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61.
The pattern and opioidergic control of the secretion of gonadotrophins in prepubertal heifer calves were examined. Ten age-matched Hereford heifer calves were weighed and a blood sample was taken every 2 weeks from 2 to 25 weeks of age and then weekly until 60 weeks of age. At 60 weeks, a fertile bull was introduced and at 75 weeks of age pregnancy diagnosis was performed by transrectal ultrasonography. At 4, 12, 18, 24 and 32 weeks of age, the opioid antagonist naloxone was injected (i.v., n = 5; 1 mg kg-1 body weight) each hour for 12 h. Control heifers received sterile saline at the same ages. Blood samples were collected every 12 min for the 12 h treatment and serum samples were analysed for luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Samples taken once every 2 weeks from 2 to 60 weeks were analysed for LH, FSH and oestradiol, and weekly samples were taken for progesterone determination. There was no effect of naloxone on the age at puberty, which was 56.2 +/- 0.7 weeks at a body weight of 388.5 +/- 8.0 kg. The mean age at conception was 63.4 +/- 0.5 weeks. On the basis of samples taken every other week, serum concentrations of LH were high at 10 weeks and between 40 and 60 weeks of age. From the periods of intensive blood collection, the early rise in mean serum concentrations of LH appeared later at 12 and 18 weeks of age and was caused by a rise in LH pulse amplitude.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
62.
63.
Activation of Ca(2+)-dependent currents in cultured rat dorsal root ganglion neurones by a sperm factor and cyclic ADP-ribose. 下载免费PDF全文
The effects of intracellular application of two novel Ca2+ releasing agents have been studied in cultured rat dorsal root ganglion (DRG) neurones by monitoring Ca(2+)-dependent currents as a physiological index of raised free cytosolic Ca2+ ([Ca2+]i). A protein based sperm factor (SF) extracted from mammalian sperm, has been found to trigger Ca2+ oscillations and to sensitize unfertilized mammalian eggs to calcium induced calcium release (CICR). In this study intracellular application of SF activated Ca(2+)-dependent currents in approximately two-thirds of DRG neurones. The SF induced activity was abolished by heat treatment, attenuated by increasing the intracellular Ca2+ buffering capacity of the cells and persisted when extracellular Ca2+ was replaced by Ba2+. In addition, activity could be triggered or potentiated by loading the cells with Ca2+ by activating a series of voltage-gated Ca2+ currents. Ca(2+)-activated inward current activity was also generated by intracellular application of cyclic ADP-ribose (cADPR), a metabolite of NAD+, which causes Ca2+ release in sea urchin eggs. This activity could also be enhanced by loading the cells with Ca2+. The cADPR induced activity, but not the SF induced activity, was abolished by depleting the caffeine sensitive Ca2+ store. Ruthenium red markedly attenuated SF induced activity but had little action on cADPR induced activity or caffeine induced activity. Our results indicate that both SF and cADPR release intracellular Ca2+ pools in DRG neurones and that they appear to act on subtly distinct stores or distinct intracellular Ca2+ release mechanisms, possibly by modulating CICR. 相似文献
64.
Fibroblast heterogeneity in glucocorticoid regulation of collagen metabolism: Genetic or epigenetic?
James D. Russell Shirley B. Russell Kathryn M. Trupin 《In vitro cellular & developmental biology. Plant》1982,18(6):557-564
Summary Cultured fibroblasts derived from normal human dermis show a consistent 62% inhibition of collagen synthesis by hydrocortisone,
whereas cultures derived from keloids average only 30% inhibition and show a much larger strain to strain variation ranging
from 75% inhibition to 49% stimulation. Examination of fibroblast clones indicates that this high variation among keloid strains
is not due to differences in the proportion of normal and keloid cells in the mass culture populations. Small but significant
differences in the effect of hydrocortisone on collagen deposition are also seen among these clonal populations, but are not
related to the type of tissue from which cultures were derived. Two to three-fold differences among clones derived from a
single individual were observed, possibly suggesting functional heterogeneity of dermal fibroblasts with regard to collagen
metabolism under control conditions and in response to hydrocortisone. However, this variation among clones may simply reflect
differences in clonal growth, inasmuch as both collagen synthesis and deposition, and the effect of hydrocortisone on these
processes, are strongly affected by population density.
This work was supported in part by PHS grants, CA-17229 from the National Cancer Institute and AG-02046 from the National
Institute on Aging, DHHS; and by Grant RIM 78-17313 from the National Science Foundation. 相似文献
65.
66.
