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Biomedical subjects

C O Parkes

Publications and source records attributed to C O Parkes.

At least 19 recordsLinked to original sources
PubMed1986

Effects of suppression and resumption of shell formation and parathyroid hormone on uterine calcium-binding protein, carbonic anhydrase activity, and intestinal calcium absorption in hens.

The calcium absorption and duodenal and uterine vitamin D-dependent calcium-binding protein (CaBP-28K) levels were decreased in hens when eggshell calcification was suppressed by premature expulsion of the egg. Nevertheless, these levels remained higher than those of immature pullets or pullets treated with estrogen. The resumption of shell formation by hens which had previously laid soft-shell eggs was associated during calcification of the first egg with increases in intestinal Ca absorption. CaBP concentration, and alkaline phosphatase activity. The increase in uterine CaBP concentration preceded the stage of rapid calcium deposition. Uterine carbonic anhydrase activity was increased by sexual maturity but not consistently by shell formation. Ablation of the parathyroids just before the resumption of shell formation suppressed the increases in duodenal calcium absorption and CaBP concentration elicited by egg calcification. In contrast, the increase in CaBP level was maintained in the uterus of parathyroidectomized hens, in spite of the decreased shell deposition. Previous studies indicated that increased uterine CaBP associated with eggshell calcification is not elicited by vitamin D. The present study confirms this observation and also shows that these changes are not elicited by either PTH or sex steroid hormones.

Animals↗
PubMed1986

Thyroid state and cholecalcin (calcium-binding protein) in cerebellum of the developing rat.

Cholecalcin (28,000 Da, vitamin D-dependent calcium-binding protein) is a marker of Purkinje cell development in the rat cerebellum from embryonic day 17 when these cells can first be distinguished. Specific antibodies raised against human cerebellar or rat renal cholecalcin were used in an immunocytochemical and quantitative study in altered thyroid states. The immunocytochemical staining was qualitatively similar in both normal and hypothyroid animals but clearly demonstrated the slowing of Purkinje cell development resulting from the lack of thyroxine. This effect was also reflected in quantitative studies which showed that the total cholecalcin per cerebellum was lower in thyroid-deficient rats. However, there was, in these animals, no specific reduction in cholecalcin level. Moreover, the response to thyroxine treatment indicated that the synthesis of cholecalcin occurred later and slower than that of the majority of cerebellar proteins and even after other more complex mechanisms of cerebellar cortex development (such as neurite outgrowth) have been induced. Thus, cholecalcin synthesis does not appear particularly sensitive to thyroid hormone level but might rather follow the increase in cell size induced by the hormone.

Animals↗
PubMed1985

28 K cholecalcin (CaBP) levels in abnormal cerebella: studies on mutant mice and harmaline- and 3-acetylpyridine-treated rats.

The cerebellar Purkinje cells of both birds and mammals contain a specific calcium-binding protein, 28 K cholecalcin (CaBP). This is the same protein as the vitamin D-dependent kidney CaBP, but its Purkinje cell level is apparently vitamin D independent. The cerebellar CaBP contents of 3-acetylpyridine- and harmaline-treated rats and 5 mutant mouse strains (Purkinje cell degeneration, reeler, weaver, staggerer and nervous) were measured using a specific radioimmunoassay. The results indicate that the level of cerebellar CaBP is not dependent on the physiological state of the Purkinje cells but is an intrinsic measure of the size of the Purkinje cell population.

Alkaloids↗
PubMed1984

Tissue distribution of human calcium-binding protein (28 000 g mol-1).

Immunoreactive calcium-binding protein (28 000 g mol-1, L-CaBP) has been quantified using a specific radioimmunoassay to human cerebellar L-CaBP. The level of L-CaBP in post-mortem tissue samples varied from undetectable in muscle to 8 micrograms/mg-1 protein in the cerebellum and 16 micrograms mg-1 protein in the dentate nucleus. L-CaBP was found to be widely distributed throughout the nervous system while the only non-nervous tissue which contained appreciable levels was the renal cortex.

