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J H Clark

Publications and source records attributed to J H Clark.

At least 163 records · Page 9Linked to original sources
PubMed1983

Preliminary characterization of an endogenous inhibitor of [3H]estradiol binding in rat uterine nuclei.

The rat uterus contains two classes of specific nuclear estrogen-binding sites which may be involved in estrogen action. Type I sites represent the classical estrogen receptor (Kd = 1 nM) and type II sites (Kd = 10-20 nM) are stimulated in the nucleus by estrogen under conditions which cause uterine hyperplasia. Dilution of uterine nuclear fractions from estrogen treated rats prior to quantitation of estrogen binding sites by [3H]estradiol exchange results in an increase (3- to 4-fold) in the measurable quantities of the type II site. Estimates of type I sites are not affected by dilution. These increases in type II sites following nuclear dilution occur independently of protein concentration and result from the dilution of a specific endogeneous inhibitor of [3H]estradiol binding to these sites. The inhibitor activity is present in cytosol preparations from rat uterus, spleen, diaphragm, skeletal muscle, and serum. Preliminary characterization of the inhibitor activity by Sephadex G-25 chromatography shows two distinct peaks which are similar in molecular weight (300). These components (alpha and beta) can be separated on LH-20 chromatography since the beta-peak component is preferentially retained on this lipophilic resin. Partial purification of the LH-20 beta inhibitor component by high performance liquid chromatography and gas-liquid chromatography-mass spectrometric analysis suggests the putative inhibitor activity is not steroidal in nature and consists of two very similar phenanthrene-like molecules (molecular weights 302 and 304). Analysis of cytosol preparations on LH-20 chromatography shows that non-neoplastic tissues (uterus, liver, lactating mammary gland) contain both and inhibitor components whereas estrogen-induced rat mammary tumors contain very low to nonmeasurable quantities of the beta-peak inhibitor activity.

Animals↗
PubMed1983

Heterogeneity of estrogen binding sites in mammary tumors.

This paper provides a brief summary of our recent work on the heterogeneity of estradiol binding sites in mammary tumors of the mouse and human. Mammary tumors from both species contain the classical estrogen receptor and a second site(s) which we call type II. These type II sites are found in the cytoplasmic and nuclear compartments of both tumors, and can interfere with the measurement of estrogen receptors. The function of type II sites is not known; however, an assessment of these sites in conjunction with an accurate measurement of the estrogen receptor may provide a clearer picture of the true hormone dependence of breast tumors.

Animals↗
PubMed1983

The estrogenic effects of clomiphene during the neonatal period in the rat.

The ability of clomiphene and its isomers to cause estrogenic responses during the neonatal period in the rat was examined. Rats were injected s.c. with clomiphene (CL), zuclomiphene (ZUC) or enclomiphene (ENC) on days 1,3, and 5 of life and the stimulation of the reproductive tract and estrogen receptor binding was observed. Uterine weight and DNA content were increased significantly by day 7 in animals treated with clomiphene or zuclomiphene. Uterine epithelial hypertrophy was present in all groups by day 10 and hyperplasia was present in the animals treated with ZUC and CL. The time of vaginal opening was greatly accelerated in all drug treated groups with the earliest day of opening occurring on day 7. Ovarian hemorrhage and blood in the periovarian sac occurred between days 12-14 and continued to be present through day 25. Drug treatment caused the estrogen receptor to accumulate in the nuclear fraction of the uterus and to be depleted from the cytosol fraction. We conclude that clomiphene administered to neonatal rats causes estrogenic stimulation of the reproductive tract in a fashion similar to other estrogens. This stimulation may account for the reproductive tract abnormalities which develop in rats treated with those drugs during the neonatal period.

Animals↗
PubMed1983

Stimulation of vaginal growth and cornification in the absence of estrogen or nuclear binding of the estrogen receptor.

