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Biomedical subjects

M Yeh

Publications and source records attributed to M Yeh.

At least 73 records · Page 4Linked to original sources
PubMed1989

Differential effects of thyroxine and cortisone on jejunal sucrase expression in suckling rats.

Effects of thyroxine (T4) and cortisone (C) on developmental expression of jejunal immunoreactive sucrase-isomaltase (S-I) and sucrase activity in suckling rats were studied to determine whether these hormones have distinctive actions. Immunoreactive S-I and sucrase activity were absent in infant rats and appeared simultaneously on days 16-18, when cells expressing S-I protein were detected at the villus base. By day 22, the entire jejunal mucosal surface was covered by new cells expressing immunoreactive S-I. Jejunal S-I content surged to adult levels on day 22, whereas the sucrase activity of immunoreactive S-I protein increased continuously until day 32. Administration of 12.5 nmol of T4 or 1.25 mumol of C on day 12 induced precocious expression of jejunal sucrase activity on day 15. T4 also induced sucrase activity in adrenalectomized rats without increasing serum corticosterone concentrations. Both T4 and C appeared to exert their effects in crypt cells, since immunoreactive S-I protein appeared only in villus base cells 24 h after administration. Pulse labeling of [14C]leucine showed that both hormones evoked de novo synthesis of S-I. The S-I induced by C had significantly higher sucrase activity than that induced by T4. We conclude that postnatal development of sucrase activity results from de novo synthesis of S-I with progressively higher catalytic activity until day 32 and these developmental processes are sequentially modulated by thyroid and adrenocortical hormones.

Adrenalectomy↗
PubMed1989

Induction of intestinal differentiation by systemic and not by luminal corticosterone in adrenalectomized rat pups.

Potential effects of corticosterone (cort) from maternal milk on intestinal differentiation were studied using adrenalectomized (adx) rat pups fed a formula containing differing amounts of cort. Formula cort concentrations in the range found in milk (0.1-0.5 micrograms/ml) increased the survival of adx rats, but did not induce intestinal differentiation. Formulae containing 1.0-50.0 micrograms/ml cort caused a dose-dependent elevation of serum cort concentrations and jejunal maltase activity and precocious jejunal sucrase induction. Adx rats receiving the formula containing 10 micrograms/ml cort showed serum cort concentrations similar to those in day 15 control rats and jejunal sucrase and maltase activities equivalent to those in day 18-20 control rats, suggesting that the rise in serum cort that occurs during postnatal development suffices to modulate intestinal differentiation. To distinguish between direct local and systemic effects of luminal cort on intestinal differentiation, expression of sucrase was determined in jejunal isografts and in host jejunum from adx rats fed luminal cort. Jejunal isografts and host jejunum expressed similar sucrase activities and showed similar immunofluorescent staining. Moreover, administration of cort by continual ip infusion was more effective than continual intragastric infusion in inducing intestinal sucrase and maltase activities. These data imply that luminal cort is absorbed and transported into the systemic circulation before inducing intestinal epithelial cell differentiation through the systemic route.

Adrenalectomy↗
PubMed1989

Induction of rat jejunal epithelial cell expression of sucrase-isomaltase by glucocorticoids in primary cell culture and in vivo.

The cell cycle phase that mediates the induction of intestinal sucrase-isomaltase (SI) expression by glucocorticoids was investigated by measuring migration rates of 3H-DNA-labeled and of SI-containing epithelial cells by autoradiography and indirect immunofluorescent staining after simultaneous administration of [3H]thymidine and cortisone to 12-d-old rat pups. By 24 and 48 h, lead 3H-DNA-labeled cells had migrated 7.8 and 12.4 cell positions higher on the villus than lead cells expressing SI. Cell migration rates from 12 to 24 h and 24 to 48 h were 0.68 and 0.97 cell position/h. Thus, commitment to SI expression occurred in cells 11.5-12.8 h after the S phase, which is calculated to be in the G1 phase. To determine whether committed cells need to replicate to express SI, cell differentiation was examined in primary cultures of crypt cells originating from corticosterone-treated rats. About two-thirds of cultured cells were retarded in the S phase after plating, as judged by no increase of DNA labeling indices, no change in epithelial cell number, and the absence of mitosis (less than 0.01%). The proportion of cells expressing SI increased from 0 to 6-8% between 12 and 24 h, and reached 48% 48 h after plating on collagen-coated dishes. SI expression did not occur in cells plated on glass or plastic surfaces. Pulse labeling with [35S]methionine confirmed that de novo synthesis of SI occurred in cell cultures. Thus, additional cell cycling of committed cells occurring in vivo is not obligatory for the expression of SI.