Aged↗
PubMed1983

Calcium-binding protein in the developing rat cerebellum. An immunocytochemical study.

Specific antibodies raised against a human 28 000 dalton cerebellar calcium-binding protein (CaBP) were used in an immunocytochemical study during development of the rat cerebellum. Both light and electron microscopy showed (1) that labelling was entirely restricted to the Purkinje cells, (2) that it appeared very early in Purkinje cell development, (3) that the entire cell was labelled from the tip of the smallest dendrites to the axonal terminals, and (4) that with increasing age, the immunoreaction appeared to be progressively restricted to the cell and organelle membranes.

Animals↗
PubMed1983

Ascorbic acid accumulation by cultured rat adrenocortical cells.

The influence of adrenocorticotrophin (ACTH) on radiolabeled ascorbic acid (AA) accumulation by adrenocortical cells was examined in primary cultures of collagenase dissociated glands from adult male rats. The cells were ACTH responsive by morphological and steroidogenic criteria. After 5 d in AA-free medium, cells pretreated with 100 mU/ml ACTH for 3 d took up two to three times more AA over a 2 h period than did untreated controls (4.0 to 10.0 nmol versus 1.7 to 3.4 nmol AA/micrograms DNA). In contrast, ACTH administered on Day 6 concurrently with AA inhibited AA accumulation compared to cultures exposed to AA alone. This acute inhibitory effect of ACTH was in the order of 30% in cultures pretreated with ACTH for 3 d but was not significant (7%) without ACTH pretreatment. The results show that ACTH has distinct long term stimulatory and acute inhibitory effects on AA accumulation by adrenocortical cells and suggest that both maximal AA accumulation and the responsiveness to acute inhibition of AA accumulation by ACTH may depend on the maintenance of the differentiated state of the adrenal cortex.

Adrenal Cortex↗
PubMed1983

Immunocytochemical demonstration of two vitamin D-dependent calcium-binding proteins in mammalian kidney.

Distribution of vitamin D-dependent calcium-binding proteins (CaBPs) were studied in four mammalian species using monospecific antibodies raised against chick duodenal CaBP (D-CaBP), human cerebellar CaBP (L-CaBP), and rat duodenal CaBP (S-CaBP). The immunoperoxidase technique of unlabelled antibodies was employed. The distribution of D-CaBP/L-CaBP was identical in all the species studied except for the monkey. In the rat, pig, and human nephrons, D-CaBP/L-CaBP was seen in the cytoplasm of the cells of the distal convoluted tubules, initial segments of the collecting ducts and interspersed cells of the collecting ducts. Proximal convoluted tubules, glomeruli and maculae densae were negative. In the monkey, in addition to the cells of the distal convoluted tubules, the cells along the entire length of the collecting ducts were also strongly positive. S-CaBP was found to be species-specific, and hence positive results were obtained only in the rat nephron. The strongest positive reaction for S-CaBP was seen in the cells of the distal convoluted tubules. These same cells were also positive for D-CaBP/L-CaBP. S-CaBP was also detected in the cells of the thick ascending limb of the loop of Henle, along the entire length of the collecting ducts and in smaller amounts in cells of the macula densa. Intracellularly the S-CaBP was present only in the apical cytoplasm of positive cells. D-CaBP/L-CaBP stained the entire cytoplasm but the staining in the apical cytoplasm was denser.

Animals↗
PubMed1982

Calcium-binding protein distribution in the rat brain.

The distribution in the rat brain of a protein with properties similar to vitamin D-dependent calcium binding protein (CaBP) was measured using a radioimmunoassay developed for mammalian brain CaBP. The cerebellum contained very high levels of CaBP in agreement with reports of CaBP distribution in the chick brain. The protein was distributed in large and unequal concentrations in different regions of the brain. Microdissection of the hippocampus revealed that, within a particular region, CaBP can have a marked differential distribution, suggesting that it is found in specific cell types. The significance of this protein is discussed in relation to the important functions of calcium in the CNS with particular emphasis being placed upon the possible role of CaBP as an intraneuronal calcium ion buffering system.

