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J H Clark

Publications and source records attributed to J H Clark.

At least 253 records · Page 14Linked to original sources
PubMed1976

RNA polymerase activity and uterine growth: Differential stimulation by estradiol, estriol, and nafoxidine.

We have shown previously that estradiol, estriol, and Nafoxidine (Upjohn 11, 100A) have differential effects on uterine growth and that these effects are associated with the retention of the estrogen receptor by the nucleus. In order to examine these relationships further, we have studied the effect of these hormones on endogenous nuclear RNA polymerase I and II in the immature rat uterus. All three compounds caused a rapid elevation in polymerase II activity that reached a peak by the first hour and declined to almost control levels by 2 h after the injection. This transient peak in polymerase II activity was followed by a second elevation by the fourth hour in estradiol- and Nafoxidine-treated animals which was not observed in estriol-treated rats. The activity of polymerase I increased monotonically to very high levels by 4 h and was maintained 12 h or longer in estradiol- and Nafoxidine-treated animals. A similar elevation was observed in estriol-treated rats but the activity declined very rapidly to control levels by 12 h. The second elevation in polymerase II activity and the sustained stimulation of polymerase I activity were correlated with the stimulation of true uterine growth. These data confirm our previous suggestion that long-term nuclear retention of the receptor is a requirement for true uterine growth and suggest that an obligatory response in the production of true growth is the stimulation of a second rise in polymerase II activity and an elevated and sustained activity of polymerase I.

Aging↗
PubMed1976

Effect of estrogen on gene expression in the chick oviduct. Correlation between nuclear-bound estrogen receptor and chromatin initiation site for transcription.

The [3H]estradiol exchange assay was used to characterize the nuclear estrogen receptor from the chick oviduct. After diethylstilibestrol (DES) treatment (14 days), the oviduct nuclei contained estrogen receptors that manifested high affinity (Kd = 2 X 10(-9)M) and low capacity binding (4000 to 5000 sites/cell) for estradiol. DES and estradiol competed significantly for [3H]estradiol binding, while testosterone and progesterone were ineffective. These binding sites were found in the oviduct and liver but not in the spleen, kidney, or muscle. Following salt extraction from nuclei, the receptor had a sedimentation coefficient of 4 S when analyzed by centrifugation in high and low salt sucrose density gradients. The [3H]estradiol exchange assay was used to examine the relationships between nuclear-bound receptor and RNA polymerase initiation sites on oviduct chromatin. Within 20 min after a single injection of 2.5 mg of DES to withdrawn chicks, a maximum number of estradiol receptor-binding sites was detected in oviduct nuclei. Within 30 min after DES injection, the total number of RNA initiation sites also increased, reaching 100% of control values. Daily injections of DES to unstimulated chicks resulted in a gradual increase in the nuclear content of estradiol receptor, which reached a maximum at 6 days and thereafter declined gradually up to 18 days of hormone treatment. A maximum number of initiation sites for RNA synthesis was also attained at 4 to 6 days of DES treatment and thereafter declined. When DES was withdrawn after 14 to 18 days of hormone stimulation, the numbers of nuclear estradiol receptor sites and initiation sites for RNA synthesis both declined gradually, reaching half-maximal values in 3 days and approached control values after 7 to 8 days of withdrawal. The increase in the concentration of nuclear estradiol receptor sites and the number of initiation sites for RNA synthesis also showed a close correlation with the dosage of DES administration. Both attained maximum levels at 1.25 mg of DES with a half-maximal value of 0.5 mg. The close correlation between the concentration of nuclear-bound estradiol receptors and the number of initiation sites for RNA synthesis in vivo is at present only a temporal correlation but does raise the possibility that gene transcription in chick oviduct may depend upon the amount of estradiol receptor bound to the target cell nuclei.

Animals↗
PubMed1976

Estrogen-receptor binding: relationship to estrogen-induced responses.

The relationship between nuclear binding of the receptor-estrogen complex (R-E) and estrogenic responses was examined. Nuclear-bound R-E was measured by the [3H] estradiol exchange assay, which permits the quantification of R-E as a function of either endogenous or non labeled estrogen. The quantity of nuclear R-E fluctuated as a function of blood levels of estrogen during the estrous cycle in the rat. This indicates that the accumulation of the R-E complex by the nucleus of uterine cells may be of physiologic significance and under the control of endogenous estrogen.

Animals↗
PubMed1976

Control of uterine estrogen receptor levels by progesterone.

