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991.
Babetta L. Marrone Jorge F. Rodriguez-Sierra Harvey H. Feder 《Hormones and behavior》1977,8(3):391-402
Progesterone has two types of inhibitory effects on female sexual behavior that have been well-documented in the guinea pig. The first occurs when high levels of progesterone are present around the start of the estrogen-priming process (“concurrent inhibition”). The second occurs immediately after the display of an estrogen-progesterone-induced period of estrous behavior (“sequential inhibition”). In the present set of experiments, we show that the rat, like the guinea pig, is capable of exhibiting both of these inhibitory effects of progesterone. However, rats require higher doses of progesterone than guinea pigs, at least for concurrent inhibition to be evident. In addition, we show that the dose of progesterone required in a single injection to produce concurrent inhibition is higher than the dose required to produce sequential inhibition in rats. A theory of how progesterone may be accomplishing its inhibitory effects on female sexual behavior in rodents is presented. 相似文献
992.
993.
The foliose red alga Gigartina papillata (C. Ag.) J. Ag. was studied in culture to determine its life history and possible relationship to the life history of Petrocelis middendorffii (Ruprecht) Kjellman. Carpospores cultured from individual female plants gave rise to either crustose Petrocelis-like plants that reproduced by tetraspores, or to another generation of foliose female (cystocarpic) plants that reproduced by carpospores. Apices cultured from blades of individual field-collected female plants produced either papillae with many procarps that developed cystocarps only when crossed with male plants, or papillae with few procarps that produced cystocarps in the absence of male plants. The results are interpreted to demonstrate that two types of life history occur in G. papillata: one, a sexual life history involving a crustose tetrasporophyte; the other, a possibly apomictic life history involving only cystocarpic plants. Hybridization experiments demonstrated, that G. papillata is interfertile with Gigartina-phase gametophytes cultured from tetraspores of P. middendorffii. Sexual plants of G. papillata are postulated to represent the naturally-occurring gametophyte of P. middendorffii in California. The possible relationships of the sexual and apomictic plants of G. papillata are discussed. 相似文献
994.
Leonard M. Hjelmeland Lewis Aronow James R. Trudell 《Biochemical and biophysical research communications》1977,76(2):541-549
Isotope effects for hydroxylation reactions catalyzed by cytochrome P-450 have usually been measured by comparing the overall reaction velocities of deuterated and nondeuterated substrates. Since the rate-limiting step is probably not the single reaction involving covalent bond cleavage, such an approach does not yield information about the primary isotope effect. We measured the primary kinetic isotope effect for benzylic hydroxylation by a method utilizing intramolecular competition, using the symmetrical substrate 1,3-diphenylpropane-1,1-d2. These experiments yield a value of , a larger effect than has previously been reported for benzylic hydroxylations. 相似文献
995.
B A Doneen D Chung D Yamashiro P Y Law H H Loh C H Li 《Biochemical and biophysical research communications》1977,74(2):656-662
The opiate activities of some derivatives and enzymatic digests of camel and human β-endorphin were determined in the guinea pig ileum and rat brain opiate receptor binding assays. Derivatives of β-endorphins altered within the amino-terminal five residues showed pronounced losses in activity. Anisylation of the C-terminal glutamic acid residue of βh-endorphin produced only small reductions in activity. Chymotryptic digestion greatly weakened the opiate activities of βh-endorphin, whereas carboxypeptidase A, tryptic and leucine aminopeptidase digests showed only small losses in potency. The C-terminus of β-endorphin appears to contribute little directly to opiate activity. Amino acid analysis and assay of the leucine aminopeptidase digests suggest that the larger potency of β-endorphin relative to Met-enkephalin may be a consequence of its greater resistance to exopeptidase attack. 相似文献
996.
The cell-cell adhesion characteristic of C-6 astrocytoma cells changes as a function of cell density. Cell suspensions prepared from monolayers having a density lower than 1 × 105 cells/cm2 show maximal affinity for plasma membranes and cells obtained from monolayers at densities greater than 1 × 106 cells/cm2 shows minimal affinity for plasma membranes. The adhesive component retained on plasma membranes is present at essentially equal levels in membranes prepared from cells at different density. This modulation in cell surface affinity appears to be due to cell-cell contact and appears to represent a suitable model for the study of the modulation of cell-cell adhesion as a result of cell contact. 相似文献
997.
N S Agarwal V J Hruby R Katz W Klee M Nirenberg 《Biochemical and biophysical research communications》1977,76(1):129-135
Nucleoli isolated from livers of rats injected intraperitoneally with one dose of thioacetamide had a five-fold increase in the rate of RNA synthesis when compared with livers of rats treated with saline or CCl4. The stimulation was maximal 24 hours after treatment and decreased to control values 73 hours after treatment. The enhanced level of nucleolar activity was maintained at that level when thioacetamide was injected daily. Along with the increase in the endogenous activity there was a 7-fold increase in the “free” RNA polymerase I activity determined by blocking the bound enzyme with actinomycin D (7). The nucleoli of the thioacetamide-treated rats offer a useful model of modulation of ribosomal gene function. 相似文献
998.
Tests for departure from normality: Comparison of powers 总被引:5,自引:0,他引:5
999.
Asymptotic solutions for the effectiveness factor and the concentration profile are obtained for mth-order chemical reactions inside a slab catalyst pellet with Robin boundary condition at the pellet's outer surface. Using perturbation analysis in the limit of large reaction order m, the effectiveness factor and the concentration profile are explicitly determined up to O(1/m). Higher-order solutions can be obtained in a systematic way if desired. 相似文献
1000.
The relationship between prolactin (PRL) secretion and the neurointermediate lobe (NIL) of the pituitary gland was investigated. Plasma PRL concentrations in rats bearing anterior pituitaries autografted with or without the NIL to the renal capsule were elevated to equal extents at 1 through 6 weeks after surgery (p > 0.10). PRL levels in ovariectomized rats in which the NIL had been removed surgically (NIL-X) or only visualized (NIL-C) were 3–7 ng/ml 4, 7, and 28 days after surgery (p > 0.10); however, they were slightly higher in NIL-X NIL-C rats 14 days after surgery (p < 0.05). Plasma luteinizing hormone (LH) concentrations in NIL-C rats increased by 36% from 2 to 4 weeks after surgery (p < 0.05); this increase was not detected in NIL-X rats. PRL and LH surges were induced by estradiol implants in ovariectomized NIL-X and NIL-C rats; the profiles of the PRL surges were superimposable, although the magnitude of the LH surge was only 50% that in NIL-C rats (p < 0.05). These results cast doubt on the importance of the NIL in the regulation of PRL secretion either secreting hypophysiotropic hormones or conducting anterior pituitary hormones directly to the median eminence. However, the NIL may have a physiologically important role in the regulation of LH secretion. 相似文献