Mechanical stimulation of the vagina in ovariectomized rats results in vaginal epithelial proliferation and cornification which is identical to that seen with estradiol benzoate treatment. The estrogen receptor is localized primarily in the cytosol of mechanically stimulated vaginae, whereas, after estradiol benzoate treatment, the receptor is found in the nuclear compartment. Thus, it is possible to obtain a biological response ordinarily controlled by estrogen without the involvement of either the hormone or its receptor.

Adrenalectomy↗
PubMed1983

Consequences of UMP synthase deficiency in cattle.

Several dairy cows have been identified as partially deficient in UMP synthase. Although erythrocytes of normal cows contained 2.54 units of enzyme per ml, four cows were discovered with only 1.08 units per ml. Cows deficient in UMP synthase secreted milk with abnormally high levels of orotate, 300-1,000 micrograms of orotate per ml compared to 80 micrograms/ml for normal cows. The deficiency also was accompanied by a lactation-induced orotic aciduria. Although bovine urinary orotate was generally less than 10 micrograms/ml, the urine of the deficient cows, when lactating, contained 20-200 micrograms/ml. Their plasma orotate also was elevated. Genetic transmission of the condition was suggested by a common bull in the pedigrees of all deficient animals. Indeed, these cows, with half the normal level of UMP synthase, are probably heterozygotes with a 50% chance of passing the deficient allele to their progeny. For these putative heterozygotes, the condition is apparently benign because longevity and production were unaffected. However, the existence of a gene for UMP synthase deficiency in the dairy cow population poses a hazard with respect to the conception of homozygotic, deficient animals. These, in analogy with a comparable human condition, would be expected to exhibit high perinatal morbidity and mortality.

Aging↗
PubMed1983

Characterization of a triphenylethylene-antiestrogen-binding site on rat serum low density lipoprotein.

Several laboratories have reported the presence of an intracellular, high affinity [dissociation constant (Kd), 1-2 nM] antiestrogen-specific binding site in estrogen target tissues. In this report, we describe the binding properties and characteristics of an additional triphenylethylene antiestrogen-binding site in the serum of rats. By using saturation and competitive binding analyses with [3H]tamoxifen as the radio-labeled ligand, we have determined that rat serum contains a relatively high affinity (Kd, 28 nM), protease-sensitive binding site that is specific for antiestrogens of the triphenylethylene type (clomiphene and nafoxidine). Since this serum site has little affinity for the benzythiophene antiestrogens (LY 117018 and 156758), we have chosen the name of triphenylethylene-antiestrogen binding site (TABS). The concentration of serum TABS (picomoles of [3H]tamoxifen bound per ml serum) is roughly the same in males and females but is significantly greater in both sexes at days 5, 10, and 15 of age (400-500 pmol/ml) than in newborn or adult animals (100-200 pmol/ml). Preliminary characterization studies indicated that the serum TABS is probably a serum lipoprotein. Separation of rat serum lipoproteins on potassium bromide density gradients revealed that the serum TABS migrated with rat low density lipoprotein (LDL). Furthermore, rat LDL purified by density gradient centrifugation has an affinity and specificity for [3H]tamoxifen that is similar to the TABS found in whole serum. In contrast, the rat liver intracellular TABS does not have these density gradient characteristics. These data suggest that the rat serum TABS is LDL; however, the role of this serum lipoprotein in the mechanism of action of antiestrogens remains to be determined.

Animals↗
PubMed1983

Estrogenic stimulation of the antiestrogen specific binding site in rat uterus and liver.