Animals↗
PubMed1982

Rat calcium-binding proteins: distribution, development, and vitamin D dependence.

The tissue distribution, developmental changes, and the vitamin D dependence in the rat of two calcium-binding proteins [CaBPs, 28,000 and 10,000 Mr (28 and 10 K)] were examined. The radioimmunoassays used employed specific antibodies to either the human cerebellar CaBP (28 K protein) or to the smaller rat intestinal CaBP (10 K protein). The assay for the 28 K CaBP may be used to detect this protein in a number of mammalian species and tissues, whereas the 10 K CaBP assay appears to be specific only for the rat intestinal CaBP. This report demonstrates that the tissue distribution of the two CaBPs is different in the rat. High levels of the 28 H protein were found in the cerebellum and kidney, whereas the smaller CaBP was concentrated in the duodenum, jejunum, and cecum. Many other organs and tissues contained small quantities of both CaBPs. Developmental studies indicated some variability in the concentration of the CaBPs. Duodenum, kidney, and cerebellum all contained small amounts of one of the CaBPs prior to birth. Adult levels in all three tissues were already reached at 30 postpartum days. Levels of both CaBPs began to decline in rats older than 2 mo. The vitamin D dependence appeared to reflect cell turnover in that the duodenal and kidney CaBPs showed a vitamin D dependence not observed for the cerebellar protein.

Aging↗
PubMed1978

The effect of parathyroid hormone and vitamin D3 metabolites on CaBP synthesis by embryonic duodenum, in vitro.

Embryonic chick duodena were incubated, in vitro, for two days in the presence of vitamin D analogues and metabolites and the ability of PTH to potentiate the vitamin-D-dependent synthesis of CaBP measured. PTH potentiated CaBP synthesis in the presence of vitamin D3, 25-OH-D3, 1 alpha-OH-D3, DHT, and 1,25(OH)2D3. The synthesis of CaBP was directly related to the log of the meddium PTH concentration over the range 1 x 10(-8) M to 5 x 10(-7) M.

Animals↗
PubMed1977

An in vitro bioassay for 1,25-dihydroxyvitamin D3 and other antirachitic agents.

Duodenal tissue from chicken embryos (19 days in ovo) has been maintained in organ culture for 48 hours. The incubation medium and culture conditions were chosen to produce a linear relationship between calcium binding protein production and the logarithm of the dose of vitamin D3 steroid in the medium. The dose-response curves are parallel for vitamin D3 and both its major metabolites, 25-hydroxyvitamin D3 and 1,25-dihydroxyVITAMIN D3. The minimum concentration of 1,25-dihydroxyvitamin D3 capable of inducing calcium-binding-protein synthesis was 1 X 10(-9) M.

Animals↗
PubMed1977

Inhibition by atropine, phenoxybenzamine and propranolol of the autonomic nervous system of the domestic fowl.

Because of the paucity and inconsistency of information on blockage of the chicken autonomic nervous system for extended periods, the effects of atropine, phenoxybenzamine and propranolol in the anesthetized hen were examined. It was found that cholinergic blockade by atropine was very short lived. For effective (80%) parasympathetic blockage a priming dose of 0.25 mg./kg;, followed by an infusion at the rate of 17.5 microgram/kg./min., was required. Similarly, inhibition of the beta-sympathetic system required propranolol in a priming dose of 0.25 mg./kg. and an infusion of 5 microgram/kg./min. The alpha-sympathetic inhibitor, phenoxybenzamine, was effective when given as a single dose of 5 mg./kg. Using these levels of inhibitor it was possible to ensure blockade in all cases for periods of two hours or more.

Acetylcholine↗