed with authentic commercially-obtained GMP. Its ultraviolet absorption spectrum was also identical with that of GMP. 1H and 31P nuclear magnetic resonance spectra of the isolated material were identical with those of GMP. The close match between the fast atom bombardment (FAB) mass spectra of the unknown material and authentic GMP indicated that the unknown material was GMP of molecular weight 363 Da. Authentic, commercial GMP stimulated the growth of cultured chick astroblasts in the same dose-dependent manner as the material from chick embryo brains; maximal stimulation was at 50 microM. Guanosine, GDP, and GTP also stimulated cell proliferation. The nucleotides were equally as effective as guanosine. 5'-Guanylyl imidodiphosphate, guanosine 5'-O-(2-thiodiphosphate), and guanosine 5'-N-(3-thiotriphosphate), guanine nucleotides which are relatively resistant to enzymatic hydrolysis, were also mitogenic, indicating that the nucleotides do not need to be degraded to nucleosides to be active and that they probably act extracellularly. Guanine nucleosides and nucleotides promoted astroblast growth when other growth factors were removed from the culture medium. The mitogenic effects of guanosine and its nucleotides were inhibited in a dose-dependent fashion by micromolar concentrations of theophylline, a characteristic of phenomena mediated by purinergic receptors. Guanosine and its nucleotides are released in micromolar concentrations by hypoxic or dying cells. Under these circumstances these compounds may stimulate division of adjacent cells in vivo.

Arginine vasopressin gene expression in chronic cardiac failure in rats

Arginine vasopressin (AVP) is known to be increased in patients and experimental animals with chronic cardiac failure (CCF). The importance of an increase in biosynthesis of AVP in the hypothalamus has, however, not heretofore been investigated and is the purpose of the present study. CCF secondary to infarction of myocardial tissue was induced by ligation of the left anterior descending coronary artery and sham operated animals served as controls. Four weeks later hypothalamic AVP mRNA was determined by solution hybridization using sense and anti-sense strand RNA. The blood pressure was lower in CCF than sham animals (131.2 +/- 3.1 vs. 112.8 +/- 4.0 mm Hg, P less than 0.05) and the total heart, and right and left ventricle weights were significantly higher in CCF rats. Plasma AVP was higher in CCF (sham 6.78 +/- 0.30; CCF 11.46 +/- 0.64 pg/ml, P less than 0.001) and plasma atrial natriuretic peptide was also higher in CCF than sham animals (205 +/- 36 vs. 554 +/- 56 pg/ml, P less than 0.001). The AVP mRNA in hypothalamus was significantly higher in CCF than sham animals (55.5 +/- 3.7 vs. 95.9 +/- 4.0 pg/micrograms total RNA, P less than 0.001). There was no difference in beta-actin mRNA in the hypothalamus of sham and CCF rats, indicating that the AVP-mRNA increase was specific in CCF. These results therefore demonstrate that increased AVP biosynthesis in the hypothalamus, in addition to release of the hormone from the posterior pituitary, may occur in CCF.