Tamoxifen and other antiestrogens bind to the estrogen receptor and to a specific antiestrogen binding site (AEBS). We have confirmed the existence of an AEBS by saturation and competitive binding analyses with [3H]tamoxifen as the radiolabeled ligand. The quantities of AEBS (pmol/g tissue) present in a low speed cytosol (25,000 X g X 30 min) of the liver and uterus vary with species and physiological state: liver, mature female rat, 82.7 +/- 6.7; ovariectomized mature rat, 46.1 +/- 2.9; immature female rat, 40.0 +/- 1.8; mature male rat, 57.3 +/- 2.7; and mature female mouse, 63.0 +/- 5.0; uterus, mature rat, 17.9 +/- 1.7; ovariectomized mature rat, 13.3 +/- 0.5; immature rat, 8.2 +/- 0.8; and mature mouse, 49.0 +/- 2.1. The dissociation constants did not differ significantly in any of the cases and were 1.5 and 2.5 nM for the liver and uterus, respectively. Developmental studies demonstrated that the liver AEBS gradually increases in both sexes from 21.0 pmol/g at birth to their respective adult levels with the only divergence occurring approximately at the time of puberty. The AEBS concentration also varied with the stage of the estrous cycle [highest at estrus (20.6 +/- 1.8) and metestrus (91.7 +/- 5.9) for the uterus and liver, respectively, and lowest at diestrus (uterus, 15.9 +/- 0.2; liver, 60.2 +/- 4.1)]. Furthermore, estradiol treatment of ovariectomized rats significantly increased both liver and uterine AEBS levels, whereas tamoxifen increased uterine AEBS concentration although having no significant effect on the level of these sites in liver. These results demonstrate the presence of a cytosolic AEBS in the liver and uterus which is distinct from the estrogen receptor and appears to be under estrogenic regulation.

Animals↗
PubMed1983

An endogenous ligand for the triphenylethylene antiestrogen binding site.

We have isolated an endogenous ligand which acts as a competitive inhibitor of the binding of 3H-tamoxifen to triphenylethylene antiestrogen-binding sites (TABS) prepared from liver and from serum low density lipoproteins (LDL). This ligand is present in boiled ethanol extracts of rat liver and may represent an "endogenous antiestrogen". "Endogenous antiestrogen" is used here as an operational term, since it has not been shown that TABS are involved in the mechanism of action of the triphenylethylene antiestrogens.

Animals↗
PubMed1983

Future improvement of milk production; potential for nutritional improvement.

Milk production/cow has increased so dramatically in the past 30 yr that some people question the wisdom of attempting to further increase milk production for fear we will shorten the lives of our dairy cows. What is the limit to milk production? At least two cows have produced over 22,000 kg of milk in a single lactation and numerous cows consistently produce 9,000 to 14,000 kg of milk/lactation. Therefore, it is evident that there is room for great progress, but it is not possible to predict the limits to milk production by the cow because we cannot see beyond the horizon to tell us what lies ahead. However, we know that nothing in sight appears to be an obstacle to further progress.

Amino Acids↗
PubMed1983

Effectiveness of acetic acid and formaldehyde for preventing protein degradation in the rumen.

Six rumen cannulated steers were in a replicated 3 X 3 Latin square arrangement to investigate degradability in the rumen of dry matter and crude protein from soybean meal that was untreated or treated with either 8% acetic acid or .3% formaldehyde. Polyester bags containing the soybean meals were suspended in the rumen of each steer and removed after 1, 2, 4, 8, 12, 16, and 24 h to calculate degradation rates. Soybean meals remaining in the polyester bags after 12 h of rumen exposure were collected and referred to as residues. Postruminal digestion was stimulated by incubating 200 mg of soybean meal residues with pepsin and pancreatin. Formaldehyde treatment of soybean meal was more effective than acetic acid treatment in preventing ruminal degradation of dry matter and crude protein under these experimental conditions. However, soybean meal treated with acetic acid and remaining in polyester bags after 12 h of ruminal exposure released a larger quantity of alpha-amino nitrogen during in vitro incubation with pepsin and pancreatin than did residue of soybean meal treated with formaldehyde. Acetic acid may prove to be an effective agent for increasing the supply of absorbable dietary amino acids.

Acetates↗
PubMed1983

Effects of formaldehyde treated soybean meal on milk yield, milk composition, and nutrient digestibility in the dairy cow.