The mechanism by which progesterone antagonizes estrogenic stimulation of uterine growth was examined in the immature rat. Rats received daily injections of 2.5 mug estradiol (E) for 2 days and on day 3 either 2.5 mug E or 2.5 mug E plus 2.5 mg of progesterone (P). The quantity of nuclear and cytoplasmic estrogen receptor was determined by [3H]estradiol exchange at various intervals after injection of E or E + P. In both groups, nuclear receptor estrogen complex (RnE) increased dramtically one hour after injection and showed a gradual decline from 4 to 24 h after injection. The quantity of cytoplasmic receptor, Rc, decreased to low levels by one hour and began a gradual increase from 4 to 8 h in both groups. However, between 8 and 24 h after injection, the level of Rc continued to increase in the E treatment group (2.39 +/- 0.21 pmol/uterus at 24 h) but remained at the 8 h level in the E + P group (1.09 +/- 0.04 pmol/uterus at 24 h). This observation suggests that two seperate processes are involved in the replenishment of Rc and that progesterone inhibits the second phase of replenishment. The binding affinity and specificity of Rc for estrogens following E + P pretreatment were identical to those of the E pretreatment group. Therefore, P does not alter the binding properties but rather the intrauterine level of Rc. Treatment with E on day 4, when Rc levels differ between E and E + P groups, stimulated uterine weight and protein content on day 5 in the E pretreatment group. However, minimal stimulation was observed in the E + P pretreatment group. The quantity of RnE and the time of nuclear retention of RnE following E injection on day 4 was greater in the E group than in the E + P group. The effect of progesterone on Rc replenishment was dose-dependent (range, 0.1-2.5 mg; 1/2 maximal, 0.5 mg). Injection of testosterone propionate (1.0 mg), a weak estrogen antagonist, with E on day 3 resulted in slightly reduced levels of Rc on day 4. This reduction also correlated with a reduced sensitivity to treatment with E on day 4. These data, together with previous studies from our laboratory, suggest that progesterone and other estrogen antagonists such as nafoxidine and testosterone propionate inhibit estrogen action by interfering with the replenishment of Rc, thereby reducing the number of receptor estrogen complexes that are translocated and retained by uterine nuclei.

Animals↗
PubMed1976

Cellular gluconeogenesis by lactating bovine mammary tissue.

The gluconeogenic capacity of mammary tissue of lactating cow was investigated by incubating mammary tissue slices with alanine, glutamate, lactate, pyruvate, or glycerol in conjunction with acetate and glucose (10mM or 1 mM). In no case was any substrate incorporated into glucose per se. In lactose synthesis, glucose was the major source of carbon although glycerol also was incorporated into lactose. Alanine, glutamate, lactate, or pyruvate were not incorporated into lactose at optimum (10 mM) or suboptimum (1 mM) concentrations of glucose. Activity of glucose-6-phosphatase was negligible in mammary tissue, less than 1% of the activity in liver or kidney tissue from the same cows. Pyruvate carboxylase, phosphoenolpyruvate carboxykinase, and fructose-1,6-diphosphatase were in cow mammary tissue, but the activities were lower than in liver. Gluconeogenic substrates were not converted to glucose regardless of whether the incubation contained an optimum (10 mM) or a suboptimum (1 mM) glucose concentration. Consistent with the inability of cow mammary tissue to convert gluconeogenic metabolites to glucose is the virtual absence of glucose-6-phosphatase and the lack of excess gluconeogenic substrates available to the intact mammary gland of lactating cow.

Animals↗
PubMed1976

Effect of sampling location, time, and method of concentration of ammonia nitrogen in rumen fluid.

In experiment 1, rumen fluid samples were obtained from dorsal, midpoint, and ventral regions of the rumen of rumenfistulated dairy cows at hourly intervals for 24 h. Dorsal, midpoint, and ventral rumen fluid samples contained 16.1, 14.2, and 12.1 mg/100 ml of ammonia nitrogen. Time after feeding resulted in differences in the concentration of ammonia in rumen fluid with the greatest concentration 30 to 90 min postfeeding. The concentration of ammonia nitrogen was greater for cows fed a high-concentrate diet (14.7% crude protein, 86% concentrate) than for cows receiving a normal diet (15.1% crude protein, 42% concentrate), 15.2 versus 13.1 mg/100 ml. In a second experiment, rumen fluid samples were obtained immediately before feeding and at 1 and 6 h postfeeding by stomach tube and from dorsal, midpoint, ventral, and mixed rumen contents via a rumen cannula. Concentrations of ammonia nitrogen (mg/100 ml) in the respective rumen fluid samples were 14.3, 23.0, 18.3, 17.2, and 19.6. Location of sampling, method of sampling, time of sampling, type of diet, and rumen fluid volume are factors that affect the concentration of ammonia nitrogen in rumen fluid.