Arginine vasopressin gene regulation in the homozygous Brattleboro rat

The Brattleboro rat, which has an autosomally recessive form of diabetes insipidus, has been reported to have a marked defect in the regulation of arginine vasopressin (AVP) gene expression. However, it is not known whether this is a primary genetic defect or occurs secondary to the urinary water losses which occur in the absence of circulating AVP in the Brattleboro rat. This present study was therefore undertaken to study AVP gene regulation in the Brattleboro rat after chronic AVP treatment by osmotic minipump for 2 wk. In Brattleboro rats without AVP treatment, neither urinary osmolality (Uosm) nor hypothalamic AVP mRNA was significantly changed after 24 h of fluid deprivation (Uosm, 413 +/- 33 to 588 +/- 44, NS; AVP mRNA, 39.33 +/- 2.95 to 46.39 +/- 2.71 pg/micrograms total RNA, NS). In contrast, when Brattleboro rats were treated with AVP for 2 wk, the regulation of AVP gene occurred in response to 24 h of fluid deprivation. In these studies, hypothalamic AVP mRNA was significantly increased compared with the Brattleboro rats still receiving AVP with free access of water (28.9 +/- 3.5 vs. 65.0 +/- 3.3 pg/micrograms total RNA, P less than 0.001). Further studies in Long-Evans rats demonstrate a similar response to a comparable degree of fluid deprivation as Uosm and AVP mRNA were significantly increased after 72 h of fluid deprivation (Uosm, 1,505 +/- 186 to 5,460 +/- 560 mosmol/kg, P less than 0.001; AVP mRNA, 31.7 +/- 3.9 to 77.5 +/- 4.6 pg/micrograms total RNA, P less than 0.001). These results indicate that AVP-replaced homozygous Brattleboro rats can regulate AVP gene expression normally in response to fluid deprivation. This finding indicates that the defect in AVP gene regulation in the Brattleboro rat not receiving AVP replacement is a secondary phenomenon rather than a primary genetic defect.

Enzymatic and binding effects of atrial natriuretic factor in glomeruli and nephrons

Atrial natriuretic factor (ANF) has been suggested to exert a tubular effect on the mammalian nephron, perhaps in part by interacting with other hormones. In the present study, the effect of ANF was examined on glomeruli (Gm) and different renal tubule segments including medullary (MAL) and cortical thick ascending limb (CAL) and cortical (CCT), outer medullary (OMCT) and inner medullary collecting tubules (IMCT). This effect of ANF was assessed by alteration in adenylate cyclase and cGMP in the various nephron segments in the presence and absence of arginine vasopressin (AVP), parathyroid hormone (PTH) and calcitonin (SCT). An effect of ANF (10(-8) M) was not demonstrated on adenylate cyclase (fmol cAMP formed/30 min/micrograms protein) in Gm, CAL, MAL, CCT, OMCT or IMCT. Nor did ANF (10(-8) M) interfere with the effect of PTH (5 IU/ml) on the Gm (PTH 35.1 +/- 3.7 vs. PTH + ANF 32.5 +/- 1.8, NS), CAL (PTH 50.5 +/- 10.9 vs. PTH + ANF 46.2 +/- 1.4, NS) or AVP (10(-8) M) on the CCT (AVP 40.8 +/- 6.6 vs. AVP + ANF 33.0 +/- 3.1, NS), OMCT (AVP 56.0 +/- 11.8 vs. AVP + ANF 42.1 +/- 6.7, NS), IMCT (AVP 66.5 +/- 4.6 vs. AVP + ANF 53.5 +/- 7.0, NS) or MAL (AVP 15.5 +/- 1.6 vs. AVP + ANF 14.0 +/- 2.6, NS). ANF also did not affect SCT (1.5 x 10(-8) M)-induced adenylate cyclase on CCT (SCT 69.8 +/- 11.3 vs. SCT + ANF 79.9 +/- 7.2, NS). ANF (10(-8) M), however, significantly increased cGMP in the Gm (6.4 +/- 1.7 to 121.3 +/- 32.4 fmol/micrograms protein, P less than 0.001) and IMCT (0.63 +/- 0.16 to 1.46 +/- 0.29 fmol/micrograms protein, P less than 0.05). However, no effect of ANF on cGMP was observed in the CAL, CCT, OMCT, and MAL even at 10(-7) M ANF. PTH (5 IU/ml) did not alter either basal or ANF-stimulated cGMP in the Gm. Also, specific ANF binding was studied in the microdissected IMCT. Kd was 6.08 x 10(-9) M and Bmax was 8.07 x 10(-11) M.(ABSTRACT TRUNCATED AT 250 WORDS)