The nutritional value of soybean meal that had been treated with formaldehyde (.3 g/100 g) to inhibit microbial degradation of soybean meal protein in the rumen was investigated. Four experimental diets were fed ad libitum during wk 4 to 43 of lactation to Holstein cows randomly assigned to diets in a 2 x 2 factorial arrangement of dietary crude protein (12 and 14%) and formaldehyde treatment (untreated and treated soybean meal). Concentrate, corn silage, and alfalfa-grass hay provided 53.0, 35.4, and 11.6% of the daily intake of dry matter. Analysis of covariance revealed that digestibility of dietary crude protein by cows fed formaldehyde treated soybean meal was lower than by cows fed untreated soybean meal (62.4 versus 65.4%). Similar quantities of milk, 4% fat-corrected milk, milk fat, and milk solids-not-fat (overall means of 7998, 7402, 281, and 660 kg/301 days of lactation) were produced by cows fed different diets. This was true whether the data were summarized during peak production (day 22 to 63), during days 22 to 119 when crude protein intake did not meet requirements, or during the complete experiment (days 22 to 301 of lactation). Milk protein (total nitrogen x 6.38) produced by cows fed soybean meal treated with formaldehyde was less than by cows fed untreated soybean meal during days 22 to 63 and during days 22 to 119 (47 versus 44 kg/cow and 103 versus 97 kg/cow). Changes in body weight of cows during lactation were similar among treatments. Treating soybean meal with .3 g formaldehyde/100 g may decrease availability of soybean meal protein for use by lactating dairy cows.

Ammonia↗
PubMed1983

Effects of combination estrogen:cyclophosphamide treatment on the growth of the MXT transplantable mammary tumor in the mouse.

The present studies were done to determine if the growth-promoting properties of estrogen on the MXT transplantable mammary tumor in the mouse would enhance the cytotoxicity of cyclophosphamide. Mice bearing these tumors had beeswax pellets implanted which contained 17 beta-estradiol (0.01 to 1.0 mg/pellet) and/or injected twice weekly with cyclophosphamide (10 to 40 mg/kg body weight in sesame oil) for 4 to 7 weeks. During this time, tumor size [(L + W)/2] and body weights were monitored every 7 to 14 days. The results show that administration of estradiol (0.01 to 1.0 mg/pellet) by implant slightly stimulated tumor growth, and in no case was tumor regression observed in response to the steroid. Likewise, cyclophosphamide treatment alone (10 to 20 mg/kg) failed to inhibit the tumor; however, combined administration of estradiol plus cyclophosphamide (10 to 40 mg/kg) resulted in significant inhibition of tumor growth. This response was time and dose dependent. These results show that while neither compound alone inhibited tumor growth, estradiol and cyclophosphamide are synergistic and completely block the growth of this transplantable mammary tumor in the mouse. The mechanism for this antagonism of mammary tumor growth remains to be resolved; however, we speculate that estradiol stimulates cellular hypertrophy and hyperplasia in these tumors, and under these conditions the cytotoxic effectiveness of cyclophosphamide is enhanced.

Animals↗
PubMed1982

Effects of estradiol-17 alpha on nuclear occupancy of the estrogen receptor, stimulation of nuclear type II sites and uterine growth.

Estriol and estradiol-17 alpha (E2-17 alpha) have classically been described as weak or impeded estrogens since they are incapable of stimulating true uterine growth when administered acutely by single injection. We have demonstrated [16] that estriol is capable of stimulating true uterine growth when the hormone is administered by paraffin implant. The possibility that E2-17 alpha is similar to estriol was examined. A single injection of E2-17 alpha causes a rapid accumulation of the estrogen receptor in uterine nuclei and this is correlated with the stimulation of early uterotropic responses. The nuclear receptor content declines rapidly and no stimulation of nuclear type II sites or true uterine growth is observed. E2-17 alpha does however stimulate the replenishment of cytoplasmic estrogen receptor. This receptor-response profile is typical of a short acting estrogen such as estriol. Chronic exposure (96 h) of mature-ovariectomized rats to estradiol-17 alpha (4 mg) by beeswax implant results in continual nuclear occupancy by estrogen receptors, dramatic stimulation of nuclear type II sites and true uterine growth. It is not possible to determine whether the uterotropic stimulation was due to direct effects of E2-17 alpha since this isomer was partially metabolized to E2-17 beta and both isomers were found in uterine nuclei after an implant of E2-17 alpha. We conclude that E2-17 alpha is capable of acting as an estrogen, either by its inherent estrogenicity or by its conversion to E2-17 beta, and that it may be dangerous to consider this steroid to be an ineffective or inadequate estrogen.