Ammonia↗
PubMed1975

Effects of estrogen on gene expression in chick oviduct: nuclear receptor levels and initiation of transcription.

Estrogen (diethylstilbesterol) was administered in vivo to chicks for various time periods. Chromatin was then prepared from oviduct nuclei and assayed for its capacity to support initiation of RNA chain synthesis in vitro in the presence of saturating levels of Escherichia coli RNA polymerase (RNA nucleotidyltransferase; nucleosidetriphosphate:RNA nucleotidyltransferase; EC 2.7.7.6). These same nuclei were also assayed by a [3H]estradiol exchange assay for their endogenous receptor content. The number of available initiation sites for RNA synthesis on chromatin was shown to correlate with the endogenous levels of nuclear estrogen receptor. A decrease in the nuclear concentration of estrogen receptor molecules and the concentration of initiation sites for RNA synthesis occurred during withdrawal of estrogen from previously stimulated chicks. Both parameters declined with a similar half-life. When estrogen was readministered to withdrawn chicks, the number of initiation sites increased 2-fold as early as 30 min and approached a maximal level (3-fold) by 1 hr. During the same period of restimulation with estrogen, the number of estrogen receptor molecules bound to nuclei increased to a maximum at 20 min and then declined at 1 hr to a steady-state level 2-fold higher than the withdrawn chicks. Simultaneous measurements of RNA chain length and RNA chain propagation rate demonstrated that parameters remained relatively constant throughout estrogen withdrawal as well as secondary stimulation. The temporal correlation between changes in the levels of nuclear-bound estrogen receptor and the number of RNA chain initiation sites on chromatin prepared from these same nuclei strongly suggested that the hormone receptor complexes act on chromatin to mediate these changes in genetic transcriptional activity.

Animals↗
PubMed1975

Milk production and nitrogen utilization in response to postruminal infusion of sodium caseinate in lactating cows.

Five lactating, rumen-fistulated Holstein cows were used to obtain additional information concerning the effects of postruminal infusion of sodium caseinate on milk production and amino acid utilization. A 7-day continuous abomasal infusion of approximately 450 g/day of sodium caseinate was preceded and followed by 7-day infusions of an isonitrogenous-isocaloric solution of glucose, monosodium glutamate, and urea. Total collections of milk, urine, and feces were obtained during the last 5 days of each infusion period. On the last day of each period, arterial and mammary venous blood samples were obtained for analysis of plasma free amino acids. During infusion of sodium caseinate, milk production, milk protein (N times 6.38) production, and efficiency of nitrogen utilization for milk crude protein production were increased. Arterial plasma concentrations of free histidine, isoleucine, phenylalanine, valine, and total essential amino acids were elevated above control levels during infusion of sodium caseinate, while ornithine and tryrosine were decreased. Calculation of the relative concentration of essential amino acids in arterial plasma and in milk protein indicated that methionine and lysine were least abundant in plasma relative to their requirement for milk protein synthesis. A high precentage extraction from arterial plasma by the mammary gland also suggested that methionine and lysine may have been the essential amino acids in most critical supply for milk protein synthesis. Calculation of uptake to output ratios of individual plasma amino acids by the mammary gland suggested that significant quantities of extracted arginine, isoleucine, leucine, threonine, and valine were utilized in pathways other than direct incorporation into milk protein.

Amino Acids↗
PubMed1975

A survey of asthma mortality in patients between ages 35 and 64 in the Greater London hospitals in 1971.

We have examined the death certificates from all patients aged 35-64 years who were recorded as dying from asthma in Greater London Council hospitals in 1971. Of the 47 death certificates studied, nine suggested that the primary cause of death was not asthma. From the remaining 38 deaths we have obtained 36 case records and found that 15 deaths occurred outside hospital and another two patients died in hospital having been admitted in a stable state. We have examined the remaining 19 case records to find out the circumstances of death in patients with asthma who die in hospital. We have been unable to exclude the possibility that many of the deaths in hospital were avoidable. Assessment of severity in most patients was incomplete, as judged by a retrospective analysis of case records, and many of the patients would be regarded as having had insufficient treatment. Four patients did not receive corticosteroids and in a further three the dose given was small. No physiological assessment of airflow obstruction was made in over half the patients. A comparison with 19 survivors of an admission to hospital with asthma did not provide enough information to account for the deaths. The survivors were in hospital for a shorter period of time, were slightly less ill, and were given comparable treatment regimens. Both groups of patients were inadequately assessed, and sedatives were given to approximately 70% of all subjects studied. The deaths in hospital usually occurred suddenly in the early morning in general medical wards.