Ovine fetal response to water deprivation: aspects on the role of vasopressin

The effect of maternal hyperosmolality as created by an acute mannitol infusion was evaluated in eight chronic sheep preparations. Fetal osmotic and haemodynamic responses were compared to those achieved during an arginine vasopressin (AVP) infusion into the fetus (approximately 400 microU/(min kg]. To assess the AVP sensitivity of the fetal kidney the urine osmolality was determined. The activity of adenylate cyclase was measured in placental cotyledons as an indicator of AVP receptors affecting water permeability. The maternal mannitol infusion induced an increase in fetal serum AVP levels from 1.18 +/- 0.25 up to 13.76 +/- 2.11 pg/ml. During the fetal AVP infusion the AVP levels were approximately 22 pg/ml, somewhat higher when given concurrently with a mannitol infusion to the ewe (peak value: 26.13 +/- 2.80 pg/ml). Fetal heart rate increased significantly during maternal hyperosmolality while this effect was blunted by exogenous AVP given to the fetus. The AVP infusion did not affect fetal or maternal serum osmolality. During the mannitol infusion fetal serum osmolality increased to peak values which were not significantly different whether or not AVP was infused into the fetus (from 298.0 +/- 0.85 to 309.0 +/- 0.90, and from 297.7 +/- 1.47 to 307.9 +/- 0.90 mosmol/kg, respectively). Similarly, there were no differences in the effect of mannitol infusion upon fetal urine osmolality with or without AVP infusion (increments: + 149.7 +/- 34.12 and + 148.7 +/- 31.30 mosmol/kg, respectively). Adenylate cyclase activity in the placenta was unchanged before and after AVP stimulation. The data suggest an unresponsiveness of placental water permeability to fetal AVP infusion. We also conclude that a maximal urine osmolality was reached already at AVP levels obtained after an osmotic maternal load whereas at AVP levels more than twice as high the cardiovascular effects were still AVP dose-dependent.

AVP-induced Ca fluxes and contraction of rat glomerular mesangial cells

Arginine vasopressin (AVP) is known to exert Ca mobilization and contraction in glomerular mesangial cells and vascular smooth muscle cells. However, the relationship between changes in intracellular Ca and transmembrane Ca fluxes is not clear at the present time. Therefore, this study was undertaken to determine the effect of AVP on cytosolic calcium ([Ca2+]i) and Ca fluxes as estimated by measurements of 45Ca2+ efflux. Changes of [Ca2+]i in response to AVP were directly measured in monolayers of adherent cultured mesangial cells. AVP induced rapid concentration-dependent increases in [Ca2+]i and Ca2+ efflux. AVP also induced contraction of mesangial cells. This effect was blocked only by the V1 (pressor)-antagonist, d(CH2)5Tyr(Me)AVP. Stimulation of Ca2+ efflux and changes in [Ca2+]i by AVP completely desensitized the mesangial cells to a subsequent identical challenge of AVP with no cross-tachyphylaxis to other hormones. Even in Ca2+-free medium, AVP increased [Ca2+]i and Ca2+ efflux, but to a lesser extent. Under this condition, contraction of mesangial cells induced by AVP was also observed. Readdition of extracellular Ca2+ following the AVP-induced increase in [Ca2+]i caused a second and slower [Ca2+]i increase. In Ca2+-containing conditions, lanthanum ion-reduced AVP evoked [Ca2+]i stimulation to the value observed in Ca2+-free medium. The Ca2+ channel blocker, verapamil, partially inhibited AVP-induced Ca2+ influx but totally blocked the increase in [Ca2+]i induced by high K. Verapamil did not inhibit AVP-stimulated Ca2+ efflux and cell contraction. Dantrolene, a blocker of Ca2+ release from endoplasmic reticulum, inhibited AVP-stimulated Ca2+ efflux and cell contraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of angiotensin II on Ca2+ kinetics and contraction in cultured rat glomerular mesangial cells