Animals↗
PubMed1987

Hydrolethalus (Salonen-Herva-Norio) syndrome: further clinicopathological delineation.

Two brothers with severe CNS abnormalities, cleft lip/palate, polydactyly, and lung hypoplasia are reported as examples of the hydrolethalus syndrome, an autosomal recessive disorder. Death from cardiopulmonary arrest occurred in patient 1 at age 4 months and in patient 2 at age 17 days. Detailed radiological and neuropathological description is provided on patient 2. We recommend realtime ultrasonography and, when indicated, fetoscopy for antenatal detection of the craniofacial and limb malformations associated with this syndrome.

Abnormalities, Multiple↗
PubMed1987

Hormonal regulation of adaptive intestinal growth in artificially reared rat pups.

Adaptive growth and precocious expression of sucrase activity occur in the small intestine of artificially reared (AR) rat pups fed a hormone-free diet. The physiological mechanisms underlying adaptive intestinal growth were studied. Day 12 rat pups that received jejunal isografts subcutaneously on day 0 were subjected to artificial feeding and were killed on day 16. Crypt cellularity and DNA labeling index in isografts from AR, but not from mother-fed, rats increased significantly to levels found in in situ host jejunum of AR rats, indicating that humoral regulatory mechanisms are responsible for intestinal cell proliferation in AR pups. Radioimmunoassays of serum corticosterone, thyroxine, insulin, and gastrin and of gastric gastrin contents revealed that only serum corticosterone concentrations were significantly elevated, suggesting that corticosterone plays a critical role for intestinal growth. To examine this possibility directly, day 12 rats were adrenalectomized (ADX) and AR by continuous infusion of diets containing 0, 10, or 50 micrograms/ml corticosterone. Serum corticosterone concentrations paralleled the infused doses of corticosterone. Jejunal DNA labeling index increased in all ADX AR rats at day 13 in a dose-dependent manner. Increased jejunal DNA labeling index was maintained on day 14 in intact AR rats and ADX AR rats fed 10 micrograms/ml corticosterone but not in ADX AR rats receiving 0 or 50 micrograms/ml. We conclude that endogenous corticosterone is one of the systemic factors responsible for the adaptive increase in intestinal growth of AR rats.

Adrenalectomy↗
PubMed1986

Enhancement of parathyroid hormone-responsive renal cortical adenylate cyclase activity by a cytosol protein activator from rat reticulocytes.

The effects of the cytosol activator protein obtained from rat reticulocytes (RCAP) were investigated in a heterologous membrane system--partially purified cell membranes from dog renal cortex. RCAP enhanced the response of dog renal cortical adenylate cyclase to bovine parathyroid hormone (1-34) [bPTH (1-34)] from two- to three-fold. RCAP also enhanced the response to 5 microM arginine vasopressin, 10 microM glucagon, and 10 microM isoproterenol. Analysis of double-reciprocal plots of substrate concentration and enzyme activity indicated that bPTH (1-34) alone and together with RCAP increased the Vmax of the adenylate cyclase enzyme and did not alter the apparent Km of the enzyme for MgATP. Membranes from dog renal cortex contain 42K and 39K proteins that are ADP-ribosylated by cholera toxin and pertussis toxin, respectively, and appear to be the stimulatory (Ns) and inhibitory (Ni) guanine nucleotide binding proteins described in many other hormone-responsive membrane preparations. Similar to its effects in rat reticulocytes, RCAP inhibited ADP-ribosylation of Ns and enhanced ADP-ribosylation of Ni. The muscarinic agonist, carbachol, inhibited PTH-responsive adenylate cyclase activity in dog renal cortical membranes and this inhibition was reversed by RCAP. These results indicate that RCAP enhances stimulation of adenylate cyclase by a variety of hormones in a heterologous membrane preparation and supports the hypothesis that RCAP's site of action is common to all adenylate cyclase systems. RCAP may facilitate coupling between Ns and the catalytic unit of adenylate cyclase by a pertussis toxin-like effect to inactivate Ni. The dual effects of RCAP upon ADP-ribosylation of Ni and Ns alpha subunits suggest that a binding site for RCAP may exist at a site of homology between Ns alpha and Ni alpha.