Adrenocorticotropic Hormone↗
PubMed1975

Estrogen-induced uterine responses and growth: relationship to receptor estrogen binding by uterine nuclei.

The relationship between estrogen receptor(R) binding by uterine nuclei and uterotrophic responses was examined. Immature rats received a single injection of estradiol (E2) or estriol (E3) and the following parameters were measured: accumulation and retention of the estrogen receptor by the nuceus of uterine cells; incorporation of 14C-glucose into CO2 lipid, protein and RNA; RNA polymerase activity; water imbibition and increased dry weight. E2 and E3 were of equal potency with regard to the rapid accumulation of R by the nucleus but differed with respect to long term retention of R. The concentrations of nuclear RE2 and RE3 complexes were equivalent between 1 and 3 hr after estrogen injection; however, by 6 hr RE2 remained significantly elevated while RE3 levels had fallen to control values. E2 and E3 were also of equal potency with respect to the stimulation of enhanced glucose utilization, water imbibition, the incorporation of 14C-glucose into lipid, protein and RNA 3 hours following an injection of the hormone. Likewise the activity of RNA polymerase was equally stimulated by E2 and E3 3 hr after injection. Thus all early uterotropic responses (0-3 hrs) that were measured were equally stimulated by E2 and E3. However, E3 failed to stimulate true uterine growth (increase dry weight 24 hr after injection), whereas E2 produced a significant stimulation of true uterine growth. These data suggest that the RE complex is capable of stimulating early uterotrohic events regardless of which estrogen is present; however, in order to produce true uterine growth the RE complex must be retained in the nucleus for long periods of time. This proposal was tested by the administration of repetitive injections of E3. This treatment resulted in an increase in dry weight that was equivalent to the growth that was produced by repetitive injections of E2. These results demonstrate that E2 and E3 elicit early uterotrophic responses with equal facility following a single injection but that only E2 causes true uterine growth. The ability of E2 to stimulate true uterine growth appears to be related to the time of residence of the RE complex in the nucleus.

Animals↗
PubMed1975

Lactational responses to postruminal administration of proteins and amino acids.

Rumen by-pass of nutrients has improved performance of lactating dairy cows, growing stepers, and sheep. Postruminal supplementation of casein has increased milk production 1 to 4 kg per cow per day and milk protein yield by 10 to 15%. Component(s) in casein eliciting the improved performance have not been determined adequately. Glucose, amino acids, hormone secretion, or a combination of these factors may be responsible for the improved performance. Future research to delineate limiting nutrients for postruminal supplementation should prove fruitful and should make a major contribution to improved production by ruminant animals.

Abomasum↗
PubMed1975

Metabolism of arginine and ornithine in the cow and rabbit mammary tissue.

Amino acid uptake by the bovine mammary gland was determined by arteriovenous difference. Extraction of arginine from the plasma by the lactating bovine mammary gland was in excess of requirements for milk protein synthesis. Ornithine and citrulline also were extracted by the gland but are not in milk protein. Incubations of slices of lactating mammary tissue from cows and rabbits indicate that nonessential amino acids, especially proline and glutamate, are the major end products of arginine and ornithine metabolism in the lactating mammary gland.

Abdomen↗
PubMed1975

Hormone dependence and estradiol receptors in the D series of mammary nodule outgrowth lines and tumors.

Preneoplastic mammary nodule outgrowth lines were examined for their ability to grow and produce tumors in ovariectomized BALB/c mice. In addition, these nodule outgrowth lines and tumors derived from them were investigated for cytoplasmic estrogen receptor proteins by qualitative and quantitative techniques. Early ovariectomy, performed within 4 weeks after transplantation, slightly delayed but did not permanently block the ability of three different nodule lines to completely fill the fat pad with nodule tissue. Ovariectomy performed later than 4 weeks after transplantation or adrenalectomy performed early or late had no effect on nodule growth. Neither early nor late ovariectomy or adrenalectomy had an effect on the maintenance of the nodule alveolar phenotype. Ovariectomy performed 3 weeks after transplantation had little effect on the tumor potential of the low oncogenic line D1 or the high oncogenic line D2. Samples of nodule outgrowths transplanted from ovariectomized mice responded to a chemical carcinogen in a similar manner, as did nodule outgrowths transplanted from control experiments. Thus, the altered hormonal environmenment in ovariectomized mice apparently did not select for subpopulations of nodule cells with altered tumorigenic potentials. The ovarian independence of the nodule lines and tumors derived from them was correlated with a very low level of cytoplasmic estrogen receptor. These results, along with other data, illustrate the nature of the independence on ovarian hormonal control for tumorigenesis in these mammary tumor virus-free nodule lines.

9,10-Dimethyl-1,2-benzanthracene↗