This in vitro study was undertaken to determine the changes in Ca2+ kinetics and cell shape of cultured putative glomerular mesangial cells in the rat in response to angiotensin II (ANG II). Intracellular Ca2+ ([Ca2+]i) was measured using quin 2. ANG II-stimulated Ca2+ efflux was also determined. ANG II induced rapid concentration-dependent increases in [Ca2+]i and Ca2+ efflux. ANG II also induced contraction of mesangial cells as assessed by alterations in cell shape. Even in Ca2+-free medium, ANG II increased [Ca2+]i and Ca2+ efflux, but to a lesser extent. Under this condition, contraction of mesangial cells induced by ANG II was also observed. Readdition of extracellular Ca2+ after the ANG II-induced increase in [Ca2+]i caused a second and slower [Ca2+]i increase. High potassium (50 mM) induced a change of [Ca2+]i, but to a lesser extent compared with the ANG II-induced change. The Ca2+ channel blocker verapamil (5 x 10(-5) M) partially inhibited ANG II-induced Ca2+ influx but totally blocked the increase in [Ca2+]i induced by high potassium. Verapamil did not inhibit ANG II-stimulated Ca2+ efflux or the change in cell shape. Dantrolene (10(-4) M), a blocker of Ca2+ release from endoplasmic reticulum, inhibited ANG II-stimulated Ca2+ efflux and change in cell shape. These results indicate that ANG II rapidly increases [Ca2+]i in cultured rat mesangial cells, in part by mobilizing Ca2+ from dantrolene-sensitive intracellular pools and in part through activation of receptor-operated and voltage-dependent Ca2+ channels. The [Ca2+]i mobilization, however, seems to be the primary modulator of initial glomerular mesangial cell contraction.

Cellular action of arginine vasopressin in the isolated renal tubules of hypothyroid rats

Hypothyroidism has been demonstrated to be associated with an impaired concentrating capacity and specific morphological changes in the thick ascending limbs. This study was performed to evaluate the cellular action of arginine vasopressin (AVP) in the isolated renal tubules from control (C) and hypothyroid (HT) rats. Hypothyroidism was induced by feeding aminotriazole for 4 wk. Urinary volume was higher in HT rats (C 13.5 +/- 0.9, HT 17.7 +/- 0.9 ml/24 h, P less than 0.005) and urinary osmolality was lower in HT rats (C 1,707 +/- 49, HT 1,229 +/- 35 mosmol/kgH2O, P less than 0.001). Plasma AVP levels were significantly higher in HT rats (C 1.93 +/- 0.59, HT 4.12 +2- 0.62 pg/ml, P less than 0.05), thus documenting AVP resistance. The adenylate cyclase response to AVP (10(-6) M) was significantly lower (P less than 0.02) in the medullary thick ascending limb of Henle's loop (mTALH) in HT (14.3 +/- 2.4 to 41.7 +/- 5.8 fm X 30 min-1 X mm-1, P less than 0.001) than in mTALH in C rats (14.4 +/- 2.8 to 110.1 +/- 24.9 fm X 30 min-1 X mm-1, P less than 0.001). In contrast, the adenylate cyclase response to AVP was not significantly different in collecting tubules of cortex, outer medulla, and inner medulla from C and HT rats, although a slight decrease in response to AVP was observed in cortical and outer medullary collecting tubules.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification of a chick brain-derived growth factor by reversed-phase high-performance liquid chromatography

A chick brain-derived growth factor (CBGF) has been purified to apparent homogeneity by a combination of ultrafiltration, DEAE ion-exchange, and reversed-phase high-performance liquid chromatography on a C18 column. CBGF has an apparent molecular mass of approximately 1500 Da. The amino acid composition of CBGF has been determined and reveals a peptide containing predominantly glycine, glutamic acid/glutamine, and aspartic acid/asparagine. This mitogen is highly active, with half-maximal stimulation of chick brain astrocytes at 5 ng/ml in an assay using incorporation of methyl-3H-thymidine into DNA. In addition to its effects on chick astrocytes, purified CBGF from the 18 d chick embryo is mitogenic for amphibian limb regeneration blastema cells in vitro. A possible role for this mitogen in the nerve-dependent regeneration of amphibian appendages is discussed.