Adenosine Diphosphate Ribose↗
PubMed1985

Cytosol activator protein from rat reticulocytes requires the stimulatory guanine nucleotide-binding protein for its actions on adenylate cyclase.

Rat reticulocytes contain a cytosol activator protein (RCAP) that augments catecholamine-sensitive adenylate cyclase activity in reticulocyte membranes. A highly purified preparation of RCAP, obtained by Sephacryl S-200 chromatography, was used to elucidate further its mechanism of action. The specific activity of the S-200 fraction to augment isoproterenol responsiveness was increased approximately 1,100-fold over the starting material, from 1.2 to 1,300 nmol cAMP formed per mg RCAP. The mol wt of RCAP is approximately 20,000. The effect of RCAP to enhance isoproterenol responsiveness was apparent within 20 sec, virtually abolishing the normal lag time of hormone-activated adenylate cyclase. In addition to its effects on catecholamine-responsive adenylate cyclase, RCAP significantly increased basal [21 +/- 3 (+/- SEM) to 41 +/- 4 pmol/mg protein X 30 min; P less than 0.02], guanyl-5'-yl-imidodiphosphate-associated (3173 +/- 213 to 4339 +/- 365 pmol/mg X 30 min; P less than 0.03), and fluoride-associated (5152 +/- 64 to 5807 +/- 58 pmol/mg X 30 min; P less than 0.05) adenylate cyclase activities. RCAP also altered the characteristics of agonist binding to the beta-adrenergic receptor of reticulocyte membranes, causing an increase in the apparent IC50 for isoproterenol from 0.7 +/- 0.2 to 7.9 +/- 1.6 microM (P less than 0.001). Similar to its effects on reticulocytes, RCAP enhanced isoproterenol- and prostaglandin E2-sensitive adenylate cyclase activity in the wild-type S49 lymphoma cell and shifted the binding isotherm for isoproterenol rightward. In cyc-, the mutant that lacks the stimulatory guanine nucleotide-binding protein (Ns) and in UNC, the mutant in which receptors are uncoupled from N, RCAP was ineffective. Moreover, RCAP decreased agonist affinity for the beta-adrenergic receptor in wild-type S49 cells, but not in cyc- or UNC cells. These observations suggest that RCAP requires a functional Ns unit for its effects on hormone-sensitive adenylate cyclase activity.

Adenylyl Cyclases↗
PubMed1985

Reticulocyte cytosol activator protein: effects on the stimulatory and inhibitory regulatory proteins of adenylate cyclase.

Rat reticulocytes contain a cytosol activator protein (RCAP) that augments hormone-sensitive adenylate cyclase activity in the rat reticulocyte and other systems. In a previous publication, using a highly purified preparation of RCAP, we reported that the stimulatory guanine nucleotide-binding protein (Ns) was required for the actions of RCAP. We investigated this possibility by studying the actions of RCAP on cholera toxin-dependent ADP ribosylation of Ns. RCAP decreased cholera toxin-dependent ADP ribosylation of the 42,000-dalton subunit of Ns of reticulocyte [40.2 +/- 3.7 (+/-SEM) to 26.5 +/- 3.8 fmol/mg; n = 10; P less than 0.001], S49 wild-type (33.9 +/- 2.4 to 24.9 +/- 2.8 fmol/mg; n = 9; P less than 0.01), and UNC (25.3 +/- 3.5 vs. 17.6 +/- 3.1; n = 5; P less than 0.02) membranes. In contrast, pertussis toxin-dependent ADP-ribosylation of the inhibitory guanine nucleotide binding protein, Ni in reticulocyte, S49 wild-type lymphoma, and its UNC and cyc- variant membranes were all significantly augmented by RCAP. Moreover, when reticulocyte Ni was functionally ablated by exposure to pertussis toxin, RCAP no longer enhanced isoproterenol-responsive adenylate cyclase activity in reticulocyte membranes. These results suggest that RCAP stimulates adenylate cyclase activity by inhibiting Ni function, thus permitting enhanced Ns coupling to the adenylate cyclase enzyme (C).