Animals↗
PubMed1982

Estimation of the proportion of non-ammonia-nitrogen reaching the lower gut of the ruminant derived from bacterial and protozoal nitrogen.

1. A method for estimating the proportions of bacterial- and protozoal-N in the total non-ammonia-N reaching the lower gut of the ruminant under steady-state conditions was evaluated. Three trials using two different diets were conducted with a Holstein steer equipped with a rumen cannula and duodenal re-entrant cannulas. 2. An intraruminal primed infusion of (15NH4)2SO4 was administered for 68 h during each trial. Bacteria and protozoa samples were isolated from rumen fluid at approximately 6 h intervals during each infusion period. Total non-ammonia-N was isolated from duodenal digesta samples taken at approximately the same times. All of these samples were analysed for 15N enrichment. A computer program was used to fit equations to the 15N-enrichment curves of bacterial- and protozoal-N. Models of both bacterial- and protozoal-N kinetics consisted of a small pool which equilibrated rapidly with rumen NH3 and a large pool with a fractional turnover rate of 0.045-0.070/h for bacterial-N and 0.056-0.069/h for protozoal-N. 3. Abomasal fluid turnover was estimated by a single injection of polyethylene glycol (molecular weight 4000) into the rumen followed by sampling of rumen fluid and duodenal digesta. 4. Estimates of abomasal fluid turnover, bacterial-N turnover, and protozoal-N turnover were entered into an equation which was adjusted by computer iteration to fit the 15N-enrichment curve of duodenal digesta non-NH3-N generated from each (15NH4)2SO4 infusion period. The computer fit of this equation to the observed results gave estimates of 0:39-0.45 and 0.22-0.41 for the proportion of duodenal non-NH3-N derived from bacterial-N and protozoal-N respectively. 5. This method is potentially useful in estimating microbial protein passage to the lower gut in ruminants. Sampling digesta from the omasum rather than the duodenum would simplify the method and possibly increase the reliability of the estimates.

Abomasum↗
PubMed1982

Rare earth elements as markers for rate of passage measurements of individual feedstuffs through the digestive tract of ruminants.

Rumen and in vitro abomasal fluid incubations of four feeds, soybean meal (SBM), 0.3% formaldehyde-treated SBM, cottonseed meal and ground corn, each labeled with one of two markers (Sm and La) were conducted to estimate the extent of marker movement from the feeds. Feeds were marked by spraying acidic solutions of the marker movement from the feeds. Feeds were marked by spraying acidic solutions of the markers uniformly over the feeds. Concentration of marker on the feeds, on the feed residues remaining in polyester bags after 12 hours of incubation in the rumen, and on the feed residues after 12 hours of incubation in the rumen and 3 hours of in vitro incubation in abomasal fluid were determined by neutron activation. Initial concentration of the markers on the feeds was used as a covariable in analysis of the restricted randomized block design. Marker concentration of Sm and La, for all feeds, averaged 1115 +/- 44 and 1503 +/- 44 ppm after the rumen incubation and 959 +/- 54 and 1666 +/- 54 ppm after the combined incubations and differed (P less than 0.01) from the mean initial marker concentration of 1294 +/- 42 ppm. Abomasal incubations allowed estimation of marker movement (contamination) between bags. For both markers, increases (P less than 0.01) were observed in marker contamination when compared to initial levels. Marker contamination increased from 2.5 +/- 0.8 to 20.1 +/- 0.1 and 10.7 +/- 0.8 ppm for Sm and La, respectively. Data indicate significant marker movement and suggest that Sm and La, when applied to feeds by this method, are not suitable markers for estimating passage rates of individual feedstuffs.

Abomasum↗