Effects of parathyroid hormone (PTH) and several prostaglandins (PGs) on cyclic AMP (cAMP) metabolism were studied and compared in isolated renal cortical tubules from male hamsters. Both production and intracellular degradation of cAMP were increased by PTH and each of the PGs tested (PGE2, PGE1, PGI2). Production of cAMP was increased to similar levels by maximal concentrations of PTH and each PG, however, degradation of cAMP was significantly higher in response to PTH than with any of the PGs. This difference in intracellular degradation of cAMP was responsible for the much higher concentrations of cAMP in renal cortical tubules exposed to PGs (PGE1, PGE2, PGI2) than to PTH. Submaximal amounts of each PG produced additive increases in cAMP concentrations in the presence of maximal amounts of PTH. Additivity of the combined responses was lost, however, as the PGs concentrations reached their maxima. The results suggest that renal PGs (PGE2 and PGI2) may modulate the effects of PTH on cAMP concentrations in renal cortical tubules. 相似文献
67.
A study of the epideictic behaviour patterns of male Xiphophorus helleri Heckel was made, and the social rank of individual fish in 12 groups of three was assessed over a ten-day period. Straight-line hierarchies were established in most groups. An anatomical study was made to locate the adrenocortical tissue, and the adrenocortical activity of each fish was assessed by measuring mean nuclear diameter of 25 adrenocortical cells. Although results were somewhat variable, the highest-ranking fish in 7 out of 12 groups showed the least adrenocortical activity. The remaining two fish showed no significant difference from each other in adrenocortical activity, though their rank was in most cases clearly distinguishable on behavioural grounds. 相似文献
68.
John F. Brandts Richard D. Taverna Easwara Sadasivan Kathryn A. Lysko 《生物化学与生物物理学报:生物膜》1978,512(3):566-578
Differential scanning calorimetry has been used to study several structural transitions of the human erythrocyte membrane. Earlier studies have shown that one of these transitions (the A transition) is due to the thermal unfolding of spectrin on the membrane. In this paper, it is shown that two of the other transitions (B and C) exhibit a high sensitivity to a local anesthetic, benzyl alcohol. Increasing the ionic strength of the suspending medium results in a splitting of the B transition into two independent transitions (B1 and B2). It is found that one of these (B2) is associated with titrating groups, since the midpoint for the transitions shifts by about 20°C, with an apparent near 7.5. Extensive bilateral proteolysis by papain causes a drastic decrease in the size of all transitions except the C transition, which remains unaltered. On the other hand, treatment with phospholipase A2 largely affects the C transition, causing its disappearance. Because of the lack of sensitivity to proteolysis and the high sensitivity to phospholipase, it appears that the C transition has a large extent of ‘lipid involvement’. It might result from the melting of a small fraction of phospholipid which exists in a crystalline state under physiological conditions. Alternatively, the C transition could arise from changes in protein-lipid interactions or from lipid-dependent changes in protein-protein interactions, providing one assumes that only protease-resistant portions of membrane proteins are participating. 相似文献
69.
In the presence of MgCl2, amounts of detergents which disrupted phospholipid vesicles caused lipopolysaccharide I from Proteus mirabilis to aggregate and form vesicular, membrane-like structures. Vesicle formation with P. mirabilis lipopolysaccharide II containing longer O-polysaccharide chains was extremely poor. Lipopolysaccharides of Salmonella minnesota R mutants (chemotypes Ra, Rc and Re) displayed a growing tendency for vesicle formation with increasing deficiency of the R core polysaccharide. Lipopolysaccharides of chemotypes Rc and Re produced vesicles even in the absence of MgCl2 and detergent. Spherical aggregates consisting of P. mirabilis lipopolysaccharide I, MgCl2 and detergent were unable to either entrap or retain [14C]-sucrose, [3H]inulin or [3H]dextran. On the other hand, S. minnesota R mutant lipopolysaccharides of chemotypes Rc and Re could entrap all three saccharides and retain them for at least short periods of time. Leakage of [3H]-inulin out of Re-lipopolysaccharide vesicles was greatly retarded by addition of MgCl2 to the vesicle system. Incorporation of P. mirabilis lipopolysaccharide I or S. minnesota Rc lipopolysaccharide into phospholipid vesicles protected these model membranes from disruption by detergent. This suggested a similar protective function of lipopolysaccharide in the outer membrane of enteric bacteria against the action of surfactants occuring in their normal intestinal habitat. 相似文献
70.
Alfonso L. Pogolotti Kathryn M. Ivanetich Hans Sommer Daniel V. Santi 《Biochemical and biophysical research communications》1976,70(3):972-978
Studies are reported on the FdUMP-CH2-H4 folate-peptide obtained upon proteolysis of the complex formed from thymidylate synthetase, FdUMP and 5,10-CH2-H4folate. Contrary to a previous report from this laboratory, the peptide does contain a cysteine residue. The sequence of the largest peptide obtained is Ala-Leu-Pro-Pro-(His,Cys)-Thr. Quantitative modification of the histidine residue with the Pauly reagent indicates that imidazole is not directly linked to the nucleotide. The stability of the peptide indicates the covalent bond to the cofactor involves its 5-nitrogen; from this, it may be concluded that the reactive form of the cofactor is the 5-iminium ion. 相似文献