Adenosine Diphosphate Ribose↗
PubMed1984

Pulsatile administration of gonadotropin-releasing hormone for induction of ovulation.

Chronic pulsatile administration of gonadotropin-releasing hormone (GnRH) was used to induce ovulation in 12 women with various ovulatory disorders. In the first group of eight patients with normal to low baseline levels of gonadotropin, seven responded favorably to the treatment. Follicular maturation was observed in 57% of the treated cycles, and normal ovulatory cycles were induced in 24% of the patients. Two patients became pregnant. The intravenous route of administration was more effective than the subcutaneous one, possibly in response to the GnRH profile after each pulse. (The amplitude of GnRH peaks after an intravenous pulse was four times that seen after a subcutaneous one.) In contrast, follicular maturation and ovulation could not be induced in four women of a second group of patients with normal baseline levels of follicle-stimulating hormone but with high and frequent pulses of luteinizing hormone. The conclusion reached was that pulsatile administration of GnRH can be a new therapeutic tool in the treatment of ovulatory disorders in women who have an insufficient endogenous release of GnRH.

Adult↗
PubMed1984

Glutamic dehydrogenase from rat heart mitochondria. I. Purification and physical properties including molecular weight determination.

Glutamic dehydrogenase extracted with tris buffer from fresh freeze-thawed rat heart mitochondria was purified by ammonium sulphate fractionation, affinity chromatography on GTP agarose, hydroxyapatite chromatography and concentration using a molecular sieve. The final specific activity is 80 units/mg protein. Thin gel SDS electrophoresis of the purified enzyme preparation after reduction with dithiothreitol shows a major band with a molecular weight of 38 000 Daltons. Two minor bands are also present. Sucrose density gradient centrifugation reveals a molecular weight of 230 000 Daltons for unreduced mitochondrial GDH activity. By gel filtration rat heart mitochondrial glutamic dehydrogenase has a major peak at 230 000 Daltons, a minor peak at 300 000 Daltons and some larger molecular weight species. Rat liver mitochondrial glutamic dehydrogenase has a minor peak at 230 000, a major peak at 300 000 and some larger molecular weight species. The rat liver mitochondrial glutamic dehydrogenase predominance at 300 000 is unchanged by incubation, extraction and purification with rat heart mitochondria. The purified GDH is stable frozen at -10 degrees C in tris-HCl buffer with EDTA. It loses activity at 4 degrees C especially when stored in 0.2 M phosphate buffer. It also loses activity when dialyzed for 24 h. This loss of activity is not completely prevented by adding nucleotides to the buffer (AMP or ADP) but is decreased by their presence.

Animals↗
PubMed1984

Glutamic dehydrogenase from rat heart mitochondria. II. Kinetic characteristics.

Glutamic dehydrogenase purified from rat heart mitochondria has been characterized with regard to its substrate kinetics and the influence of nucleotides and potassium phosphate on its kinetic properties. The enzyme had characteristics similar to liver mitochondrial glutamic dehydrogenase. These included several double reciprocal plots which were biphasic, indicating homotropic interaction; inhibition by GTP, which was overcome by ADP and phosphate; and activity with both NAD(H) and NADP(H). There were a number of significant differences however, in the specific kinetic properties of heart mitochondrial glutamic dehydrogenase. The Vmax of reductive amination was four-fold greater with NADH than with NADPH. The maximum rate of oxidative deamination was ten-fold greater with NAD compared to NADP. The differences also included: saturating levels of NADH and NADPH were stimulatory rather than inhibitory; ammonia was stimulatory at millimolar levels; NADP and alpha-ketoglutarate were both inhibitory at saturating levels; and ADP increased reductive amination 30% at lower levels of NADH but inhibited at higher (stimulatory) levels of NADH.

Adenosine Diphosphate↗