Comparison of bioassay and radioimmunoassay data for study of changes in the pattern of LH secretion from birth to puberty in the heifer

To define gonadotrophin secretion rates in the prepubertal heifer, 12 Hereford x Friesian heifers were blood-sampled at 15-min intervals for periods of 24 h every 4 weeks from 3 weeks of age until puberty. Radioimmunoassay of plasma LH concentrations showed that, although LH episode frequency increased with age, overall mean LH concentrations and basal LH concentrations decreased between 3 and 15 weeks of age and then increased to 35 weeks of age. The validity of these trends in relation to biological activity of plasma LH was investigated using an in-vitro Leydig cell bioassay. Samples were selected from 24-h profile bleeds of 4 heifers at 3, 7, 11, 15, 19, 27 and 39 weeks of age. No significant differences were found in the patterns of change in overall mean LH concentrations, basal LH concentrations or LH episode amplitude when comparing the estimates obtained by radioimmunoassay with those by bioassay from birth over the prepubertal period. These results indicate that the changes with age observed by radioimmunoassay are representative of changes in biologically active hormone.     

Blood flow changes following 137Cs irradiation in a rat glioma model

Blood flow changes in response to 20 Gy 137Cs whole brain irradiation were measured with quantitative autoradiography of [14C]iodoantipyrine (IAP) in intracerebral grafts of the 36B-10 rat glioma, the brain around tumor (BAT), the contralateral corpus callosum, and the contralateral cerebral cortex. Irradiations were delivered on Day 14 post-transplantation, and measurements of flow (F) were performed with IAP on Day 15 or Day 16. Mean values of F were determined in individual tumors and in treatment groups. In 15- and 16-day-old unirradiated control tumors, the group mean F was 0.31 ml.g-1.min-1. In both 15- and 16-day-old tumor groups irradiated on Day 14 (Day 1 and 2 postirradiation tumors) the mean F for each day's group was 0.52 ml.g-1.min-1, 68% higher than the control (P less than 0.01). Flow in the BAT and the contralateral corpus callosum similarly was increased at these times (P less than 0.01). Flow in the contralateral cerebral cortex was 1.1, 1.5, and 1.3 ml.g-1.min-1 in the control, 1 day postirradiated, and 2 day postirradiated groups, respectively, but these increases were not significantly different from the control. These data indicate that flow increases in the intracerebral gliomas as well as in normal brain regions during the 2 days following 20 Gy irradiation. Changes such as these following radiotherapy may have important effects on the bioavailability of chemotherapeutic drugs.     

Mapping of the structural gene for S-adenosyl homocysteine hydrolase to mouse Chromosome 2, and related sequences to Chromosomes 8 and X

Comparative mapping studies in human and mouse have shown that, to date, human Chromosome (Chr) 20 is completely syntenic with distal mouse Chr 2. The structural locus for S-adenosyl-l-homocysteine hydrolase (EC 3.3.1.1) in human, AHCY, maps to 20 qterq13.1, and we report here that the homologous locus in the mouse, Ahcy, maps to distal mouse Chr 2 with gene order Pcna-Ahcy-Ada. Analysis of 123 progeny of an interspecific backcross between a laboratory stock, AN, and Mus spretus using a rat cDNA probe revealed the presence of at least two other Ahcy-related sequences segregating independently in the mouse genome. One, Ahcy-rs1, was mapped to Chr 8 in the BXH recombinant inbred strains, and the other, Ahcy-rs2, shows a pattern of inheritance consistent with X-linkage.     

K+ accumulation in the space between giant axon and Schwann cell in the squid Alloteuthis. Effects of changes in osmolarity.

In a train of impulses in squid giant axon, accumulation of extracellular potassium causes successive afterhyperpolarizations to be progressively less negative. In Loligo, Frankenhaeuser and Hodgkin had satisfactorily accounted for the characteristics of this effect with a model in which the axon is surrounded by a space, width theta, and a barrier of permeability P. In axons isolated from Alloteuthis, we found that the model fitted the observations quite well. Superfusing the axon with hypotonic artificial seawater (ASW) caused theta and P to decrease, and, conversely, hypertonic ASW caused them to increase: this would be the case if both the space and the pathway through the barrier were extracellular. In some cases, in normal ASW, the afterhyperpolarizations in a train decreased very little, less than 0.7 mV. In these extreme cases, theta was estimated to be 190 nm and P to be 7 x 10(-4) cm s-1, both several times the values of 30 nm and 6 x 10(-5) cm s-1 estimated by Frankenhaeuser and Hodgkin. We suggest that in vivo the periaxonal space may be considerably wider than that seen in conventionally fixed squid tissue.     

Characterization of nucleotide-binding sites on the chloroplast coupling factor 1 using two photolabile analogs

Nucleotide-binding sites on the chloroplast coupling factor 1 (CF1) have been probed using two photoreactive ADP analogs: 2-azido-ADP (2-N3-ADP) and 2',3'-O-(4-benzoyl)benzoyl-ADP (Bz-ADP). Photolabeling of the isolated CF1 with 2-N3-ADP results in incorporation of the analog exclusively into the beta-subunit of the enzyme. The location of the nucleotide-binding site(s) within the beta-subunit of the CF1 was investigated using peptide mapping. Within the discrimination limits of this technique, it is concluded that the azido- and benzoyl-modified analogs both bind to the same conformation of the nucleotide-binding site(s) of soluble CF1. Bz-ADP, however, labels the binding site(s) on membrane-bound CF1 in a slightly different manner.     

A backpack system for long-term osmotic minipump infusions into unrestrained marmoset monkeys

A backpack system is described whereby osmotic minipumps are used to infuse gonadotrophin-releasing hormone (GnRH) subcutaneously in a pulsatile manner into infertile socially subordinate female marmoset monkeys (Callithrix jacchus jacchus). This procedure enables long-term infusion of GnRH without the necessity of repeated subcutaneous implantation of pumps and GnRH reservoirs. The backpack and cannulae system is inexpensive and can be constructed from commonly available materials. The GnRH treatment successfully overcame the suppression of pituitary luteinizing hormone secretion imposed by the low social status of female marmoset monkeys.     

Suppression of ATP in Candida albicans by imidazole and derivative antifungal agents

Several antifungal agents, at concentrations of 10 micrograms/ml, were shown to suppress ATP concentrations very rapidly in intact cells and spheroplasts of Candida albicans. The highest ATP-suppressing activity was shown by the highly lipophilic imidazole derivatives difonazole, clotrimazole, econazole, isoconazole, miconazole, oxiconazole and tioconazole, which all caused a reduction of cellular ATP content of more than 50% in 10 min. Relatively hydrophilic imidazole derivatives such as ketoconazole were essentially inactive in the test, as were the triazole derivatives fluconazole, ICI 153066, itraconazole and terconazole, and 5-fluorocytosine. Amphotericin B and terbinafine possessed intermediate ATP-suppressing activity, and the dose-response and pH-response curves for these compounds suggested their mechanism of ATP suppression differed from that of the active imidazole derivatives. ATP suppression by azole antifungals did not involve leakage of ATP from the cells and the effect was entirely abrogated by the presence of serum. Intact cells and spheroplasts of yeast-form and hyphal-form C. albicans were generally equally sensitive to ATP suppression, but stationary-phase cells of both morphological forms were less sensitive than exponential-phase cells. The extent of ATP suppression was significantly reduced in stationary-phase yeast cells of a C. albicans strain with known resistance to azole antifungals, but exponential-phase cells of resistant and susceptible strains were equally sensitive. The effect is tentatively ascribed to membrane damage caused directly by the antifungals.     

Selection for yield and yield components in the early generations of a potato breeding programme

Summary A number of unselected potato (Solanum tuberosum L.) clones were grown at two locations (a seed site and a ware site) in three consecutive years. The repeatability of total yield and yield components in the first two clonal years was compared with the same characters recorded in the third clonal year. Selection for yield in the first clonal year was only marginally more effective than a random reduction in number of genotypes, while selection in the second clonal year appeared to be somewhat more effective as judged by performance in the third clonal year. The inefficiency of selection in the first clonal year was ascribed, at least in part, to the inaccuracy of yield assessment as well as the carry-over effect of the mother tubers. Correlations of total yield were higher between different years in the same location than between different locations. Selection under growing conditions suitable for production of seed tubers tended to result in selection of early maturing clones which would not necessarily be optimal for ware growing conditions.